Evaluating the Relative Role of Natural Flow Variation of the Athabasca River on the Hydrologic Regime of the Slave River and the Slave River Delta

Prabin Rokaya

Thursday 2 july 2015

18:06 - 18:09h at Central America (level 0)

Themes: Poster pitches, (T) Water resources and hydro informatics (WRHI), (ST) Catchment hydrology

Parallel session: Poster pitches: 13A. Sediment - Coast

The need for improved and scientific evaluation of potential impacts of flow alteration on northern deltaic environments remains large. This is very significant as river hydrograph largely governs ice jams and breakups in northern rivers that result in flooding which is essential to revitalize the deltaic ecosystem. This is particularly the case for the Slave River Delta (SRD) which is believed to be drying due to streamflow regulation and climate change impacts. Therefore, insights into natural flows is imperative to understand the effect of natural variation in the hydrologic regime of the Slave River, the hydrological functioning of the SRD and the triggering of flood events by ice jams. The Athabasca River Basin (ARB), one of the major tributaries of Slave River, is not regulated and provides a good case to first understand the natural influences. Long-term discharge trend analysis of 12 hydrometric stations across the ARB using the Standardized Discharge Indices (SDI) method and Mann-Kendal Trend Test for a period of 40 years (1971-2010) showed negative trends in annual streamflows in the middle and lower basin but not in the upper headwaters with glaciers, showing positive trends in winter. In fact, seasonal trend analysis showed positive trends in winter in headwater stations. Corresponding precipitation and temperature trend analysis of data from 6 weather stations across the basin for the same period of time showed that this is due to warmer winters as there were no trends in precipitation but a significant rise in temperature. However, the net effect was still negative, and this decreasing pattern could significantly affect the Peace-Athabasca Delta and the SRD especially since other major tributaries of the Peace River are already regulated. Furthermore, a large-scale, physically based and distributed land surface and hydrology model (MESH) was developed for the ARB to generate and understand natural flow conditions. Three different climate forcing datasets, i.e. CaPA, WFDEI and dataset from Princeton were compared and evaluation showed that Princeton data outperforms WFDEI slightly and CAPA greatly at both daily and monthly temporal resolution in terms of NSE, R2 and PVE. The results also revealed that performance measures are better at longer time scales, monthly compared to daily; and in this basin, the model simulated better the headwater regions compared to the lower and middle part of the basin. The study shows that climate forcing datasets and large scale hydrological modelling could provide important insights to understand rainfall-runoff generation process in large and poorly gauged basin such as the ARB which could be useful to understand future water management implications.