BASIN-SCALE GEOHYDROLOGIC DROUGHT FLOW FEATURES OF RIPARIAN AQUIFERS IN THE SOUTHERN GREAT-PLAINS

Low-streamflow hydrographs from 22 subbasins in the U.S. Department of Agriculture-Agricultural Research Service (USDA-ARS) Washita River Ex perimental Watershed complex in central Oklahoma were subjected to rec ession slope analysis; this method, after that of Brutsaert and Nieber [1977], was derived from a Dupuit-Boussinesq formulation for the grou ndwater outflows from the adjoining phreatic aquifers. The longtime aq uifer response characteristics were generally found to be close to lin ear, and the short-time response characteristics were consistent with Boltzmann similarity. Representative values of the resulting basin-sca le effective groundwater parameters were (35 days)(-1) for the low-flo w extinction coefficient (i.e., a storage half-life of 25 days); 0.021 m(2) s(-1) for the hydraulic diffusivity, D-h; 0.0035 m(2)s(-1/2) for the hydraulic desorptivity, De(h); 8 x 10(-4) ms(-1) for the hydrauli c conductivity k; and 0.018 for the drainable porosity (or specific yi eld), f. The variabilities of D-h, De(h), and k from basin to basin co uld be better represented by the log-normal than by the normal distrib ution; f could be described nearly equally well by both. The storage h alf-life is moderately and positively correlated with basin size; in t he case of k the correlation is negative but weaker. Any scale depende nce of D-h, De(h), and f appears to be negligible.