Grain Size‐Specific Engelund‐Hansen Type Relation for Bed Material Load in Sand‐Bed Rivers, With Application to the Mississippi River

Abstract

Many sand‐bed rivers worldwide have been experiencing significant reductions in sediment load over the past several decades. This is one of the causes of river delta drowning worldwide. This problem, however, has not been studied in detail in the context of sediment grain sorting. Considering the good performance of the original Engelund‐Hansen relation (OEH) for uniform sediment, and the fact that bulk grain size‐specific relations for bed material load that allow for sorting are relatively rare in the case of sand‐bed rivers, a grain size‐specific Engelund‐Hansen type relation (SEH) is proposed in this study based on data from a large flume. We embed both the OEH and the SEH in a one‐dimensional river morphodynamic model to simulate the morphodynamic evolution of the middle Mississippi River in response to the upstream cutoff of sediment supply. Simulation results using a single characteristic grain size show that bed material load delivered to the delta reduces only gradually in response to the cutoff of sediment supply, in agreement with previous studies. However, implementing the full grain size distribution of sediment leads to a much faster reduction of bed material load delivered to the delta, because the bed surface coarsens in response to grain sorting. This armoring inhibits the bed degradation that would replenish sediment load along the channel. The bed material load of finer sediment declines more rapidly than that of coarser sediment. The results of this study have practical implications for river delta restoration.

Median bed-material sediment particle size across rivers in the contiguous U.S.

“…Bed-material sediment particle size information is critical for understanding and modeling riverine sediment processes, including sediment erosion, entrainment, deposition, and transportation. Various sedimentology formulas have been proposed to quantify the sediment processes, with sediment particle size being a critical parameter in those formulas (Meyer-Peter and Müller, 1948;Einstein, 1950;Engelund and Hansen, 1967;Ackers and White, 1973;Van Rijn, 1984;Parker 1990;Garcia and Parker, 1991;Wu et al, 2000;An et al, 2021). Moreover, sediment particle size is a critical factor in riverine dynamics of heavy metal (Unda-Calvo et al, 2019;Zhang et al, 2020), nutrients (Xia et al, 2017;Glaser et al, 2020), microplastic (Corcoran et al, 2019;He et al, 2020), and fish habitats and benthic lives (Dalu et al, 2020;Rieck and Sullivian, 2020).…”

Impact of Artificial Floods on the Quantity and Grain Size of River‐Borne Sediment: A Case Study of a Dam Regulation Scheme in the Yellow River Catchment

“…On the other hand, with continuous scouring of dam‐released flood, particles of surface sediment on the riverbed that are easily to be eroded have already been initiated and transported downstream, making the surface of the lower river channel more coarsely grained (Miao et al., 2016). Accordingly, the grain‐sorting phenomenon produces an armoring layer whereby sediment has a progressively higher entrainment threshold over time, further hindering sediment scour (An et al., 2021). As a consequence, even for similar flows, less and finer sediment could be scoured and transported by the dam‐released flood during the later water regulation period than that during the earlier period.…”

Balancing Sediment Connectivity and Energy Production via Optimized Reservoir Sediment Management Strategies

“…The reach transport capacity is calculated via Engelund and Hansen (1967) equation for the total load (i.e., both suspended and bed load), which has already been employed previously for large sediment connectivity models on the Mekong and 3S (Schmitt et al, 2018a(Schmitt et al, , 2018b) and other rivers (An et al, 2021;Naito et al, 2019). As this formula returns the total transport capacity, we obtain fractional transport rates for the five classes considered via the Bed Material Fraction (BMF) approach described in Molinas and Wu (2000).…”