TRADEOFFS BETWEEN HYDROLOGY AND GEOMORPHOLOGY IN HABITAT REHABILITATION, LOWER MISSOURI RIVER

Engineered changes in many large, multi-purpose rivers can be categorized into semi-independent hydrologic and geomorphic components. Reservoir regulation is the dominant influence on the hydrologic component and bank stabilization/navigation structures comprise the dominant influence on the geomorphic component. Both components can have profound effects on temporal and spatial ecosystem patterns; on the Lower Missouri River, the interaction of these components is a critical question in management and rehabilitation strategies. Two-dimensional hydraulic modeling of a 8-km reach at Hermann, Missouri using pre- and post-reservoir hydrologic times series, and pre- and post-engineered channel morphology, documents changes in ecosystem pattern measured as habitat diversity, habitat connectivity/fragmentation, and timing of habitat availability. In this part of the Lower Missouri River – where hydrologic alteration is moderate and geomorphic alteration has been substantial – desired shallow-water habitat areas are relatively insensitive to hydrologic management alternatives. The analysis indicates that rehabilitation engineering can achieve large increases in habitat areas, but such engineering cannot alone address temporal hydrologic cues thought to be important in life histories of many species.