RELEVANCE OF THE HISTORICAL MISSOURI RIVER TO HABITAT RESTORATION

River restoration typically depends on a reference river to define goals and progress. On large, multipurpose rivers, the relevance of historical conditions to restoration goals has been questioned due to society’s unwillingness to surrender economic benefits of development. Nevertheless, historical understanding can provide insight into river processes that would be desirable in a future river. The challenge is to quantify spatial and temporal characteristics of the historical river processes given incomplete historical data.

I developed 2-dimensional hydraulic models of the Missouri River at Hermann, Missouri for the historical and present-day channels. Two-dimensional hydraulic models can map habitat patches defined as biologically relevant ranges of depths and velocities. Models for the natural and the present-day hydrologic regime also allow the temporal distribution of habitats to be quantified. The present-day hydraulic model was calibrated and validated under current river conditions. The historical hydraulic model was compiled by using a late 19th century map of the river and sparse early 20th century channel cross sections to define a statistical model of minimally disturbed channel geometry. While it is impossible to validate the historical model, it reproduces many Missouri River features described by Lewis and Clark in 1804 and 1806.

One aspect of debate on the Missouri River is how to restore the river to make more slow, shallow-water habitat (SWH, < 1.5 m deep, < 0.75 m/s) available for juvenile fish in the summer. Comparison of present-day and historical models shows tradeoffs between flow and morphology in restoring SWH. The model results indicate that total SWH availability is very sensitive to channel morphology and minimally sensitive to the hydrograph. SWH availability at particular times of the year, however, relates more strongly to the hydrograph as channel depth diversity increases. While SWH in the present-day river is optimized by minimum flows (and competes heavily with other uses), SWH in the historical river was abundant during the entire year and increased in area with increasing discharge.