Water Resources Assessment, Lower Rio Grande Basin

SSP&A has provided technical hydrologic and water management support to the State of New Mexico for basin-wide evaluation of groundwater resources, conjunctive use, and groundwater/surface water interaction since 1998. This work has been conducted to support state and regional planning efforts; NEPA water supply alternatives analysis review; litigation related to state-court water rights adjudication; mediation of a federal lawsuit; modeling, expert reporting and deposition in support of Original Action Number 141 (Texas vs. Colorado and New Mexico); and support in evaluation of administrative/management guidelines. This work has involved consultation with the New Mexico Office of the State Engineer technical and legal staff to address issues related to active water resources management, in addition to extensive technical work and modeling.

SSP&A developed and calibrated a highly-detailed and refined historical groundwater flow model of the Lower Rio Grande Basin. Processes represented in the model include irrigation and Data Center Management Interface (DCMI) pumping, recharge from both irrigation and urban return flows, riparian evapotranspiration from vegetation along the Rio Grande River, and an extensive network of irrigation canals, laterals and drains explicitly simulated using the MODFLOW Streamflow Routing (SFR) package.

The groundwater model was loosely coupled with Hydrosphere’s RiverWare surface water model capable of simulating a complex set of reservoir operational rules. The surface water model provides critical model stresses derived from a simulated farm budget, including surface water diversions (where diversions are dictated by reservoir operation rules), supplementary groundwater pumping, and recharge. The groundwater model passes back simulated canal seepage losses, groundwater levels, and lateral and vertical groundwater fluxes across alluvium boundaries.

The coupled surface water and groundwater models have been utilized for scenario analysis conducted in support of Original Action Number 141 and the associated settlement agreement under consideration by the U.S. Supreme Court. Hydrosphere’s RiverWare model allows the scenario simulations to consider realistic reservoir operations in response to changes in system dynamics. In turn, the groundwater model provides much more refined inputs critical to the farm budget calculations such as canal seepage losses, than the surface water model could have estimated.