A spatial assessment of hydrologic alteration within a river network

Maintaining natural hydrologic variability is essential in conserving native riverine biota and river ecosystem integrity. Hydrologic variation plays a major role in structuring the biotic diversity within river ecosystems as it controls key habitat conditions within the river channel, the floodplain, and hyporheic (stream-influenced ground water) zones. Alterations in streamflow regimes may modify many of these habitat attributes and impair ecosystem connectivity. We demonstrate use of the ‘Range of Variability Approach’ for assessing hydrologic alteration at available streamgauge sites throughout a river basin. We then illustrate a technique for spatially mapping the degree of hydrologic alteration for river reaches at and between streamgauge sites. Such maps can be used to assess the loss of natural hydrologic variation at a river basin scale, thereby facilitating river restoration planning. © 1998 John Wiley & Sons, Ltd.