Effects of flow regulation on hydrologic patterns of a large, inland delta

The Peace-Athabasca River Delta (PAD) is one of the largest freshwater delt as and most biologically productive in the world. Because regional evaporat ion is greater than precipitation, the thousands of lakes and wetlands dott ing this area rely on periodic flooding from the Peace and Athabasca rivers to be replenished. Flood frequency significantly declined beginning in the mid-1970s, several years after the initiation of flow regulation of the Pe ace River. However, the drying trend was interrupted in 1996 when the PAD e xperienced extensive inland inundation on two separate occasions, one in th e spring and one in the summer. A one-dimensional numerical hydrodynamic model was used to evaluate the rol e of flow regulation and hydroclimatic conditions on the water levels of ma jor lakes found in the PAD. Three Peace River flow scenarios were analysed: the observed flows, the flow regime without the 'precautionary drawdown' s pill which was required because of the discovery of a sinkhole at the crest of the dam, and the naturalized flow regime, which assumed no dam regulati on. Modelling results indicated that the effect of the spill on the flow re gime within the PAD was approximately equivalent in magnitude, although dif ferent in timing, to what would have resulted from the prevailing hydroclim atic conditions in an unregulated system. Furthermore, even in the absence of the precautionary drawdown spill, the lake levels would have risen well above the maximum daily average, suggesting that 1996 was one of the wettes t years on record. Finally, the hydrodynamic regime observed at the end of the summer 1996 was very similar to that modelled under unregulated flow co nditions, suggesting that flow regulation could be used to alter the hydrod ynamic regime of a large delta to at least partially restore natural condit ions and potentially improve ecosystem health. Copyright (C) 2001 John Wile y & Sons, Ltd.