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1. Incorporating a Dynamic Irrigation Demand
Module into an Integrated Surface
Water/Groundwater Model to Assess Drought
Response
Dirk Kassenaar, E.J. Wexler
Peter J. Thompson, Michael Takeda
Toward Sustainable Groundwater in Agriculture
San Francisco, CA
June 30, 2016

2. Presentation Outline
1. Background: Source Water Protection in Ontario, Canada
2. Dynamic irrigation demand and consumptive use
3. Integrated SW/GW Modelling
4. Pilot Watershed: Source Water Protection Study/ Low Water Response
Project
5. GSFLOW Code modifications and conceptual testing
6. Simulation of farm operations in study sub watershed Conclusions
Integrated Simulation of Irrigation Demand - Introduction 2

3. Source Water Protection in Ontario, Canada
 2000 – Town of Walkerton Tragedy: 7 deaths and 2500 illnesses
▪ Municipal water supply well contaminated by E. Coli from farm runoff
▪ 2004: Local water manager sentenced to 1 year in prison
 2006 – Ontario Clean Water Act:
▪ Provincial law creates local “Source Protection Committees” (SPC)
▪ Each SPC required to develop an “Assessment Report” including:
• Detailed wellhead protection analysis, water budget/drought modelling, threats
identification
▪ Many parallels with SGMA (GSA=SPC , GSP=Assessment Report)
 2006 - 2016: $330 million spent to date developing SPC Assessment Reports
▪ 2008: USGS GSFLOW released; Earthfx Inc. begins use for all integrated modelling
Integrated Simulation of Irrigation Demand - Modelling Approach 3

4. Agricultural Water Use
 Irrigation in Ontario is growing in response to:
▪ Increase in climate variability
▪ Contract farming: “Supply chain” management approach and need for production certainty
• Contractual obligation to irrigate throughout the growing season
▪ Advances in precision agriculture
 Irrigation operations
▪ Shift from SW sources to GW sources both for supply certainty and ecosystem protection
▪ Regulators looking for modelling tools and insights for better permit allocation and water
use monitoring
 Need to comprehensively simulate “soil moisture-based irrigation water use”
▪ Consumptive use assessment: GW pumping, ET losses, enhanced runoff, GW return flow,
changes in baseflow, induced stream losses, etc.
Integrated Simulation of Irrigation Demand - Modelling Approach 4

5. Fully Integrated SW/GW Modelling: Advantages
 Better estimate of groundwater recharge and feedback
(rejected recharge)
 Better representation streamflow and head-dependent
leakage
 Better representation of SW/GW storage.
 Better representation of cumulative effects of takings.
 Better calibration: input total precipitation, calibrate to
total flows (no baseflow separation)
 It’s just better...
Integrated Simulation of Irrigation Demand - Modelling Approach 5
California Department of Water Resources

6. USGS GSFLOW
 USGS integrated GW/SW model
▪ Based on MODFLOW-NWT and PRMS
(Precipitation-Runoff Modelling System)
▪ Fully-distributed: Cell-based representation
▪ Excellent balance of hydrology, hydraulics and GW
▪ Open-source, proven and very well documented
6- Modelling Approach

7. Irrigation Demand Modelling
 Extensive history of irrigation demand model development in California
▪ IWFM Model – IWMFM Demand Calculator (IDC)
▪ MODFLOW Farm Process (MODFLOW OWHM)
▪ Both excellent models, but all models have compromises
 Why GSFLOW?
▪ Includes a mature, fully-distributed hydrologic soil zone sub-model: PRMS
• Detailed representation of soil zone moisture, canopy interception, imperviousness,
cascading inter-cell runoff (3D recharge/re-infiltration), interflow, and snowpack
▪ GW feedback: GW discharge to the soil zone (seepage), Dunnian rejected recharge
▪ Somewhat more generalized and comprehensive integration of sub-models
• Designed for a broader range of SW/GW analysis issues
• Farm processes not currently included
Integrated Simulation of Irrigation Demand - Modelling Approach 7

8. GSFLOW Sub-Models
 Hydrology (PRMS) Hydraulics (SFR2) GW (MODFLOW-NWT)
 Soil zone processes Stream routing and lakes GW flow

9. GSFLOW Spatial and Temporal Resolution
 Spatial resolution: Three grid definitions for climate, soils and GW system
▪ We typically use a soil zone resolution 10 to 100 times finer resolution to represent
 Temporal resolution: Daily time step for groundwater, option for hourly climate-driven
processes
9- Modelling Approach
Climate: NEXRAD Precip.
Soils: LIDAR, MODIS, ELC land
use, remote sensing data
GW: Variable cell MODFLOW
grid

10. PILOT WATERSHED -
STUDY SUB WATERSHED
Integrated Simulation of Irrigation Demand – Watershed Overview 10

11. Study Area
 Study sub watershed is located
southwest of Cambridge, Ontario
Integrated Simulation of Irrigation Demand - Modelling Approach 11

12. Current Land Use
12Integrated Simulation of Irrigation Demand - Watershed Overview
(SOLRIS v2, 2015)

13.  Main branch of study sub watershed is a
provincially significant cold-water stream
supporting Brown, Brook, and Rainbow trout.
 Numerous groundwater-supported wetlands.
 Main river valley serves as an important
continuous habitat corridor through the region.
Wetlands and streams in the Study
subwatershed
Natural Heritage Features
Integrated Simulation of Irrigation Demand - Watershed Overview 13

14. Agricultural Usage
14
 Corn, sod farms, tobacco, mixed..
 Water usage can vary
considerably by crop type (sod vs.
hay/pasture).
 Includes significant irrigated
water use in Norfolk Sand Plain
Integrated Simulation of Irrigation Demand - Watershed Overview

15. Integrated Simulation of Irrigation Demand - Geologic & Hydrostratigraphic Model 15
Conceptual Hydrostratigraphic Model

16.  Wisconsinan glaciation (85,000 to 11,000 years ago)
 Regional Till Sheets (minor tills in report)
▪ Canning Till – very stiff clay till; overlies discontinuous “pre-
Canning” tills and “pre-Canning” sands.
▪ Catfish Creek Till - stony, over-consolidated, sandy silt to silty
sand till; outcrops at Bright.
▪ Tavistock Till – major unit; outcrops in north and to west of
Whitemans; clayey silt till.
▪ Port Stanley Till - major unit; outcrops in middle of study area;
stiff clayey silt to silt till; sandier to north.
▪ Wentworth Till – Outcrops to east near Bethel Rd; silty sand till;
overrides outwash and Lake Whittlesey deposits.
 Erie Phase Deposits
▪ Waterloo Moraine-age deposits; Catfish Creek and Maryhill Tills.
 Grand River Outwash Sands and Gravels
▪ Ice recession during Mackinaw phase.
▪ Difficult to distinguish from overlying Lake Whittlesey sands.
▪ Very high irrigation water use
 Lacustrine Deposits
▪ Associated with Glacial Lake Whittlesey
▪ Source of the fine sands of Norfolk sand plain
Integrated Simulation of Irrigation Demand - Geologic & Hydrostratigraphic Model 16
Quaternary Geology

17.  Section A-A’ follows Study sub watershed.
 Shows the complex three-dimensional
geometry.
 Many of the units are regionally
discontinuous.
Whitemans Creek Tier 3 - Peer Review Meeting - Geologic & Hydrostratigraphic Model 17
Cross-Section of 3-D Hydrostratigraphic Model

18.  North-South Section through eastern portion of
watershed
 Sand Plain/ unconfined Outwash Aquifer extensively
used for irrigation, and targeted for increase pumping
during shift from SW to GW takings
Whitemans Creek Tier 3 - Peer Review Meeting - Geologic & Hydrostratigraphic Model 18
Cross-Section G
G
G’

19. Stream Network
Integrated Simulation of Irrigation Demand - GW Model Construction/Calibration 19
 1,767 km (1000 m) of simulated streams
▪ 15,729 Reaches (GW Cell Interactions)
 Channel properties by Strahler Class
▪ Manning’s Roughness, 8-Point Cross Section, Bed
Conductances
▪ Class 1 headwaters represents 842 of 1767 km

20. Simulation Results: Long Term Average ET (WY1976-WY2010)
Integrated Simulation of Irrigation Demand – PRMS (Hydrologic Submodel) 20
Potential Actual

21. Simulated Runoff: Average
Integrated Simulation of Irrigation Demand – PRMS (Hydrologic Submodel) 21

22. Simulated Runoff: Monthly
 Monthly average overland
cascading runoff
 Peak runoff during March (spring
freshette/snowmelt)
 Higher runoff during fall after ET
processes shut down
Click for Animation
Integrated Simulation of Irrigation Demand – PRMS (Hydrologic Submodel) 22

23. Simulated Runoff: Daily
23
Click for Animation

24. 24
Actual ET
Integrated Simulation of Irrigation Demand – Preliminary GSFLOW Model Calibration
 Animation shows daily Actual ET
from the PRMS submodel for
WY2007, a relatively dry year
 AET response is sinusoidal but varies
spatially depending on available soil
moisture
 AET is reduced in the dry years
because of basin-wide limitations in
available soil moisture
 Click for Animation

25. Long Term Average Recharge Comparison
Integrated Simulation of Irrigation Demand – PRMS (Hydrologic Submodel) 25
PRMS
(248 mm/year)
GAWSER
(243 mm/year)

26. 26
Water Levels
Integrated Simulation of Irrigation Demand – Preliminary GSFLOW Model Calibration
 Animation shows transient water
levels from the MODFLOW submodel
in Layer 3 for WY2007
 Groundwater response appears
muted because of contour interval
places but change is in range of 1-2
metres
Click for Animation

27. 27
Streamflow
Integrated Simulation of Irrigation Demand – Preliminary GSFLOW Model Calibration
 Animation shows transient streamflow
for WY2007
 Results show daily stream during a
relatively dry year
Click for Animation

28. 28
Streamflow
Integrated Simulation of Irrigation Demand – Preliminary GSFLOW Model Calibration
 Animation shows transient streamflow
for WY2007
 Results highlight an area of the
watershed with relatively low
permeability surface materials.
Click for Animation

29.  A total of 470 permitted GW takings
located in the study area
Integrated Simulation of Irrigation Demand - Water Use 29
GW Pumping

30. SW Diversions
Integrated Simulation of Irrigation Demand - GW Model Construction/Calibration 30
 A total of 70 surface water diversion
permits with 92 sources simulated in
the model
 Surface water permits processed to
assign location of source streams:
▪ Represented using MODFLOW-SFR package
▪ Script used to assign takings (diversions) to
closest simulated stream segment
▪ All ponds assumed to be online with no
mitigative storage effects

31. Daily Takings for
Wet vs. Dry Year
(2011-2012)
Integrated Simulation of Irrigation Demand - Water Use 31
Variation in Water Use by Year

32. Study Sub Watershed GSFLOW Model
 Results present the current coarse model resolution (240m cell size)
preliminary calibration
 All components of the hydrologic cycle are represented and functioning
 Simulation of irrigation demand necessary for final calibration and water budget
assessment under drought conditions
Integrated Simulation of Irrigation Demand - Modelling Approach 32

33. SOIL MOISTURE DEMAND-
BASED IRRIGATION MODULE
Earthfx GSFLOW Code Extension
Integrated Simulation of Irrigation Demand - Streamflow Data 33

34. Irrigation Module for GSFLOW
 Earthfx Inc. has developed a new irrigation module for GSFLOW
 The general technical approach is based on work by the USGS for the
simulation of water use in California’s Central Valley
▪ Based on MODFLOW-OWHM and the “Farm Process” module
▪ While functionally similar to OWHM, the new GSFLOW module uses PRMS soil zone
hydrologic parameter and processes
 Testing and implementation support funding provided by the the Ontario MNR,
MOECC and Grand River Conservation Authority
Integrated Simulation of Irrigation Demand - Modelling Approach 34

35. Simulation of Soil Moisture-based Agricultural Water Use
 Simulation of irrigation (GW or SW diversions) based on soil moisture levels:
▪ Pumping representation in the model is only the start:
• Need to estimate consumptive use
▪ Water applied as precipitation (spray irrigation) or after canopy interception (drip)
▪ Losses of irrigation water to ET or enhanced runoff to streams
▪ Return flows – irrigation water re-infiltrates, but not necessarily to the same aquifer
▪ Induced changes in stream interaction
 Applications of moisture demand-based simulations:
▪ Can be used to estimate actual historic consumptive water use
▪ Evaluation of projected water use under future drought
▪ Climate change conditions: earlier spring means longer summer GW level recession
Integrated Simulation of Irrigation Demand - Modelling Approach 35

36. Irrigation Demand Submodel - Methodology
 General methodology to estimate water use requires daily takings:
▪ GSFLOW/PRMS daily estimate of soil moisture used to “trigger” irrigation.
▪ Irrigation starts when available soil moisture falls below trigger
▪ Trigger can be defined based on soil and crop type
▪ Irrigation water can be lost to ET, runoff or returned to the GW system
▪ Impacts of GW pumping or SW diversions fully represented
 Predictive irrigation submodel can be calibrated to actual water use data, or
used to estimate historical, current or future water use
Integrated Simulation of Irrigation Demand - Water Use 36

37. GSFLOW Irrigation Module
 Low soil moisture levels can
trigger irrigation from wells or
in-stream diversions.
 Spray irrigation is applied to
canopy and subject to
interception and evaporation
 With drip irrigation, water is
added directly to soil zone
Integrated Simulation of Irrigation Demand - Climate Data 37
PRMS
GW Pumping
SW
Diversion
MODFLOW-NWT
Drip
Spray
Drip
Spray

38. Irrigation Demand Submodel – Code Features
 Each farm represented by multiple PRMS soil zone cells
▪ Fine resolution, fully distributed
▪ Each farm can have multiple crop types and unique field moisture content triggers
▪ Each GW well is linked to a Farm ID with max pumping rate
▪ Farm SW diversions can take a defined percentage of current daily streamflow
 Soil moisture calculated on a daily basis in PRMS and used to trigger GW
pumping or SW diversion
 Total GW well pumping or SW diversion water applied to PRMS
▪ Spray Irrigation: Pumped volume added to precipitation
▪ Drip Irrigation: Pumped volume added to net precipitation after canopy interception
▪ PRMS calculates infiltration and runoff in usual manner
Integrated Simulation of Irrigation Demand - Water Use 38

39. Basic Sub-model Testing
 Example shows one Water Year (Oct 1-Sept 30)
▪ Colors indicate soil moisture on irrigated farm fields
▪ Groundwater levels as blue contours
▪ Pumping wells shown as small circles
 Irrigation triggered by soil moisture
 GW drawdown cones develop over the summer
and recover in the fall after irrigation stops
Click for Animation
Integrated Simulation of Irrigation Demand - Water Use 39

40. Study Sub WatershedTest Simulation
 Testing of GSFLOW Farm Process module
in the study sub watershed model
Integrated Simulation of Irrigation Demand - Water Use 40

41. Study Sub Watershed Test Simulation
 Each farm
assigned Farm ID
 Irrigation type
assigned to crop
 Each well linked
to a crop/farm
 Moisture deficit
trigger assigned
to each well
Integrated Simulation of Irrigation Demand - Water Use 41

42. Simulation Results
 Example shows average moisture
deficit on each farm during the
2012 (dry year) growing season
(May 1 – August 31)
 Wells cycle on and off based on
trigger
Click for Animation
Integrated Simulation of Irrigation Demand - Water Use 42

43. Total Soil Moisture Animation
 Example shows
Integrated Simulation of Irrigation Demand - Water Use 43

44. Net Precipitation
 Example shows net precipitation (after
interception) during the 2012 growing
season
 Applied irrigation included in net
precipitation
 Water applied before or after interception
depending on irrigation type
 Irrigation shuts down on rainy days
 Note: Forested wetlands have high
interception. Small storms have
throughfall only on bare areas
Click for Animation
Integrated Simulation of Irrigation Demand - Water Use 44

45. Whitemans Simulation: Soil Moisture and Pumping
 Example compares soil moisture deficit
versus trigger in an irrigated field.
 Pump comes on when moisture levels
drop below target
 Example also compares simulated
pumping versus reported for the farm.
 Simulated irrigation season likely starts
too early. Pumps may stay on too
long. More calibration needed.
Integrated Simulation of Irrigation Demand - Water Use 45

46. Simulation Results: Increases in Water Budget Items
 Example shows increase in water
budget components compared to a
baseline (no-irrigation) scenario.
 “Net precipitation” increases due to
applied irrigation
 ET increases over baseline due to
increased available soil moisture
 GW recharge during storm events
increases due to wetter soil
 Overland runoff did not change due
to high infiltration capacity of the
sandy soil
Integrated Simulation of Irrigation Demand - Water Use 46

47. 47
Conclusions
Integrated Simulation of Irrigation Demand - Conclusions & Next Steps
 Predicting and simulating cumulative water use under future drought conditions requires
an understanding of farm irrigation processes and triggers
 The new GSFLOW irrigation module developed by Earthfx integrates farm water
management practices into a comprehensive and fully integrated SW/GW model
 Model provides detailed farm water budget
 Historic climate and water use data can be used to develop farm-specific water use
practices and triggers.
▪ Alternatively, standard or best management practices could be represented in the model to
simulate and evaluate improved water use and informed permit renewal