The Peace-Athabasca Delta (PAD) is a unique and ecologically sensitive area made up of many interconnected lakes, wetlands, streams and rivers. The hydrology of the Delta is heavily influenced by inflows from the Athabasca River and the complex river ice regime within it. In this study, a detailed one-dimensional network hydraulic model of the Athabasca River Delta (comprising the southern portion of the PAD) is presented and applied to demonstrate how variable stream-flow and ice cover conditions affect the distribution of flow among the major channels conveying water to Lake Athabasca and the rest of the Delta.The current channel network model, based on new measurements concentrated at the main channel junctions combined with carefully designed geometry throughout the un-surveyed reaches, is shown to provide flow allocations to the major channels that are within 3% of the corresponding observations. At the three main flow-split junctions, steady flow simulations at varying discharge, Lake Athabasca level, and ice thickness were performed to assess their impact on the percentage of flow carried by each channel. Each junction was found to exhibit a unique response arising from its physical geometry and location within the Delta.Transient simulations for the historical period 1960-2007 demonstrate that water demand on the Athabasca River upstream of the PAD may have a significant impact on the availability of fish habitat in winter. Imposing a 20 m 3 /s water demand increased the total occurrences of a no-flow condition in the Fletcher Channel, analogous to it freezing to the bed, by 53%.

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Winter can be a critical time on many rivers, during which ice conditions and a number of environmental factors can lead to rapidly developing and damaging flood events. Also, in northern Canada, rivers are important for both summer (ferry) and winter (ice bridge) transportation; however, during periods of variable ice conditions these transportation links are temporarily interrupted. As a result, northern communities can become isolated for periods of time. With climate warming becoming an increasing concern, it is important to know how elevated temperatures might affect river ice covers so that we can assess the implications for ice jam events, hydropower dam operation, and winter transportation. The Peace River in northern British Columbia and Alberta was used as a case study in this paper to assess the validity of a newly developed, public domain, thermo-hydraulic river ice model, River1D. The Canadian second-generation coupled global climate model (CGCM2) provided an offset for the historical air temperature input, and a future climate analogue for the mid-21st century ice regime was generated. The historical and future climate simulation results indicated significant potential reductions in the duration and extent of ice cover on the Peace River and a longer period over which the river will be impassible by ferry or ice bridge. Specifically, the number of days an ice bridge could be sustained at the Shaftesbury Ferry site was shown to decrease by 60% to 78%.

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