Streamflow trends in northwest BC : implications for closure water balance modelling Jackson, S. I.
The increasing complexity of long-term predictions of water quantity and its variability for mine closure planning requires that the non-stationarity of streamflow is taken into account. In particular and given the high probability of climate-induced changes to streamflow conditions in many regions, regulatory decisions based on historical data may not necessarily reflect future conditions. From a closure planning perspective, therefore, consideration to ongoing changes in streamflow may be necessary. The analysis described here focuses on the Skeena Region in north-western British Columbia, an area characterized by: 1) large scale industrial development; 2) a high degree of spatial variability in stream flow; and 3) large scale changes in predicted future flow conditions associated with climate change. Trends were calculated for up to 55 Water Survey of Canada hydrometric stations, and for four time periods of varying duration. Trends were not uniformly significant for all water bodies considered, emphasizing the importance of acquiring site-specific information. Nevertheless, on the basis of cases where statistically significant trends were identified, some broad patterns were identified and included: • Trends in average annual flows are mixed but show some tendency toward increases; • There is a general but not universal tendency toward increasing winter minimum flows and declining summer flows; • Most glaciated basins are experiencing reductions in median August flows; • Evidence is observed for a general trend toward earlier freshets; and • Most variables maintained the same trend direction at a given station for all periods analysed, although the statistical significance of the trends varied depending on the period. This paper focuses on variables of interest for future water balance estimates required for engineering design, permitting, effluent discharge and/or water treatment scheduling.
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