International Construction Specialty Conference of the Canadian Society for Civil Engineering (ICSC) (5th : 2015)

System dynamics modelling for an urban water system : net-zero water analysis for Peachland (BC) Chhipi-Shrestha, Gyan K.; Hewage, Kasun; Sadiq, Rehan Jun 30, 2015

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5th International/11th Construction Specialty Conference 5e International/11e Conférence spécialisée sur la construction    Vancouver, British Columbia June 8 to June 10, 2015 / 8 juin au 10 juin 2015   SYSTEM DYNAMICS MODELLING FOR AN URBAN WATER SYSTEM: NET-ZERO WATER ANALYSIS FOR PEACHLAND (BC) Gyan K. Chhipi-Shrestha1, 2, Kasun Hewage1 and Rehan Sadiq1 1 School of Engineering, University of British Columbia, Canada 2 Gyan.Shrestha@ubc.ca Abstract: A Net-zero water (NZW) community limits the consumption of freshwater resources and returns water back to the same watershed, so as not to deplete the groundwater and surface water resources of that region in quantity and quality over the course of a year. A NZW study includes the analysis of various combinations of water supply sources, water conservation, and reuse over time. Such dynamics can be modelled by using system dynamics. This article aims to develop a system dynamics model (SDM) to achieve NZW at the urban community level. The SDM was developed by including all life cycle stages of urban water using STELLA® software. The developed SDM was validated using the historical data of Peachland water consumption (BC). Moreover, the model was applied to analyze NZW of the Peachland community during 2015-34 by considering six different scenarios. In the base case scenario, two thirds of the supplied water will be used for irrigation and will not be directly available to the community for reuse. As the community is in a semi-arid region, the Peachland community can only achieve NZW or even net-plus water for the initial five years by considering Peachland as a typical urban community without agriculture, and by implementing various water efficiency improvement measures. However, due to the projected increase in water demand, the NZW cannot be achieved after 2019.  1 INTRODUCTION 1.1 Urban Water Systems and Peachland The world’s urban population is more than half (~54%) of the total population and is expected to increase rapidly (UN DESA 2014). In Canada, the urban population is very high (~ 81%) and is growing (Statistics Canada 2014a). The growing population requires a large volume of water served by the urban water supply. Urban water processes, such as water abstraction, treatment, distribution, wastewater treatment, disposal, and stormwater drainage are essential in any urban area. They are necessary for the human consumption of safe water and reduction of environmental impacts due to wastewater discharge (Termes-Rifé et al. 2013). These human regulated urban water processes constitute a human hydrologic cycle (Bagley et al. 2005), or simply an urban water system (UWS). The District of Peachland (DoP) is located in the Okanagan Valley, British Columbia (BC), Canada. The DoP covers an area of 17.98 square kilometres (DoP 2008). The estimated population of the DoP is 6320 in 2014 with an annual population growth of 6.5% (Statistics Canada 2014b). The public water is supplied from two creeks (Trapanier Creek and Deep Creek), Okanagan Lake, and two Ponderosa wells (groundwater) (DoP 2007). Major consumers of the municipal water are residential (indoor and outdoor) buildings, agriculture, public parks, golf courses, and commercial and institutional sectors. The 063-1 wastewater generated from the water use is treated at the Westside Regional Wastewater Treatment Plant and then discharged to Okanagan Lake.      1.2 System Dynamics Model (SDM) for Urban Water Systems System dynamics is a well-established methodology to quantify complex feedbacks in system interactions (Forrester, 1961; Forrester, 1968). The system dynamics model (SDM) is often used to quantify system behaviors with feedback loops for more accurate projections (Qi and Chang 2011). The model allows for the effective trade-off analysis of multi-scenarios and the multi-attributes of UWSs over time (Sehlke and Jacobson 2005). A SDM can help users better understand and express how complex systems function through visualization and computer simulation (Sehlke and Jacobson 2005). System dynamics involves the construction of “causal loop diagrams” or “stock and flow diagrams” to mimic a dynamic system. System dynamics has not been explored much in water demand estimation studies (Qi and Chang 2011; Zarghami and Akbariyeh 2012).  1.3 Net-Zero Water (NZW) Analysis The concept of net-zero water (NZW) is similar to the carrying capacity of a system (Holtzhower et al. 2014). NZW refers to the balance of water demand and supply within a given areal boundary (Holtzhower et al., 2014). The US Army states that “net-zero water limits the consumption of freshwater resources and returns water back to the same watershed so not to deplete the groundwater and surface water resources of that region in quantity or quality over the course of a year” (US Army 2011). The central theme of NZW  emphasizes a balance so that the sum of all input water is offset by comparable output water (Joustra and Yeh 2014). NZW presupposes that a community system can secure an adequate water supply within its boundaries, typically from surface water, groundwater, reclaimed water, and rainfall (Holtzhower et al. 2014). Achieving net-zero water similar to the natural cycle requires both the conservation of water and the creation of balanced water feedback loops (Joustra and Yeh 2014).  A recent report published by the US National Research Council showed that “The use of reclaimed water to augment potable water supplies has significant potential for helping to meet future needs, ….” and also recommended potable reuse with or without an environmental buffer as an alternative water management approach (National Research Council 2012). Similarly, water recycling for the augmentation of drinking water supplies has been promoted by the Australian government, who published guidelines for reclaimed water quality management (EPHC/NHMRC/NRMMC 2008). Also, in Canada, the provincial government of British Columbia has planned for the mandatory construction of dual water-plumbing (additional purple pipes for reclaimed water flow) in new buildings (MoE 2008). These initiatives show an increasing aspiration for reclaimed water use. This research develops a system dynamics model for the urban water system of Peachland and analyze its potentiality to achieve NZW.   2 METHODOLOGY The system dynamics model for the UWS of Peachland was developed by using STELLA® software (Karamouz et al., 2012; Qi and Chang, 2011). The SDM includes three sub-models: population, water, and wastewater sub-models. These sub-models and NZW analysis method are described below:  a. Population Sub-model The population dynamics of the District of Peachland was analyzed using the population growth equation as given in Equation 1 (Nasiri et al. 2013). The data required for the population sub-model, such as base population, population growth rate, and dwelling size were obtained from Statistics Canada (2014b).  [1] Nt = N0er t                     where Nt = population in a month, N0 = Base population, r = population growth rate (monthly), t = time duration in months  063-2 b. Water Sub-model The water sub-model represents the flow of supplied water within the Peachland community. The water flow occurs through the urban water stages: abstraction, treatment, distribution, and use. The water use dynamics was modelled using Equation 2. The equation includes the water consumed by different activities of the urban sectors: residential; industrial, commercial, and institutional (ICI); agricultural; public parks; and golf courses over time.  [2] (Water use)t = (Residential water use)t + (Agricultural water use)t + (Institutional water use)t + (Commercial water use)t + (Industrial water use)t + (Parks and golf courses water use)t where ‘”t” refers to a month  The rates of water consumption by different residential indoor activities were obtained from modified Mayer et al. (1999). The extensive study on the end uses of residential water also included Canadian cities. The efficiencies of conventional and efficient water fixtures and appliances were obtained from Mayer et al. (1999), ENERGY STAR (2014a), and ENERGY STAR (2014b). The rate of irrigation demand for different land covers such as agriculture, lawns, community parks, and golf courses of the Okanagan valley (OBWB 2010) was used for Peachland. The agricultural land area (121.6 ha) was estimated from the land use map of Peachland (DoP 2008). The average maximum site coverage of lot area is 48% for different types of residential buildings with an average lot size of 1178 m2 in the district (DoP 1996). The site not covered by building structures or paved areas is required to be landscaped. Based on these requirements, the average lawn area per dwelling unit was considered as 50% of the average lot size. In addition, the area of community parks is 14.49 ha and new neighbourhood development is required to maintain a community park of 3.04 ha per 1000 population (DoP 2014a). Also, a golf course of 0.6 ha is located in Peachland (Ponderosa Golf 2015). The rates of commercial and institutional (CI) water use were obtained from the CI water use studies by US EPA (2009) and Dziegielewski et al. (2000). The data on the present industrial, commercial, and institutional floor space and their future growth were obtained from (DoP 2012). However, Peachland has no major industries (DoP 2012).        c. Wastewater Sub-model The wastewater dynamic was modelled in the wastewater sub-model. This sub-model includes wastewater (WW) collection and its treatment for residential and ICI sectors. [3] (WW)t = (Residential WW)t + (Industrial WW)t + (Commercial WW)t + (Institutional WW)t  Where ‘”t” refers to a month  d. Net-Zero Water Analysis The potentiality of Peachland to achieve net-zero water was analyzed using the developed SDM. Equation 4 was used for the analysis. [4] (Net water)t = (Water use)t – (Rooftop rainwater harvested)t – (Greywater reused)t – (Reclaimed water use)t – (Stormwater harvested)t Where ‘”t” refers to a month The average monthly rainfall data of the past 35 years (1980 to 2014) of the nearby meteorological stations of Penticton and Kelowna (Government of Canada 2015) was used for the estimation of rooftop rainwater harvesting and stormwater harvesting potential.  Prior to the development of a complete SDM, a causal loop diagram (CLD) was developed. A CLD is a foundation of a SDM, and is used to identify relationships between individual system components and to show feedback loops that affect system regulation (Nasiri et al. 2013). The CLD of the SDM of the 063-3 Peachland UWS is given in Figure 1. In the CLD as shown in Figure 1, a ‘‘+’’ sign indicates a positive (reinforcing) relationship between two variables. An increase in the arrow tail variable causes an increase in the arrow head variable. A ‘‘-’’ sign indicates a negative (balancing) relationship between two variables. An increase in the arrow tail variable causes a decrease in the arrow head variable (Nasiri et al. 2013). Based on the CLD, a SDM was developed. The SDM was validated using the historical monthly data of municipal water consumption by Peachland from 2010 to 2014.  Water abstractionWastewaterIC WaterResidential wateruseGreywaterrecyclingResidentialindoor useResidentialoutdoor useDwelling unitsWaterappliances/faucets++++ +-IndustrialwaterCommercial waterInstitutional water+++ Agricultural waerParks and golfcourses waterWater use+++++Rooftop rainwaterharvesting Stormwaterharvesting+Net water++-Population +Population growth++Industrial indoorwaterIndustrial outdoorwaterCommercialindoor waterComercialoutdoor waterInstitutionaloutdoor waterInstitutional indoorwater+++ +++Wastewatertreament ++Wastewaterreclaimed++ Figure 1: Causal loop diagram of the urban water system of Peachland 3 RESULTS AND DISCUSSION 3.1 System Dynamics Model for the Peachland UWS The monthly water consumption of Peachland was simulated for five years from 2010 to 2014. The result was compared with the historical data of Peachland (DoP 2015) and is shown in Figure 2. The coefficient of determination (r2) of the model is 0.85, which is high and is acceptable. Both historical data and SDM result showed an equal average water consumption of Peachland: 1104 L/capita/day for the five-year duration. In particular, the average residential water consumption of Peachland from 2010 to 2014 was 711 L/capita/day based on the SDM. The residential water consumption of Peachland is very high compared to the Canadian average of 343 L/capita/day (Environment Canada 2014), British Columbia average of 490 L/capita/day, and Okanagan valley average of 675 L/capita/day (OBWB 2011). The important causal factor for high residential water consumption by Peachland may be a low density residential neighbourhood with a large area of outdoor landscaping. For example, a minimum lot size of a single family residential building is 1350 m2 (0-25% slope) to 4000 m2 (≥ 35% slope) in an area without sewer connection and is 830 m2 in an area with sewer connection and can have a maximum site coverage of 40%. Also, a site not covered by building structures or paved areas is required to be landscaped  (DoP 1996). In addition, neighbourhood developments are required to maintain the standard of 4.04 ha parks per 1000 population (neighbourhood parks of 1.01 ha and community parks of 3.04 ha) (DoP 2014a).  063-4 Table 1: Scenarios for net-zero water analysis Scenario Community water features Methods 1 Base case scenario Future community water features similar to the present. 2 Scenario 1 with the efficient water fixtures Efficient toilets, faucets, showers, dish washers, and cloth washers in all sectors with waterless urinals in CI sector. 3 Scenario 2 with irrigation demand reduction Irrigation demand reduction by: 50% in residential lawns and 30% in agriculture and community parks/golf courses; use xeriscaping; water efficient crops, and efficient irrigation; 15% water conservation by behavioural change 4 Scenario 3 with rooftop rainwater harvesting and greywater recycling Short term storage and use of harvested rainwater and recycled greywater 5 Scenario 4 with treated wastewater use Use of treated wastewater (black water) 6A Scenario 5 with stormwater harvesting and use Stormwater harvesting of built up area (downtown, neighbourhoods, and residential areas) of 520 ha 6B Typical urban setting of Scenario 6A Scenario 6A without considering agricultural water use The results of scenario analysis for achieving NZW from 2015 to 2034 are presented in Table 2 and Figure 5. As shown in Table 2, the average annual freshwater withdrawal of the UWS gradually decreases from Scenarios 1 to 6. The freshwater withdrawal and water use can be reduced by about 10% by using efficient water fixtures and appliances (Scenarios 1 to 2). However, water withdrawal and use can be reduced by 40% from Scenarios 1 to 3 by using efficient water fixtures and irrigation demand reduction. Peachland can reduce up to approximately 80% of freshwater withdrawal by using harvested rainwater, recycled greywater, treated wastewater (black water), and harvested stormwater (Scenario 6A compared to Scenario 1). Moreover, considering a typical urban setting without agriculture (Scenario 6B), Peachland can reduce up to 90% of water withdrawal by implementing similar measures to those of Scenario 6A.    Table 2: Average annual net water in six different scenarios for 2015 to 2034 period Scenarios Water use (ML) Freshwater withdrawal (ML) Net water (ML) Internal water reuses/harvesting Return to env. (Treated) 1 4974.5 4974.5 -3630.1 - WW 2 4485.7 (-9.8%) 4485.7 (-9.8%) -3537.0 (-2.6%) - WW 3 3018.8 (-39.3%) 3018.8 (-39.9%) -2203.1 (-39.3%) - WW 4 3018.8 (-39.3%) 1721.8 (-65.4%) -1426.5 (-60.7%) GW, RW WW 5 3018.8 (-39.3%) 1426.5 (-71.3%) -1426.5 (-60.7%) GW, RW, WW - 6A 3018.8 (-39.3%) 985.9 (-80.2%) -985.9 (-72.8%) GW, RW, WW, SW - 6B 2569.3 (-48.3) 536.4 (-89.2%) -536.4 (-85.2%) GW, RW, WW, SW - Note:  i. GW: Greywater recycling; RW: Rain water harvesting: WW: Wastewater (black water); SW: Stormwater harvesting; env: environment  ii. Parenthesis indicates a percentage change in the value from Scenario 1 iii. Negative sign indicates a reduction  063-7 conservation, reclaimed water use, rooftop rainwater harvesting, and stormwater harvesting (Scenario 6B). However, due to the projected increase in water demand, the NZW water condition cannot be achieved after 2019. Acknowledgements We acknowledge the financial assistance of the Natural Sciences and Engineering Research Council of Canada (NSERC) to conduct this research. We also acknowledge the financial and in-kind support of the industrial partners (New Monaco Enterprise, District of Peachland, Focus Engineering, Urban Systems, and FortisBC) for the NSERC Collaborative Research and Development Grants. Moreover, the research assistance of Dr. Bahareh Reza and the Okanagan Sustainability Institute (OSI) is appreciated.  References Bagley, David, Robert Andrews, Barry Adams, and Bryan Karney. 2005. “Development of Sustainable Water Systems for Urban Areas: A Human Hydrologic Cycle Approach.” In 33rd Annual Conference of the Canadian Society for Civil Engineering, 1698–1707. Toronto: Canadian Society for Civil Engineers. DoP. 1996. The District Of Peachland Zoning Bylaw Number 1375 (Amended October, 2014). Peachland, BC: District of Peachland. https://peachland.civicweb.net/Documents/DocumentList.aspx?ID=40844. DoP. 2007. Final Report: District of Peachland Water Master Plan. Kelowna, BC. DoP. 2008. “Land Use Designations.” In Official Community Plan. Peachland: District of Peachland. DoP. 2012. Economic Impact Analysis of Major Development Projects in Peachland. Peachland. DoP. 2014a. District of Peachland Official Community Plan: Consolidated Bylaw. Peachland, BC: District of Peachland. DoP. 2014b. Water Licenses: District of Peachland Official Database 2014. Peachland. DoP. 2015. District of Peachland Water Consumption: Official Database. Peachland. Dziegielewski, B, J. C Kiefer, G. L Lantz, E. M Opitz, G. A. Porter, W. B. Deoreo, P.W. Mayer, and J.O. Nelson. 2000. Commercial and Institutional End Uses of Water. Denver, CO: American Water Works Association Research Foundation and AWWA. ENERGY STAR. 2014a. “ENERGY STAR Certified Residential Clothes Washers.” http://www.energystar.gov/productfinder/product/certified-clothes-washers/results? ENERGY STAR. 2014b. “ENERGY STAR Certified Residential Dishwashers.” http://www.energystar.gov/productfinder/product/certified-residential-dishwashers/results. Environment Canada. 2014. “Wise Water Use.” http://www.ec.gc.ca/eau-water/default.asp?lang=En&n=F25C70EC-1. EPHC/NHMRC/NRMMC. 2008. Australian Guidelines for Water Recycling: Augmentation of Drinking Water Supplies. Canberra: Environment Protection and Heritage Council, National Health and Medical Research Council, Natural Resource Management Ministerial Council. Forrester, J.W. 1961. Industrial Dynamics. Cambridge, MA, USA: M.I.T. Press. Forrester, J.W. 1968. Principles of System Dynamics. Cambridge, MA, USA: Productivity Press. Government of Canada. 2015. “Climate: Accessing the Data.” http://climate.weather.gc.ca/index_e.html#access. Harma, Kirsten J., Mark S. Johnson, and Stewart J. Cohen. 2011. “Future Water Supply and Demand in the Okanagan Basin, British Columbia: A Scenario-Based Analysis of Multiple, Interacting Stressors.” Water Resources Management 26 (3): 667–89. doi:10.1007/s11269-011-9938-3. Holtzhower, D. Lantz, Kevin Priest, Rodrigo Castro-Raventós, and Robert J. Ries. 2014. “Value and Limits of Net Zero Energy, Water, and Agriculture.” In iiSBE Net Zero Built Environment: Nature-Based Building Performance - Net Zero Energy, Water, Carbon, and Waste, edited by Charles J. Kibert, Ravi Srinivasan, Lantz Holzhower, Hamed Hakim, and Ruthwik Pasunuru, 7–20. Gainesville, Florida: Rinker School of Construction Management, University of Florida. Joustra, Caryssa M., and Daniel H. Yeh. 2014. “Net-Zero Building Water Cycle Decision Support.” In iSBE Net Zero Built Environment: Nature-Based Building Performance - Net Zero Energy, Water, Carbon, and Waste, edited by Charles J. Kibert, Ravi Srinivasan, Lantz Holzhower, Hamed Hakim, and Ruthwik Pasunuru, 56–67. Gainesville, Florida: Rinker School of Construction Management, University of Florida. 063-9 Karamouz, Mohammad, Erfan Goharian, and Sara Nazif. 2012. “Development of a Reliability Based Dynamic Model of Urban Water Supply System : A Case Study,” 2067–78. Mayer, P.W., W.B. DeOreo, E.M. Opitz, J.C. Kiefer, W.Y. Davis, and B. Dziegielewski. 1999. Residential End Uses of Water. MoE. 2008. Living Water Smart: British Columbia’s Water Plan. BC Ministry of Environment. Nasiri, Fuzhan, Troy Savage, Ranran Wang, Nico Barawid, and Julie B. Zimmerman. 2013. “A System Dynamics Approach for Urban Water Reuse Planning: A Case Study from the Great Lakes Region.” Stochastic Environmental Research and Risk Assessment 27 (3): 675–91. doi:10.1007/s00477-012-0631-8. National Research Council. 2012. Water Reuse : Potential for Expanding the Nation’s Water Supply Through Reuse of Municipal Wastewater. Washington DC, USA: National Academies Press. OBWB. 2010. Agriculture Water Demand Model. Kelowna: Okanagan Basin Water Board. OBWB. 2011. Local Government User Guide: Okanagan Water Supply and Demand Project. Ponderosa Golf. 2015. “Building Ponderosa Golf.” http://ponderosaliving.ca/play/golf/building-ponderosa-golf. Qi, Cheng, and Ni-Bin Chang. 2011. “System Dynamics Modeling for Municipal Water Demand Estimation in an Urban Region under Uncertain Economic Impacts.” Journal of Environmental Management 92 (6). Elsevier Ltd: 1628–41. doi:10.1016/j.jenvman.2011.01.020. Sehlke, Gerald, and Jake Jacobson. 2005. “System Dynamics Modeling of Transboundary Systems: The Bear River Basin Model.” Ground Water 43 (5): 722–30. doi:10.1111/j.1745-6584.2005.00065.x. Statistics Canada. 2014a. “Population, Urban and Rural, by Province and Territory (Canada).” http://www.statcan.gc.ca/tables-tableaux/sum-som/l01/cst01/demo62a-eng.htm. Statistics Canada. 2014b. “Focus on Geography Series 2011 Census: Census Subdivision of Peachland, DM - British Columbia.” Termes-Rifé, Monserrat, María Molinos-Senante, Francesc Hernández-Sancho, and Ramón Sala-Garrido. 2013. “Life Cycle Costing: A Tool to Manage the Urban Water Cycle.” Journal of Water Supply: Research and Technology—AQUA 62 (7): 468. doi:10.2166/aqua.2013.110. UN DESA. 2014. World Urbanization Prospects: The 2014 Revision, Highlights (ST/ESA/SER.A/352). New York: United Nations Department of Economic and Social Affairs, Population Division. US Army. 2011. Net Zero Water for Army Installations: Cons Iderations for Policy and Technology. Edited by Elisabeth M Jenicek, Laura E Curvey, Annette L Stumpf, and Kelly Fishman. US Army Corps of Engineers. http://acwc.sdp.sirsi.net/client/search/asset/1002026. US EPA. 2009. Water Efficiency in the Commercial and Institutional Sector: Considerations for a WaterSense Program. EPA White Paper. Las Vegas: US Environmental Protection Agency. Zarghami, Mahdi, and Simin Akbariyeh. 2012. “System Dynamics Modeling for Complex Urban Water Systems: Application to the City of Tabriz, Iran.” Resources, Conservation and Recycling 60 (March). Elsevier B.V.: 99–106. doi:10.1016/j.resconrec.2011.11.008.   063-10  5th International/11th Construction Specialty Conference 5e International/11e Conférence spécialisée sur la construction    Vancouver, British Columbia June 8 to June 10, 2015 / 8 juin au 10 juin 2015   SYSTEM DYNAMICS MODELLING FOR AN URBAN WATER SYSTEM: NET-ZERO WATER ANALYSIS FOR PEACHLAND (BC) Gyan K. Chhipi-Shrestha1, 2, Kasun Hewage1 and Rehan Sadiq1 1 School of Engineering, University of British Columbia, Canada 2 Gyan.Shrestha@ubc.ca Abstract: A Net-zero water (NZW) community limits the consumption of freshwater resources and returns water back to the same watershed, so as not to deplete the groundwater and surface water resources of that region in quantity and quality over the course of a year. A NZW study includes the analysis of various combinations of water supply sources, water conservation, and reuse over time. Such dynamics can be modelled by using system dynamics. This article aims to develop a system dynamics model (SDM) to achieve NZW at the urban community level. The SDM was developed by including all life cycle stages of urban water using STELLA® software. The developed SDM was validated using the historical data of Peachland water consumption (BC). Moreover, the model was applied to analyze NZW of the Peachland community during 2015-34 by considering six different scenarios. In the base case scenario, two thirds of the supplied water will be used for irrigation and will not be directly available to the community for reuse. As the community is in a semi-arid region, the Peachland community can only achieve NZW or even net-plus water for the initial five years by considering Peachland as a typical urban community without agriculture, and by implementing various water efficiency improvement measures. However, due to the projected increase in water demand, the NZW cannot be achieved after 2019.  1 INTRODUCTION 1.1 Urban Water Systems and Peachland The world’s urban population is more than half (~54%) of the total population and is expected to increase rapidly (UN DESA 2014). In Canada, the urban population is very high (~ 81%) and is growing (Statistics Canada 2014a). The growing population requires a large volume of water served by the urban water supply. Urban water processes, such as water abstraction, treatment, distribution, wastewater treatment, disposal, and stormwater drainage are essential in any urban area. They are necessary for the human consumption of safe water and reduction of environmental impacts due to wastewater discharge (Termes-Rifé et al. 2013). These human regulated urban water processes constitute a human hydrologic cycle (Bagley et al. 2005), or simply an urban water system (UWS). The District of Peachland (DoP) is located in the Okanagan Valley, British Columbia (BC), Canada. The DoP covers an area of 17.98 square kilometres (DoP 2008). The estimated population of the DoP is 6320 in 2014 with an annual population growth of 6.5% (Statistics Canada 2014b). The public water is supplied from two creeks (Trapanier Creek and Deep Creek), Okanagan Lake, and two Ponderosa wells (groundwater) (DoP 2007). Major consumers of the municipal water are residential (indoor and outdoor) buildings, agriculture, public parks, golf courses, and commercial and institutional sectors. The 063-1 wastewater generated from the water use is treated at the Westside Regional Wastewater Treatment Plant and then discharged to Okanagan Lake.      1.2 System Dynamics Model (SDM) for Urban Water Systems System dynamics is a well-established methodology to quantify complex feedbacks in system interactions (Forrester, 1961; Forrester, 1968). The system dynamics model (SDM) is often used to quantify system behaviors with feedback loops for more accurate projections (Qi and Chang 2011). The model allows for the effective trade-off analysis of multi-scenarios and the multi-attributes of UWSs over time (Sehlke and Jacobson 2005). A SDM can help users better understand and express how complex systems function through visualization and computer simulation (Sehlke and Jacobson 2005). System dynamics involves the construction of “causal loop diagrams” or “stock and flow diagrams” to mimic a dynamic system. System dynamics has not been explored much in water demand estimation studies (Qi and Chang 2011; Zarghami and Akbariyeh 2012).  1.3 Net-Zero Water (NZW) Analysis The concept of net-zero water (NZW) is similar to the carrying capacity of a system (Holtzhower et al. 2014). NZW refers to the balance of water demand and supply within a given areal boundary (Holtzhower et al., 2014). The US Army states that “net-zero water limits the consumption of freshwater resources and returns water back to the same watershed so not to deplete the groundwater and surface water resources of that region in quantity or quality over the course of a year” (US Army 2011). The central theme of NZW  emphasizes a balance so that the sum of all input water is offset by comparable output water (Joustra and Yeh 2014). NZW presupposes that a community system can secure an adequate water supply within its boundaries, typically from surface water, groundwater, reclaimed water, and rainfall (Holtzhower et al. 2014). Achieving net-zero water similar to the natural cycle requires both the conservation of water and the creation of balanced water feedback loops (Joustra and Yeh 2014).  A recent report published by the US National Research Council showed that “The use of reclaimed water to augment potable water supplies has significant potential for helping to meet future needs, ….” and also recommended potable reuse with or without an environmental buffer as an alternative water management approach (National Research Council 2012). Similarly, water recycling for the augmentation of drinking water supplies has been promoted by the Australian government, who published guidelines for reclaimed water quality management (EPHC/NHMRC/NRMMC 2008). Also, in Canada, the provincial government of British Columbia has planned for the mandatory construction of dual water-plumbing (additional purple pipes for reclaimed water flow) in new buildings (MoE 2008). These initiatives show an increasing aspiration for reclaimed water use. This research develops a system dynamics model for the urban water system of Peachland and analyze its potentiality to achieve NZW.   2 METHODOLOGY The system dynamics model for the UWS of Peachland was developed by using STELLA® software (Karamouz et al., 2012; Qi and Chang, 2011). The SDM includes three sub-models: population, water, and wastewater sub-models. These sub-models and NZW analysis method are described below:  a. Population Sub-model The population dynamics of the District of Peachland was analyzed using the population growth equation as given in Equation 1 (Nasiri et al. 2013). The data required for the population sub-model, such as base population, population growth rate, and dwelling size were obtained from Statistics Canada (2014b).  [1] Nt = N0er t                     where Nt = population in a month, N0 = Base population, r = population growth rate (monthly), t = time duration in months  063-2 b. Water Sub-model The water sub-model represents the flow of supplied water within the Peachland community. The water flow occurs through the urban water stages: abstraction, treatment, distribution, and use. The water use dynamics was modelled using Equation 2. The equation includes the water consumed by different activities of the urban sectors: residential; industrial, commercial, and institutional (ICI); agricultural; public parks; and golf courses over time.  [2] (Water use)t = (Residential water use)t + (Agricultural water use)t + (Institutional water use)t + (Commercial water use)t + (Industrial water use)t + (Parks and golf courses water use)t where ‘”t” refers to a month  The rates of water consumption by different residential indoor activities were obtained from modified Mayer et al. (1999). The extensive study on the end uses of residential water also included Canadian cities. The efficiencies of conventional and efficient water fixtures and appliances were obtained from Mayer et al. (1999), ENERGY STAR (2014a), and ENERGY STAR (2014b). The rate of irrigation demand for different land covers such as agriculture, lawns, community parks, and golf courses of the Okanagan valley (OBWB 2010) was used for Peachland. The agricultural land area (121.6 ha) was estimated from the land use map of Peachland (DoP 2008). The average maximum site coverage of lot area is 48% for different types of residential buildings with an average lot size of 1178 m2 in the district (DoP 1996). The site not covered by building structures or paved areas is required to be landscaped. Based on these requirements, the average lawn area per dwelling unit was considered as 50% of the average lot size. In addition, the area of community parks is 14.49 ha and new neighbourhood development is required to maintain a community park of 3.04 ha per 1000 population (DoP 2014a). Also, a golf course of 0.6 ha is located in Peachland (Ponderosa Golf 2015). The rates of commercial and institutional (CI) water use were obtained from the CI water use studies by US EPA (2009) and Dziegielewski et al. (2000). The data on the present industrial, commercial, and institutional floor space and their future growth were obtained from (DoP 2012). However, Peachland has no major industries (DoP 2012).        c. Wastewater Sub-model The wastewater dynamic was modelled in the wastewater sub-model. This sub-model includes wastewater (WW) collection and its treatment for residential and ICI sectors. [3] (WW)t = (Residential WW)t + (Industrial WW)t + (Commercial WW)t + (Institutional WW)t  Where ‘”t” refers to a month  d. Net-Zero Water Analysis The potentiality of Peachland to achieve net-zero water was analyzed using the developed SDM. Equation 4 was used for the analysis. [4] (Net water)t = (Water use)t – (Rooftop rainwater harvested)t – (Greywater reused)t – (Reclaimed water use)t – (Stormwater harvested)t Where ‘”t” refers to a month The average monthly rainfall data of the past 35 years (1980 to 2014) of the nearby meteorological stations of Penticton and Kelowna (Government of Canada 2015) was used for the estimation of rooftop rainwater harvesting and stormwater harvesting potential.  Prior to the development of a complete SDM, a causal loop diagram (CLD) was developed. A CLD is a foundation of a SDM, and is used to identify relationships between individual system components and to show feedback loops that affect system regulation (Nasiri et al. 2013). The CLD of the SDM of the 063-3 Peachland UWS is given in Figure 1. In the CLD as shown in Figure 1, a ‘‘+’’ sign indicates a positive (reinforcing) relationship between two variables. An increase in the arrow tail variable causes an increase in the arrow head variable. A ‘‘-’’ sign indicates a negative (balancing) relationship between two variables. An increase in the arrow tail variable causes a decrease in the arrow head variable (Nasiri et al. 2013). Based on the CLD, a SDM was developed. The SDM was validated using the historical monthly data of municipal water consumption by Peachland from 2010 to 2014.  Water abstractionWastewaterIC WaterResidential wateruseGreywaterrecyclingResidentialindoor useResidentialoutdoor useDwelling unitsWaterappliances/faucets++++ +-IndustrialwaterCommercial waterInstitutional water+++ Agricultural waerParks and golfcourses waterWater use+++++Rooftop rainwaterharvesting Stormwaterharvesting+Net water++-Population +Population growth++Industrial indoorwaterIndustrial outdoorwaterCommercialindoor waterComercialoutdoor waterInstitutionaloutdoor waterInstitutional indoorwater+++ +++Wastewatertreament ++Wastewaterreclaimed++ Figure 1: Causal loop diagram of the urban water system of Peachland 3 RESULTS AND DISCUSSION 3.1 System Dynamics Model for the Peachland UWS The monthly water consumption of Peachland was simulated for five years from 2010 to 2014. The result was compared with the historical data of Peachland (DoP 2015) and is shown in Figure 2. The coefficient of determination (r2) of the model is 0.85, which is high and is acceptable. Both historical data and SDM result showed an equal average water consumption of Peachland: 1104 L/capita/day for the five-year duration. In particular, the average residential water consumption of Peachland from 2010 to 2014 was 711 L/capita/day based on the SDM. The residential water consumption of Peachland is very high compared to the Canadian average of 343 L/capita/day (Environment Canada 2014), British Columbia average of 490 L/capita/day, and Okanagan valley average of 675 L/capita/day (OBWB 2011). The important causal factor for high residential water consumption by Peachland may be a low density residential neighbourhood with a large area of outdoor landscaping. For example, a minimum lot size of a single family residential building is 1350 m2 (0-25% slope) to 4000 m2 (≥ 35% slope) in an area without sewer connection and is 830 m2 in an area with sewer connection and can have a maximum site coverage of 40%. Also, a site not covered by building structures or paved areas is required to be landscaped  (DoP 1996). In addition, neighbourhood developments are required to maintain the standard of 4.04 ha parks per 1000 population (neighbourhood parks of 1.01 ha and community parks of 3.04 ha) (DoP 2014a).  063-4 Table 1: Scenarios for net-zero water analysis Scenario Community water features Methods 1 Base case scenario Future community water features similar to the present. 2 Scenario 1 with the efficient water fixtures Efficient toilets, faucets, showers, dish washers, and cloth washers in all sectors with waterless urinals in CI sector. 3 Scenario 2 with irrigation demand reduction Irrigation demand reduction by: 50% in residential lawns and 30% in agriculture and community parks/golf courses; use xeriscaping; water efficient crops, and efficient irrigation; 15% water conservation by behavioural change 4 Scenario 3 with rooftop rainwater harvesting and greywater recycling Short term storage and use of harvested rainwater and recycled greywater 5 Scenario 4 with treated wastewater use Use of treated wastewater (black water) 6A Scenario 5 with stormwater harvesting and use Stormwater harvesting of built up area (downtown, neighbourhoods, and residential areas) of 520 ha 6B Typical urban setting of Scenario 6A Scenario 6A without considering agricultural water use The results of scenario analysis for achieving NZW from 2015 to 2034 are presented in Table 2 and Figure 5. As shown in Table 2, the average annual freshwater withdrawal of the UWS gradually decreases from Scenarios 1 to 6. The freshwater withdrawal and water use can be reduced by about 10% by using efficient water fixtures and appliances (Scenarios 1 to 2). However, water withdrawal and use can be reduced by 40% from Scenarios 1 to 3 by using efficient water fixtures and irrigation demand reduction. Peachland can reduce up to approximately 80% of freshwater withdrawal by using harvested rainwater, recycled greywater, treated wastewater (black water), and harvested stormwater (Scenario 6A compared to Scenario 1). Moreover, considering a typical urban setting without agriculture (Scenario 6B), Peachland can reduce up to 90% of water withdrawal by implementing similar measures to those of Scenario 6A.    Table 2: Average annual net water in six different scenarios for 2015 to 2034 period Scenarios Water use (ML) Freshwater withdrawal (ML) Net water (ML) Internal water reuses/harvesting Return to env. (Treated) 1 4974.5 4974.5 -3630.1 - WW 2 4485.7 (-9.8%) 4485.7 (-9.8%) -3537.0 (-2.6%) - WW 3 3018.8 (-39.3%) 3018.8 (-39.9%) -2203.1 (-39.3%) - WW 4 3018.8 (-39.3%) 1721.8 (-65.4%) -1426.5 (-60.7%) GW, RW WW 5 3018.8 (-39.3%) 1426.5 (-71.3%) -1426.5 (-60.7%) GW, RW, WW - 6A 3018.8 (-39.3%) 985.9 (-80.2%) -985.9 (-72.8%) GW, RW, WW, SW - 6B 2569.3 (-48.3) 536.4 (-89.2%) -536.4 (-85.2%) GW, RW, WW, SW - Note:  i. GW: Greywater recycling; RW: Rain water harvesting: WW: Wastewater (black water); SW: Stormwater harvesting; env: environment  ii. Parenthesis indicates a percentage change in the value from Scenario 1 iii. Negative sign indicates a reduction  063-7 conservation, reclaimed water use, rooftop rainwater harvesting, and stormwater harvesting (Scenario 6B). However, due to the projected increase in water demand, the NZW water condition cannot be achieved after 2019. Acknowledgements We acknowledge the financial assistance of the Natural Sciences and Engineering Research Council of Canada (NSERC) to conduct this research. We also acknowledge the financial and in-kind support of the industrial partners (New Monaco Enterprise, District of Peachland, Focus Engineering, Urban Systems, and FortisBC) for the NSERC Collaborative Research and Development Grants. Moreover, the research assistance of Dr. Bahareh Reza and the Okanagan Sustainability Institute (OSI) is appreciated.  References Bagley, David, Robert Andrews, Barry Adams, and Bryan Karney. 2005. “Development of Sustainable Water Systems for Urban Areas: A Human Hydrologic Cycle Approach.” In 33rd Annual Conference of the Canadian Society for Civil Engineering, 1698–1707. Toronto: Canadian Society for Civil Engineers. DoP. 1996. The District Of Peachland Zoning Bylaw Number 1375 (Amended October, 2014). Peachland, BC: District of Peachland. https://peachland.civicweb.net/Documents/DocumentList.aspx?ID=40844. DoP. 2007. Final Report: District of Peachland Water Master Plan. Kelowna, BC. DoP. 2008. “Land Use Designations.” In Official Community Plan. Peachland: District of Peachland. DoP. 2012. Economic Impact Analysis of Major Development Projects in Peachland. Peachland. DoP. 2014a. District of Peachland Official Community Plan: Consolidated Bylaw. Peachland, BC: District of Peachland. DoP. 2014b. Water Licenses: District of Peachland Official Database 2014. Peachland. DoP. 2015. District of Peachland Water Consumption: Official Database. Peachland. Dziegielewski, B, J. C Kiefer, G. L Lantz, E. M Opitz, G. A. Porter, W. B. Deoreo, P.W. Mayer, and J.O. Nelson. 2000. Commercial and Institutional End Uses of Water. Denver, CO: American Water Works Association Research Foundation and AWWA. ENERGY STAR. 2014a. “ENERGY STAR Certified Residential Clothes Washers.” http://www.energystar.gov/productfinder/product/certified-clothes-washers/results? ENERGY STAR. 2014b. “ENERGY STAR Certified Residential Dishwashers.” http://www.energystar.gov/productfinder/product/certified-residential-dishwashers/results. Environment Canada. 2014. “Wise Water Use.” http://www.ec.gc.ca/eau-water/default.asp?lang=En&n=F25C70EC-1. EPHC/NHMRC/NRMMC. 2008. Australian Guidelines for Water Recycling: Augmentation of Drinking Water Supplies. Canberra: Environment Protection and Heritage Council, National Health and Medical Research Council, Natural Resource Management Ministerial Council. Forrester, J.W. 1961. Industrial Dynamics. Cambridge, MA, USA: M.I.T. Press. Forrester, J.W. 1968. Principles of System Dynamics. Cambridge, MA, USA: Productivity Press. Government of Canada. 2015. “Climate: Accessing the Data.” http://climate.weather.gc.ca/index_e.html#access. Harma, Kirsten J., Mark S. Johnson, and Stewart J. Cohen. 2011. “Future Water Supply and Demand in the Okanagan Basin, British Columbia: A Scenario-Based Analysis of Multiple, Interacting Stressors.” Water Resources Management 26 (3): 667–89. doi:10.1007/s11269-011-9938-3. Holtzhower, D. Lantz, Kevin Priest, Rodrigo Castro-Raventós, and Robert J. Ries. 2014. “Value and Limits of Net Zero Energy, Water, and Agriculture.” In iiSBE Net Zero Built Environment: Nature-Based Building Performance - Net Zero Energy, Water, Carbon, and Waste, edited by Charles J. Kibert, Ravi Srinivasan, Lantz Holzhower, Hamed Hakim, and Ruthwik Pasunuru, 7–20. Gainesville, Florida: Rinker School of Construction Management, University of Florida. Joustra, Caryssa M., and Daniel H. Yeh. 2014. “Net-Zero Building Water Cycle Decision Support.” In iSBE Net Zero Built Environment: Nature-Based Building Performance - Net Zero Energy, Water, Carbon, and Waste, edited by Charles J. Kibert, Ravi Srinivasan, Lantz Holzhower, Hamed Hakim, and Ruthwik Pasunuru, 56–67. Gainesville, Florida: Rinker School of Construction Management, University of Florida. 063-9 Karamouz, Mohammad, Erfan Goharian, and Sara Nazif. 2012. “Development of a Reliability Based Dynamic Model of Urban Water Supply System : A Case Study,” 2067–78. Mayer, P.W., W.B. DeOreo, E.M. Opitz, J.C. Kiefer, W.Y. Davis, and B. Dziegielewski. 1999. Residential End Uses of Water. MoE. 2008. Living Water Smart: British Columbia’s Water Plan. BC Ministry of Environment. Nasiri, Fuzhan, Troy Savage, Ranran Wang, Nico Barawid, and Julie B. Zimmerman. 2013. “A System Dynamics Approach for Urban Water Reuse Planning: A Case Study from the Great Lakes Region.” Stochastic Environmental Research and Risk Assessment 27 (3): 675–91. doi:10.1007/s00477-012-0631-8. National Research Council. 2012. Water Reuse : Potential for Expanding the Nation’s Water Supply Through Reuse of Municipal Wastewater. Washington DC, USA: National Academies Press. OBWB. 2010. Agriculture Water Demand Model. Kelowna: Okanagan Basin Water Board. OBWB. 2011. Local Government User Guide: Okanagan Water Supply and Demand Project. Ponderosa Golf. 2015. “Building Ponderosa Golf.” http://ponderosaliving.ca/play/golf/building-ponderosa-golf. Qi, Cheng, and Ni-Bin Chang. 2011. “System Dynamics Modeling for Municipal Water Demand Estimation in an Urban Region under Uncertain Economic Impacts.” Journal of Environmental Management 92 (6). Elsevier Ltd: 1628–41. doi:10.1016/j.jenvman.2011.01.020. Sehlke, Gerald, and Jake Jacobson. 2005. “System Dynamics Modeling of Transboundary Systems: The Bear River Basin Model.” Ground Water 43 (5): 722–30. doi:10.1111/j.1745-6584.2005.00065.x. Statistics Canada. 2014a. “Population, Urban and Rural, by Province and Territory (Canada).” http://www.statcan.gc.ca/tables-tableaux/sum-som/l01/cst01/demo62a-eng.htm. Statistics Canada. 2014b. “Focus on Geography Series 2011 Census: Census Subdivision of Peachland, DM - British Columbia.” Termes-Rifé, Monserrat, María Molinos-Senante, Francesc Hernández-Sancho, and Ramón Sala-Garrido. 2013. “Life Cycle Costing: A Tool to Manage the Urban Water Cycle.” Journal of Water Supply: Research and Technology—AQUA 62 (7): 468. doi:10.2166/aqua.2013.110. UN DESA. 2014. World Urbanization Prospects: The 2014 Revision, Highlights (ST/ESA/SER.A/352). New York: United Nations Department of Economic and Social Affairs, Population Division. US Army. 2011. Net Zero Water for Army Installations: Cons Iderations for Policy and Technology. Edited by Elisabeth M Jenicek, Laura E Curvey, Annette L Stumpf, and Kelly Fishman. US Army Corps of Engineers. http://acwc.sdp.sirsi.net/client/search/asset/1002026. US EPA. 2009. Water Efficiency in the Commercial and Institutional Sector: Considerations for a WaterSense Program. EPA White Paper. Las Vegas: US Environmental Protection Agency. Zarghami, Mahdi, and Simin Akbariyeh. 2012. “System Dynamics Modeling for Complex Urban Water Systems: Application to the City of Tabriz, Iran.” Resources, Conservation and Recycling 60 (March). Elsevier B.V.: 99–106. doi:10.1016/j.resconrec.2011.11.008.   063-10  5th International/11th Construction Specialty Conference 5e International/11e Conférence spécialisée sur la construction    Vancouver, British Columbia June 8 to June 10, 2015 / 8 juin au 10 juin 2015   SYSTEM DYNAMICS MODELLING FOR AN URBAN WATER SYSTEM: NET-ZERO WATER ANALYSIS FOR PEACHLAND (BC) Gyan K. Chhipi-Shrestha1, 2, Kasun Hewage1 and Rehan Sadiq1 1 School of Engineering, University of British Columbia, Canada 2 Gyan.Shrestha@ubc.ca Abstract: A Net-zero water (NZW) community limits the consumption of freshwater resources and returns water back to the same watershed, so as not to deplete the groundwater and surface water resources of that region in quantity and quality over the course of a year. A NZW study includes the analysis of various combinations of water supply sources, water conservation, and reuse over time. Such dynamics can be modelled by using system dynamics. This article aims to develop a system dynamics model (SDM) to achieve NZW at the urban community level. The SDM was developed by including all life cycle stages of urban water using STELLA® software. The developed SDM was validated using the historical data of Peachland water consumption (BC). Moreover, the model was applied to analyze NZW of the Peachland community during 2015-34 by considering six different scenarios. In the base case scenario, two thirds of the supplied water will be used for irrigation and will not be directly available to the community for reuse. As the community is in a semi-arid region, the Peachland community can only achieve NZW or even net-plus water for the initial five years by considering Peachland as a typical urban community without agriculture, and by implementing various water efficiency improvement measures. However, due to the projected increase in water demand, the NZW cannot be achieved after 2019.  1 INTRODUCTION 1.1 Urban Water Systems and Peachland The world’s urban population is more than half (~54%) of the total population and is expected to increase rapidly (UN DESA 2014). In Canada, the urban population is very high (~ 81%) and is growing (Statistics Canada 2014a). The growing population requires a large volume of water served by the urban water supply. Urban water processes, such as water abstraction, treatment, distribution, wastewater treatment, disposal, and stormwater drainage are essential in any urban area. They are necessary for the human consumption of safe water and reduction of environmental impacts due to wastewater discharge (Termes-Rifé et al. 2013). These human regulated urban water processes constitute a human hydrologic cycle (Bagley et al. 2005), or simply an urban water system (UWS). The District of Peachland (DoP) is located in the Okanagan Valley, British Columbia (BC), Canada. The DoP covers an area of 17.98 square kilometres (DoP 2008). The estimated population of the DoP is 6320 in 2014 with an annual population growth of 6.5% (Statistics Canada 2014b). The public water is supplied from two creeks (Trapanier Creek and Deep Creek), Okanagan Lake, and two Ponderosa wells (groundwater) (DoP 2007). Major consumers of the municipal water are residential (indoor and outdoor) buildings, agriculture, public parks, golf courses, and commercial and institutional sectors. The 063-1 wastewater generated from the water use is treated at the Westside Regional Wastewater Treatment Plant and then discharged to Okanagan Lake.      1.2 System Dynamics Model (SDM) for Urban Water Systems System dynamics is a well-established methodology to quantify complex feedbacks in system interactions (Forrester, 1961; Forrester, 1968). The system dynamics model (SDM) is often used to quantify system behaviors with feedback loops for more accurate projections (Qi and Chang 2011). The model allows for the effective trade-off analysis of multi-scenarios and the multi-attributes of UWSs over time (Sehlke and Jacobson 2005). A SDM can help users better understand and express how complex systems function through visualization and computer simulation (Sehlke and Jacobson 2005). System dynamics involves the construction of “causal loop diagrams” or “stock and flow diagrams” to mimic a dynamic system. System dynamics has not been explored much in water demand estimation studies (Qi and Chang 2011; Zarghami and Akbariyeh 2012).  1.3 Net-Zero Water (NZW) Analysis The concept of net-zero water (NZW) is similar to the carrying capacity of a system (Holtzhower et al. 2014). NZW refers to the balance of water demand and supply within a given areal boundary (Holtzhower et al., 2014). The US Army states that “net-zero water limits the consumption of freshwater resources and returns water back to the same watershed so not to deplete the groundwater and surface water resources of that region in quantity or quality over the course of a year” (US Army 2011). The central theme of NZW  emphasizes a balance so that the sum of all input water is offset by comparable output water (Joustra and Yeh 2014). NZW presupposes that a community system can secure an adequate water supply within its boundaries, typically from surface water, groundwater, reclaimed water, and rainfall (Holtzhower et al. 2014). Achieving net-zero water similar to the natural cycle requires both the conservation of water and the creation of balanced water feedback loops (Joustra and Yeh 2014).  A recent report published by the US National Research Council showed that “The use of reclaimed water to augment potable water supplies has significant potential for helping to meet future needs, ….” and also recommended potable reuse with or without an environmental buffer as an alternative water management approach (National Research Council 2012). Similarly, water recycling for the augmentation of drinking water supplies has been promoted by the Australian government, who published guidelines for reclaimed water quality management (EPHC/NHMRC/NRMMC 2008). Also, in Canada, the provincial government of British Columbia has planned for the mandatory construction of dual water-plumbing (additional purple pipes for reclaimed water flow) in new buildings (MoE 2008). These initiatives show an increasing aspiration for reclaimed water use. This research develops a system dynamics model for the urban water system of Peachland and analyze its potentiality to achieve NZW.   2 METHODOLOGY The system dynamics model for the UWS of Peachland was developed by using STELLA® software (Karamouz et al., 2012; Qi and Chang, 2011). The SDM includes three sub-models: population, water, and wastewater sub-models. These sub-models and NZW analysis method are described below:  a. Population Sub-model The population dynamics of the District of Peachland was analyzed using the population growth equation as given in Equation 1 (Nasiri et al. 2013). The data required for the population sub-model, such as base population, population growth rate, and dwelling size were obtained from Statistics Canada (2014b).  [1] Nt = N0er t                     where Nt = population in a month, N0 = Base population, r = population growth rate (monthly), t = time duration in months  063-2 b. Water Sub-model The water sub-model represents the flow of supplied water within the Peachland community. The water flow occurs through the urban water stages: abstraction, treatment, distribution, and use. The water use dynamics was modelled using Equation 2. The equation includes the water consumed by different activities of the urban sectors: residential; industrial, commercial, and institutional (ICI); agricultural; public parks; and golf courses over time.  [2] (Water use)t = (Residential water use)t + (Agricultural water use)t + (Institutional water use)t + (Commercial water use)t + (Industrial water use)t + (Parks and golf courses water use)t where ‘”t” refers to a month  The rates of water consumption by different residential indoor activities were obtained from modified Mayer et al. (1999). The extensive study on the end uses of residential water also included Canadian cities. The efficiencies of conventional and efficient water fixtures and appliances were obtained from Mayer et al. (1999), ENERGY STAR (2014a), and ENERGY STAR (2014b). The rate of irrigation demand for different land covers such as agriculture, lawns, community parks, and golf courses of the Okanagan valley (OBWB 2010) was used for Peachland. The agricultural land area (121.6 ha) was estimated from the land use map of Peachland (DoP 2008). The average maximum site coverage of lot area is 48% for different types of residential buildings with an average lot size of 1178 m2 in the district (DoP 1996). The site not covered by building structures or paved areas is required to be landscaped. Based on these requirements, the average lawn area per dwelling unit was considered as 50% of the average lot size. In addition, the area of community parks is 14.49 ha and new neighbourhood development is required to maintain a community park of 3.04 ha per 1000 population (DoP 2014a). Also, a golf course of 0.6 ha is located in Peachland (Ponderosa Golf 2015). The rates of commercial and institutional (CI) water use were obtained from the CI water use studies by US EPA (2009) and Dziegielewski et al. (2000). The data on the present industrial, commercial, and institutional floor space and their future growth were obtained from (DoP 2012). However, Peachland has no major industries (DoP 2012).        c. Wastewater Sub-model The wastewater dynamic was modelled in the wastewater sub-model. This sub-model includes wastewater (WW) collection and its treatment for residential and ICI sectors. [3] (WW)t = (Residential WW)t + (Industrial WW)t + (Commercial WW)t + (Institutional WW)t  Where ‘”t” refers to a month  d. Net-Zero Water Analysis The potentiality of Peachland to achieve net-zero water was analyzed using the developed SDM. Equation 4 was used for the analysis. [4] (Net water)t = (Water use)t – (Rooftop rainwater harvested)t – (Greywater reused)t – (Reclaimed water use)t – (Stormwater harvested)t Where ‘”t” refers to a month The average monthly rainfall data of the past 35 years (1980 to 2014) of the nearby meteorological stations of Penticton and Kelowna (Government of Canada 2015) was used for the estimation of rooftop rainwater harvesting and stormwater harvesting potential.  Prior to the development of a complete SDM, a causal loop diagram (CLD) was developed. A CLD is a foundation of a SDM, and is used to identify relationships between individual system components and to show feedback loops that affect system regulation (Nasiri et al. 2013). The CLD of the SDM of the 063-3 Peachland UWS is given in Figure 1. In the CLD as shown in Figure 1, a ‘‘+’’ sign indicates a positive (reinforcing) relationship between two variables. An increase in the arrow tail variable causes an increase in the arrow head variable. A ‘‘-’’ sign indicates a negative (balancing) relationship between two variables. An increase in the arrow tail variable causes a decrease in the arrow head variable (Nasiri et al. 2013). Based on the CLD, a SDM was developed. The SDM was validated using the historical monthly data of municipal water consumption by Peachland from 2010 to 2014.  Water abstractionWastewaterIC WaterResidential wateruseGreywaterrecyclingResidentialindoor useResidentialoutdoor useDwelling unitsWaterappliances/faucets++++ +-IndustrialwaterCommercial waterInstitutional water+++ Agricultural waerParks and golfcourses waterWater use+++++Rooftop rainwaterharvesting Stormwaterharvesting+Net water++-Population +Population growth++Industrial indoorwaterIndustrial outdoorwaterCommercialindoor waterComercialoutdoor waterInstitutionaloutdoor waterInstitutional indoorwater+++ +++Wastewatertreament ++Wastewaterreclaimed++ Figure 1: Causal loop diagram of the urban water system of Peachland 3 RESULTS AND DISCUSSION 3.1 System Dynamics Model for the Peachland UWS The monthly water consumption of Peachland was simulated for five years from 2010 to 2014. The result was compared with the historical data of Peachland (DoP 2015) and is shown in Figure 2. The coefficient of determination (r2) of the model is 0.85, which is high and is acceptable. Both historical data and SDM result showed an equal average water consumption of Peachland: 1104 L/capita/day for the five-year duration. In particular, the average residential water consumption of Peachland from 2010 to 2014 was 711 L/capita/day based on the SDM. The residential water consumption of Peachland is very high compared to the Canadian average of 343 L/capita/day (Environment Canada 2014), British Columbia average of 490 L/capita/day, and Okanagan valley average of 675 L/capita/day (OBWB 2011). The important causal factor for high residential water consumption by Peachland may be a low density residential neighbourhood with a large area of outdoor landscaping. For example, a minimum lot size of a single family residential building is 1350 m2 (0-25% slope) to 4000 m2 (≥ 35% slope) in an area without sewer connection and is 830 m2 in an area with sewer connection and can have a maximum site coverage of 40%. Also, a site not covered by building structures or paved areas is required to be landscaped  (DoP 1996). In addition, neighbourhood developments are required to maintain the standard of 4.04 ha parks per 1000 population (neighbourhood parks of 1.01 ha and community parks of 3.04 ha) (DoP 2014a).  063-4 Table 1: Scenarios for net-zero water analysis Scenario Community water features Methods 1 Base case scenario Future community water features similar to the present. 2 Scenario 1 with the efficient water fixtures Efficient toilets, faucets, showers, dish washers, and cloth washers in all sectors with waterless urinals in CI sector. 3 Scenario 2 with irrigation demand reduction Irrigation demand reduction by: 50% in residential lawns and 30% in agriculture and community parks/golf courses; use xeriscaping; water efficient crops, and efficient irrigation; 15% water conservation by behavioural change 4 Scenario 3 with rooftop rainwater harvesting and greywater recycling Short term storage and use of harvested rainwater and recycled greywater 5 Scenario 4 with treated wastewater use Use of treated wastewater (black water) 6A Scenario 5 with stormwater harvesting and use Stormwater harvesting of built up area (downtown, neighbourhoods, and residential areas) of 520 ha 6B Typical urban setting of Scenario 6A Scenario 6A without considering agricultural water use The results of scenario analysis for achieving NZW from 2015 to 2034 are presented in Table 2 and Figure 5. As shown in Table 2, the average annual freshwater withdrawal of the UWS gradually decreases from Scenarios 1 to 6. The freshwater withdrawal and water use can be reduced by about 10% by using efficient water fixtures and appliances (Scenarios 1 to 2). However, water withdrawal and use can be reduced by 40% from Scenarios 1 to 3 by using efficient water fixtures and irrigation demand reduction. Peachland can reduce up to approximately 80% of freshwater withdrawal by using harvested rainwater, recycled greywater, treated wastewater (black water), and harvested stormwater (Scenario 6A compared to Scenario 1). Moreover, considering a typical urban setting without agriculture (Scenario 6B), Peachland can reduce up to 90% of water withdrawal by implementing similar measures to those of Scenario 6A.    Table 2: Average annual net water in six different scenarios for 2015 to 2034 period Scenarios Water use (ML) Freshwater withdrawal (ML) Net water (ML) Internal water reuses/harvesting Return to env. (Treated) 1 4974.5 4974.5 -3630.1 - WW 2 4485.7 (-9.8%) 4485.7 (-9.8%) -3537.0 (-2.6%) - WW 3 3018.8 (-39.3%) 3018.8 (-39.9%) -2203.1 (-39.3%) - WW 4 3018.8 (-39.3%) 1721.8 (-65.4%) -1426.5 (-60.7%) GW, RW WW 5 3018.8 (-39.3%) 1426.5 (-71.3%) -1426.5 (-60.7%) GW, RW, WW - 6A 3018.8 (-39.3%) 985.9 (-80.2%) -985.9 (-72.8%) GW, RW, WW, SW - 6B 2569.3 (-48.3) 536.4 (-89.2%) -536.4 (-85.2%) GW, RW, WW, SW - Note:  i. GW: Greywater recycling; RW: Rain water harvesting: WW: Wastewater (black water); SW: Stormwater harvesting; env: environment  ii. Parenthesis indicates a percentage change in the value from Scenario 1 iii. Negative sign indicates a reduction  063-7 conservation, reclaimed water use, rooftop rainwater harvesting, and stormwater harvesting (Scenario 6B). However, due to the projected increase in water demand, the NZW water condition cannot be achieved after 2019. Acknowledgements We acknowledge the financial assistance of the Natural Sciences and Engineering Research Council of Canada (NSERC) to conduct this research. We also acknowledge the financial and in-kind support of the industrial partners (New Monaco Enterprise, District of Peachland, Focus Engineering, Urban Systems, and FortisBC) for the NSERC Collaborative Research and Development Grants. Moreover, the research assistance of Dr. Bahareh Reza and the Okanagan Sustainability Institute (OSI) is appreciated.  References Bagley, David, Robert Andrews, Barry Adams, and Bryan Karney. 2005. “Development of Sustainable Water Systems for Urban Areas: A Human Hydrologic Cycle Approach.” In 33rd Annual Conference of the Canadian Society for Civil Engineering, 1698–1707. Toronto: Canadian Society for Civil Engineers. DoP. 1996. The District Of Peachland Zoning Bylaw Number 1375 (Amended October, 2014). Peachland, BC: District of Peachland. https://peachland.civicweb.net/Documents/DocumentList.aspx?ID=40844. DoP. 2007. Final Report: District of Peachland Water Master Plan. Kelowna, BC. DoP. 2008. “Land Use Designations.” In Official Community Plan. Peachland: District of Peachland. DoP. 2012. Economic Impact Analysis of Major Development Projects in Peachland. Peachland. DoP. 2014a. District of Peachland Official Community Plan: Consolidated Bylaw. Peachland, BC: District of Peachland. DoP. 2014b. Water Licenses: District of Peachland Official Database 2014. Peachland. DoP. 2015. District of Peachland Water Consumption: Official Database. Peachland. Dziegielewski, B, J. C Kiefer, G. L Lantz, E. M Opitz, G. A. Porter, W. B. Deoreo, P.W. Mayer, and J.O. Nelson. 2000. Commercial and Institutional End Uses of Water. Denver, CO: American Water Works Association Research Foundation and AWWA. ENERGY STAR. 2014a. “ENERGY STAR Certified Residential Clothes Washers.” http://www.energystar.gov/productfinder/product/certified-clothes-washers/results? ENERGY STAR. 2014b. “ENERGY STAR Certified Residential Dishwashers.” http://www.energystar.gov/productfinder/product/certified-residential-dishwashers/results. Environment Canada. 2014. “Wise Water Use.” http://www.ec.gc.ca/eau-water/default.asp?lang=En&n=F25C70EC-1. EPHC/NHMRC/NRMMC. 2008. Australian Guidelines for Water Recycling: Augmentation of Drinking Water Supplies. Canberra: Environment Protection and Heritage Council, National Health and Medical Research Council, Natural Resource Management Ministerial Council. Forrester, J.W. 1961. Industrial Dynamics. Cambridge, MA, USA: M.I.T. Press. Forrester, J.W. 1968. Principles of System Dynamics. Cambridge, MA, USA: Productivity Press. Government of Canada. 2015. “Climate: Accessing the Data.” http://climate.weather.gc.ca/index_e.html#access. Harma, Kirsten J., Mark S. Johnson, and Stewart J. Cohen. 2011. “Future Water Supply and Demand in the Okanagan Basin, British Columbia: A Scenario-Based Analysis of Multiple, Interacting Stressors.” Water Resources Management 26 (3): 667–89. doi:10.1007/s11269-011-9938-3. Holtzhower, D. Lantz, Kevin Priest, Rodrigo Castro-Raventós, and Robert J. Ries. 2014. “Value and Limits of Net Zero Energy, Water, and Agriculture.” In iiSBE Net Zero Built Environment: Nature-Based Building Performance - Net Zero Energy, Water, Carbon, and Waste, edited by Charles J. Kibert, Ravi Srinivasan, Lantz Holzhower, Hamed Hakim, and Ruthwik Pasunuru, 7–20. Gainesville, Florida: Rinker School of Construction Management, University of Florida. Joustra, Caryssa M., and Daniel H. Yeh. 2014. “Net-Zero Building Water Cycle Decision Support.” In iSBE Net Zero Built Environment: Nature-Based Building Performance - Net Zero Energy, Water, Carbon, and Waste, edited by Charles J. Kibert, Ravi Srinivasan, Lantz Holzhower, Hamed Hakim, and Ruthwik Pasunuru, 56–67. Gainesville, Florida: Rinker School of Construction Management, University of Florida. 063-9 Karamouz, Mohammad, Erfan Goharian, and Sara Nazif. 2012. “Development of a Reliability Based Dynamic Model of Urban Water Supply System : A Case Study,” 2067–78. Mayer, P.W., W.B. DeOreo, E.M. Opitz, J.C. Kiefer, W.Y. Davis, and B. Dziegielewski. 1999. Residential End Uses of Water. MoE. 2008. Living Water Smart: British Columbia’s Water Plan. BC Ministry of Environment. Nasiri, Fuzhan, Troy Savage, Ranran Wang, Nico Barawid, and Julie B. Zimmerman. 2013. “A System Dynamics Approach for Urban Water Reuse Planning: A Case Study from the Great Lakes Region.” Stochastic Environmental Research and Risk Assessment 27 (3): 675–91. doi:10.1007/s00477-012-0631-8. National Research Council. 2012. Water Reuse : Potential for Expanding the Nation’s Water Supply Through Reuse of Municipal Wastewater. Washington DC, USA: National Academies Press. OBWB. 2010. Agriculture Water Demand Model. Kelowna: Okanagan Basin Water Board. OBWB. 2011. Local Government User Guide: Okanagan Water Supply and Demand Project. Ponderosa Golf. 2015. “Building Ponderosa Golf.” http://ponderosaliving.ca/play/golf/building-ponderosa-golf. Qi, Cheng, and Ni-Bin Chang. 2011. “System Dynamics Modeling for Municipal Water Demand Estimation in an Urban Region under Uncertain Economic Impacts.” Journal of Environmental Management 92 (6). Elsevier Ltd: 1628–41. doi:10.1016/j.jenvman.2011.01.020. Sehlke, Gerald, and Jake Jacobson. 2005. “System Dynamics Modeling of Transboundary Systems: The Bear River Basin Model.” Ground Water 43 (5): 722–30. doi:10.1111/j.1745-6584.2005.00065.x. Statistics Canada. 2014a. “Population, Urban and Rural, by Province and Territory (Canada).” http://www.statcan.gc.ca/tables-tableaux/sum-som/l01/cst01/demo62a-eng.htm. Statistics Canada. 2014b. “Focus on Geography Series 2011 Census: Census Subdivision of Peachland, DM - British Columbia.” Termes-Rifé, Monserrat, María Molinos-Senante, Francesc Hernández-Sancho, and Ramón Sala-Garrido. 2013. “Life Cycle Costing: A Tool to Manage the Urban Water Cycle.” Journal of Water Supply: Research and Technology—AQUA 62 (7): 468. doi:10.2166/aqua.2013.110. UN DESA. 2014. World Urbanization Prospects: The 2014 Revision, Highlights (ST/ESA/SER.A/352). New York: United Nations Department of Economic and Social Affairs, Population Division. US Army. 2011. Net Zero Water for Army Installations: Cons Iderations for Policy and Technology. Edited by Elisabeth M Jenicek, Laura E Curvey, Annette L Stumpf, and Kelly Fishman. US Army Corps of Engineers. http://acwc.sdp.sirsi.net/client/search/asset/1002026. US EPA. 2009. Water Efficiency in the Commercial and Institutional Sector: Considerations for a WaterSense Program. EPA White Paper. Las Vegas: US Environmental Protection Agency. Zarghami, Mahdi, and Simin Akbariyeh. 2012. “System Dynamics Modeling for Complex Urban Water Systems: Application to the City of Tabriz, Iran.” Resources, Conservation and Recycling 60 (March). Elsevier B.V.: 99–106. doi:10.1016/j.resconrec.2011.11.008.   063-10  5th International/11th Construction Specialty Conference 5e International/11e Conférence spécialisée sur la construction    Vancouver, British Columbia June 8 to June 10, 2015 / 8 juin au 10 juin 2015   SYSTEM DYNAMICS MODELLING FOR AN URBAN WATER SYSTEM: NET-ZERO WATER ANALYSIS FOR PEACHLAND (BC) Gyan K. Chhipi-Shrestha1, 2, Kasun Hewage1 and Rehan Sadiq1 1 School of Engineering, University of British Columbia, Canada 2 Gyan.Shrestha@ubc.ca Abstract: A Net-zero water (NZW) community limits the consumption of freshwater resources and returns water back to the same watershed, so as not to deplete the groundwater and surface water resources of that region in quantity and quality over the course of a year. A NZW study includes the analysis of various combinations of water supply sources, water conservation, and reuse over time. Such dynamics can be modelled by using system dynamics. This article aims to develop a system dynamics model (SDM) to achieve NZW at the urban community level. The SDM was developed by including all life cycle stages of urban water using STELLA® software. The developed SDM was validated using the historical data of Peachland water consumption (BC). Moreover, the model was applied to analyze NZW of the Peachland community during 2015-34 by considering six different scenarios. In the base case scenario, two thirds of the supplied water will be used for irrigation and will not be directly available to the community for reuse. As the community is in a semi-arid region, the Peachland community can only achieve NZW or even net-plus water for the initial five years by considering Peachland as a typical urban community without agriculture, and by implementing various water efficiency improvement measures. However, due to the projected increase in water demand, the NZW cannot be achieved after 2019.  1 INTRODUCTION 1.1 Urban Water Systems and Peachland The world’s urban population is more than half (~54%) of the total population and is expected to increase rapidly (UN DESA 2014). In Canada, the urban population is very high (~ 81%) and is growing (Statistics Canada 2014a). The growing population requires a large volume of water served by the urban water supply. Urban water processes, such as water abstraction, treatment, distribution, wastewater treatment, disposal, and stormwater drainage are essential in any urban area. They are necessary for the human consumption of safe water and reduction of environmental impacts due to wastewater discharge (Termes-Rifé et al. 2013). These human regulated urban water processes constitute a human hydrologic cycle (Bagley et al. 2005), or simply an urban water system (UWS). The District of Peachland (DoP) is located in the Okanagan Valley, British Columbia (BC), Canada. The DoP covers an area of 17.98 square kilometres (DoP 2008). The estimated population of the DoP is 6320 in 2014 with an annual population growth of 6.5% (Statistics Canada 2014b). The public water is supplied from two creeks (Trapanier Creek and Deep Creek), Okanagan Lake, and two Ponderosa wells (groundwater) (DoP 2007). Major consumers of the municipal water are residential (indoor and outdoor) buildings, agriculture, public parks, golf courses, and commercial and institutional sectors. The 063-1 wastewater generated from the water use is treated at the Westside Regional Wastewater Treatment Plant and then discharged to Okanagan Lake.      1.2 System Dynamics Model (SDM) for Urban Water Systems System dynamics is a well-established methodology to quantify complex feedbacks in system interactions (Forrester, 1961; Forrester, 1968). The system dynamics model (SDM) is often used to quantify system behaviors with feedback loops for more accurate projections (Qi and Chang 2011). The model allows for the effective trade-off analysis of multi-scenarios and the multi-attributes of UWSs over time (Sehlke and Jacobson 2005). A SDM can help users better understand and express how complex systems function through visualization and computer simulation (Sehlke and Jacobson 2005). System dynamics involves the construction of “causal loop diagrams” or “stock and flow diagrams” to mimic a dynamic system. System dynamics has not been explored much in water demand estimation studies (Qi and Chang 2011; Zarghami and Akbariyeh 2012).  1.3 Net-Zero Water (NZW) Analysis The concept of net-zero water (NZW) is similar to the carrying capacity of a system (Holtzhower et al. 2014). NZW refers to the balance of water demand and supply within a given areal boundary (Holtzhower et al., 2014). The US Army states that “net-zero water limits the consumption of freshwater resources and returns water back to the same watershed so not to deplete the groundwater and surface water resources of that region in quantity or quality over the course of a year” (US Army 2011). The central theme of NZW  emphasizes a balance so that the sum of all input water is offset by comparable output water (Joustra and Yeh 2014). NZW presupposes that a community system can secure an adequate water supply within its boundaries, typically from surface water, groundwater, reclaimed water, and rainfall (Holtzhower et al. 2014). Achieving net-zero water similar to the natural cycle requires both the conservation of water and the creation of balanced water feedback loops (Joustra and Yeh 2014).  A recent report published by the US National Research Council showed that “The use of reclaimed water to augment potable water supplies has significant potential for helping to meet future needs, ….” and also recommended potable reuse with or without an environmental buffer as an alternative water management approach (National Research Council 2012). Similarly, water recycling for the augmentation of drinking water supplies has been promoted by the Australian government, who published guidelines for reclaimed water quality management (EPHC/NHMRC/NRMMC 2008). Also, in Canada, the provincial government of British Columbia has planned for the mandatory construction of dual water-plumbing (additional purple pipes for reclaimed water flow) in new buildings (MoE 2008). These initiatives show an increasing aspiration for reclaimed water use. This research develops a system dynamics model for the urban water system of Peachland and analyze its potentiality to achieve NZW.   2 METHODOLOGY The system dynamics model for the UWS of Peachland was developed by using STELLA® software (Karamouz et al., 2012; Qi and Chang, 2011). The SDM includes three sub-models: population, water, and wastewater sub-models. These sub-models and NZW analysis method are described below:  a. Population Sub-model The population dynamics of the District of Peachland was analyzed using the population growth equation as given in Equation 1 (Nasiri et al. 2013). The data required for the population sub-model, such as base population, population growth rate, and dwelling size were obtained from Statistics Canada (2014b).  [1] Nt = N0er t                     where Nt = population in a month, N0 = Base population, r = population growth rate (monthly), t = time duration in months  063-2 b. Water Sub-model The water sub-model represents the flow of supplied water within the Peachland community. The water flow occurs through the urban water stages: abstraction, treatment, distribution, and use. The water use dynamics was modelled using Equation 2. The equation includes the water consumed by different activities of the urban sectors: residential; industrial, commercial, and institutional (ICI); agricultural; public parks; and golf courses over time.  [2] (Water use)t = (Residential water use)t + (Agricultural water use)t + (Institutional water use)t + (Commercial water use)t + (Industrial water use)t + (Parks and golf courses water use)t where ‘”t” refers to a month  The rates of water consumption by different residential indoor activities were obtained from modified Mayer et al. (1999). The extensive study on the end uses of residential water also included Canadian cities. The efficiencies of conventional and efficient water fixtures and appliances were obtained from Mayer et al. (1999), ENERGY STAR (2014a), and ENERGY STAR (2014b). The rate of irrigation demand for different land covers such as agriculture, lawns, community parks, and golf courses of the Okanagan valley (OBWB 2010) was used for Peachland. The agricultural land area (121.6 ha) was estimated from the land use map of Peachland (DoP 2008). The average maximum site coverage of lot area is 48% for different types of residential buildings with an average lot size of 1178 m2 in the district (DoP 1996). The site not covered by building structures or paved areas is required to be landscaped. Based on these requirements, the average lawn area per dwelling unit was considered as 50% of the average lot size. In addition, the area of community parks is 14.49 ha and new neighbourhood development is required to maintain a community park of 3.04 ha per 1000 population (DoP 2014a). Also, a golf course of 0.6 ha is located in Peachland (Ponderosa Golf 2015). The rates of commercial and institutional (CI) water use were obtained from the CI water use studies by US EPA (2009) and Dziegielewski et al. (2000). The data on the present industrial, commercial, and institutional floor space and their future growth were obtained from (DoP 2012). However, Peachland has no major industries (DoP 2012).        c. Wastewater Sub-model The wastewater dynamic was modelled in the wastewater sub-model. This sub-model includes wastewater (WW) collection and its treatment for residential and ICI sectors. [3] (WW)t = (Residential WW)t + (Industrial WW)t + (Commercial WW)t + (Institutional WW)t  Where ‘”t” refers to a month  d. Net-Zero Water Analysis The potentiality of Peachland to achieve net-zero water was analyzed using the developed SDM. Equation 4 was used for the analysis. [4] (Net water)t = (Water use)t – (Rooftop rainwater harvested)t – (Greywater reused)t – (Reclaimed water use)t – (Stormwater harvested)t Where ‘”t” refers to a month The average monthly rainfall data of the past 35 years (1980 to 2014) of the nearby meteorological stations of Penticton and Kelowna (Government of Canada 2015) was used for the estimation of rooftop rainwater harvesting and stormwater harvesting potential.  Prior to the development of a complete SDM, a causal loop diagram (CLD) was developed. A CLD is a foundation of a SDM, and is used to identify relationships between individual system components and to show feedback loops that affect system regulation (Nasiri et al. 2013). The CLD of the SDM of the 063-3 Peachland UWS is given in Figure 1. In the CLD as shown in Figure 1, a ‘‘+’’ sign indicates a positive (reinforcing) relationship between two variables. An increase in the arrow tail variable causes an increase in the arrow head variable. A ‘‘-’’ sign indicates a negative (balancing) relationship between two variables. An increase in the arrow tail variable causes a decrease in the arrow head variable (Nasiri et al. 2013). Based on the CLD, a SDM was developed. The SDM was validated using the historical monthly data of municipal water consumption by Peachland from 2010 to 2014.  Water abstractionWastewaterIC WaterResidential wateruseGreywaterrecyclingResidentialindoor useResidentialoutdoor useDwelling unitsWaterappliances/faucets++++ +-IndustrialwaterCommercial waterInstitutional water+++ Agricultural waerParks and golfcourses waterWater use+++++Rooftop rainwaterharvesting Stormwaterharvesting+Net water++-Population +Population growth++Industrial indoorwaterIndustrial outdoorwaterCommercialindoor waterComercialoutdoor waterInstitutionaloutdoor waterInstitutional indoorwater+++ +++Wastewatertreament ++Wastewaterreclaimed++ Figure 1: Causal loop diagram of the urban water system of Peachland 3 RESULTS AND DISCUSSION 3.1 System Dynamics Model for the Peachland UWS The monthly water consumption of Peachland was simulated for five years from 2010 to 2014. The result was compared with the historical data of Peachland (DoP 2015) and is shown in Figure 2. The coefficient of determination (r2) of the model is 0.85, which is high and is acceptable. Both historical data and SDM result showed an equal average water consumption of Peachland: 1104 L/capita/day for the five-year duration. In particular, the average residential water consumption of Peachland from 2010 to 2014 was 711 L/capita/day based on the SDM. The residential water consumption of Peachland is very high compared to the Canadian average of 343 L/capita/day (Environment Canada 2014), British Columbia average of 490 L/capita/day, and Okanagan valley average of 675 L/capita/day (OBWB 2011). The important causal factor for high residential water consumption by Peachland may be a low density residential neighbourhood with a large area of outdoor landscaping. For example, a minimum lot size of a single family residential building is 1350 m2 (0-25% slope) to 4000 m2 (≥ 35% slope) in an area without sewer connection and is 830 m2 in an area with sewer connection and can have a maximum site coverage of 40%. Also, a site not covered by building structures or paved areas is required to be landscaped  (DoP 1996). In addition, neighbourhood developments are required to maintain the standard of 4.04 ha parks per 1000 population (neighbourhood parks of 1.01 ha and community parks of 3.04 ha) (DoP 2014a).  063-4 Table 1: Scenarios for net-zero water analysis Scenario Community water features Methods 1 Base case scenario Future community water features similar to the present. 2 Scenario 1 with the efficient water fixtures Efficient toilets, faucets, showers, dish washers, and cloth washers in all sectors with waterless urinals in CI sector. 3 Scenario 2 with irrigation demand reduction Irrigation demand reduction by: 50% in residential lawns and 30% in agriculture and community parks/golf courses; use xeriscaping; water efficient crops, and efficient irrigation; 15% water conservation by behavioural change 4 Scenario 3 with rooftop rainwater harvesting and greywater recycling Short term storage and use of harvested rainwater and recycled greywater 5 Scenario 4 with treated wastewater use Use of treated wastewater (black water) 6A Scenario 5 with stormwater harvesting and use Stormwater harvesting of built up area (downtown, neighbourhoods, and residential areas) of 520 ha 6B Typical urban setting of Scenario 6A Scenario 6A without considering agricultural water use The results of scenario analysis for achieving NZW from 2015 to 2034 are presented in Table 2 and Figure 5. As shown in Table 2, the average annual freshwater withdrawal of the UWS gradually decreases from Scenarios 1 to 6. The freshwater withdrawal and water use can be reduced by about 10% by using efficient water fixtures and appliances (Scenarios 1 to 2). However, water withdrawal and use can be reduced by 40% from Scenarios 1 to 3 by using efficient water fixtures and irrigation demand reduction. Peachland can reduce up to approximately 80% of freshwater withdrawal by using harvested rainwater, recycled greywater, treated wastewater (black water), and harvested stormwater (Scenario 6A compared to Scenario 1). Moreover, considering a typical urban setting without agriculture (Scenario 6B), Peachland can reduce up to 90% of water withdrawal by implementing similar measures to those of Scenario 6A.    Table 2: Average annual net water in six different scenarios for 2015 to 2034 period Scenarios Water use (ML) Freshwater withdrawal (ML) Net water (ML) Internal water reuses/harvesting Return to env. (Treated) 1 4974.5 4974.5 -3630.1 - WW 2 4485.7 (-9.8%) 4485.7 (-9.8%) -3537.0 (-2.6%) - WW 3 3018.8 (-39.3%) 3018.8 (-39.9%) -2203.1 (-39.3%) - WW 4 3018.8 (-39.3%) 1721.8 (-65.4%) -1426.5 (-60.7%) GW, RW WW 5 3018.8 (-39.3%) 1426.5 (-71.3%) -1426.5 (-60.7%) GW, RW, WW - 6A 3018.8 (-39.3%) 985.9 (-80.2%) -985.9 (-72.8%) GW, RW, WW, SW - 6B 2569.3 (-48.3) 536.4 (-89.2%) -536.4 (-85.2%) GW, RW, WW, SW - Note:  i. GW: Greywater recycling; RW: Rain water harvesting: WW: Wastewater (black water); SW: Stormwater harvesting; env: environment  ii. Parenthesis indicates a percentage change in the value from Scenario 1 iii. Negative sign indicates a reduction  063-7 conservation, reclaimed water use, rooftop rainwater harvesting, and stormwater harvesting (Scenario 6B). However, due to the projected increase in water demand, the NZW water condition cannot be achieved after 2019. Acknowledgements We acknowledge the financial assistance of the Natural Sciences and Engineering Research Council of Canada (NSERC) to conduct this research. We also acknowledge the financial and in-kind support of the industrial partners (New Monaco Enterprise, District of Peachland, Focus Engineering, Urban Systems, and FortisBC) for the NSERC Collaborative Research and Development Grants. Moreover, the research assistance of Dr. Bahareh Reza and the Okanagan Sustainability Institute (OSI) is appreciated.  References Bagley, David, Robert Andrews, Barry Adams, and Bryan Karney. 2005. “Development of Sustainable Water Systems for Urban Areas: A Human Hydrologic Cycle Approach.” In 33rd Annual Conference of the Canadian Society for Civil Engineering, 1698–1707. Toronto: Canadian Society for Civil Engineers. DoP. 1996. The District Of Peachland Zoning Bylaw Number 1375 (Amended October, 2014). Peachland, BC: District of Peachland. https://peachland.civicweb.net/Documents/DocumentList.aspx?ID=40844. DoP. 2007. Final Report: District of Peachland Water Master Plan. Kelowna, BC. DoP. 2008. “Land Use Designations.” In Official Community Plan. Peachland: District of Peachland. DoP. 2012. Economic Impact Analysis of Major Development Projects in Peachland. Peachland. DoP. 2014a. District of Peachland Official Community Plan: Consolidated Bylaw. Peachland, BC: District of Peachland. DoP. 2014b. Water Licenses: District of Peachland Official Database 2014. Peachland. DoP. 2015. District of Peachland Water Consumption: Official Database. Peachland. Dziegielewski, B, J. C Kiefer, G. L Lantz, E. M Opitz, G. A. Porter, W. B. Deoreo, P.W. Mayer, and J.O. Nelson. 2000. Commercial and Institutional End Uses of Water. Denver, CO: American Water Works Association Research Foundation and AWWA. ENERGY STAR. 2014a. “ENERGY STAR Certified Residential Clothes Washers.” http://www.energystar.gov/productfinder/product/certified-clothes-washers/results? ENERGY STAR. 2014b. “ENERGY STAR Certified Residential Dishwashers.” http://www.energystar.gov/productfinder/product/certified-residential-dishwashers/results. Environment Canada. 2014. “Wise Water Use.” http://www.ec.gc.ca/eau-water/default.asp?lang=En&n=F25C70EC-1. EPHC/NHMRC/NRMMC. 2008. Australian Guidelines for Water Recycling: Augmentation of Drinking Water Supplies. Canberra: Environment Protection and Heritage Council, National Health and Medical Research Council, Natural Resource Management Ministerial Council. Forrester, J.W. 1961. Industrial Dynamics. Cambridge, MA, USA: M.I.T. Press. Forrester, J.W. 1968. Principles of System Dynamics. Cambridge, MA, USA: Productivity Press. Government of Canada. 2015. “Climate: Accessing the Data.” http://climate.weather.gc.ca/index_e.html#access. Harma, Kirsten J., Mark S. Johnson, and Stewart J. Cohen. 2011. “Future Water Supply and Demand in the Okanagan Basin, British Columbia: A Scenario-Based Analysis of Multiple, Interacting Stressors.” Water Resources Management 26 (3): 667–89. doi:10.1007/s11269-011-9938-3. Holtzhower, D. Lantz, Kevin Priest, Rodrigo Castro-Raventós, and Robert J. Ries. 2014. “Value and Limits of Net Zero Energy, Water, and Agriculture.” In iiSBE Net Zero Built Environment: Nature-Based Building Performance - Net Zero Energy, Water, Carbon, and Waste, edited by Charles J. Kibert, Ravi Srinivasan, Lantz Holzhower, Hamed Hakim, and Ruthwik Pasunuru, 7–20. Gainesville, Florida: Rinker School of Construction Management, University of Florida. Joustra, Caryssa M., and Daniel H. Yeh. 2014. “Net-Zero Building Water Cycle Decision Support.” In iSBE Net Zero Built Environment: Nature-Based Building Performance - Net Zero Energy, Water, Carbon, and Waste, edited by Charles J. Kibert, Ravi Srinivasan, Lantz Holzhower, Hamed Hakim, and Ruthwik Pasunuru, 56–67. Gainesville, Florida: Rinker School of Construction Management, University of Florida. 063-9 Karamouz, Mohammad, Erfan Goharian, and Sara Nazif. 2012. “Development of a Reliability Based Dynamic Model of Urban Water Supply System : A Case Study,” 2067–78. Mayer, P.W., W.B. DeOreo, E.M. Opitz, J.C. Kiefer, W.Y. Davis, and B. Dziegielewski. 1999. Residential End Uses of Water. MoE. 2008. Living Water Smart: British Columbia’s Water Plan. BC Ministry of Environment. Nasiri, Fuzhan, Troy Savage, Ranran Wang, Nico Barawid, and Julie B. Zimmerman. 2013. “A System Dynamics Approach for Urban Water Reuse Planning: A Case Study from the Great Lakes Region.” Stochastic Environmental Research and Risk Assessment 27 (3): 675–91. doi:10.1007/s00477-012-0631-8. National Research Council. 2012. Water Reuse : Potential for Expanding the Nation’s Water Supply Through Reuse of Municipal Wastewater. Washington DC, USA: National Academies Press. OBWB. 2010. Agriculture Water Demand Model. Kelowna: Okanagan Basin Water Board. OBWB. 2011. Local Government User Guide: Okanagan Water Supply and Demand Project. Ponderosa Golf. 2015. “Building Ponderosa Golf.” http://ponderosaliving.ca/play/golf/building-ponderosa-golf. Qi, Cheng, and Ni-Bin Chang. 2011. “System Dynamics Modeling for Municipal Water Demand Estimation in an Urban Region under Uncertain Economic Impacts.” Journal of Environmental Management 92 (6). Elsevier Ltd: 1628–41. doi:10.1016/j.jenvman.2011.01.020. Sehlke, Gerald, and Jake Jacobson. 2005. “System Dynamics Modeling of Transboundary Systems: The Bear River Basin Model.” Ground Water 43 (5): 722–30. doi:10.1111/j.1745-6584.2005.00065.x. Statistics Canada. 2014a. “Population, Urban and Rural, by Province and Territory (Canada).” http://www.statcan.gc.ca/tables-tableaux/sum-som/l01/cst01/demo62a-eng.htm. Statistics Canada. 2014b. “Focus on Geography Series 2011 Census: Census Subdivision of Peachland, DM - British Columbia.” Termes-Rifé, Monserrat, María Molinos-Senante, Francesc Hernández-Sancho, and Ramón Sala-Garrido. 2013. “Life Cycle Costing: A Tool to Manage the Urban Water Cycle.” Journal of Water Supply: Research and Technology—AQUA 62 (7): 468. doi:10.2166/aqua.2013.110. UN DESA. 2014. World Urbanization Prospects: The 2014 Revision, Highlights (ST/ESA/SER.A/352). New York: United Nations Department of Economic and Social Affairs, Population Division. US Army. 2011. Net Zero Water for Army Installations: Cons Iderations for Policy and Technology. Edited by Elisabeth M Jenicek, Laura E Curvey, Annette L Stumpf, and Kelly Fishman. US Army Corps of Engineers. http://acwc.sdp.sirsi.net/client/search/asset/1002026. US EPA. 2009. Water Efficiency in the Commercial and Institutional Sector: Considerations for a WaterSense Program. EPA White Paper. Las Vegas: US Environmental Protection Agency. Zarghami, Mahdi, and Simin Akbariyeh. 2012. “System Dynamics Modeling for Complex Urban Water Systems: Application to the City of Tabriz, Iran.” Resources, Conservation and Recycling 60 (March). Elsevier B.V.: 99–106. doi:10.1016/j.resconrec.2011.11.008.   063-10  5th International/11th Construction Specialty Conference 5e International/11e Conférence spécialisée sur la construction    Vancouver, British Columbia June 8 to June 10, 2015 / 8 juin au 10 juin 2015   SYSTEM DYNAMICS MODELLING FOR AN URBAN WATER SYSTEM: NET-ZERO WATER ANALYSIS FOR PEACHLAND (BC) Gyan K. Chhipi-Shrestha1, 2, Kasun Hewage1 and Rehan Sadiq1 1 School of Engineering, University of British Columbia, Canada 2 Gyan.Shrestha@ubc.ca Abstract: A Net-zero water (NZW) community limits the consumption of freshwater resources and returns water back to the same watershed, so as not to deplete the groundwater and surface water resources of that region in quantity and quality over the course of a year. A NZW study includes the analysis of various combinations of water supply sources, water conservation, and reuse over time. Such dynamics can be modelled by using system dynamics. This article aims to develop a system dynamics model (SDM) to achieve NZW at the urban community level. The SDM was developed by including all life cycle stages of urban water using STELLA® software. The developed SDM was validated using the historical data of Peachland water consumption (BC). Moreover, the model was applied to analyze NZW of the Peachland community during 2015-34 by considering six different scenarios. In the base case scenario, two thirds of the supplied water will be used for irrigation and will not be directly available to the community for reuse. As the community is in a semi-arid region, the Peachland community can only achieve NZW or even net-plus water for the initial five years by considering Peachland as a typical urban community without agriculture, and by implementing various water efficiency improvement measures. However, due to the projected increase in water demand, the NZW cannot be achieved after 2019.  1 INTRODUCTION 1.1 Urban Water Systems and Peachland The world’s urban population is more than half (~54%) of the total population and is expected to increase rapidly (UN DESA 2014). In Canada, the urban population is very high (~ 81%) and is growing (Statistics Canada 2014a). The growing population requires a large volume of water served by the urban water supply. Urban water processes, such as water abstraction, treatment, distribution, wastewater treatment, disposal, and stormwater drainage are essential in any urban area. They are necessary for the human consumption of safe water and reduction of environmental impacts due to wastewater discharge (Termes-Rifé et al. 2013). These human regulated urban water processes constitute a human hydrologic cycle (Bagley et al. 2005), or simply an urban water system (UWS). The District of Peachland (DoP) is located in the Okanagan Valley, British Columbia (BC), Canada. The DoP covers an area of 17.98 square kilometres (DoP 2008). The estimated population of the DoP is 6320 in 2014 with an annual population growth of 6.5% (Statistics Canada 2014b). The public water is supplied from two creeks (Trapanier Creek and Deep Creek), Okanagan Lake, and two Ponderosa wells (groundwater) (DoP 2007). Major consumers of the municipal water are residential (indoor and outdoor) buildings, agriculture, public parks, golf courses, and commercial and institutional sectors. The 063-1 wastewater generated from the water use is treated at the Westside Regional Wastewater Treatment Plant and then discharged to Okanagan Lake.      1.2 System Dynamics Model (SDM) for Urban Water Systems System dynamics is a well-established methodology to quantify complex feedbacks in system interactions (Forrester, 1961; Forrester, 1968). The system dynamics model (SDM) is often used to quantify system behaviors with feedback loops for more accurate projections (Qi and Chang 2011). The model allows for the effective trade-off analysis of multi-scenarios and the multi-attributes of UWSs over time (Sehlke and Jacobson 2005). A SDM can help users better understand and express how complex systems function through visualization and computer simulation (Sehlke and Jacobson 2005). System dynamics involves the construction of “causal loop diagrams” or “stock and flow diagrams” to mimic a dynamic system. System dynamics has not been explored much in water demand estimation studies (Qi and Chang 2011; Zarghami and Akbariyeh 2012).  1.3 Net-Zero Water (NZW) Analysis The concept of net-zero water (NZW) is similar to the carrying capacity of a system (Holtzhower et al. 2014). NZW refers to the balance of water demand and supply within a given areal boundary (Holtzhower et al., 2014). The US Army states that “net-zero water limits the consumption of freshwater resources and returns water back to the same watershed so not to deplete the groundwater and surface water resources of that region in quantity or quality over the course of a year” (US Army 2011). The central theme of NZW  emphasizes a balance so that the sum of all input water is offset by comparable output water (Joustra and Yeh 2014). NZW presupposes that a community system can secure an adequate water supply within its boundaries, typically from surface water, groundwater, reclaimed water, and rainfall (Holtzhower et al. 2014). Achieving net-zero water similar to the natural cycle requires both the conservation of water and the creation of balanced water feedback loops (Joustra and Yeh 2014).  A recent report published by the US National Research Council showed that “The use of reclaimed water to augment potable water supplies has significant potential for helping to meet future needs, ….” and also recommended potable reuse with or without an environmental buffer as an alternative water management approach (National Research Council 2012). Similarly, water recycling for the augmentation of drinking water supplies has been promoted by the Australian government, who published guidelines for reclaimed water quality management (EPHC/NHMRC/NRMMC 2008). Also, in Canada, the provincial government of British Columbia has planned for the mandatory construction of dual water-plumbing (additional purple pipes for reclaimed water flow) in new buildings (MoE 2008). These initiatives show an increasing aspiration for reclaimed water use. This research develops a system dynamics model for the urban water system of Peachland and analyze its potentiality to achieve NZW.   2 METHODOLOGY The system dynamics model for the UWS of Peachland was developed by using STELLA® software (Karamouz et al., 2012; Qi and Chang, 2011). The SDM includes three sub-models: population, water, and wastewater sub-models. These sub-models and NZW analysis method are described below:  a. Population Sub-model The population dynamics of the District of Peachland was analyzed using the population growth equation as given in Equation 1 (Nasiri et al. 2013). The data required for the population sub-model, such as base population, population growth rate, and dwelling size were obtained from Statistics Canada (2014b).  [1] Nt = N0er t                     where Nt = population in a month, N0 = Base population, r = population growth rate (monthly), t = time duration in months  063-2 b. Water Sub-model The water sub-model represents the flow of supplied water within the Peachland community. The water flow occurs through the urban water stages: abstraction, treatment, distribution, and use. The water use dynamics was modelled using Equation 2. The equation includes the water consumed by different activities of the urban sectors: residential; industrial, commercial, and institutional (ICI); agricultural; public parks; and golf courses over time.  [2] (Water use)t = (Residential water use)t + (Agricultural water use)t + (Institutional water use)t + (Commercial water use)t + (Industrial water use)t + (Parks and golf courses water use)t where ‘”t” refers to a month  The rates of water consumption by different residential indoor activities were obtained from modified Mayer et al. (1999). The extensive study on the end uses of residential water also included Canadian cities. The efficiencies of conventional and efficient water fixtures and appliances were obtained from Mayer et al. (1999), ENERGY STAR (2014a), and ENERGY STAR (2014b). The rate of irrigation demand for different land covers such as agriculture, lawns, community parks, and golf courses of the Okanagan valley (OBWB 2010) was used for Peachland. The agricultural land area (121.6 ha) was estimated from the land use map of Peachland (DoP 2008). The average maximum site coverage of lot area is 48% for different types of residential buildings with an average lot size of 1178 m2 in the district (DoP 1996). The site not covered by building structures or paved areas is required to be landscaped. Based on these requirements, the average lawn area per dwelling unit was considered as 50% of the average lot size. In addition, the area of community parks is 14.49 ha and new neighbourhood development is required to maintain a community park of 3.04 ha per 1000 population (DoP 2014a). Also, a golf course of 0.6 ha is located in Peachland (Ponderosa Golf 2015). The rates of commercial and institutional (CI) water use were obtained from the CI water use studies by US EPA (2009) and Dziegielewski et al. (2000). The data on the present industrial, commercial, and institutional floor space and their future growth were obtained from (DoP 2012). However, Peachland has no major industries (DoP 2012).        c. Wastewater Sub-model The wastewater dynamic was modelled in the wastewater sub-model. This sub-model includes wastewater (WW) collection and its treatment for residential and ICI sectors. [3] (WW)t = (Residential WW)t + (Industrial WW)t + (Commercial WW)t + (Institutional WW)t  Where ‘”t” refers to a month  d. Net-Zero Water Analysis The potentiality of Peachland to achieve net-zero water was analyzed using the developed SDM. Equation 4 was used for the analysis. [4] (Net water)t = (Water use)t – (Rooftop rainwater harvested)t – (Greywater reused)t – (Reclaimed water use)t – (Stormwater harvested)t Where ‘”t” refers to a month The average monthly rainfall data of the past 35 years (1980 to 2014) of the nearby meteorological stations of Penticton and Kelowna (Government of Canada 2015) was used for the estimation of rooftop rainwater harvesting and stormwater harvesting potential.  Prior to the development of a complete SDM, a causal loop diagram (CLD) was developed. A CLD is a foundation of a SDM, and is used to identify relationships between individual system components and to show feedback loops that affect system regulation (Nasiri et al. 2013). The CLD of the SDM of the 063-3 Peachland UWS is given in Figure 1. In the CLD as shown in Figure 1, a ‘‘+’’ sign indicates a positive (reinforcing) relationship between two variables. An increase in the arrow tail variable causes an increase in the arrow head variable. A ‘‘-’’ sign indicates a negative (balancing) relationship between two variables. An increase in the arrow tail variable causes a decrease in the arrow head variable (Nasiri et al. 2013). Based on the CLD, a SDM was developed. The SDM was validated using the historical monthly data of municipal water consumption by Peachland from 2010 to 2014.  Water abstractionWastewaterIC WaterResidential wateruseGreywaterrecyclingResidentialindoor useResidentialoutdoor useDwelling unitsWaterappliances/faucets++++ +-IndustrialwaterCommercial waterInstitutional water+++ Agricultural waerParks and golfcourses waterWater use+++++Rooftop rainwaterharvesting Stormwaterharvesting+Net water++-Population +Population growth++Industrial indoorwaterIndustrial outdoorwaterCommercialindoor waterComercialoutdoor waterInstitutionaloutdoor waterInstitutional indoorwater+++ +++Wastewatertreament ++Wastewaterreclaimed++ Figure 1: Causal loop diagram of the urban water system of Peachland 3 RESULTS AND DISCUSSION 3.1 System Dynamics Model for the Peachland UWS The monthly water consumption of Peachland was simulated for five years from 2010 to 2014. The result was compared with the historical data of Peachland (DoP 2015) and is shown in Figure 2. The coefficient of determination (r2) of the model is 0.85, which is high and is acceptable. Both historical data and SDM result showed an equal average water consumption of Peachland: 1104 L/capita/day for the five-year duration. In particular, the average residential water consumption of Peachland from 2010 to 2014 was 711 L/capita/day based on the SDM. The residential water consumption of Peachland is very high compared to the Canadian average of 343 L/capita/day (Environment Canada 2014), British Columbia average of 490 L/capita/day, and Okanagan valley average of 675 L/capita/day (OBWB 2011). The important causal factor for high residential water consumption by Peachland may be a low density residential neighbourhood with a large area of outdoor landscaping. For example, a minimum lot size of a single family residential building is 1350 m2 (0-25% slope) to 4000 m2 (≥ 35% slope) in an area without sewer connection and is 830 m2 in an area with sewer connection and can have a maximum site coverage of 40%. Also, a site not covered by building structures or paved areas is required to be landscaped  (DoP 1996). In addition, neighbourhood developments are required to maintain the standard of 4.04 ha parks per 1000 population (neighbourhood parks of 1.01 ha and community parks of 3.04 ha) (DoP 2014a).  063-4 Table 1: Scenarios for net-zero water analysis Scenario Community water features Methods 1 Base case scenario Future community water features similar to the present. 2 Scenario 1 with the efficient water fixtures Efficient toilets, faucets, showers, dish washers, and cloth washers in all sectors with waterless urinals in CI sector. 3 Scenario 2 with irrigation demand reduction Irrigation demand reduction by: 50% in residential lawns and 30% in agriculture and community parks/golf courses; use xeriscaping; water efficient crops, and efficient irrigation; 15% water conservation by behavioural change 4 Scenario 3 with rooftop rainwater harvesting and greywater recycling Short term storage and use of harvested rainwater and recycled greywater 5 Scenario 4 with treated wastewater use Use of treated wastewater (black water) 6A Scenario 5 with stormwater harvesting and use Stormwater harvesting of built up area (downtown, neighbourhoods, and residential areas) of 520 ha 6B Typical urban setting of Scenario 6A Scenario 6A without considering agricultural water use The results of scenario analysis for achieving NZW from 2015 to 2034 are presented in Table 2 and Figure 5. As shown in Table 2, the average annual freshwater withdrawal of the UWS gradually decreases from Scenarios 1 to 6. The freshwater withdrawal and water use can be reduced by about 10% by using efficient water fixtures and appliances (Scenarios 1 to 2). However, water withdrawal and use can be reduced by 40% from Scenarios 1 to 3 by using efficient water fixtures and irrigation demand reduction. Peachland can reduce up to approximately 80% of freshwater withdrawal by using harvested rainwater, recycled greywater, treated wastewater (black water), and harvested stormwater (Scenario 6A compared to Scenario 1). Moreover, considering a typical urban setting without agriculture (Scenario 6B), Peachland can reduce up to 90% of water withdrawal by implementing similar measures to those of Scenario 6A.    Table 2: Average annual net water in six different scenarios for 2015 to 2034 period Scenarios Water use (ML) Freshwater withdrawal (ML) Net water (ML) Internal water reuses/harvesting Return to env. (Treated) 1 4974.5 4974.5 -3630.1 - WW 2 4485.7 (-9.8%) 4485.7 (-9.8%) -3537.0 (-2.6%) - WW 3 3018.8 (-39.3%) 3018.8 (-39.9%) -2203.1 (-39.3%) - WW 4 3018.8 (-39.3%) 1721.8 (-65.4%) -1426.5 (-60.7%) GW, RW WW 5 3018.8 (-39.3%) 1426.5 (-71.3%) -1426.5 (-60.7%) GW, RW, WW - 6A 3018.8 (-39.3%) 985.9 (-80.2%) -985.9 (-72.8%) GW, RW, WW, SW - 6B 2569.3 (-48.3) 536.4 (-89.2%) -536.4 (-85.2%) GW, RW, WW, SW - Note:  i. GW: Greywater recycling; RW: Rain water harvesting: WW: Wastewater (black water); SW: Stormwater harvesting; env: environment  ii. Parenthesis indicates a percentage change in the value from Scenario 1 iii. Negative sign indicates a reduction  063-7 conservation, reclaimed water use, rooftop rainwater harvesting, and stormwater harvesting (Scenario 6B). However, due to the projected increase in water demand, the NZW water condition cannot be achieved after 2019. Acknowledgements We acknowledge the financial assistance of the Natural Sciences and Engineering Research Council of Canada (NSERC) to conduct this research. We also acknowledge the financial and in-kind support of the industrial partners (New Monaco Enterprise, District of Peachland, Focus Engineering, Urban Systems, and FortisBC) for the NSERC Collaborative Research and Development Grants. Moreover, the research assistance of Dr. Bahareh Reza and the Okanagan Sustainability Institute (OSI) is appreciated.  References Bagley, David, Robert Andrews, Barry Adams, and Bryan Karney. 2005. “Development of Sustainable Water Systems for Urban Areas: A Human Hydrologic Cycle Approach.” In 33rd Annual Conference of the Canadian Society for Civil Engineering, 1698–1707. Toronto: Canadian Society for Civil Engineers. DoP. 1996. The District Of Peachland Zoning Bylaw Number 1375 (Amended October, 2014). Peachland, BC: District of Peachland. https://peachland.civicweb.net/Documents/DocumentList.aspx?ID=40844. DoP. 2007. Final Report: District of Peachland Water Master Plan. Kelowna, BC. DoP. 2008. “Land Use Designations.” In Official Community Plan. Peachland: District of Peachland. DoP. 2012. Economic Impact Analysis of Major Development Projects in Peachland. Peachland. DoP. 2014a. District of Peachland Official Community Plan: Consolidated Bylaw. Peachland, BC: District of Peachland. DoP. 2014b. Water Licenses: District of Peachland Official Database 2014. Peachland. DoP. 2015. District of Peachland Water Consumption: Official Database. Peachland. Dziegielewski, B, J. C Kiefer, G. L Lantz, E. M Opitz, G. A. Porter, W. B. Deoreo, P.W. Mayer, and J.O. Nelson. 2000. Commercial and Institutional End Uses of Water. Denver, CO: American Water Works Association Research Foundation and AWWA. ENERGY STAR. 2014a. “ENERGY STAR Certified Residential Clothes Washers.” http://www.energystar.gov/productfinder/product/certified-clothes-washers/results? ENERGY STAR. 2014b. “ENERGY STAR Certified Residential Dishwashers.” http://www.energystar.gov/productfinder/product/certified-residential-dishwashers/results. Environment Canada. 2014. “Wise Water Use.” http://www.ec.gc.ca/eau-water/default.asp?lang=En&n=F25C70EC-1. EPHC/NHMRC/NRMMC. 2008. Australian Guidelines for Water Recycling: Augmentation of Drinking Water Supplies. Canberra: Environment Protection and Heritage Council, National Health and Medical Research Council, Natural Resource Management Ministerial Council. Forrester, J.W. 1961. Industrial Dynamics. Cambridge, MA, USA: M.I.T. Press. Forrester, J.W. 1968. Principles of System Dynamics. Cambridge, MA, USA: Productivity Press. Government of Canada. 2015. “Climate: Accessing the Data.” http://climate.weather.gc.ca/index_e.html#access. Harma, Kirsten J., Mark S. Johnson, and Stewart J. Cohen. 2011. “Future Water Supply and Demand in the Okanagan Basin, British Columbia: A Scenario-Based Analysis of Multiple, Interacting Stressors.” Water Resources Management 26 (3): 667–89. doi:10.1007/s11269-011-9938-3. Holtzhower, D. Lantz, Kevin Priest, Rodrigo Castro-Raventós, and Robert J. Ries. 2014. “Value and Limits of Net Zero Energy, Water, and Agriculture.” In iiSBE Net Zero Built Environment: Nature-Based Building Performance - Net Zero Energy, Water, Carbon, and Waste, edited by Charles J. Kibert, Ravi Srinivasan, Lantz Holzhower, Hamed Hakim, and Ruthwik Pasunuru, 7–20. Gainesville, Florida: Rinker School of Construction Management, University of Florida. Joustra, Caryssa M., and Daniel H. Yeh. 2014. “Net-Zero Building Water Cycle Decision Support.” In iSBE Net Zero Built Environment: Nature-Based Building Performance - Net Zero Energy, Water, Carbon, and Waste, edited by Charles J. Kibert, Ravi Srinivasan, Lantz Holzhower, Hamed Hakim, and Ruthwik Pasunuru, 56–67. Gainesville, Florida: Rinker School of Construction Management, University of Florida. 063-9 Karamouz, Mohammad, Erfan Goharian, and Sara Nazif. 2012. “Development of a Reliability Based Dynamic Model of Urban Water Supply System : A Case Study,” 2067–78. Mayer, P.W., W.B. DeOreo, E.M. Opitz, J.C. Kiefer, W.Y. Davis, and B. Dziegielewski. 1999. Residential End Uses of Water. MoE. 2008. Living Water Smart: British Columbia’s Water Plan. BC Ministry of Environment. Nasiri, Fuzhan, Troy Savage, Ranran Wang, Nico Barawid, and Julie B. Zimmerman. 2013. “A System Dynamics Approach for Urban Water Reuse Planning: A Case Study from the Great Lakes Region.” Stochastic Environmental Research and Risk Assessment 27 (3): 675–91. doi:10.1007/s00477-012-0631-8. National Research Council. 2012. Water Reuse : Potential for Expanding the Nation’s Water Supply Through Reuse of Municipal Wastewater. Washington DC, USA: National Academies Press. OBWB. 2010. Agriculture Water Demand Model. Kelowna: Okanagan Basin Water Board. OBWB. 2011. Local Government User Guide: Okanagan Water Supply and Demand Project. Ponderosa Golf. 2015. “Building Ponderosa Golf.” http://ponderosaliving.ca/play/golf/building-ponderosa-golf. Qi, Cheng, and Ni-Bin Chang. 2011. “System Dynamics Modeling for Municipal Water Demand Estimation in an Urban Region under Uncertain Economic Impacts.” Journal of Environmental Management 92 (6). Elsevier Ltd: 1628–41. doi:10.1016/j.jenvman.2011.01.020. Sehlke, Gerald, and Jake Jacobson. 2005. “System Dynamics Modeling of Transboundary Systems: The Bear River Basin Model.” Ground Water 43 (5): 722–30. doi:10.1111/j.1745-6584.2005.00065.x. Statistics Canada. 2014a. “Population, Urban and Rural, by Province and Territory (Canada).” http://www.statcan.gc.ca/tables-tableaux/sum-som/l01/cst01/demo62a-eng.htm. Statistics Canada. 2014b. “Focus on Geography Series 2011 Census: Census Subdivision of Peachland, DM - British Columbia.” Termes-Rifé, Monserrat, María Molinos-Senante, Francesc Hernández-Sancho, and Ramón Sala-Garrido. 2013. “Life Cycle Costing: A Tool to Manage the Urban Water Cycle.” Journal of Water Supply: Research and Technology—AQUA 62 (7): 468. doi:10.2166/aqua.2013.110. UN DESA. 2014. World Urbanization Prospects: The 2014 Revision, Highlights (ST/ESA/SER.A/352). New York: United Nations Department of Economic and Social Affairs, Population Division. US Army. 2011. Net Zero Water for Army Installations: Cons Iderations for Policy and Technology. Edited by Elisabeth M Jenicek, Laura E Curvey, Annette L Stumpf, and Kelly Fishman. US Army Corps of Engineers. http://acwc.sdp.sirsi.net/client/search/asset/1002026. US EPA. 2009. Water Efficiency in the Commercial and Institutional Sector: Considerations for a WaterSense Program. EPA White Paper. Las Vegas: US Environmental Protection Agency. Zarghami, Mahdi, and Simin Akbariyeh. 2012. “System Dynamics Modeling for Complex Urban Water Systems: Application to the City of Tabriz, Iran.” Resources, Conservation and Recycling 60 (March). Elsevier B.V.: 99–106. doi:10.1016/j.resconrec.2011.11.008.   063-10  System Dynamics Modelling for an Urban Water System: Net-Zero Water Analysis for Peachland (BC) International Construction Specialty Confernce’15  1 Gyan K. Chhipi-Shrestha, Kasun Hewage & Rehan Sadiq  School of Engineering The University of British Columbia Okanagan June 9, 2015 Presentation Outline 2 1. Introduction 2. Objectives 3. Methodology  4. Results and Discussion  5. Conclusions 1. Introduction 3 Urban Water Systems and Peachland: q  Population 6320 in 2014 (annual growth rate 6.5%)  q  Water supply: Trapanier Creek, Deep Creek, Okanagan Lake q  Wastewater to Westside treatment plant  4 System Dynamics (SD) ¨  Well-established methodology to quantify complex feedbacks in system interactions  ¨  Effective trade-off analysis of multi-attributes over time ¨  Complex systems function through visualization and computer simulation 5 Net-Zero Water (NZW) ¨  Concept similar to carrying      capacity ¨  NZW limits consumption of      freshwater resources  ¨  Returns water back to the same watershed so not to deplete the groundwater and surface water resources of that region in quantity or quality over a year Treated water Wastewater Wastewater treatment Surface/ground water Water treatment   Energy Consumption Rain 2. Objectives 6 q  Develop a system dynamics model for an urban water system of Peachland (BC)  q  Analyze Net-Zero (NZ) water potential by developing various scenarios     3. Methodology 7 q  SDM using STELLA® software 1. Population sub-model q  Nt = N0er t                         where Nt = population in a month, N0 = Base population, r =   population growth rate (monthly), t = time duration in months  2. Water sub-model q  (Water use)t = (Residential water use)t + (Agricultural water use)t + (Institutional water use)t + (Commercial water use)t + (Industrial water use)t + (Parks and golf courses water use)t     where ‘”t” refers to a month  8 3. Wastewater sub-model ¨  (WW)t = (Residential WW)t + (Industrial WW)t + (Commercial WW)t + (Institutional WW)t      Where ‘”t” refers to a month Net-Zero Water Analysis ¨  (Net water)t = (Water returned)t - (Water withdrawal)t  ¨  (Water withdrawal)t = (Water use)t – (Rooftop rainwater harvested)t – (Greywater reused)t – (Reclaimed water use)t – (Stormwater harvested)t     Where ‘”t” refers to a month 9 Water abstractionWastewaterIC WaterResidential wateruseGreywaterrecyclingResidentialindoor useResidentialoutdoor useDwelling unitsWaterappliances/faucets++++ +-IndustrialwaterCommercial waterInstitutional water+++ Agricultural waerParks and golfcourses waterWater use++ +++Rooftop rainwaterharvesting Stormwaterharvesting+Net water++-Population +Population growth++Industrial indoorwaterIndustrial outdoorwaterCommercialindoor waterComercialoutdoor waterInstitutionaloutdoor waterInstitutional indoorwater+++ +++Wastewatertreament ++Wastewaterreclaimed++Fig: Causal loop diagram of the urban water system of Peachland 4. Results and Discussion 10 Figure: Comparison of historical (real) and modelled data of monthly water consumption from January 2010 to December 2014 r2 = 0.85; Historical data and SDM = 1104 L/capita/day (5 yrs) 11 Figure : Sectorial water consumption in Peachland 2010 to 2014  Net-zero Water Analysis of Peachland 12 Scenario Community water features 1 Base case scenario 2 Scenario 1 with the efficient water fixtures 3 Scenario 2 with irrigation demand reduction 4 Scenario 3 with rooftop rainwater harvesting and greywater recycling 5 Scenario 4 with wastewater recycling and use 6A Scenario 5 with stormwater harvesting and use 6B Typical urban setting of Scenario 6A Table: Six scenarios considered 13 Figure: Net-zero water potential in different scenarios -7000 -6000 -5000 -4000 -3000 -2000 -1000 0 1000 2015 2017 2019 2021 2023 2025 2027 2029 2031 2033 2035 Net water (Million Litres) Scenario 1 Scenario 2 Scenario 3 Scenario 4 Scenario 5 Scenario 6A Scenario 6B Note:  S1: Base case,           S2: S1+ efficient fixtures     S3: S2+low irrigation   S4: S3+rainwater+greywater        S5: S4+ treated WW  S6A: S5+stormwater harvest          S6B: S6A without agriculture 14 Table: Average annual water for 2015 to 2034 Note:  S1: Base case,           S2: S1+efficient fixtures     S3: S2+low irrigation   S4: S3+rainwater+greywater    S5: S4+treated WW  S6A: S5+stormwater harvest      S6B: S6A without agriculture Scenarios Water use (ML) Freshwater withdrawal (ML) Net water (ML) 1 4974.5 4974.5 -3630.1 2 4485.7 (-9.8%) 4485.7 (-9.8%) -3537.0 (2.6%) 3 3018.8 (-39.3%) 3018.8 (-39.9%) -2203.1 (39.3%) 4 3018.8 (-39.3%) 1721.8 (-65.4%) -1426.5 (60.7%) 5 3018.8 (-39.3%) 1426.5 (-71.3%) -1426.5 (60.7%) 6A 3018.8 (-39.3%) 985.9 (-80.2%) -985.9 (72.8%) 6B 2569.3 (-48.3) 536.4 (-89.2%) -536.4 (85.2%) 15 Within system water generation potential: •  Rooftop rainwater harvesting (≈149L/cap/day)  •  Greywater recycling in houses (≈126L/cap/day)  •  Wastewater recycling (except greywater) (≈64L/cap/day)  •  Stormwater harvesting & treatment (≈95L/cap/day) 5. Conclusions 16 q  Two thirds of supplied water used by irrigation  q  Multiple measures required to achieve net-zero (semi-arid)  q  Achieve net-zero or even net-plus water only for initial 5 yrs (without considering agriculture)  Acknowledgements 17 For you attention 18 

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