HYDROLOGIC INDEXES FOR NONTIDAL WETLANDS

Two sets of hydrologic indices were developed to characterize the wate r-budget components of nontidal wetlands. The first set consisted of s ix water-budget indices for input and output variables, and the second set consisted of two hydrologic interaction indices derived from the water-budget indices. The indices then were applied to 19 wetlands wit h previously published water-budget data. Two trilinear diagrams for e ach wetland were constructed, one for the three input indices and anot her for the three output indices. These two trilinear diagrams then we re combined with a central quadrangle to form a Piper-type diagram, wi th data points from the trilinear diagrams projected onto the quadrang le. The quadrangle then was divided into nine fields that summarized t he water-budget information. Two quantitative ''interaction indices'' were calculated from two of the six water-budget indices (precipitatio n and evapotranspiration). They also were obtained graphically from th e water-budget indices, which were first projected to the central quad rangle of a Piper-type diagram from the flanking trilinear plots. The first interaction index (I) defines the strength of interaction betwee n a wetland and the surrounding ground- and surface-water system. The second interaction index (S) defines the nature of the interaction bet ween the wetland and the surrounding ground- and surface-water system (source versus sink). Evaluation of these indices using published wetl and water-budget data illustrates the usefulness of the technique.