Chert gravel sources, hydrology, transportation, and deposition within the lower Neosho River, Southeastern Kansas.

Abstract

This study involves the creation and analysis of a geographical information system (GIS) database depicting six counties of southeastern Kansas, the analysis of steam-gage records, and field observations to determine potential chert gravel sources and the hydrology involved in transporting these gravels into the lower Neosho River to replenish gravel bars. The GIS, IDRISI, was used to create several maps depicting upland chert gravel sources, low-terrace, and floodplain alluvium in the vicinity of and surrounding the lower Neosho River and its main tributaries. Steam-gage records taken at the Iola gaging station, water budget years 1917-1992, were analyzed to determine the peak annual discharge for each year and the mean annual flood for the lower Neosho River before and after John Redmond Reservoir. The areal coverages of local upland chert gravels, low-terrace sediment, and floodplain alluvium were determined using IDRISI. Field observations were noted on the typical channel and gravel bar features of the lower Neosho River. The flooding behavior of the lower Neosho River has changed significantly since the impoundment of John Redmond Reservoir. The lower Neosho River had a mean annual flood close to bank-full flow before the reservoir, and after the reservoir the mean annual Hood was reduced to well below bank-full How. This means the lower Neosho River has stabilized since the impoundment of the reservoir and no longer floods on a regular basis.Chert gravels, derived from upstream sources in the Flint Hills region, formerly replenished the gravel bars and riffles on the lower Neosho River due to frequent flooding events. Now, John Redmond Reservoir acts as an absolute barrier to the transportation of tractive sediment downstream. The only chert gravel sources with the potential to enter the lower Neosho River channel are from the low-terrace and Hoodplain alluvium. The upland chert gravels are not a viable source due to their high and remote topographic positions above and away from the river valley. The lack of floods of magnitude, bank-full or out-of-bank, has significantly reduced the erosion of channel banks and bed. Therefore, the chert gravels entering and replenishing downstream gravel bars and riffles are a finite, non-renewable resource. The threatened Neosho madtom, Noturlls placidus, catfish species uses riffles as a habitat. The dredging of riffle-bars on the lower Neosho River would significantly affect the catfish species because of the lack of chert gravels entering the river channel to replace the extracted gravels.