MULTIVARIATE GEOSPATIAL ANALYSIS OF IMPACTS OF RIVER ENGINEERING UPON FLOOD RESPONSE: PRELIMINARY RESULTS

We present preliminary results of a multi-year project to empirically test the impacts of a broad spectrum of channel and floodplain modifications upon flood magnitudes along >4000 km of the Mississippi and Lower Missouri Rivers. The surface processes research group at Southern Illinois University has been compiling a regional database of hydrologic data, engineering histories, and channel changes during the past 100+ years on the study rivers, which include the Mississippi River from Minneapolis to the Gulf of Mexico and the Lower Missouri River from Gavins Point Dam to the Missouri-Mississippi confluence. In this study area, we have digitized maps, charts, surveys, structure-history databases and other quantitative measurements stretching back 100 to (locally) 200 years or more.

Hydrologic data utilized in this analysis include stage (or water-surface elevation) and discharge (flow), including existing digital data from a variety of sources as well as some paper-only data. A number of measurement sites are unrated (stage-only) stations or include years of stage data only, for which we extend the record by extrapolating discharge values from nearby rated stations wherever possible. We have also parameterized a number of potential explanatory variables, including (at present) 130 bridges, 54 dam structures (including lock-and-dams), 25 artificial meander cut-offs, 1093 levees enclosing 9016 km2 of floodplain area, and 13,231 individual wing-dam segments with a cumulative length of 3137 km.

The purpose of this work is to construct a multivariate geospatial model to test for empirical links between incremental engineering modifications of the river system and changes in flood response documented by hydrologic analyses. Preliminary results from the Middle Mississippi River – which we have used as a prototype reach to develop and refine our methodology – show strong correlations between the dates and locations of wing-dam emplacement and large-scale increases in flood levels.