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Michael Dietz, Ph.D.Assistant Professor/Extension Specialist in Sustainable Living 

Utah State University

November 16, 2007Harvesting Water in the Landscape: Implementing Low Impact Development

University of Nevade Cooperative ExtensionReno, NV

Point Source PollutionPoint Source Pollution

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Polluted Runoff is the #1 Water Quality Problem in the U.S.*

Polluted Runoff is the #1 Water Quality Problem in the U.S.*

* USEPA* USEPA

INTENSITY OF LAND USEINTENSITY OF LAND USEINTENSITY OF LAND USEINTENSITY OF LAND USEINTENSITY OF LAND USEINTENSITY OF LAND USEINTENSITY OF LAND USEINTENSITY OF LAND USE

WATER QWATER Q UANTITY/QUALITY PROBLEMSUANTITY/QUALITY PROBLEMSWATER QWATER Q UANTITY/QUALITY PROBLEMSUANTITY/QUALITY PROBLEMS

Amount of IMPERVIOUS SURFACESAmount of IMPERVIOUS SURFACESAmount of IMPERVIOUS SURFACESAmount of IMPERVIOUS SURFACES

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8080

7070

6060

5050

4040

3030 DEGRADED

HED

IM

PERV

IOU

SNES

SH

ED I

MPE

RVIO

USN

ESS

(%)

(%)

ADAPTED FROM SCHUELER, ET. AL., 1992

2020

1010

00

STREAM IMPACTSTREAM IMPACT

WAT

ERSH

WAT

ERSH

PROTECTED

IMPACTED

Low Impact Development (LID) Site Planning and Design Concepts

□ The Goal: To preserve pre-development □ The Goal: To preserve pre development hydrology □ Runoff volume and rate□ Groundwater recharge□ Stream baseflow□ Runoff water quality□ Runoff water quality

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…”so our biggest problem is water supply…”

Supply is a bigger issue in arid climates, but nonpoint pollution still is a problem  and LID can help maintain pollution still is a problem, and LID can help maintain supply

Bioretention/Rain Gardens

Ponding area

Flow entrance

Ponding area

Overflow pathSoil, mulch and plants

Vegetated areas designed to infiltrate and process stormwater

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Bioretention/Rain Gardens

Rain Garden, Glen Brook Green, Waterford, CTRain Garden, Glen Brook Green, Waterford, CT

Rain Garden, Suburban MarylandRain Garden, Suburban Maryland

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I filt t d Infiltrated 99% of roof runoff!!

Bark mulchlayer

Bark mulchlayer

Flow entrance Overflow

2.5 cm roundstone w/ pea gravel blanket

Perforatedunder-drain

Bioretention soil mixture

2.5 cm roundstone w/ pea gravel blanket

Perforatedunder-drain

Bioretention soil mixture

8-10” of crushed stone (1-2”)

Dddd d d

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Underdrain (not always necessary) and stonenecessary) and stone

Typically 4” corrugated, perforated black pipe surrounded by crushed stone, run out to grade or connected to catch basin

Avoid geotextile fabric!!Avoid geotextile fabric!!

Commercial applications‐usually engineered systems 

Prince George’s County, MD

Wisconsin design manual

UConn design manual**Geared towards homeowners**

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More than 10 feet from foundation with basementAvoid placing over septic system or close to wellAvoid placing in wet areas of yard‐don’t forget, a 

rain garden IS NOT a water garden!Site to most effectively catch storm runoffC id   flConsider overflow

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Avoid areas with:Shallow (<3 feet) depth to bedrockSeasonal high water table

Be aware of the infiltration capacity of native soilssoils

UnderdrainOnly necessary in some situations

Quick percolation testDig hole 6 inches deep, and fill with water.Ideally, infiltration rate should be more than 1 inch per hourIf there is still water in the hole after 24 hours, the site is not suitable for a rain garden

*S i l  t  f     t ti*Special note for new construction…Soil compaction is common

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50‐60% sand20 30% topsoil 20‐30% topsoil 

Low clay content20‐30% leaf compost

Low phosphorus

Sandy loam, loamy sand, loam soils usually OK as is

Source: The Bioretention Manual (PGC, 2002)

Calculate area of roof feeding to garden

30 ft

50 feet

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50 feet x 30 feet = 1500 square feet1500 feet / 2 = 750 square feet

This is because only half the roof contributes to the garden750 square feet / 6 = 125 square feet

This just sizes the garden to hold 1 inch of water from the roof in a 6 inch deep rain gardenp g

In the East and Midwest, 90% of storms are 1” or less

Wisconsin design guide

UConn design guide

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Precipitation Frequency Estimates (inches)Precipitation Frequency Estimates (inches)

ARI* 5 10 15 30 60 120 3 6 12 24 48 4 7 10 20 30 45 60

(years) min min min min min min hr hr hr hr hr day day day day day day day

1 0.09 0.13 0.16 0.22 0.27 0.36 0.43 0.58 0.73 0.89 1.05 1.22 1.43 1.58 1.87 2.09 2.48 2.82

2 0.11 0.16 0.2 0.27 0.33 0.45 0.53 0.73 0.92 1.11 1.32 1.54 1.81 2.01 2.37 2.65 3.15 3.59

5 0.14 0.22 0.27 0.36 0.45 0.57 0.67 0.9 1.16 1.42 1.68 1.98 2.33 2.6 3.06 3.4 4.04 4.6

10 0.18 0.27 0.33 0.45 0.55 0.68 0.77 1.03 1.35 1.66 1.97 2.34 2.75 3.06 3.58 3.98 4.7 5.32

25 0.23 0.35 0.44 0.59 0.73 0.84 0.91 1.2 1.58 2 2.38 2.84 3.34 3.7 4.28 4.74 5.56 6.22

50 0.28 0.43 0.53 0.71 0.88 0.97 1.02 1.32 1.76 2.27 2.7 3.25 3.81 4.2 4.81 5.32 6.19 6.87

100 0.34 0.52 0.64 0.86 1.07 1.13 1.17 1.44 1.94 2.55 3.04 3.67 4.3 4.72 5.36 5.91 6.81 7.48

200 0.41 0.63 0.78 1.05 1.29 1.32 1.35 1.57 2.12 2.84 3.39 4.12 4.82 5.25 5.9 6.49 7.41 8.04

500 0.53 0.8 0.99 1.34 1.66 1.7 1.71 1.76 2.36 3.24 3.88 4.76 5.54 5.98 6.63 7.26 8.17 8.74

1000 0.63 0.96 1.19 1.6 1.98 2.04 2.06 2.08 2.54 3.55 4.27 5.27 6.12 6.55 7.17 7.85 8.71 9.2

From: http://hdsc.nws.noaa.gov/hdsc/pfds/index.html

1.80

2.00

Days with precipitation, Reno, NV, 1977-2007

0.80

1.00

1.20

1.40

1.60

80

ecip

itatio

n (in

ches

)

0.00

0.20

0.40

0.60

0 10 20 30 40 50 60 70 80 90 100

Pre

1-Probability of Exceedance

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Not necessary to use 1” storage sizeNot necessary to use 1” storage size

Size rain garden to contain ½ inch of runoffCut previous size calculation in half, so instead of 125 ft2, make it 63 ft2

If soils are slow to infiltrate, make the garden bigger or reduce the area of roof that contributes to the garden

125 square feetGarden can be shaped in a variety of waysGarden can be shaped in a variety of ways

10’10’

12.5’12.5’

10

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Call hotline to locate underground utilitiesCall hotline to locate underground utilities

Smaller gardens can be dug by hand (friends+beer=rain garden), or equipment can be rented for larger gardens

Mark area to be dug

Dig out 8‐9 inches of il  k i  th  b tt  soil, keeping the bottom 

fairly levelA string or board can be used as a guideBerm the bottom end, if necessaryP id     d l  l  t  Provide a gradual slope to the sides

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Avoid compaction/sealing of bottom with bucket

AVOID COMPACTION!!!Compacted soil will causea rain garden to fail

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SOIL COMPACTION before, during construction

Make sure flow paths and storage areas are properly constructed (per plan details)properly constructed (per plan details)

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Don’t allow runoff from an open, unstabilized construction site to enter the garden

Surface of garden will become clogged 

Make sure storage depth is correct at installation

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“Over‐Engineering”

See the UConn or WI publications for a plants to publications for a plants to use in Midwest or East

USU Extension plant list

Apply about 3 inches of pp y 3shredded hardwood mulch (not pine bark‐it floats)

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Has open flow paths, overflow and an d t l   i d  t g    (   l )adequately sized storage area (per plan)Has proper materials installed (per plan)Has NON‐COMPACTED soils!Is only used after the surrounding site is 

stabilizedHas proper plantings/ground coverHas a provision for short term care 

(watering), and in arid climates irrigation

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Similar to other landscaped areasSimilar to other landscaped areasYearly mulch, if desiredPrune plants, if desiredIrrigate/water as necessary

MOST IMPORTANTLY: Maintain flow paths and storage areastorage area

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http://www.dnr.state.wi.us/org/water/wm/nps/rg/#plant_lists

http://www.raingardens.org/Index.php

http://www.nemo.uconn.edu/tools/publications.htm

Any questions?