M ODELING P LAN PEIR FOR G ROUNDWATER O RDINANCE I MPLEMENTATION June 16, 2016 Presented to: Turlock Groundwater Basin Association Facilitated by: Mike Tietze, PG, CEG, CHG Robert Abrams, PhD, PG, CHG 1
Overview 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 2
Work Plan Revisions and Modeling Approach Refinements
Revised Task Structure 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 4
Revised Modeling Scenarios Removed speculative modeling of unimpaired flow and GSP implementation. Added modeling of “Alternative Management Strategies”: Scenarios Forecast Component 1 2 3 4 Current and Forecasted Groundwater Demand Ordinance Implementation Alternative Management Strategies Mitigation Concepts Climate Change 5
Work Plan Clarifications 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 6
Model Domain and Boundaries 52 x 52 miles 2,704 mi 2 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 Model Forecast Scenarios Primary Effects from Ordinance Primary Effects from GSP Implementation
Review of Available Models and Codes
MODFLOW-OWHM vs. IWFM 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 10
Model Adaptability and Support C2VSim Model Feature CVHM MERSTAN (Fine Grid) Expected Updates 2017 Late 2016 or 2017 None Planned Not Applicable Beta Data DWR will make Generally not Availability beta data available available Expected Assistance Assistance offered Some assistance Some assistance Availability may be available may be available Compatibility with Good Fair Fair IDC Compatibility with Good Fair Fair CalLite Ease of Update with Fair Good Not Applicable MERSTAN lithology
Key Model Code Features Model Code C2VSim (IWFM) CVHM (MODFLOW-OHM) Feature Riparian ET Only simulates downward flux; does Simulates upward flux from water not simulate root-zone anoxia. table and root zone anoxia. Irrigation User specified or dynamically User specified or dynamically Demand calculated soil moisture deficit calculated as unmet water irrigation, similar to actual practice demand Root Zone Dynamically adjusts root zone Root zone moisture storage is moisture storage modeled as steady state Moisture Actual ET Linear interpolation when soil Hydrus 2D model – about 75% of moisture < 50% Field Capacity IWFM results Runoff from SCS curve number method; runoff User specified and routing of Precipitation subtracted from water available for infiltration in excess of K sat ; infiltration and ET fraction of excess left over after ET
Model Resolution and Accuracy C2VSim Model Feature CVHM MERSTAN (Fine Grid) 0.6 mi 2 cell size 1 mi 2 cell size 0.25 mi 2 cell size Cell Size Calibration Wells 40-50 wells 10-15 wells 109 wells Lithology Data Set Based on cross ~8,500 wells in ~4,500 wells in 20,000 mi 2 1,000 mi 2 sections from earlier model versions (?) Simulation of Fair to good match Fair to good match Good match to Stanislaus and to stream data to stream data stream data Tuolumne Rivers Simulation of East Poor resolution Poor resolution Reasonable Turlock Subbasin 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 Net Net Total Total Applied Water Groundwater Groundwater Water Groundwater Irrigation Year Extraction – Extraction – Demand Pumpage Water High 1 Low 2 2000 3 590,000 AF 206,500 AF 534,000 AF 121,000 AF 78,000 AF 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)
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 Et a Measurement 20
SEBS Et a Measurement Conversion from Rangeland to Orchard 21
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