The estimation of bedload in poorly-gauged mountain rivers

Abstract

Bedload transport is one major driver of gravel-bed river morphodynamics, and its quantification is capital for many environmental issues and river engineering applications, as well as for landscape evolution studies. To this point, bedload transport rates and volumes have been classically computed by means of sediment transport formulae. The most used bedload transport equations compute the bulk bedload mass based on section-averaged hydraulic parameters. However, due to the non-linear behavior of sediment transport, bedload formulae are sensitive to the input parameters. Then, some doubts arise when applying bedload equations on poorly gauged river reaches, i.e. rivers where there are no hydrological records and rating curves. In this paper, we assess the application of bedload equations in the case of poorly gauged river reaches, and we test a workflow to follow in such situations. This workflow consists of three steps: (i) Reconstructing the flow duration curve, based on gauging records from neighboring river basins; (ii) Solving the hydraulic geometry relations of the study-case river-reach, based on a flow friction equation; and finally, (iii) Computing bedload with a sediment transport equation. We tested this approach against the bedload information available in the literature for Idaho streams and we found that it could potentially approximate annual bedload volumes in ungauged reaches under certain conditions. To illustrate the potential of this workflow, we also computed bedload volumes for two ungauged river reaches from the Cantabrian mountains (NW Spain).