As much as 57 million acre-feet of groundwater may be stored in the subsurface of the New Mexico part of the Salt Basin in southern Otero County, New Mexico. Recharge to a system such as the Salt Basin aquifer can result largely from focused recharge of surface water in channels and at mountain fronts. The Salt Basin is a closed basin that covers about 2,400 square miles of southeastern New Mexico and continues across the State line into Texas. A graben underlies the central valley, which is buried by hundreds of feet of alluvial deposits. Bedrock that underlies the alluvial deposits and forms the surrounding plateaus is composed primarily of carbonate and mixed carbonate/evaporate units that can be karst forming in places. Karst features in the downstream parts of some areas of the Salt Basin also may provide opportunities for substantial recharge. Annual recharge to an aquifer such as the Salt Basin aquifer is commonly estimated in groundwater models by mean-annual streamflow. In 2009, the U.S. Geological Survey, in cooperation with the New Mexico Interstate Stream Commission, estimated mean-annual streamflow for selected channels in the Salt Basin.

Mean-annual streamflow was estimated for four main subbasins in the internally drained Salt Basin in southeastern New Mexico. These four main subbasins account for 30 percent of the Salt Basin area in New Mexico. Estimates of mean-annual streamflow were generated at multiple sites down the length of each basin by using two regional regression equations based on channel geometry and one based on the basin characteristics of area and precipitation. Results indicate that, on average, an estimated 60,414 acre-feet of flow is generated annually among the four main subbasins in the New Mexico part of the Salt Basin.

The use of the channel-geometry method at multiple locations down the length of each channel also provided information on the locations of flow accumulation and losses. By contrast, application of the basin-characteristics method will always produce increased runoff estimates with downstream distance in a single basin; therefore, the method is not sensitive to flow losses. Channels that were measured achieved maximum active-channel widths from 6 to 16 stream miles upstream from the locations in which channels bifurcate and lose shape altogether when they reach the lowlands of the internally drained basin. Active-channel-width measurements indicate that each of the four main subbasin channels studied loses between 27 and 56 percent of annual flow from the point of maximum active-channel width to the most downstream measureable section in the channel.

First posted June 6, 2011