Water quality modeling for the Kennet and Avon Canal, a navigational canal in an inland catchment
The Kennet and Avon Canal in southern England is experiencing severe water quality problems caused by inorganic sediment and algae. These water quality problems are affecting the angling sport of fishermen downstream of the confluence of the canal with the River Kennet. The Environment Agency has been called upon to remedy these issues, but before proceeding they desire a computer model capable of predicting the water quality impacts of various scenarios under consideration. No such model was available to them. This project identified the key solids generation and transport processes to be included in a water quality model for inland navigational canals. Where available, equations from the literature describing relevant processes were used or modified for inclusion in a canal modeling algorithm. Where literature was not available, water quality samples were taken to characterize needed relationships. The final algorithm was coded and tested using a simplified dataset that allowed clear evaluation of the simulated processes. After successful testing, the canal model was applied to the Kennet and Avon Canal. The time series predicted by the model were compared to observed hydrological, solids, and chlorophyll-a (representing algae) data at multiple points in the canal. The model adequately predicted all of these constituents at the monitored locations. The final task in the project required evaluation of six management scenarios proposed by the Environment Agency to address the water quality problem. The model suggests that filtration or other treatment of water in the canal near the confluence with the river is the best management option, as it will address both the elevated inorganic sediment and algae concentrations at the most critical point in the canal. Less desirable options include efforts that only target inorganic sediment, which could increase algal concentrations by increasing light availability; and diversion of surface flows from the canal, which could possibly damage the hydrologic balance of the canal while encouraging undesirable algal growth.