DEVELOPMENT OF HYDROLOGICAL INDEXES TO AID CUMULATIVE IMPACT ANALYSISOF RIVERINE WETLANDS

A hydrological analysis of historic stream data collected with the gau ge on the Cache River at Patterson, Arkansas, USA, is presented as the basis for cumulative impact analysis of riverine wetlands. Subtle, lo ng-term changes in hydroperiod, which could collectively have major ef fects on wetland function, are quantified. Harmonic analysis, time-sca le analysis, and conventional methods of hydrological analysis of gaug e data, at decade intervals, are employed, showing a steady decline in the magnitude and predictability of the baseflow during low flow peri ods, beginning with the 1920s and becoming increasingly more pronounce d into the 1980s. Complementary information suggests that hydroperiod alterations are associated with increased groundwater pumping to suppo rt rice agriculture in the basin. These hydrological methods are simpl e enough for routine application (when adequate data are available) bu t sufficiently sophisticated to identify subtle changes in hydroperiod associated with cumulative effects. The changes in hydroperiod identi fied using these methods may have potential to explain changes in biot ic communities or wetlands structure as part of comprehensive wetlands studies. (C) 1997 by John Wiley & Sons, Ltd.