# Presentation: 260071

## 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

- Socorro Main Canal

- Low Flow
- Conveyance Channel

- San Acacia Diversion** **Dam

- Aerial view of San Acacia Diversion Dam, looking southwest

- Aerial view of Elephant Butte Reservoir and Dam, looking northeast

## CONCEPTUAL MODEL OF WATER DYNAMICS

**CONCEPTUAL MODEL OF WATER DYNAMICS**

**West**

**East**

**drain**

**LFCC**

**Rio Grande**

## 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

## Slide 13

## Slide 14

## Slide 15

**Notes:**
Reinforce that diurnal fluctuations are just that [in talk, this slide was with HWY slides, even though it shows ESC wells]

## Slide 16

## 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

## Stratigraphy

## Aquifer Testing

## Aquifer Test Instrumentation

**Aquifer Test Instrumentation**

- 0.5 miles north of Highway 380 in San Antonio

- Socorro Riverside Drain

- LFCC

- Rio Grande

**10**

**07**

**09**

## Time-drawdown of nested well W07A,B,C

- r of W07 = 15 feet

## AREA OF INTEREST FOR HIGH-RESOLUTION MODELING

**AREA OF INTEREST FOR HIGH-RESOLUTION MODELING**

- Magdalena Mountains

**N**

- Socorro

- San Antonio

**60**

**380**

- San Acacia

**I-25**

- San Marcial

- Rio Grande

- 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 miles2

- Telescopic model grid
- is 100 feet x 100 feet

**MODEL CONSTRUCTION - Model Grid**

## Three-Layer Model

- Layer 2 -  clay/silt

**Three-Layer Model**

## Surface Water System

- Each cell has values for:
- stage
- conductance
- bottom elevation
- bed thickness
- vertical hydraulic conductivity

**Surface Water System**

## Riverbed Conductance =

**Stream –aquifer System**

**Representation of Stream –aquifer System**

- River
- Surface

- Water Table

- Streambed

- River Stage
- (HRIV)

- Impermeable Walls

- M

- W

- RBOT

- _KLW_
- M

- MODFLOW River Package:
- - Riv1    (MODFLOW 83)

- Land
- Surface

- Head in
- Cell (h)

## Estimation of River Stage

## Evapotranspiration

**Evapotranspiration**

- IKONOS – July 2000

## Prescribed Head

**regional**
**model**

- Constant head boundary determined from regional model for every stress period

**telescopic**
**model**

## Groundwater Budget

- Model Calibration

## Removal of the Low Flow Conveyance Channel

- Relocation of the River Channel
- Decrease in Riparian Evapotranspiration

**EVALUATION OF MANAGEMENT ALTERNATIVES**

## Effects of Removing the LFCC

- Groundwater levels rise
- 8% increase in riparian ET
- Seepage from river decreases by ~70%

- Without LFCC

- With LFCC

## Evaluation of Relocation of River Channel 

- Present day Rio Grande location

- LFCC

- Neil Cupp

- Highway 380

**N**

- Simulated Rio Grande location

- LFCC

- Neil Cupp

- Highway 380

- 0.5 Miles

**N**

- W-91.28-1

- W-Perini

- W-91.28-1

- W-Perini

## 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...

- Last Updated: November 3, 2002

*www.ees.nmt.edu\bowman\research\RioGrandeProject*