Lower Rio Grande Salinity Monitoring

Transcription

1 Lower Rio Grande Salinity Monitoring Chad Johannesen, DBS&A Beiling Liu, NM Interstate Stream Commission James F. Hogan, NM Environment Department Amy Ewing, DBS&A Chris Wolf, DBS&A

2 Rio Grande Surface Water Basin From NOAA Climate.gov

3 Lower Rio Grande Multiple basins Inner valley vs. bolsons Highly regulated streamflow Reservoirs Irrigation-driven seasons

4 Management Streamflow almost entirely regulated by releases from reservoirs and diversion control dams. Reservoirs operated to support agricultural activities in New Mexico/Texas and fulfill international treaty obligations with Mexico.

5 Lower Rio Grande Salinization Water quality has been extensively studied for more than 100 years. Past studies have focused on agricultural activities and surface flow. Salinization increases in the downstream direction.

6 Points of Salt Addition Fraction Cl added vs. flow distance 1.0 Fraction Cl Added Flow distance (km) = basin terminus From Phillips et al., 2006

7 Basic Groundwater System Schematic hydrogeologic cross section, parallel to river path From Mills, 2003

8 Salinity Sources

9 Potential Salinity Sources Reservoir releases Deep saline groundwater Geothermal groundwater Wastewater Agricultural drains Agricultural drain within Elephant butte Irrigation District

10 Evaluation of Salinity (2004) New Mexico Interstate Stream Commission (NMISC) Historical data review Geochemical modeling Synoptic water quality events Irrigation vs. nonirrigation

11 Historical Lessons Salinization documented before reservoirs, agricultural drains, and wastewater treatment plants (WWTPs) were present. Observed increases in Cl loads cannot be caused by evapotranspiration alone; increases may be due to other sources such as: Inflow of deep saline groundwater Geothermal groundwater

12 Lower Rio Grande Water Quality Monitoring Program Initiated and funded by NMED and NMISC in May DBS&A began assisting in quarterly water quality sampling events in February Collaborators: Elephant Butte Irrigation District United States Geological Survey El Paso Electric

13 LRG Program Objectives Evaluate hypothesis: Majority of observed salinity increase can be attributed to natural sources. Improve understanding of water quality. Fill existing data gaps. Identify areas where additional study may be warranted. Provide a basis for initiating an effective salinity control program.

14 Rio Grande Sampling 28 sample locations: Below dams and diversion structures Drain entrance USGS gauging stations and sample locations

15 Agricultural Drains Drains intercept: Shallow alluvial groundwater Unused agricultural water Intercepted water is returned to main stream of Rio Grande.

16 Wastewater Treatment Plants Nine locations sampled, including industrial wastewater outfalls at EL Paso Electric plant.

17 Shallow Alluvial Wells Screened in Rio Grande alluvium. Total depths of 11 to 45 feet. 108 wells sampled, including NMED compliance wells.

18 NMISC Piezometers Screened in Santa Fe Group sediments. Total depths of 75 to 1,321 feet. Total of 19 wells.

19 Observations: Surface Water Total dissolved solids, chloride, and sulfate concentrations in Rio Grande increase in downstream direction. Salinity increases are more pronounced during winter season (no reservoir releases). Drains represent agricultural return flows, generally more concentrated than Rio Grande. Not a significant contributor to chloride loading in Rio Grande. Corroborates other investigations and USGS WRDA Salinity Study

20 Distribution of Chloride ( ) 10,000 1,000 Chloride (mg/l) Nogal Canyon Elephant Butte Rio Grande-Summer Rio Grande-Winter Geothermal-Winter Caballo Dam Drain-Summer Drain-Winter Las Cruces El Paso ,050 River Distance Downstream from Rio Grande Reservoir (km)

21 Rio Grande at Leasburg Dam, Winter 2006

22 Observations: Groundwater Basic chemistry varies widely throughout the basin. Groundwater samples generally have less seasonal variability then Rio Grande samples. Most concentrated salinity is found in southernmost portion of the Lower Rio Grande.

23 NMISC Wells in the New Mexico-Texas Border Region

24 Depth (feet) TDS and Cl Concentration Cross Section N S 0 ISC-1 ISC-2 ISC-3 ISC-7 ISC-6 ISC-5 ISC , ,400 1,800 4,600 1,700 31,000 14, ??? 1, Bedrock Distance from State Line in Anthony (miles)

25 Continuation of Support Assistance with USGS seepage study ( ) Basin monitoring well sampling ( )

26 Irrigation Well Sampling Support ( )

27 Response to Climate Variability Recent drought conditions have reduced available streamflow. Conditions have led to less surface water flow, resulting in reduced reservoir releases, lower groundwater levels, and reduced drain flow. Salt concentrations in the Rio Grande and possible salt accumulation in the aquifer will continue to be monitored.

28 Rio Grande Salinity Management Coalition Composed of Texas, New Mexico, and Colorado management water agencies, irrigation districts, El Paso and Las Cruces water utilities, and university researchers. Formed in 2008 to improve Rio Grande water quality in the New Mexico-Texas border region; provides technical guidance.

29 Water Resources Development Act Section 729 Rio Grande Salinity Management Program Implementation agreement between U.S. Army Corps of Engineers and New Mexico Interstate Stream Commission in support of the RG Salinity Coalition's objectives. Purpose: To study, account, and ultimately intercept sources of salinity in the Lower Rio Grande Basin that adversely affect water quality and limit full utilization of the water resources in the basin.

30 Value of the Lower Rio Grande Salinity Monitoring Program Improved understanding of salinity and processes effecting changes in salinity in the Rio Grande. Provide ongoing data in support of Rio Grande Salinity Coalition's efforts Provided technical basis for an effective salinity control program.

31 Questions?