Modeling Ground Water/Surface Water Interactions along the Rio Grande to Assess the Sustainability of Desired Flows for River Management and Restoration

Sustaining desired river flows under a variety of inflow, water use and climatic conditions is critical to meeting downstream delivery obligations and to maintaining adequate riverine habitat on the Rio Grande in New Mexico.  For the Rio Grande between Cochiti and Elephant Butte reservoirs, a series of high-resolution groundwater models have been developed for the near-river zone to provide insight on surface water/groundwater interactions that variously impact the degree of river gains and losses, and the ability to sustain desired flows in specific river sub-reaches given changes in regional groundwater conditions, flood magnitude and duration, and following drought.   The model domains include the river channel, overbank area and parts of the adjacent floodplain, and the underlying shallow alluvium.   Processes modeled include seepage from the river, interception of shallow groundwater by drains or the river, recharge to shallow groundwater from flooded overbank areas and water depletions due to open water evaporation and riparian evaportranspiration.   Transient river boundary conditions are modeled using flow-dependent river width and depth, obtained from companion surface water models.  In this discussion, models for the Albuquerque and Isleta reaches are described, including their calibration and application.  Information used in model calibration includes seepage run results and groundwater elevation data under variable flow conditions.  The models are applied to potential water management and restoration scenarios to assess the sustainability of river flows under variable external conditions.