1
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
2
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
4
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
5
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
6
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
10
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
20
21
SEBS Eta Measurement
Conversion from Rangeland to Orchard