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

Matthew R. Grabau, PhD, Karen J. Schlatter, Eliana Rodríguez Burgueño, Jorge RamírezHernández, PhD, Jeff Milliken, Chad McKenna, Jason Keller, and Francisco Zamora-Arroyo, PhD

Upper Gulf of California

U.S.

MEXICO

“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

Historic Delta

Photo source: IBWC

Historic Delta

Photo source: IBWC

International Water and Boundary Commission, 2010

Colorado River Compact Signed

Hoover Dam Completion

Treaty With Mexico Signed

Glen Canyon DamCompletion

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Annual Discharge (Billion Cubic M

eters)Annu

al D

isch

arge

(Mill

ion

Acre

Fee

t)

Year

Colorado River Flow at U.S. - Mexico Border 1878-2009

Treaty obligation

Colorado River Flow to Mexico during 19th Century

The Delta Today

Laguna Grande Restoration Area

Colorado River Corridor in Mexico

Reach 1

Reach 2

Reach 3

Reach 4: Laguna Grande Restoration Area

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Reach 4: Laguna Grande Complex

~15 Miles from the Gulf of California

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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

River Inflow/Outflow

Environmental Flows and Rainfall

Evaporation and Transpiration

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 % Irrigation volume (Feirstein et al, 2008)

Model ComponentsInput

CategoryInput Level Input Amount Drivers

Agricultural Return Flows

Baseline 20% of existing water rights

Canal lining, fallowing, crop changes

Increased 30% of water rights

Reduced 15% of water rights

Riparian Corridor ET

Baseline Current Saltcedar removal, saltcedar defoliation, vegetation composition.

Increased Conversion of saltcedar to native vegetation

Decreased Saltcedar ET reduction based on leaf beetle (16% annually)

Environmental Flow

Deliveries

None 0 a-f/yearInternational water agreements (Min 32X)

Low 5,000 a-f/yearHigh 17,600 a-f/year

Upstream Subsurface

Inflow

Reduced Minimum values in period of record (2005-2007)

Groundwater pumping, reduced agricultural application, upstream environmental flows, extreme weather events.

Increased Modified pulse flow

Intermediate Average of reduced and increased

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 Coefficient Pre-

Beetle Post-

Beetle Reduction

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

Model Inputs For each model grid cell: Percolation rate. Evapotranspiration rate.

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: Groundwater Depth

2014-2015 Water Year

Pending Work: Depth to Groundwater Threshold Analysis

Habitat Potential

Open Water

Marsh

Wet RiparianDense RiparianOpen Riparian

Mesquite

HalophytesOpen Mesquite/Upland

Current Project Status and Next Steps

Completed

Refinement of groundwater model for Reach 4.

Compilation of historic groundwater data.

Existing vegetation mapping for Reach 4.

ET and Percolation scenarios and intersections.

Ongoing

Refinement of depth to groundwater thresholds.

Spatial analysis of model results.

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?