Development and Application of a Large‐Scale, Physically Based, Distributed Suspended Sediment Transport Model on the Fraser River Basin, British Columbia, Canada

Abstract

Modeling sediment transport through large basins presents a challenging problem. The relation between water flux and sediment load is complex, and substantial erosion and transport can occur over small spatial and temporal scales. Analysis of large‐scale basins often relies on lumped empirical models that do not consider spatial or subannual variability. In this study, we adapt a small‐scale, mechanistic, distributed suspended sediment transport model for application to large basins. The model is integrated into the Terrestrial Hydrology Model with Biochemistry to make use of the Terrestrial Hydrology Model with Biochemistry's dynamic water routing. The coupled model is applied to the 230,000‐km2 Fraser River Basin in British Columbia, Canada, using climatic and hydrological inputs provided by a historical run of the Variable Infiltration Capacity model. Hourly simulations are aggregated into monthly and long‐term averages which are compared against observations. Simulated long‐term lake sedimentation values are within an order of magnitude of observations, and monthly load simulations have an average R2 of 0.70 across the five study stations with available data. Model results indicate that sediment loads from tributaries do not heavily influence dynamics along the main stem and suggest the importance of network connectivity. Sensitivity analysis indicates that models may benefit from characterizing bed load irrespective of its contribution to total sediment load. Historical simulations over the 1965–2004 period reveal important changes in sediment dynamics that could not be captured with a lumped model, including a decrease in basin sediment load interannual variability driven by changes in runoff and load variability within a key subbasin.

Modelling the effects of climatic and hydrological regime changes on the sediment dynamics of the Fraser River Basin, British Columbia, Canada

“…Run‐off within the mountainous regions of the basin is snowmelt driven, whereas the interior plateau hosts both hybrid and rain‐dominated regimes (Figure ). Tsuruta et al () found that hillslope erosion and in‐channel transport within the FRB were driven primarily by run‐off. The study also concluded that although the FRB's sediment supply was generated mainly within the Rocky and coastal mountains, sinks within these regions such as the Lillooet and Kamloops Rivers (Figure ) play an important role in the sediment load of the main stem of the Fraser.…”

“…BCSD: bias corrected spatial disaggregation; BCGS: British Columbia Geological Survey; GCM: general circulation models; GMTED: global multi‐resolution terrain elevation data; ISRIC: International Soil and Reference Centre; THMB: terrestrial hydrology model with biochemistry; VIC: variable infiltration capacity. This figure is modified from figure 1 in Tsuruta et al ()…”

“…Hydrometric relationships and landscape data match those used in Tsuruta et al (). Stage discharge and river width relations were determined using WSC hydrometric data from 1965 to 1986: where Q bf is the bank‐full discharge.…”

“…The FRB has only two small hydroelectric dams, the Kenney dam (25,000 km 2 upstream drainage area) and the Terzaghi dam (4,700 km 2 upstream drainage area), and agricultural and urban impacts are either small in scale or confined to areas downstream of the last gauging station. Due in part to its size, the net effect of geomorphic events (i.e., landslides) and ecological disturbances (i.e., pest outbreaks) on basin-scale sediment dynamics has historically been small relative to hillslope erosion and in-channel processes (Tsuruta, Hassan, Donner, & Alila, 2018). Because of these factors and the very low human disturbances upstream of Mission ( Figure 1, Station 14), we expect basin-scale sediment processes over time to be most sensitive to variability in climate and hydrology.…”

“…In this study, we use a new large-scale, mechanistic, distributed sediment transport model that has been developed and calibrated in the FRB (Tsuruta et al, 2018)…”