Uncertainty for the ISSDOTv2 Bedload Measurement Method

Abstract

The Integrated, Section Surface Difference Over Time, version 2 (ISSDOTv2) method provides a means of quantifying bedload in large sandbed rivers. Like all measurements, it is important to understand the uncertainty associated with the method before making management decisions based on its results. A methodology is presented for quantifying and combining the uncertainty for each component of the ISSDOTv2 method including particle density, bed porosity, acoustically measured bed topography, the timing of measurements, sand wave identification, and regression analysis used for geometric correction of bedload measurements. The approach provides an indication of the relative magnitude of each source of uncertainty in addition to the uncertainty in the final resultant transport rate. Laboratory flume measurements were used to evaluate the uncertainty limits and verify the approach. The greatest contributor to uncertainty was found to be the bathymetric uncertainty, and, at the highest transport rates, cumulative relative uncertainty was found to be approximately 10%. Cumulative relative uncertainties grew rapidly with decreasing flow rates, driven primarily by the higher relative contribution of the effect of bathymetric uncertainty on the smaller bedforms that are typically present at lower transport rates. The approach documented here will be transferrable to real-world systems to determine the uncertainty in measured bedload sediment transport rates using the ISSDOTv2 method.