Watershed Hydrology Watershed Hydrology

and Water Qualityand Water Quality

Southeast Southeast StormwaterStormwater AssociationAssociation

Stormwater Solutions for Your JurisdictionStormwater Solutions for Your JurisdictionStormwater Solutions for Your JurisdictionStormwater Solutions for Your Jurisdiction

April 20, 2012April 20, 2012

Jeffrey L. Herr, P.E., D.WREJeffrey L. Herr, P.E., D.WRE

National National StormwaterStormwater LeaderLeader

Brown and CaldwellBrown and Caldwell

&&

Brett Cunningham, P.E.Brett Cunningham, P.E.

Water Resources DirectorWater Resources Director

Jones EdmundsJones Edmunds

Global Water PerspectiveGlobal Water Perspective

Freshwater accounts for less than 3% of the Freshwater accounts for less than 3% of the total water on the earthtotal water on the earth

Groundwater accounts for ~ 0.7% of the Groundwater accounts for ~ 0.7% of the earth’s freshwaterearth’s freshwater

< 0.1% of the freshwater on the earth is in < 0.1% of the freshwater on the earth is in surface waterssurface waterssurface waterssurface waters

Average Annual US RainfallAverage Annual US Rainfall

Region 4 Region 4

Rainfall and Water Use EstimatesRainfall and Water Use Estimates

SurfaceArea

AnnualRainfall

Estimated

Annual WaterState

(sq. mi.) (in./yr.)(MG) Population

Consumption

(MG)

Alabama 51,609 56.9 51,029,934 4,627,851 506,750

Florida 58,560 49.9 50,789,734 18,251,243 1,998,511Florida 58,560 49.9 50,789,734 18,251,243 1,998,511

Georgia 58,876 48.6 49,733,751 9,544,750 1,045,150

Kentucky 40,409 43.6 30,588,154 4,241,474 464,441

Mississippi 47,716 52.8 43,797,541 2,918,785 319,607

Missouri 69,686 33.9 41,063,941 5,878,415 643,686

North Carolina 52,586 42.5 38,800,509 9,061,032 992,183

South Carolina 31,055 51.6 27,840,970 4,407,709 482,644

Tennessee 42,244 48.5 35,596,272 6,156,719 674,161

Based on 300 gpdpcBased on 300 gpdpc

Understanding Hydrology, Understanding Hydrology,

Rainfall and RunoffRainfall and Runoff

Rainfall event distributionRainfall event distribution

Event runoff flow rates and volumesEvent runoff flow rates and volumesEvent runoff flow rates and volumesEvent runoff flow rates and volumes

Dry weather baseflow timing, rates and Dry weather baseflow timing, rates and

volumesvolumes

Watershed Hydrology Watershed Hydrology

Influenced by:Influenced by:

PrePre--development (natural)development (natural)

RainfallRainfall

Vegetative cover (ET)Vegetative cover (ET)Vegetative cover (ET)Vegetative cover (ET)

Soil characteristicsSoil characteristics

DepressionalDepressional storagestorage

Ground surface slopeGround surface slope

Groundwater systemGroundwater system

Minimal runoff typicalMinimal runoff typical

Watershed Hydrology Watershed Hydrology

Influenced by:Influenced by:

PostPost--development development

RainfallRainfall

ET reduced (less vegetation and ET reduced (less vegetation and depressionaldepressional storage)storage)

Fill soil characteristics (modifications due to filling and Fill soil characteristics (modifications due to filling and Fill soil characteristics (modifications due to filling and Fill soil characteristics (modifications due to filling and compaction)compaction)

DepressionalDepressional storage reducedstorage reduced

Addition of impervious areaAddition of impervious area

Addition of irrigation water and in some cases septic tank Addition of irrigation water and in some cases septic tank drainfielddrainfield dischargesdischarges

Vegetation modificationsVegetation modifications

Annual Runoff Depth vs. Land Use(50 inches annual rainfall)

15

20

25

30

Undeveloped

Agriculture Land

Single Use

17.0

19.9

28.8

0

5

10

15

Estimated Runoff Depth (in./yr)

Single Use

Multi Family

Highway

Commercial7.2

11.9

13.2

Development significantly increases surface water runoff volume.

Development Impacts on Development Impacts on

StreamflowStreamflow

Summary of Rainfall Event Characteristics at the Orlando Summary of Rainfall Event Characteristics at the Orlando

International Airport from 1/1/42 to 12/31/95International Airport from 1/1/42 to 12/31/95Rainfall Event

Range (inches)

Mean Rainfall

Depth (inches)

Mean Rainfall Duration

(hours)

Fraction of Annual

Rain Events

Number of Annual Events

in Range

0.00-0.10 0.041 1.203 0.427 56.683

0.11-0.20 0.152 2.393 0.142 18.866

0.21-0.30 0.252 3.073 0.080 10.590

0.31-0.40 0.353 3.371 0.055 7.312

0.41-0.50 0.456 3.702 0.048 6.325

0.51-1.00 0.713 4.379 0.129 17.102 (117)

1.01-1.50 1.221 5.758 0.051 6.733

1.51-2.0 1.726 7.852 0.024 3.145

2.01-2.50 2.271 8.090 0.011 1.4702.01-2.50 2.271 8.090 0.011 1.470

2.51-3.00 2.704 10.675 0.006 0.726

3.01-3.50 3.246 9.978 0.003 0.391

3.51-4.00 3.667 13.362 0.002 0.260

4.01-4.50 4.216 15.638 0.001 0.149

4.51-5.00 4.796 17.482 0.000 0.056

5.01-6.00 5.454 23.303 0.001 0.167

6.01-7.00 6.470 40.500 0.000 0.019

7.01-8.00 7.900 31.500 0.000 0.019

8.01-9.00 8.190 3.500 0.000 0.019

>9.00 10.675 46.250 0.001 0.075

Mean Annual Rainfall = 49.63 inches, Total number of events per year = 130

Conventional Low Imapct

Functional Lanscape DesignGood Drainage

CN alone

often

underestimates

Runoff Volume

for common

rain events

and annual

runoff volume.runoff volume.

SUMMARY OF LITERATURESUMMARY OF LITERATURE--BASED RUNOFF COEFFICIENTS FOR BASED RUNOFF COEFFICIENTS FOR

SELECTED LAND USE CATEGORIES IN CENTRAL AND SOUTH FLORIDASELECTED LAND USE CATEGORIES IN CENTRAL AND SOUTH FLORIDA

(Harper, 1994)(Harper, 1994)

LAND USE CATEGORYLAND USE CATEGORY PERCENT IMPERVIOUS (%)PERCENT IMPERVIOUS (%) RUNOFF COEFFICIENTRUNOFF COEFFICIENT

1. Low1. Low--Density ResidentialDensity Residential11 14.714.7 0.2680.268

2. Single2. Single--FamilyFamily 27.827.8 0.3730.373

3. Multi3. Multi--Family Family 67.067.0 0.6750.675

4. Low4. Low--Intensity CommercialIntensity Commercial 91.091.0 0.8370.837

5. High5. High--Intensity CommercialIntensity Commercial 97.597.5 0.8870.887

6. Industrial6. Industrial 86.886.8 0.7930.793

7. Highway7. Highway 85.085.0 0.7830.783

8. Agricultural8. Agricultural

a. Pasturea. Pasture

b. Citrusb. Citrus

c. Row Cropsc. Row Crops

d. General Agricultured. General Agriculture

0.000.00

0.000.00

0.000.00

0.000.00

0.3550.355

0.2820.282

0.2040.204

0.3040.304

9. Recreational/Open Space9. Recreational/Open Space 1.501.50 0.1630.163

10. Mining10. Mining 23.023.0 0.3610.361

11. Wetland11. Wetland 0.000.00 0.2250.225

12. Open Water/Lake12. Open Water/Lake 100100 0.5000.500

Runoff coefficients commonly overestimate

common storm and annual runoff volume.

Best Approach is to use DCIA Best Approach is to use DCIA

and Curve Number for and Curve Number for N-DCIA

ParameterDrainage Basin

1 2 3 6 7

Area (acres) 368.8 420.6 621.3 281.5 493.2

DCIA (%) 37.2 36.1 27.3 27.6 36.5DCIA (%) 37.2 36.1 27.3 27.6 36.5

Non-DCIA CN 76.5 82.4 76.4 79.2 84.6

tc (min) 81.3 66.7 77.0 61.1 57.4

DCIA is the primary source of runoff from

common events and thus annual runoff volume.

This is why LID is effective.

Summary of Rainfall Event and Annual Runoff Summary of Rainfall Event and Annual Runoff

Depths for SingleDepths for Single--Family Residential AreasFamily Residential Areas

RainfallRainfall

IntervalInterval

PointPoint

(inches)(inches)

EventEvent

RunoffRunoff

DepthDepth

(inches)(inches)

AnnualAnnual

RunoffRunoff

DepthDepth

(inches)(inches)

CumulativeCumulative

RunoffRunoff

DepthDepth

(inches)(inches)

RainfallRainfall

IntervalInterval

PointPoint

(inches)(inches)

EventEvent

RunoffRunoff

DepthDepth

(inches)(inches)

AnnualAnnual

RunoffRunoff

DepthDepth

(inches)(inches)

CumulativeCumulative

RunoffRunoff

DepthDepth

(inches)(inches)

0.050.05 0.000.00 0.000.00 0.000.00 2.752.75 1.211.21 1.731.73 12.7612.76

0.080.08 0.000.00 0.000.00 0.000.00 3.253.25 1.581.58 1.241.24 14.0014.00

0.150.15 0.000.00 0.170.17 0.170.17 3.753.75 1.971.97 1.171.17 15.1715.17

0.250.25 0.030.03 0.330.33 0.500.50 4.254.25 2.372.37 0.510.51 15.6815.68

0.350.35 0.050.05 0.440.44 0.940.94 4.754.75 2.792.79 0.450.45 16.1316.13

0.450.45 0.070.07 0.510.51 1.451.45 5.505.50 3.443.44 0.930.93 17.0617.06

0.750.75 0.130.13 2.392.39 3.843.84 6.606.60 4.334.33 0.940.94 18.0018.00

1.251.25 0.310.31 2.822.82 6.666.66 7.507.50 5.245.24 0.570.57 18.5718.57

1.751.75 0.560.56 2.542.54 9.209.20 8.508.50 6.176.17 0.170.17 18.7418.74

2.252.25 0.870.87 1.831.83 11.0311.03 9.509.50 7.117.11 0.580.58 19.3219.32

C ~ 0.32 (C = 0.37 in Table)

Summary of Rainfall Event and AnnualSummary of Rainfall Event and Annual

Runoff Depths for Commercial AreasRunoff Depths for Commercial Areas

RainfallRainfall

IntervalInterval

PointPoint

(inches)(inches)

EventEvent

RunoffRunoff

DepthDepth

(inches)(inches)

AnnualAnnual

RunoffRunoff

DepthDepth

(inches)(inches)

CumulativeCumulative

RunoffRunoff

DepthDepth

(inches)(inches)

RainfallRainfall

IntervalInterval

PointPoint

(inches)(inches)

EventEvent

RunoffRunoff

DepthDepth

(inches)(inches)

AnnualAnnual

RunoffRunoff

DepthDepth

(inches)(inches)

CumulativeCumulative

RunoffRunoff

DepthDepth

(inches)(inches)

0.050.05 0.000.00 0.000.00 0.000.00 2.752.75 1.851.85 2.652.65 24.2124.21

0.080.08 0.000.00 0.000.00 0.000.00 3.253.25 2.292.29 1.791.79 26.0026.00

0.150.15 0.020.02 0.340.34 0.340.34 3.753.75 2.752.75 1.641.64 27.6427.64

0.250.25 0.060.06 0.650.65 0.990.99 4.254.25 3.213.21 0.690.69 28.3328.33

0.350.35 0.100.10 0.880.88 1.871.87 4.754.75 3.693.69 0.600.60 28.9328.93

0.450.45 0.140.14 1.021.02 2.892.89 5.505.50 4.404.40 1.191.19 30.1230.12

0.750.75 0.300.30 5.515.51 8.408.40 6.606.60 5.365.36 1.161.16 31.2831.28

1.251.25 0.620.62 5.655.65 14.0514.05 7.507.50 6.326.32 0.680.68 31.9631.96

1.751.75 1.001.00 4.544.54 18.5918.59 8.508.50 7.317.31 0.200.20 32.1632.16

2.252.25 1.411.41 2.972.97 21.5621.56 9.509.50 8.298.29 0.670.67 32.8332.83

C ~ 0.55 (C = 0.85 in Table)

Paradigm for Water Quality TreatmentParadigm for Water Quality Treatment

0.6

0.7

0.8

0.9

1

Cu

mu

lati

ve P

rob

ab

ilit

y

Orlando International Airport

0

0.1

0.2

0.3

0.4

0.5

0 2 4 6 8 10

Cu

mu

lati

ve P

rob

ab

ilit

y

Rainfall (inches)

Estimating Annual FlowsEstimating Annual Flows

Runoff CoefficientsRunoff Coefficients–– Not from Rational MethodNot from Rational Method

–– Best from continuous simulationBest from continuous simulation

Modified CN methodModified CN method–– Separate DCIASeparate DCIA–– Separate DCIASeparate DCIA

–– Account for UCIAAccount for UCIA

–– Account for antecedent conditionsAccount for antecedent conditions

–– Harvey Harper methodHarvey Harper method

–– Account for high groundwaterAccount for high groundwater

Continuous Simulation ModelsContinuous Simulation Models–– SWMM, HSPF, SPAW, etc.SWMM, HSPF, SPAW, etc.

NRCS MethodNRCS Method

World’s Worst Hydrologic AssumptionWorld’s Worst Hydrologic Assumption

SIa

2.0=

National Engineering Handbook,

Section 4 – Hydrology, 1985

NRCS MethodNRCS Method

Considering

DCIA

separately

reduces

some of this

problem.

Figure source:

Pitt, 2012

Comparison of Pollutant Loading Models

Must Have Volumes Correct

LEMON BAY SITES

Alligator Creek Ainger Creek

Paper Field

Different methods and Different methods and assumptions assumptions

lead lead to to highly variable results.highly variable results.

Paper Field

Comparison of

Pollutant Loading Models

ANNUAL TOTAL NITROGEN LOADS (lb/yr) FROM BASEFLOW

SURFACE WATER RUNOFF & SEPTIC

988

4,063Baseflow

3,850

18,800

4,063

Total = 19,788

Surface

Water FlowSeptic

Total = 41,36027,130

10,380

Highly variable results with significantly different management Highly variable results with significantly different management

implications. Are septic tanks or surface water runoff the implications. Are septic tanks or surface water runoff the

primary source of tributary pollutants?primary source of tributary pollutants?

Importance of All Source TermsImportance of All Source Terms

Baseflow Direct Runoff Irrigation

Point Sources Septic Tanks Direct Rainfall

Roberts Bay, Sarasota County

Variations in Base Flow Variations in Base Flow

ConcentrationsConcentrations

Variations in Groundwater Variations in Groundwater

ConcentrationsConcentrationsConcentrations

will vary widely

based on land

use and redox

condition

This has

implications on

watershed

assessment

and BMP

design

Nitrogen TreatmentNitrogen Treatment

http://ecosystems.mbl.edu/research/clue/nitrogen.html

Average Water Use in the HomeAverage Water Use in the Home

The ResourceThe Resource

SE states receive 34 to 57 inches of SE states receive 34 to 57 inches of

rainfall each year rainfall each year

Rainfall volume is >>>> water demandRainfall volume is >>>> water demand

Much of our rainfall becomes runoff and is Much of our rainfall becomes runoff and is Much of our rainfall becomes runoff and is Much of our rainfall becomes runoff and is

lost to tidelost to tide

Stormwater runoff is naturally selfStormwater runoff is naturally self--

sustaining; pending major changes from sustaining; pending major changes from

climate change it will continue to rainclimate change it will continue to rain

Potential UsesPotential Uses

Irrigation for Ag, golf courses, commercial and Irrigation for Ag, golf courses, commercial and

residential propertyresidential property

Gray water for commercial and residential Gray water for commercial and residential

propertiesproperties

Cooling water for power generationCooling water for power generation

With minimal treatment (settling and/or filtration), With minimal treatment (settling and/or filtration),

could be used for cleaning, vehicle washing, etccould be used for cleaning, vehicle washing, etc

Any use if treated at a public water treatment Any use if treated at a public water treatment

facilityfacility

Questions?Questions?

Jeffrey Jeffrey L. Herr, P.E., D.WREL. Herr, P.E., D.WREJeffrey Jeffrey L. Herr, P.E., D.WREL. Herr, P.E., D.WRE

National National StormwaterStormwater LeaderLeader

Brown and CaldwellBrown and Caldwell

jherr@brwncald.comjherr@brwncald.com

&&

Brett Cunningham, P.E.Brett Cunningham, P.E.

Water Resources DirectorWater Resources Director

bcunningham@jonesedmunds.combcunningham@jonesedmunds.com