Abstract
Fine-grained cohesive sediment is the primary vector for nutrient and contaminant redistribution through aquatic systems and is a critical indicator of land disturbance. A critical limitation of most existing sediment transport models is that they assume that the transport characteristics of fine sediment can be described using the same approaches that are used for coarse-grained non-cohesive sediment, thereby ignoring the tendency of fine sediment to flocculate. Here, a modelling framework to simulate flow and fine sediment transport in the Crowsnest River, the Castle River, the Oldman River and the Oldman Reservoir after the 2003 Lost Creek wildfire in Alberta, Canada was developed and validated. It is the first to include explicit description of fine sediment deposition/erosion processes as a function of bed shear stress and the flocculation process. This framework integrates four existing numerical models: MOBED, RIVFLOC, RMA2 and RMA4 using river geometry, flow, fine suspended sediment characteristics and bathymetry data. Sediment concentration and particle size distributions computed by RIVFLOC were used as the upstream boundary condition for the reservoir dispersion model RMA4. The predicted particle size distributions and mass of fine river sediment deposited within various sections of the reservoir indicate that most of the fine sediment generated by the upstream disturbance deposits in the reservoir. Deposition patterns of sediment from wildfire-impacted landscapes were different than those from unburned landscapes because of differences in settling behaviour. These differences may lead to zones of relatively increased internal loading of phosphorus to reservoir water columns, thereby increasing the potential for algae proliferation. In light of the growing threats to water resources globally from wildfire, the generic framework described herein can be used to model propagation of fine river sediment and associated nutrients or contaminants to reservoirs under different flow conditions and land use scenarios. The framework is thereby a valuable tool to support decision making for water resources management and catchment planning.
Highlights
Forested regions provide approximately 86% of surface water supplies in the UnitedStates (Caldwell et al [1]) and more than 58% for the largest Canadian urban and rural communities as well as the majority of Canadian Indigenous communities
[68]; cohesive sediment entrapment was evaluated in an annular flume using fine sediment Packman al. [69]; RehgRiver et al.in[70]; Krishnappan and Engel
The results show that the amount of iment entrapment dynamics in the Crowsnest River to refine model predictions
Summary
Forested regions provide approximately 86% of surface water supplies in the UnitedStates (Caldwell et al [1]) and more than 58% for the largest Canadian urban and rural communities as well as the majority of Canadian Indigenous communities. National and international commitment to source water protection in forested watersheds has been increasingly advocated (Vörösmarty et al [7]; Emelko and Sham [8]). Wildfire is the most severe large-scale landscape disturbance in critical forested source water regions (Emelko and Sham [8]; Vose et al [9]; Khan et al [10]). Recent increases in the size and severity of wildfires related to climate warming (Westerling et al [11]; Flannigan et al [12]) have been shown to degrade terrestrial ecosystems, ecological processes and functions, and surface water quality (Benda et al [13]; Khan et al [10]), whilst threatening human life and property (Kinoshita et al [14])
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