RELATIONSHIP OF FLOOD-WAVE TRAVEL RATE TO ALLUVIAL AQUIFER RECHARGE IN KANSAS

Substantial variations in the travel rate of river flood waves occur in Kansas in response to river-water recharge to the alluvial aquifer. The recharge can have a greater effect on the rate than other channel characteristics and flood-wave size. In general, the higher the permeability of the alluvial aquifer sediments along the channel perimeter and the greater the depth to the water table in the alluvial aquifer, the slower is the flood-wave travel rate. Flood-wave travel rates in Kansas rivers with substantial alluvial aquifers range from 1 m/sec (3 ft/sec) starting from baseflow conditions down to 0.07 m/sec (0.2 ft/sec) along previously dry river channels. An example of the upper end of the travel rate range is a large flood wave in June 2003 in the Republican River in north-central Kansas. The front and peak of the flood wave took 29.8 and 31.5 hours, respectively, to travel the 97.0 km (60.3 mi) between two USGS gaging stations. An example of the low end of the rate range is the high flow in the Arkansas River that crossed the Colorado-Kansas state line in early July 1995. Water-level declines in the High Plains aquifer underlying the alluvial aquifer had caused the river to become dry in part of southwest Kansas prior to July 1995. The flood wave took approximately 15 days to travel from Garden City to Dodge City, a channel distance of 85.8 km (53.3 mi). In comparison, the travel time between the same cities for a flood wave of similar size in May 1999 was about 1.5 days. There was baseflow at both gaging stations prior to the 1999 high flow and the water level in the alluvial aquifer was higher than in 1995. Recharge to the alluvial aquifer also substantially reduces the flood-wave amplitude downstream. The observations imply the impact of consumptive pumping from the alluvial and hydraulically connected aquifers on flood waves, and indicate the importance of river recharge in hydrograph separation.