Hydrologic Alteration of Great Plains Rivers

Hydrologic alteration by dams is well documented; however, the Great Plains are often excluded from these analyses. The goal of this analysis is to evaluate the pre and post-dam hydrologic alteration throughout the Great Plains. Using the National Inventory of Dams with long standing U.S. Geological Survey gages, nine sites were identified to document the magnitude, duration, and direction of hydrologic alteration attributable to the dams. One site, the Red River of the North, was selected to quantify hydrologic alteration without the presence of impoundments. Hydrologic alteration was determined using the Indicators of Hydrologic Alteration, a model that calculates many hydrologic and ecologically relevant parameters. For many of the parameters, the magnitude, duration, and direction were similar across the sites. There is an overall statistically significant increase in the 1 through 90 day minimum discharges and a statistically significant decrease in the 1 through 90 day maximum discharge; though the magnitude of alteration decreases with increased time the discharge is calculated over. The greatest alteration is in the number of annual hydrograph reversals and the percent change in raise and fall rates of hydrographs. Results of this study are the first to quantify the widespread hydrologic alteration of large and small Great Plains rivers following impoundment.