Watershed Modeling in areas with Intensive Agricultural Irrigation

Presented by:

Jeremy Wyss, H.I.TTetra Tech

25th Annual Alabama Water Resources ConferenceOrange Beach, Alabama

Ag Irrigation Extent and Importance 2007 Census of Agriculture combined with the 2008 Farm and

Ranch Irrigation Survey “provide one of the most complete and detailed profiles of irrigation in the United States”• 55,000,000 Irrigated Acres or 28% of farm land• 93% of irrigated land is Cropland • 60% by sprinkler and 40% by gravity• Estimated average of 1.7 acre-feet/acre (20”) of water application• 40% increased corn yield and 30% increased soybean yield

Climate models for the southeast project precipitation to come in less frequent, more intense events and also project temperature increases, thus decreasing soil moisture storage• Irrigation will become very important to augment soil moisture storage

to sustain crop yields

Reduced Infiltration• Soil Crusting

• Chemical and Physical• Increased soil moisture storage

• Maximum infiltration reached sooner

Stream-flow Impacts• Reduction due to direct and indirect pumping• Peak flow and storm-flow increases due to reduced infiltration• Return flows and consumptive use are difficult to characterize and

quantify

Conceptual Hydrologic Impacts

LSPC Watershed Model

LSPC = Loading Simulation Program, C++ Rainfall-runoff, lumped land use, pollutant loading simulation model Streamlined Hydrologic Simulation Program FORTRAN (HSPF)

algorithms for pervious and impervious land flow and pollutant transport Potential for very large-scale modeling A series of individual hydrologically connected sub-watersheds

Sub-WatershedWeather Data

Land Use DistributionRepresentative Soil Type

ReachWeather Data

FTableReach Group

LSPC Simulated Irrigation Demand

TimeET Days

To Compute Deficit

Irrigation Demand = f ( ) evaluated over…

If ET Days = 0, then Irrigation Demand= f (ETc * PEVT) Only

PREC & PEVT

ETc (Crop Factor)

PEVT* ETc - PRECIP

Surface Water• From a simulated Reach• Can be from any simulated Reach

• Allows for “regional” irrigation withdrawals

Groundwater• New water to the model• Can not withdraw water from groundwater storage of the model…yet?

*In the basic model structure you can not have water from two different sources being applied to the irrigated land within a modeled sub-watershed

LSPC Irrigation Source Water

1. To PREC

2. To SURS

3. To UZS

4. To LZS

5. To AGWS

Sprinkler

Flood

Buried Shallow

Buried Deep

Seepage

Model Storage Irrigation Type

LSPC Options for Irrigation Application

Ag Water Pumping ReportUGA selectively monitored irrigators application amounts

Divided Georgia into four Reporting/Summary regions Monthly Averaged irrigation depth by Source and Region

• Min, Mean, Max values

• Supplied Mean for normal years and Max for drought years

Irrigated Field Coverage

A shape file, reflecting 2007 irrigated area, was created by the University of Georgia27,275 Polygons (fields)

Individual field acreage

Individual field source water percent

In theory…the impact of each individual field is represented in the model

Georgia- Agricultural Irrigation AreasNAD_1983_UTM_Zone_17N

Map produced 09-03-2010 - P. Cada

CartersLake

AllatoonaLake

Chattah

oochee R

iver

Flint R

iver

FL

SC

AL

NCTN

Apal

achi

cola

Rive

r

Oconee R

iver

Altamaha River

SatillaRiver

Ocmulgee River

Savannah River

LakeJackson Lake

Sinclair

LakeOconee

Coosa River

0 40 8020 Miles

0 40 8020 Kilometers

LakeSidneyLanier

WestPointLake

J. StromThurmond

Lake

Walter F.GeorgeReservoir

LakeBlackshear

LakeSeminole

LakeHartwell

BrunswickHarbor

LegendMajor WaterwayAg. Irrigation AreaLakeState Boundary

AtlanticOcean

Irrigated Field10 acres

25% Surface75% Ground A B

Irrigated Field100 acres

75% Surface25% Ground

Groundwater Groundwater

Watershed B 50 acres Surface water30 acres Groundwater

Watershed A 47.5 acres Surface water22.5 acres Groundwater

Use acreage and regional mean irrigation depth to determine volume of water from source

acre-inch per month converted to cubic feet per second

Irrigated Field40 acres

50% Surface50% Ground

A B

Data Processing and Simulation

Irrigated FieldCalculation

2.5 acres SW7.5 acres GW

Irrigated FieldCalculation

75 acres SW25 acres GW

Irrigated FieldCalculation

20 acres SW20 acres GW

Split Field B 40%Recalculated30 acres SW10 acres GW

Split Field A 60%Recalculated45 acres SW15 acres GW

Withdrawals occur independently of irrigation demandWater is irrigated back onto the land based on irrigation demand calculation

If pond is empty then no irrigation occursIrrigated area became its own simulated land use and was removed from the

original land use by determining the land use “under” the polygons

“Observed” vs. Simulated Irrigation

Scenario LayoutScenarios compared at USGS 02355350 – Ichawaynochaway Creek below

Newton , Georgia • 1040 square miles• 160 square miles are irrigated (15% of area)

• 54% Surface Water and 46% Groundwater

Scenario 1 – No Application Irrigation water pulled from surface sources but not applied back to the

land Analogous to treating irrigated water as a loss from the system

Scenario 2 – No Irrigation No water being pulled from surface sources Analogous to ignoring irrigation

Scenario Results – Timeseries

1

10

100

1000

10000

100000

1/1/1998 10/1/1998 7/1/1999 4/1/2000 1/1/2001 10/1/2001 7/1/2002 4/1/2003 1/1/2004 10/1/2004 7/1/2005 4/1/2006 1/1/2007 10/1/2007

Date

Flo

w (

cfs)

0

1

2

3

4

5

6

7

8

9

10

Dai

ly R

ainf

all (

in.)

Avg Daily Rainfall (in.) Avg Baseline Flow (1/1/1998 to 12/31/2007 ) Avg Modeled Flow (Same Period)

Scenario 1

Scenario 2

1

10

100

1000

10000

100000

1/1/1998 10/1/1998 7/1/1999 4/1/2000 1/1/2001 10/1/2001 7/1/2002 4/1/2003 1/1/2004 10/1/2004 7/1/2005 4/1/2006 1/1/2007 10/1/2007

Date

Flo

w (

cfs)

0

1

2

3

4

5

6

7

8

9

10

Dai

ly R

ainf

all (

in.)

Avg Daily Rainfall (in.) Avg Baseline Flow (1/1/1998 to 12/31/2007 ) Avg Modeled Flow (Same Period)

Scenario Results – Duration/Accumulation

1

10

100

1000

10000

100000

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

Percent of Time that Flow is Equaled or Exceeded

Dai

ly A

vera

ge F

low

(cfs

)

Baseline Flow Duration (1/1/1998 to 12/31/2007 )

Modeled Flow Duration (1/1/1998 to 12/31/2007 )

0%

20%

40%

60%

80%

100%

120%

Jan-98 Jul-99 Jan-01 Jul-02 Jan-04 Jul-05 Jan-07

Nor

mal

ized

Flo

w V

olum

e (O

bser

ved

as 1

00%

)

Baseline Flow Volume (1/1/1998 to 12/31/2007 )

Modeled Flow Volume (1/1/1998 to 12/31/2007 )

1

10

100

1000

10000

100000

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

Percent of Time that Flow is Equaled or Exceeded

Dai

ly A

vera

ge F

low

(cfs

)

Baseline Flow Duration (1/1/1998 to 12/31/2007 )

Modeled Flow Duration (1/1/1998 to 12/31/2007 )

0%

20%

40%

60%

80%

100%

120%

Jan-98 Jul-99 Jan-01 Jul-02 Jan-04 Jul-05 Jan-07

Nor

mal

ized

Flo

w V

olum

e (O

bser

ved

as 1

00%

)

Baseline Flow Volume (1/1/1998 to 12/31/2007 )

Modeled Flow Volume (1/1/1998 to 12/31/2007 )

Scenario 1 Scenario 2

Scenario Results – Statistics

Lower volumes for Scenario 1 are expected (remove water from system) Large differences in low flow simulation (low flow = drought) Soil moisture storage causes lower peak flows and storm volumes

Agricultural irrigation is not insignificant and just removing water from the system over predicts the hydrologic impact.

Applying irrigation water back to the land is an important component of simulating Irrigation

Modeling Irrigation in areas with Intensive Agricultural Irrigation

Comments/Questions?