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<br />In this paper, we present an analytical technique to statistically characterize the <br /> <br />temporal variability in hydrologic regimes at specific locations during selected time frames <br /> <br />using biologically relevant attributes. Furthermore, we propose a method for quantifying . <br /> <br />hydrologic alterations associated with presumed perturbations (e.g., dam operations, flow <br /> <br />diversion, or intensive conversion of land uses in a watershed) by comparing the hydrologic <br /> <br />regimes from "pre-impact" and "post-impact" time frames. Finally, we illustrate the' ,g J:l <br /> <br />...,,- <br /> <br />application of this methodwith.twocase,studies .focusing on a river system and. a grounG:lNater <br /> <br />system. Our purpose in presenting this method for characterizing hydrologic regime5'andft--F.f <br /> <br />assessing hydrologic alteration is fourfold: 1) to communicate the multi-faceted nature of <br /> <br />..',- <br /> <br />altered by human activities; 3) to stimulate consideration of the ways in which hydrologic' . <br /> <br />alter;ttions influence ecological components of interest; and 4) to suggest hydrologic measures <br /> <br />that can be employed (along with other biotic and abiotic measures) in evaluating the success <br /> <br />of ecosystem managementand.restoration,;efforts'" '-'.,.0' <br /> <br />Conceptual Framework <br /> <br />The general approach for hydrologic assessment described here is to fu-st define a serieS <br /> <br />~_ ;', i'-' . <br /> <br />of biologically.relevant hydrologic attributes that characterize intra-annual variation in water.' <br /> <br />conditions, and then use an analysis of the inter-annual variation of these attributes as the <br /> <br />foundation for-comparing pre. and post.impact 'hydrologic regimes. B~use the prop6sed ' <br /> <br />I. <br /> <br />5 <br />