Heather Moser

Application of Stage IV Application of Stage IV Precipitation Data to Estimate Precipitation Data to Estimate

Spatially Spatially Variable Recharge for a Variable Recharge for a

Groundwater Flow ModelGroundwater Flow Model

Heather MoserHeather Moser

Mentor: Dr. William SimpkinsMentor: Dr. William Simpkins

Groundwater for MeteorologistsGroundwater for Meteorologists Groundwater and the atmosphere: Groundwater and the atmosphere:

very similar!very similar! Both are fluidsBoth are fluids Flows from high to low potentialFlows from high to low potential

(USGS)(USGS)

Groundwater for MeteorologistsGroundwater for Meteorologists Recharge: precipitation that percolates Recharge: precipitation that percolates

through soil to the water tablethrough soil to the water table Why is it important?Why is it important?

Sustains vital fresh water sourceSustains vital fresh water source Drinking waterDrinking water IrrigationIrrigation IndustryIndustry

(USGS)(USGS)

For groundwater flow modeling, For groundwater flow modeling, recharge is:recharge is:

estimated based on local factorsestimated based on local factors assumed to be uniform everywhere in assumed to be uniform everywhere in

model domainmodel domain used as the “tweaking” termused as the “tweaking” term

Recharge EstimationRecharge Estimation

HypothesesHypotheses If recharge is spatially variable to If recharge is spatially variable to

reflect actual conditions, will reflect actual conditions, will incorporating it improve groundwater incorporating it improve groundwater modeling accuracy?modeling accuracy?

Is radar precipitation data useful to Is radar precipitation data useful to estimate recharge for modeling? How estimate recharge for modeling? How does it compare to other methods of does it compare to other methods of estimating recharge?estimating recharge?

How Much Recharge?How Much Recharge?

Difficult to measure directlyDifficult to measure directly

Large variability over space and timeLarge variability over space and time

Only 10% to 20% of precipitation actually Only 10% to 20% of precipitation actually reaches water table in Midwestreaches water table in Midwest EvapotranspirationEvapotranspiration Overland flowOverland flow Tile Drainage?Tile Drainage?

Agricultural Tile DrainageAgricultural Tile Drainage

(Mark Tomer, USDA)(Mark Tomer, USDA)

GFLOWGFLOW 2-D Groundwater flow model2-D Groundwater flow model Steady-state and single-layerSteady-state and single-layer Analytic ElementAnalytic Element

Non-griddedNon-gridded Groundwater flow interpolated between line sinks Groundwater flow interpolated between line sinks

(stream segments)(stream segments) Allows for heterogeneity (inhomogeneities)Allows for heterogeneity (inhomogeneities)

T

R

y

h

x

h

2

2

2

2

Recharge Scenario 1: RainfallRecharge Scenario 1: Rainfall

Stage IV Precipitation Stage IV Precipitation data from NWSdata from NWS

Gridded dataset (4 km Gridded dataset (4 km resolution)resolution)

Multisensor productMultisensor product Quality controlledQuality controlled

Estimate recharge as Estimate recharge as 10% and 20% of 10% and 20% of annual precipitation for annual precipitation for three years (6 total)three years (6 total)

YearYear TypeType Rainfall Rainfall (mean)(mean) 1 - 21 - 2

20022002

1. Stage 1. Stage IV:IV:

2. Gages:2. Gages:

28.51 28.51 inin

30.03 30.03 inin

-1.53 -1.53 inin

20032003


2. Gages:2. Gages:

26.49 26.49 inin

28.32 28.32 inin

-1.83 -1.83 inin

20042004


2. Gages:2. Gages:

28.55 28.55 inin

34.47 34.47 inin

-5.92 -5.92 inin

2002 Stage IV Data2002 Stage IV Data

Annual Rainfall TotalsAnnual Rainfall Totals Rainfall Map by QuantilesRainfall Map by Quantiles





USGS FORTRAN programUSGS FORTRAN program Input USGS streamflow to calculate recharge as Input USGS streamflow to calculate recharge as

average over a watershedaverage over a watershed Six gaging stations selected to cover watersheds Six gaging stations selected to cover watersheds

in domainin domain Continuous streamflow records from 1996-2004Continuous streamflow records from 1996-2004 Recharge averaged over entire period for mean stateRecharge averaged over entire period for mean state

Recharge calculated empirically -- about ½ of Recharge calculated empirically -- about ½ of stream discharge exceeding baseflow stream discharge exceeding baseflow

R = 2(QR = 2(Q22 - Q - Q11)K)K 2.30262.3026

R = Recharge (L/t)R = Recharge (L/t)

QQ22 = Discharge after storm event (L = Discharge after storm event (L33/t)/t)

QQ11 = Discharge before storm event (L = Discharge before storm event (L33/t)/t)

K = Recession index constantK = Recession index constant

Recharge Scenario 2: RORARecharge Scenario 2: RORA

Recharge Scenario 2: RORARecharge Scenario 2: RORA

Control to test spatial variabilityControl to test spatial variability Average of all RORA watershed Average of all RORA watershed

recharge valuesrecharge values Approximation of mean recharge Approximation of mean recharge

based on real databased on real data

Recharge Scenario 3: UniformRecharge Scenario 3: Uniform

7.09 in/yr7.09 in/yr(21.4% of mean annual ppt)(21.4% of mean annual ppt)

Water Table Elevation

Feet

650 - 700

700 - 750

750 - 800

800 - 850

850 - 900

900 - 950

950 - 1,000

1,000 - 1,050

1,050 - 1,100

1,100 - 1,150

1,150 - 1,200

1,200 - 1,250

1,250 - 1,300

1,300 - 1,350

1,350 - 1,400

Uniform

Model ResultsModel Results

Uniform

Large errors in modeled head found in Large errors in modeled head found in certain locationscertain locations

Calibration required to account for Calibration required to account for variable soil hydraulic conductivityvariable soil hydraulic conductivity

Impact of glacial Impact of glacial formationsformations

Alluvial MaterialsAlluvial Materials

Uniform

UniformUniform RORARORA

Stage IVStage IV

MAE =MAE = |modeled - observed||modeled - observed|

NN

(mean absolute error)(mean absolute error)

Discussion of ResultsDiscussion of Results

What happened with Stage IV?What happened with Stage IV? Inaccurate rainfall estimation led to Inaccurate rainfall estimation led to

inaccurate recharge estimationinaccurate recharge estimation Rainfall data from years tested may not Rainfall data from years tested may not

adequately reflect current hydraulic adequately reflect current hydraulic head levelshead levels

Recharge based on rainfall alone does Recharge based on rainfall alone does not consider geologic factorsnot consider geologic factors

Discussion of ResultsDiscussion of Results

Why did RORA and uniform show Why did RORA and uniform show better results?better results? Recharge estimates from streamflow do Recharge estimates from streamflow do

reflect geologic conditionsreflect geologic conditions Uniform field based on RORA dataUniform field based on RORA data Mean conditions rather than time Mean conditions rather than time

sensitivesensitive

ConclusionsConclusions

Spatially variable recharge based on Spatially variable recharge based on precipitation did not improve model precipitation did not improve model accuracy.accuracy. Other factors may have affected results.Other factors may have affected results.

Spatially variable recharge from Spatially variable recharge from streamflow did slightly improve over streamflow did slightly improve over uniform distribution.uniform distribution.

Radar-derived rainfall estimates are still Radar-derived rainfall estimates are still not accurate enough to be useful for not accurate enough to be useful for hydrological modeling.hydrological modeling. However, spatial qualities still carry promise.However, spatial qualities still carry promise.

Future WorkFuture Work

Put rainfall and soil data togetherPut rainfall and soil data together

Account for effective hydraulic Account for effective hydraulic conductivityconductivity

Test a watershed where tile drainage Test a watershed where tile drainage does not effect aquiferdoes not effect aquifer

AcknowledgementsAcknowledgements

Dr. William SimpkinsDr. William Simpkins Daryl HerzmannDaryl Herzmann Lucie MacalisterLucie Macalister USDA Soil Tilth LabUSDA Soil Tilth Lab Iowa USGSIowa USGS

Questions?Questions?

[email protected]@iastate.edu

http://www.meteor.iastate.edu/~miraje/http://www.meteor.iastate.edu/~miraje/thesisthesis

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