Modeling Shallow Groundwater for Support of Riparian Areas in the Colorado River Delta

Transcription

1 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

2 U.S. MEXICO Upper Gulf of California

3 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

4 Photo source: IBWC Historic Delta

5 Historic Delta Photo source: IBWC

6 Colorado River Flow to Mexico during 19 th Century 30 Colorado River Flow at U.S. - Mexico Border Annual Discharge (Million Acre Feet) Hoover Dam Completion Colorado River Compact Signed Treaty With Mexico Signed Glen Canyon Dam Completion Annual Discharge (Billion Cubic Meters) Treaty obligation Year International Water and Boundary Commission, 2010

7 The Delta Today

8 Colorado River Corridor in Mexico Laguna Grande Restoration Area

9 Reach 1

10 Reach 2

11 Reach 3

12 Reach 4: Laguna Grande Restoration Area

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14 14

15 Reach 4: Laguna Grande Complex

16 ~15 Miles from the Gulf of California 16

17 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.

18 Conceptual Reach 4 Water Balance Model Agricultural Return Flows Evaporation and Transpiration River Inflow/Outflow Environmental Flows and Rainfall

19 Groundwater Trend at Laguna Grande

20 Groundwater with Environmental Flows

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22 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?

23 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.

24 Existing Groundwater Model (UABC) Conductivity: Diaz, 2001; Rodriguez- Burgueño, 2011 Pumping: CONAGUA Recharge: % (Feirstein et al, 2008) Irrigation volume

25 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 ( ) 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

26 Agricultural Return Flows

27 Riparian Corridor ET

28 Saltcedar ET and Beetle Effects Month Monthly ET, mm Reduction Pre- Post- Reduction Coefficient Beetle Beetle January February March April May June July August September October November December Annual Following Liebert et al. (2015)

29 Monthly ET Curves for Model Scenarios

30 Theoretical Reach 4 ET Balance

31 Upstream Subsurface Inflows/Boundary Conditions

32 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.

33 Model Boundary Conditions Upstream boundary conditions. Assigned head boundary. Agricultural subsurface return flows. Parent model for Mexicali Valley.

34 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

35 Cori Concession Polygon: Water Year Groundwater Depth

36 Pending Work: Depth to Groundwater Threshold Analysis

37 Habitat Potential Open Water Marsh Wet Riparian Dense Riparian Open Riparian Mesquite Halophytes Open Mesquite/Upland

38 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.

39 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.

40 Acknowledgments Desert Landscape Conservation Cooperative The Lincoln Institute The Colorado River Delta Water Trust CONAGUA Universidad Autónoma de Baja California

41 Questions?