By Noel Demulier [CC0], via Wikimedia Commons

Parsimonious sediment transport equations based on Bagnold's stream power approach


It is increasingly recognized that effective river management requires a catchment scale approach. Sediment transport processes are relevant to a number of river functions but quantifying sediment fluxes at network scales is hampered by the difficulty of measuring the variables required for most sediment transport equations (e.g. shear stress, velocity, and flow depth). We develop new bedload and total load sediment transport equations based on specific stream power. These equations use data that are relatively easy to collect or estimate throughout stream networks using remote sensing and other available data: slope, discharge, channel width, and grain size. The new equations are parsimonious yet have similar accuracy to other, more established, alternatives. We further confirm previous findings that the dimensionless critical specific stream power for incipient particle motion is generally consistent across datasets, and that the uncertainty in this parameter has only a minor impact on calculated sediment transport rates. Finally, we test the new bedload transport equation by applying it in a simple channel incision model. Our model results are in close agreement to flume observations and can predict incision rates more accurately than a more complicated morphodynamic model. These new sediment transport equations are well suited for use at stream network scales, allowing quantification of this important process for river management applications.

Earth Surface Processes and Landforms

What we did and why it is important

Rivers move a lot of sediment. This silt, sand, gravel, and boulders forms the boundaries of shifting river channels and is transported downstream to create and maintain coastal ecosystems. Understanding this sediment movement is important — especially as we realize how much we have impacted natural sediment flows in rivers. Sediment transport rates are usually calculated based on the shearing force or velocity of the moving water. These calculations require knowing flow depth and/or velocity throughout an entire river — something that is difficult to measure directly at these large spatial scales and which is constantly changing over time.

Another variable that is useful for calculating sediment transport rates is stream power. Stream power is just that — the power of the moving water in the stream. Stream power can be easier to calculate than other variables because you only need to know the discharge (i.e. flow rate), channel slope, and channel width. In the U.S., at least, their is a large network of stream gaging stations that are constantly monitoring discharge. Slope and width can be calculated from digital elevation models — essentially digital topographic maps. We developed new sediment transport equations using stream power which are easier to apply to river networks because they use data that are more easily collected at this scale. These new equations may be useful for sediment transport analyses to guide river management.