Using sediment impact sensors to improve the morphological sediment budget approach for estimating bedload transport rates

Constructing a sediment budget from morphological channel change, typically measured using repeat cross-sectional surveys, has proven a useful technique for estimating mean bedload transport rates in gravel-bed rivers. We apply and suggest improvements to the approach using new data sources from an intensely monitored 5.6 km reach of an upland gravel-bed river in northern England. Sediment impact sensors were placed in the bed to record the instantaneous passage of grains during transport events. These sensors provide valuable information for the budget including: (1) a downstream budget limit from which the rest of the budget can be calculated; (2) estimates of sediment input from tributaries; and (3) a better indication of active transport time used in the calculation of average transport rates. Further information collected from field studies include estimates of lateral inputs from the banks using field surveys and bank erosion pins and estimates of the variability of sediment porosity from bed grain size distributions. Budget calculations for different locations and time periods demonstrate large spatial and temporal variabilities in bedload transport rates over a short distance (< 3 km). Whilst some uncertainty in the new data sources remains, this work highlights some limitations of the traditional budget approach and some potential solutions; in particular the value of sediment impact sensors for sediment transport studies.