Uncertainty for the ISSDOTv2 bed-load measurement method

Authors: MCALPIN, TATE - Us Army Corp Of Engineers (USACE); Wren, Daniel; JONES, KEATON - Us Army Corp Of Engineers (USACE); ABRAHAM, DAVID - Us Army Corp Of Engineers (USACE); Kuhnle, Roger; WILLSON, CLINTON - Louisiana State University

Submitted to: Journal of Hydraulic Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/21/2023
Publication Date: 7/13/2023
Citation: Mcalpin, T.O., Wren, D.G., Jones, K.E., Abraham, D.D., Kuhnle, R.A., Willson, C.S. 2023. Uncertainty for the ISSDOTv2 bed-load measurement method. Journal of Hydraulic Engineering. 149 (9): 04023036. https://doi.org/10.1061/jhend8.hyeng-13505.
DOI: https://doi.org/10.1061/jhend8.hyeng-13505

Interpretive Summary: Accurate knowledge of the sediment that is transported along the bottom of streams and rivers (bed load) is important to assess the stability of the channel, the suitability of the habitat for aquatic organisms, and for determining the rate of net erosion of the land surface upstream of the measurement location. Many methodologies are available to determine the rate of sediment movement; however, most of these methodologies have not had the uncertainty associated with the calculated rates of transport evaluated in a rigorous manner. It is important to quantify the uncertainty associated with bed load transport rates before management decisions are made based on those values. In this study, the sources of uncertainty of the Integrated Section, Surface Difference Over Time, Version 2 (ISSDOTv2) method of calculating bed load transport rates was tested and validated using independently measured rates of bed load in a laboratory flume located at the USDA-ARS National Sedimentation Laboratory. The fact that the ISSDOTv2 uncertainty analysis was grounded to bed load data collected in a model river channel under controlled conditions of steady and unsteady flows insures that the results are robust and representative of the bed load transport process. This analysis provides an enhanced method of determining the highest and lowest rates of transport that are likely to exist based on measurements using the ISSDOTv2 method for each bed load transport rate and should be considered before management decisions are made associated with sediment transport in streams and rivers.

Technical Abstract: The Integrated, Section Surface Difference Over Time, version 2 (ISSDOTv2) method provides a means of quantifying the bed load in large sand bed rivers. Like all measurements, it is important to understand the uncertainty associated with the method before making management decisions based on its results. Methodology is presented for quantifying and combining the uncertainty for each component of the ISSDOTv2 method including particle density, acoustically measured bed topography, the timing of measurements, sand wave identification, and regression analysis used for geometric correction of bed-load measurements. This provides an indication of the relative magnitude of each source of uncertainty in addition to uncertainty in the final resultant transport rate. Laboratory flume measurements were used to evaluate the uncertainty limits and verify the approach, and the resulting uncertainty bounds included all but the lowest sediment transport rates that were obtained during the testing process. Uncertainty estimates will be included in bed-load sediment transport rates for measurements made in rivers by implementing the methods described here in the ISSDOTv2 method.