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The suburban water balance : daily, monthly and annual results from Vancouver, B.C. Grimmond, Christine Susan Betham


This study presents a method for the assessment of the daily water balance at a suburban site. It is applied to a suburb of south central Vancouver, B.C. for the year 1982. Precipitation and piped water supply were measured. Evaporation was calculated using a model developed by Oke and Steyn (pers. comm.) which utilises measured climatological data. Runoff was determined for pervious and impervious surface types using assumptions related to soil retention, infiltration and storage capacity. The net change in water storage was calculated by difference. Sensitivity analyses were conducted on the input values in order to determine their impact on the model output. The appropriate range for input values was determined from analyses of their variability. Results indicate that the objective of a water balance study is important in determining how carefully the catchment describing parameters should be defined. For instance, if the purpose of the study is to determine the daily water balance only, and not the daily moisture status of the suburban environment, then the definition of the parameters may be less rigorous. The results show that the summer water balance of the suburban environment is modified to a considerable extent by the amount of water piped in and applied to the external environment. In the Vancouver study area the piped supply is equal to the input of precipitation. Summer water use by the residents is found to be related to air temperature and the occurrence of precipitation. The daily water balances included days when the amount of water being added to the external environment is sufficient not only to support the calculated evaporation but also to add to storage. The primary means of water output from the system in the summer months was evaporation, which represented 81% of the water loss. The calculated results compared favourably with previous research within the Vancouver region. Daily water balance results for July and August were similar to those of an earlier pilot study in the area; evaporation rates were similar in magnitude to those reported for a nearby suburban area by Kalanda et al. (1980); and the monthly runoff ratios showed the same pattern as those for a nearby undeveloped catchment.

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