Evaluation of Management Alternatives in the San Acacia

Evaluation of Management Alternatives in the San Acacia Reach Based on High-Resolution Modeling Robert Bowman and Laura Wilcox, Department of Earth and Environmental Science New Mexico Tech Nabil Shafike New Mexico Interstate Stream Commission

Acknowledgements • Collaborators – SS Papadopulos & Associates • Funding Agencies – NM Interstate Stream Commission – US Army Corps of Engineers

Motivation for Understanding: Better Balance of Competing Demands • Agriculture • Municipal/Industrial • Environmental • Interstate compacts

The San Acacia Reach: Critical for Rio Grande Compact Compliance

Relevant Issues • Water consumption by riparian vegetation • Removal of exotic vegetation • Environmental effects of drying of the river • Potential engineering alternatives

Demands On Water Resources

Study Area Aerial view of San Acacia Diversion Dam, looking southwest Low Flow Conveyance Channel San Acacia Diversion Dam Socorro Main Canal Aerial view of Elephant Butte Reservoir and Dam, looking northeast Elephant Butte Dam

CONCEPTUAL MODEL OF WATER DYNAMICS transpiration Well pumping irrigation precipitation evaporation River flow LFCC gain Rio Grande drain LFCC W est t Eas Groundwater recharge and discharge

Approach to Determining Surface Water/Groundwater Interactions • Water dynamics • Water chemistry • Hydrologic modeling

Water Dynamics • Determine • • connectivity between surface water bodies Determine groundwater response to changing river stage Evaluate temporal changes

Monitoring Network • 7 transects over ~50 • • • miles ~175 monitoring wells 25 surface-water-level gauges ~70 transducers taking hourly water level readings

Monitoring Transect Cross Section Socorro Main Canal LFCC Rio Grande

SRD Groundwater Levels Rise in Winter LFCC Rio Grande Groundwater Wells LFCC Rio Grande

Groundwater Levels Rise in Winter LFCC Rio Grande Groundwater Wells LFCC

Groundwater Responds to ET

Groundwater Responds to Flooding

Hydrological Modeling • Integrate current • • • understanding of GW/SW interactions Evaluate operations of the river and the LFCC Evaluate impact of groundwater levels on riparian ET Investigate management alternatives

Key Data Collected Geologic Data • Stratigraphy (color, grain size, hydraulic conductivity) Aquifer Data • Hydraulic conductivities (aquifer testing) • Water-elevation time series

Legend Stratigraphy 20 ft No Sample Clay, Sandy Clay Silt, Silt & Fine Sand Fine to Medium Sand, Medium Sand 4560 Rio Grande HWY-W 06 HWY-W 04 HWY-W 07 HWY-E 01 HWY-E 02 HWY-W 03 West LFCC HWY-W 02 4540 Layer 1 4520 4500 4480 4460 Layer 2 Valley alluvium Layer 3 Santa Fe Formation 400 ft Fine to Coarse Sand, Coarse Sand and Gravel, Gravel Clayey Gravel Santa Fe Group Bedrock Water Surface East HWY-E 03

Aquifer Testing

Legend Aquifer Test Instrumentation Well 0 -20 feet 0. 5 miles north of Highway 380 in San Antonio Well 40 -50 feet Well 80 -90 feet Staff gage rai n 10 Extraction well ers id e. D 07 Gra C LFC So LFCC Rio co rro Riv 09 Rio Grande Low-permeability zone

Time-drawdown of nested well W 07 A, B, C LFCC r of W 07 = 15 feet Rio Grande Low-permeability zone Legend Well 0 -20 feet Well 40 -50 feet Well 80 -90 feet

AREA OF INTEREST FOR HIGH-RESOLUTION MODELING N Magdalena Mountains San Acacia 60 Socorro San Antonio I-25 San Marcial Rio Grande 380 Telescopic model Regional model - ISC -smaller domain -refined grid -constant head from regional model

River water losses in this reach are extreme

MODEL CONSTRUCTION - Model Grid Domain is 320 rows x 170 columns = 54400 grid cells OR 6 miles x 3 miles = 18 miles 2 regional model grid is 1000 feet x 1000 feet Telescopic model grid is 100 feet x 100 feet

Three-Layer Model Layer 1 - sand Layer 2 - clay/silt Layer 3 - sand/gravel 0 feet 75 35 feet

Surface Water System Designation of grid cells to represent drains, LFCC, and river. Each cell has values for: • stage • conductance • bottom elevation • bed thickness • vertical hydraulic conductivity

Stream –aquifer System Land Surface Water Table River Surface Riverbed Conductance = KLW M Streambed Representation of Stream –aquifer System Impermeable Walls River Stage (HRIV) Head in Cell (h) MODFLOW River Package: M RBOT W - Riv 1 (MODFLOW 83)

Estimation of River Stage

Evapotranspiration IKONOS – July 2000 Legend Crop and pasture Riparian Sandbars Riparian Other or inactive Crops

Prescribed Head regional model telescopic model Constant head boundary determined from regional model for every stress period

Model Calibration Groundwater Budget

EVALUATION OF MANAGEMENT ALTERNATIVES • Removal of the Low Flow Conveyance Channel • Relocation of the River Channel • Decrease in Riparian Evapotranspiration

Effects of Removing the LFCC • Groundwater levels rise • 8% increase in riparian ET • Seepage from river decreases by ~70% With LFCC Without LFCC

Evaluation of Relocation of River Channel Neil Cupp LFCC W-91. 28 -1 Present day Rio Grande location W-Perini Simulated Rio Grande location N N 0. 5 Miles Highway 380

Effect of Channel Relocation • Groundwater rises to the east of the river • 2% decrease in riparian ET • Seepage losses from the river decrease by 34% Original channel Relocated channel

Effect of Decreased Riparian ET • Groundwater rises to the east of river • 50% decrease in riparian evapotranspiration translates to a 6% decrease in river seepage

Conclusions • The Rio Grande and the shallow groundwater system are highly interconnected • Most of the shallow groundwater is of Rio Grande origin • Channel adjustments and control of riparian vegetation can increase river flows

For More Information… www. ees. nmt. edubowmanresearchRio. Grande. Project