Numerical modelling of ice-jam flooding on the Peace-Athabasca delta

Ice jamming during the spring breakup of the ice cover in the lower reaches of the Peace River has been identified as the main agent of flooding and replenishment of the Peace-Athabasca delta (PAD) ecosystems. The relative rarity of major ice jams in the lower Peace River following construction of the Bennett Dam has resulted in serious habitat degradation and risk to local ecology, and concern has been raised over potential climate change impacts. This issue is under active study that encompasses use of various types of model, field data collection, and analysis of archived records. An important component of the study aims at determination of threshold flows that can result in significant flooding when a jam is in place in the PAD reach of the Peace. This question is investigated by means of RIVJAM, a numerical model that computes the water surface and thickness profiles of a jam in a given river reach. First, the model is calibrated using field data obtained during the 1996 and 1997 ice-jam floods. Calibration coefficients are shown to be the same for both events and consistent with default values determined from previous applications in other rivers. A by-product of the calibration process is the quantification of the flow reversals occurring under high-stage conditions in the three major tributaries of the lower Peace. Next, the model is applied with increasing flow values and the resulting water surface profiles are compared with bank elevations. These comparisons indicate that an incoming flow of at least 4000 m(3) s(-1) is required to produce significant flooding of the delta. The calibrated model can also be used to examine the efficacy of controlled water releases at the Bennett Dam as a means of enhancing flooding potential. Copyright (C) 2003 Crown in the fight of Canada. Published by John Wiley Sons, Ltd.