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MODELING PLAN PEIR FOR GROUNDWATER ORDINANCE

IMPLEMENTATION

June 16, 2016

Presented to:

Turlock Groundwater Basin Association

Facilitated by: Mike Tietze, PG, CEG, CHG

Robert Abrams, PhD, PG, CHG

Overview

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Objectives: Discussion and solicitation of feedback regarding modeling objectives and approach

Expected Outcome: Input for preparation of a Draft Modeling Plan

Topics 1. Work Plan Revisions and Modeling Approach

Refinements 2. Review of Available Models and Codes 3. Review and Discussion of Options

Work Plan Revisions and

Modeling Approach Refinements

Revised Task Structure

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Rearranged tasks to emphasize dual purpose of GSP Support and Local Groundwater Ordinance Support:

Task 1 Grant Administration Task 2 GSP Development Support

Task 2.1 Hydrologic Modeling Task 2.2 GSA Support

Task 3 Local Groundwater Ordinance Support Task 3.1 PEIR Preparation and Processing

Revised Modeling Scenarios

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Forecast Component Scenarios

1 2 3 4 Current and Forecasted Groundwater

Demand

Ordinance Implementation

Alternative Management Strategies

Mitigation Concepts

Climate Change

Removed speculative modeling of unimpaired flow and GSP implementation. Added modeling of “Alternative Management Strategies”:

Work Plan Clarifications

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Clarified language around impact assessment:

• Explicitly recognized that Ordinance impacts will occur primarily prior to GSP implementation

• Clarified that impacts will be evaluated under CEQA • References to undesirable results are tied to the

definition under the Ordinance, and evaluated under CEQA criteria, not GSP standards

• References to unsustainable extraction are tied to the definition under the Ordinance

Model Domain and Boundaries

52 x 52 miles

2,704 mi2

NE and SW No-Flow boundaries

NW and SE General Head boundaries based on larger model results

Includes entire Modesto and Turlock Subbasins

Temporal Boundaries

2000 - - - -

2005 - - - -

2010 - - - -

2015 - - - -

2020 - - - -

2025 - - - -

2030 - - - -

2035 - - - -

2040 -

2042

Existing Model Data

Model

Update

SCHM Calibration Period

Primary Effects

from Ordinance

Primary Effects from GSP Implementation

Model Forecast Scenarios

Review of Available Models

and Codes

MODFLOW-OWHM vs. IWFM

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MODFLOW-OWHM (USGS) • Source code for CVHM and MERSTAN • Farm Process: Land use-based water budgets • Vision for future updates includes cloud-based data

updates and compatibility with remote sensing data

IWFM (DWR) • Source code for C2V-Sim, Merced County model

and San Joaquin County model • Used by DWR for Water Plan updates • Will be used by DWR to assess GSP performance

Model Adaptability and Support

Model Feature C2VSim

(Fine Grid) CVHM MERSTAN

Expected Updates 2017 Late 2016 or 2017 None Planned

Beta Data Availability

DWR will make beta data available

Generally not available

Not Applicable

Expected Assistance Availability

Assistance offered Some assistance may be available

Some assistance may be available

Compatibility with IDC

Good Fair Fair

Compatibility with CalLite

Good Fair Fair

Ease of Update with MERSTAN lithology

Fair Good Not Applicable

Key Model Code Features Model Code Feature

C2VSim (IWFM) CVHM (MODFLOW-OHM)

Riparian ET Only simulates downward flux; does not simulate root-zone anoxia.

Simulates upward flux from water table and root zone anoxia.

Irrigation Demand

User specified or dynamically calculated soil moisture deficit irrigation, similar to actual practice

User specified or dynamically calculated as unmet water demand

Root Zone Moisture

Dynamically adjusts root zone moisture storage

Root zone moisture storage is modeled as steady state

Actual ET Linear interpolation when soil moisture < 50% Field Capacity

Hydrus 2D model – about 75% of IWFM results

Runoff from Precipitation

SCS curve number method; runoff subtracted from water available for infiltration and ET

User specified and routing of infiltration in excess of Ksat; fraction of excess left over after ET

Model Resolution and Accuracy

Model Feature C2VSim (Fine Grid)

CVHM MERSTAN

Cell Size 0.6 mi2 cell size 1 mi2 cell size 0.25 mi2 cell size

Calibration Wells 40-50 wells 10-15 wells 109 wells

Lithology Data Set Based on cross sections from earlier model versions (?)

~8,500 wells in 20,000 mi2

~4,500 wells in 1,000 mi2

Simulation of Stanislaus and Tuolumne Rivers

Fair to good match to stream data

Fair to good match to stream data

Good match to stream data

Simulation of East Turlock Subbasin

Poor resolution Poor resolution Reasonable dimensions, but location wrong

Model Water Balance C2VSim vs. CVHM

Model Feature C2VSim CVHM

Total Water Demand 737,000 AFY 491,000 AFY

Return Fraction of Applied Water 16 % 24 %

Recharge from Applied Water 62,000 AFY 13,000 AFY

Net Groundwater Demand 185,000 AFY 59,000 AFY

Change in Groundwater Storage - 22,000 AFY 10,000 AFY

Modesto Subbasin water budget averages for 1980 to 1993 from Chou, et al, 2013

• Negative storage change consistent with developing cone of depression in Modesto area during this time

Reported Water Demand and Calculated Net Groundwater Extraction

1. Calculated using a return fraction of applied irrigation water of 16%. 2. Calculated using a return fraction of applied irrigation water of 24%. 3. Taken from the Integrated Regional Groundwater Management Plan for the Modesto Subbasin,

Bookman Edmonston, 2005 (Based on Burrow, 2004)

Water Year

Total Water

Demand

Total Groundwater

Pumpage

Applied Irrigation

Water

Net Groundwater Extraction –

High 1

Net Groundwater Extraction –

Low 2

2000 3 590,000 AF 206,500 AF 534,000 AF 121,000 AF 78,000 AF

Review and Discussion of

Options

Model Options Considered

1. CVHM with embedded MERSTAN model

Retains features and details of MERSTAN model

Geographic limitation and boundary condition issues of MERSTAN addressed by incorporating within CVHM

Some work focused on combining models

Requires additional effort to develop model interface

Advantages and limitations of Farm Process

Advantages of future CVHM upgrades and ability to incorporate remote sensing data

Model Options Considered

2. C2VSim with imported MERSTAN lithology

Incorporates lithologic and permeability details of MERSTAN

Advantage of DWR support and availability of beta data

Easier interface with CalLite

Advantages and limitations of Irrigation Demand Calculator

Compatibility with source codes for models to the north and south

Model Options Considered

3. Optional Addition of Remote Sensing Data to Support Model Update

Use of remote sensing data to calibrate crop coefficients in IDC or Farm Process during model update period

Possibility to use data for direct update of model with direct measurement of ET data

Improves reliability of groundwater extraction calculations and model results in either CVHM or C2VSim

Calibrates a key unknown variable

SEBS Eta Measurement

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SEBS Eta Measurement

Conversion from Rangeland to Orchard