Relation of Missouri river flows to sandbar morphology with implications for selected biota

Abstract

Channel modification and flow regulation in historically braided large rivers, have reduced sandbars and associated highly productive habitats for riverine biota. Sandbars are an important interface between aquatic and terrestrial environments, i.e. an aquatic-terrestrial zone (ATTZ), within the main channel of the lower Missouri River. Predictive models of sandbar morphometry (area, wetted perimeter, elevation, and water-surface slope) were developed to determine how changes in discharge affect the quantity of submergent-sandbar ATTZ (depth) and emergent-sandbar ATTZ (elevation) for point and wing-dike sandbars within a segment of the lower Missouri River. Point sandbars were as much as 22 times greater in mean area than wing-dike sandbars for submergent and emergent ATTZ, whereas wing-dike sandbars were more abundant, composing 85% of all sandbars in the Grand River to Osage River segment of the lower Missouri River. Reduced summer flows associated with alternatives GP1528 and GP2021 increased available wetted perimeter in July and August for post breeding wading birds and during the beginning of autumn shorebird migration while also creating more emergent sandbar habitat during softshell turtle nesting. Flows under the current flow regime and selected management alternatives provided greater area of submergent-sandbar ATTZ during the initial months of age-0 riverine fish nursery than historical flow conditions under ROR.