EVALUATING RECHARGE FROM WATERSHEDS ALONG THE TEXAS REACH OF THE RIO GRANDE

Recharge to the Texas reach of the Rio Grande is mostly derived from a limited number of rivers and spring systems that discharge to the river from contributing watersheds located in Mexico and Texas. A significant portion of flow in the lower half of the Rio Grande comes from a limited reach near Amistad Reservoir, namely the watersheds of the lower Pecos River, the Devils River, San Felipe Springs, and Goodenough Springs. With the exception of Goodenough Springs, these contributing areas are characterized to be located north of the Rio Grande. Recent surface-water/groundwater assessments suggest that the upland portions of adjoining watersheds, where the principal aquifer of the watershed is unconfined, do not communicate hydraulically. This important attribute allows for each of these watersheds to be parsed out separately for individual analysis. Challenges arise where the aquifers become partially or fully confined. Under these conditions, the aquifers comingle and the individual watersheds cannot be parsed out from the regional system and investigated separately. Parsing watersheds and aquifers that recharge the Rio Grande near Amistad Reservoir from the regional aquifer system has enabled improved assessment of water budget of this critical transboundary resource. Improved assessment of the resource will, in turn, enable greater insight and reduce uncertainty in resource-management decision making.