Development of hydrological indices to aid cumulative impact analysis of riverine wetlands

A hydrological analysis of historic stream data collected with the gauge on the Cache River at Patterson, Arkansas, USA, is presented as the basis for cumulative impact analysis of riverine wetlands. Subtle, long-term changes in hydroperiod, which could collectively have major effects on wetland function, are quantified. Harmonic analysis, time-scale analysis, and conventional methods of hydrological analysis of gauge data, at decade intervals, are employed, showing a steady decline in the magnitude and predictability of the baseflow during low flow periods, beginning with the 1920s and becoming increasingly more pronounced into the 1980s. Complementary information suggests that hydroperiod alterations are associated with increased groundwater pumping to support rice agriculture in the basin. These hydrological methods are simple enough for routine application (when adequate data are available) but sufficiently sophisticated to identify subtle changes in hydroperiod associated with cumulative effects. The changes in hydroperiod identified using these methods may have potential to explain changes in biotic communities or wetlands structure as part of comprehensive wetlands studies.