Rainwater harvesting and Irrigation management

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Rainwater harvestin and Irri ation

management

Presentation for thea ec n ca ee ng

Low Impact Development-Current Practice and Research NeedsWetland Studies & Solutions Inc., Gainesville VA

David Sample, Ph.D., P.E., D.WREAssistant Professor

Biological Systems Engineering

October 9, 2009, 1

Manassas, VA



Outline

ntro uct on

The Hydrologic Cycle and Water Demand

Runoff and Stormwater Quality Estimated Water Needs

n t a creen ng xamp es

RHS Design for Runoff Control in Virginia

Function

Design using Cistern Spreadsheet/Runoff Reduction

Simulation/Operation of RHS Systems

c emat c Operational Policies

Conclusion

October 9, 2009, 2



CEE-OWML has been monitoringthe Occoquan watershed in NOVAfor over 35 ears

Tom Grizzard, CEE Glenn Moglen, CEE

,

David Sample, BSE

Campus epar men

BSE Department

Center for Watershed Studies

October 9, 2009, 3



The Hydrologic Cycle and Water Demand



Hydrologic Cycle

rec p tat on

Infiltration Recharge

Evapotranspiration o o s ure

40.92 in/year,1039 mm/year

Inflow:0.87 in/year22 mm/yr

Outflow:14.09 in/year358 mm/year

25.83 in/year,656 mm/year

Surface Reservoir

Groundwater Storage:45.16 in1147 mm

Storage:0.10 in2.5 mm

October 9, 2009, 5

Source: VDEQ (2009) Virginia’s Water Resources, http://www.vanaturally.com/vanaturally/guide/water.html



Precipitation

Averages 40-42 inches/year (1016-1067 mm)

October 9, 2009, 6

Source: National Atlas, at www.usgs.gov



Infiltration

Infiltration function of:

Soil t es/ orosit

Soils hydraulic properties

Vegetation

October 9, 2009, 7



Evapotranspiration

Temperature Based Methods

Bowen

Thornthwaite More Accurate Method-

Modified Penman-Monteith

(Allen 1998) unc on o a a on, vapor

pressure, wind speed, air

October 9, 2009, 8



Runoff

Depends upon:

Rainfall intensity

Antecedent moisture Density of vegetation

,

Imperviousness

c h a r g e

Pre-development

Post-development

D i s

October 9, 2009, 9Sources: Tess Wynn, “Low Impact Development”, 2009, Biological Systems Engineering, Virginia Tech

Time



Recharge

Recharge-SaturatedZone

Process is extremely-

areas

calibration parameter

October 9, 2009, 10

Source: USGS - GROUND WATER ATLAS of the UNITED STATES: Delaware, Maryland,New Jersey,North Carolina, Pennsylvania, Virginia, West Virginia, HA 730-L



Soil Moisture Storage

“Leaky Reservoir”

Field Capacity

Wilting Point

Readily Available Water

Total Available Water

(TAW)

October 9, 2009, 11

Source: Allen, R.G., Pereira, L.S., Raes, D., and Smith, M. (1998) Crop Evapotranspiration: Guidelines for Computing Crop Water Requirements. United Nations Food and Agricultural Organization (FAO), Irrigation and Drainage Paper 56, Rome, Italy.



Water Budget

Rainwater Harvesting Systems Function Like

October 9, 2009, 12

Soil Storage



Estimating Demand/Water Needs

Indoor Use

Potable Use

Toilet flushing Clothes washing

Outdoor use

Active Irrigation

Passive Irri ation

October 9, 2009, 13Grimmond and Oke 1986



Rainwater Harvesting/Cisterns (RR)

Captures imperviousrunoff

Underground/Above

Reuse-can beOutdoor or indoor

Supplements water

Volume benefits-maximize if managed

Variable Removal(runoff reduction only)

Source: Virginia Rainwater Harvest Manual, at www.CabellBrandCenter.organd

WSSI/Wetland Studies and Solutions, Inc., at http://www.wetlandstudies.com.



Preliminary Screening Model

Garage=400 sf

Evapotranspiration

Evaporation/Runoff Loss

from Impervious Area

Driveway=800 sf

Storage Tank=

Variable SizeRoof=1500 sf

Landscaping=5000 sf

IrrigationRainfall Input

Infiltration Loss

October 9, 2009, 15



Average Monthly Water Budget

October 9, 2009, 16



Screening Results

October 9, 2009, 17



RHS Design for Runoff Control in Virginia



Configurations

1. Interior Non-Potable-

. -Demand year-round,

October 9, 2009, 19

Source: VDCR (2009) Draft Virginia DCR Stormwater Design Specification No. 6,

Rainwater Harvesting, Version 1.2.



More Configurations

3. Interior Non-potableDemand year-round,

Demand, On-siteStormwater Disposalduring non-irrigationmonths

4. Interior Non-potableDemand year-round, On-

site Stormwater DisposalYear-round

October 9, 2009, 20Source: VDCR (2009) Draft Virginia DCR Stormwater Design Specification No. 6,




Even More Configuraitons

5. Year round or SeasonalDemand with Dedicated

-

Drawdown with On-siteInfiltration

6. On-site Infiltration for ,No Re-use of StoredWater

October 9, 2009, 21Source: VDCR (2009) Draft Virginia DCR Stormwater Design Specification No. 6,




Calculate Demand Met

90

70

80

d e m a n d ( % )

60

w a t e r c a n m e e t

40

50

P e r c e n t r a i n

30

0 10,000 20,000 30,000 40,000 50,000 60,000 70,000 80,000 90,000 100,000

October 9, 2009, 22

Source: VDCR (2009) Draft Virginia DCR Stormwater Design Specification No. 6, Rainwater Harvesting, Version 1.2.



Calculate Runoff Reduction Credit

35

40

85

)

25

3075

a l l s t o r m e v

e n t s (

i n w a t e r ( %

)

15

20

55

65

o w F

r e q u e n c y f o r

e m a n d M e t b y R

% demand met by rainwater

Overflow Frequency (%)

10

45

O v e r f l

0

5

35

0 10,000 20,000 30,000 40,000 50,000 60,000 70,000 80,000 90,000 100,000

October 9, 2009, 23

Source: VDCR (2009) Draft Virginia DCR Stormwater Design Specification No. 6, Rainwater Harvesting, Version 1.2.



Steps

a cu ate ncrementa es gnVolumes

omp e e es gn o ys em

Enter Final Volumes/Credits

Spreadsheet

Volume Credit

Roof Area treated

Evaluate with otherBMPs to Assess WQ

October 9, 2009, 24

Status



Simulation/Operation of RHS Systems

(Work in Progress)



LID Design/ImplementationScience Museum, Richmond

Bioretention

Rainwater Harvesting

ege a e oo



Clermont Elementary, Alexandria

October 9, 2009, 27



Development of Rainwater HarvestingSystem Rule Curves

RHS is currently given a 40% runoff credit (but only for50% of runoff volume)

Objective: Use simulation model and duration analysis todevelop generalized rule curves for WQ credits

Collaboration with T. Younos



Operational Dynamics

Reserve Target

Dead Storage

October 9, 2009, 29



Summary

Screening Tool

Avera e Climatolo

Water Budget

Water Budget

Proposed Rule Curves

Water Budget

Simulation

October 9, 2009, 30

Duration Analysis



Contact Info: David Sample, [email protected](703)361-5606x128

Documents

Rainwater harvesting and Irrigation management