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Hydrologic Flashiness

Flashiness is an important characteristic of the stream hydrologic regime. A "flashy" stream is one that experiences a rapid increase in flow shortly after onset of a precipitation event, and an equally rapid return to base conditions shortly after the end of the precipitation event. Flashiness in a stream can be increased or decreased by a variety of land use/land cover changes in the stream's watershed. For example, an increase in impervious surfaces (urbanization) or agricultural land typically leads to an increase in flashiness. Land management practices that increase infiltration of precipitation into the soil, such as restoration of native vegetation, or implementation of best management practices like rain gardens, grass swales, and forested riparian buffers, typically decrease stream flashiness. Streams that experience an increase in flashiness will undergo a period of channel adjustment to accommodate the increased peak flows. This may include incision (downcutting) and widening of the stream channel, which affects in-stream and near-stream infrastructure as well as stream-adjacent lands.

The Richards-Baker (R-B) Flashiness Index (see map and graphs below) is based on mean daily flows, and is calculated by dividing the path length of flow oscillations for a time interval (i.e. the sum of the absolute values of day-to-day changes in mean daily flow) by total discharge during that time interval. This index is useful in detecting trends in stream flashiness over time. The R-B index was calculated for major tributaries of the Kansas River, which helps us understand the impacts of land use on the hydrology of the overall Kansas River basin, as well as factors controlling sediment delivery to the main channel.

Daily mean discharge data courtesy of the U.S. Geological Survey Kansas Water Science Center