Predicting river width, depth and velocity at ungauged sites in England and Wales using multilevel models

Using a dataset of gauged river discharges taken from sites in England and Wales, we applied linear multilevel models, also known as mixed effects models, to quantify the variability in discharge and the discharge-hydraulic geometry relationships across three nested spatial scales. A jackknifing procedure was used to test the ability of the multilevel models to predict hydraulic geometry, and therefore width, mean depth and mean velocity, at ungauged stations. These models provide a framework for making predictions of hydraulic geometry parameters, with associated level of uncertainty, using different levels of data availability. Results indicate that as one travels downstream along a river there is greater variability in hydraulic geometry than is the case between rivers of similar sizes. This indicates that hydraulic geometry is driven by catchment area, and therefore hydrology, to a greater extent than by natural geomorphological variations in the streamwise direction such as changes in meso-habitat types and local channel engineering, but these geomorphological variations can still have a major impact on channel structure.