Hydrologic flashiness is the reflection of how quickly a rivers flow increases and decreases after a rain event - the quicker a stream rises and falls, the more "flashy" it is. Flashiness is, in part, determined by the land use in a rivers watershed.

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FLASHINESS

FLASHINESS

Photo by Douglas Gayeton

FLASHINESS

FLASHINESS
Flashy conditions on a stream or river are defined by rapid increases in flow shortly after the onset of a precipitation event, followed by an equally rapid return to base conditions. This condition occurs in watersheds that lack storage – typically urban settings or shallow soil over bedrock. Channels adapt to the geology and typically become stable; however, if the climate changes, such that higher magnitude and more intense precipitation events fall upon a watershed with stable channels, they erode!

INCREASED MAGNITUDE AND INTENSITY OF PRECIPITATION EVENTS (CHANGING CLIMATE) + CONVERSION OF PRAIRIES AND WETLANDS INTO CROPLAND AND TOWNS = CHANNEL ENLARGEMENT = BANK EROSION. Erosion increases turbidity (which is also referred to as TSS or Total Suspended Solids). Sediment can smother grasses, decrease fish habitat and places for them to lay eggs in the gravel, and negatively impact macroinvertebrate habitat. Signs of erosion include downcutting and widening, steep bluffs, eroded banks with less vegetation, an increase in visible tree roots, downed trees which can dam up rivers, collapsed banks, and highly suspended sediment.

HEALTHY LANDSCAPES = HEALTHY WATERWAYS
(HOW TO MITIGATE FLASHINESS)

These are three ways to add storage back into the watershed:

RIPARIAN CORRIDOR CONNECTIVITY: to slow and capture water runoff from agricultural lands allowing it to be stored
PERENNIAL VEGETATION to keep the ground covered throughout the year, store water, and transpire it back to the atmosphere.
RESTORE WETLANDS, which work as a sponge, absorbing and holding water.

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