Modeling Shallow Groundwater for Support of Riparian Areas in the Colorado River Delta Matthew R. Grabau, PhD, Karen J. Schlatter, Eliana Rodríguez Burgueño, Jorge Ramírez Hernández, PhD, Jeff Milliken, Chad McKenna, Jason Keller, and Francisco Zamora-Arroyo, PhD
U.S. MEXICO Upper Gulf of California
On the map the Delta was bisected by the river, but in fact the river was nowhere and everywhere, for he could not decide which of a hundred lagoons offered the most pleasant and least speedy path to the Gulf For the last word in procrastination, go travel with a river reluctant to lose its freedom to the sea. Aldo Leopold, A Sand County Almanac
Photo source: IBWC Historic Delta
Historic Delta Photo source: IBWC
Colorado River Flow to Mexico during 19 th Century 30 Colorado River Flow at U.S. - Mexico Border 1878-2009 35 Annual Discharge (Million Acre Feet) 25 20 15 10 5 Hoover Dam Completion Colorado River Compact Signed Treaty With Mexico Signed Glen Canyon Dam Completion 30 25 20 15 10 5 Annual Discharge (Billion Cubic Meters) Treaty obligation 0 0 1875 1880 1885 1890 1895 1900 1905 1910 1915 1920 1925 1930 Year 1935 1940 1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 International Water and Boundary Commission, 2010
The Delta Today
Colorado River Corridor in Mexico Laguna Grande Restoration Area
Reach 1
Reach 2
Reach 3
Reach 4: Laguna Grande Restoration Area
14
Reach 4: Laguna Grande Complex
~15 Miles from the Gulf of California 16
Groundwater Concerns Shallow, low-salinity groundwater required to support desired riparian habitat. Existing vegetation and hydrology Completed restoration projects Potential restoration sites Groundwater levels determined by a range of factors: Agricultural return flows Groundwater pumping Local evapotranspiration Basin-wide precipitation Environmental flows Shallow groundwater areas targeted for active restoration: Reach 1 Reach 4: Current research project.
Conceptual Reach 4 Water Balance Model Agricultural Return Flows Evaporation and Transpiration River Inflow/Outflow Environmental Flows and Rainfall
2005-2007 Groundwater Trend at Laguna Grande
2014-2015 Groundwater with Environmental Flows
Current Groundwater Analysis for Reach 4 Groundwater Monitoring UABC/Minute 319 piezometer transects Additional ~20 piezometers at Laguna Grande Restoration Area Groundwater depth and elevation Groundwater salinity Use results to: Monitor effects of irrigation and environmental flows Adaptively manage restoration sites Groundwater Modeling Determine depth to groundwater under different scenarios. What are the reasonable expectations for groundwater changes in Reach 4 in the future? Use results to inform: Restoration planning site selection, long-term irrigation needs. Future environmental flows what are the effects of different volumes, where can they be applied to maximize ecological benefits in Reach 4?
Groundwater Modeling Refine existing groundwater model to predict mean monthly groundwater depth under different input combinations (model scenarios). Use literature values, on-site observations, and remote sensing results to establish groundwater depth thresholds for riparian plants in the Delta. Determine the extent of groundwater support for existing and potential open water, marsh, and riparian areas under different modeled scenarios.
Existing Groundwater Model (UABC) Conductivity: Diaz, 2001; Rodriguez- Burgueño, 2011 Pumping: CONAGUA 1994-2006 Recharge: 15-32 % (Feirstein et al, 2008) Irrigation volume
Model Components Input Category Input Level Input Amount Drivers Baseline 20% of existing water rights Agricultural Return Flows Increased Reduced 30% of water rights 15% of water rights Canal lining, fallowing, crop changes Riparian Corridor ET Environmental Flow Deliveries Baseline Increased Decreased None Low High Current Conversion of saltcedar to native vegetation Saltcedar ET reduction based on leaf beetle (16% annually) 0 a-f/year 5,000 a-f/year 17,600 a-f/year Saltcedar removal, saltcedar defoliation, vegetation composition. International water agreements (Min 32X) Upstream Subsurface Inflow Reduced Increased Intermediate Minimum values in period of record (2005-2007) Modified pulse flow Average of reduced and increased Groundwater pumping, reduced agricultural application, upstream environmental flows, extreme weather events. 3 X 3 X 3 X 3 = 81 Scenarios
Agricultural Return Flows
Riparian Corridor ET
Saltcedar ET and Beetle Effects Month Monthly ET, mm Reduction Pre- Post- Reduction Coefficient Beetle Beetle January 18 21-3 -0.17 February 18 25-8 -0.43 March 35 43-8 -0.23 April 95 96-2 -0.02 May 178 183-5 -0.03 June 208 180 28 0.13 July 199 156 44 0.22 August 192 116 76 0.40 September 142 89 54 0.38 October 90 73 16 0.18 November 46 38 9 0.19 December 25 21 4 0.16 Annual 1245 1041 205 0.16 Following Liebert et al. (2015)
Monthly ET Curves for Model Scenarios
Theoretical Reach 4 ET Balance
Upstream Subsurface Inflows/Boundary Conditions
For each model grid cell: Percolation rate. Evapotranspiration rate. Model Inputs Dependent on: Current land use (ag or not ag). Current vegetation (saltcedar or not saltcedar). Restoration plans (inside or outside restoration polygons). Application: Assigned values for each of 20,000 grid cells. Fractional calculations based on current cover.
Model Boundary Conditions Upstream boundary conditions. Assigned head boundary. Agricultural subsurface return flows. Parent model for Mexicali Valley.
Anticipated Analysis of Model Results Model outputs: Mean monthly groundwater elevation in each model cell (81 scenarios X 12 months = 972 elevation surfaces). Will have to focus on key months. Summarize groundwater depth conditions for Reach 4. Convert groundwater depth to habitat support. Open water Marsh Cottonwood-Willow Mesquite Transitional
Cori Concession Polygon: 2014-2015 Water Year Groundwater Depth
Pending Work: Depth to Groundwater Threshold Analysis
Habitat Potential Open Water Marsh Wet Riparian Dense Riparian Open Riparian Mesquite Halophytes Open Mesquite/Upland
Current Project Status and Next Steps Completed Refinement of groundwater model for Reach 4. Compilation of historic groundwater data. Ongoing Refinement of depth to groundwater thresholds. Spatial analysis of model results. Existing vegetation mapping for Reach 4. ET and Percolation scenarios and intersections.
Recap of Modeling Objectives Determine how sensitive the groundwater and supported ecosystem in Reach 4 is to factors that are not managed by restoration practitioners. Determine if management actions can mitigate declines in groundwater levels. Understand the potential negative impacts of restoration on the water budget.
Acknowledgments Desert Landscape Conservation Cooperative The Lincoln Institute The Colorado River Delta Water Trust CONAGUA Universidad Autónoma de Baja California
Questions?