Conservation

Strategies for

Growing Communities

Urban Conservation Practices for 

Protecting and Enhancing

Natural Resources 

Iowa NRCS - 2004

Urban communities are expanding to

meet demands of growing populations. More homes, schools, shopping

centers, and more roads must be built

to connect people with these services.

Local developers, planners, engineers, government officials and

resource agencies must respond to

these demands. They must collectively manage land development in ways

that minimize negative environmental

impacts that development activities

can create.

Developing areas can account for a

significant amount of soil erosion and

o ff-site damage from sediment.

Construction sites typically have far

greater erosion rates than agricultural

land, making runoff from urbanizing

landscapes a significant source of

sediment in surface water.

With urban development comes more

impervious surfaces. Roofs, roads,

parking lots, and compacted turf

areas increase runoff and deliver

more sediment, nutrients, hydrocarbons and other pollutants to receiving

streams. Flood problems can also be

aggravated, causing damage for residents and municipalities.

With the growing demand to address

urban conservation issues, USDA’s

Natural Resources Conservation

Service (NRCS) is working with its

partners (Iowa Soil and Wa t e r

Conservation Districts, Division of

Soil Conservation, Department of

Natural Resources, ISU Extension

Service, Iowa Association of

Municipal Utilities) to develop services that meet these needs. Providing

conservation assistance in urban areas

complements the traditional conservation services provided to agricultural lands. Fostering urban-rural

coalitions for conservation will

strengthen support for natural

resource enhancement throughout the

watersheds of Iowa.

The Growth of Urban Conservation

“Conservation Strategies for Growing Communities” provides information

and direction relating to conservation in urban areas. This brochure discusses water quality laws and regulations and elements of effective erosion and

sediment control plans. It includes sections on erosion control practices,

sediment control practices, and concludes with a section on storm water

management practices. For each practice, this guide will:

• provide a description

• list design techniques for implementation

• indicate challenges or limitations that may limit effectiveness 

• illustrate with photos

3

What is in this brochure?
Storm Water Regulations

Phase I of the EPA’s storm water

program relied on NPDES permit

coverage to improve the quality of

storm water runoff from “medium”

and “large” municipalities with separate storm sewer systems (MS4’s).

Construction activity disturbing five

acres of land or more was required

to develop and implement a pollution prevention plan and obtain an

NPDES permit. Ten categories of

industrial activity were also regulated under Phase I. The only Iowa

cities impacted by Phase I were Des

Moines and Cedar Rapids.

NPDES Phase II expands Phase I

by requiring 43 additional Iowa

cities to improve storm water quality. Land disturbing activities affecting one acre or more are also subject to Phase II. Phase I and II cities

in Iowa are listed on the next page.

Iowa State University and the

University of Iowa are also subject

to Phase II.

NPDES

Pollutants degrade surface waters,

making them unsafe for drinking,

fishing, swimming and other activities. As authorized by the Clean

Water Act, the Environmental

Protection Agency’s (EPA)

National Pollutant Discharge

Elimination System (NPDES)

permit program is designed to control water pollution by regulating

point and nonpoint sources that

discharge pollutants into waters.

Great strides have been made to

control point source pollution (i.e.

pipes discharging industrial waste,

outlets of waste water treatment

facilities). Attention has now

turned to Nonpoint Source

Pollution (NPS), which is precipitation driven storm water runoff

generated by land-based activities.

Examples include runoff from

agriculture, construction, mining

or silviculture activities, which

carries pollutants from the land to

surface waters.

What the Law Requires

4

Nonpoint Pollutants 

Most Commonly Discharged

From Construction Sites:

• Sediment

• Oil and Greases

• Concrete Truck Washout

• Construction Debris

• Construction Chemicals

Nonpoint Pollutants 

Most Commonly Discharged

From Urban Land After

Construction Is Completed:

• Nutrients

• Hydrocarbons

• Pathogens

• Sediment & Road Grit

• Organic Matter 

(i.e. Lawn Clippings)

• Litter

• Thermal Pollution (heated runoff

from impervious surfaces)
Iowa Cities Subject to 

Phase I and II of NPDES

Phase I and II cities are required to:

1. Control erosion and retain sediment on construction sites.

2. Improve storm water management to control flooding and protect

water quality.

3.Inspect storm drain outlets regularly to detect and eliminate any

unwanted discharges.

4.Implement “good housekeeping” practices to ensure municipal operations are not contributing to water quality degradation.

5.Educate residents how to contribute to water quality protection.

6.Involve the public, as communities implement their plan for protecting water quality.

1 Altoona

2 Ames

3 Ankeny

4 Asbury

5 Bettendorf

6 Bondurant

7 Buffalo

8 Carter Lake

9 Cedar Falls

10 Cedar Rapids

11 Clinton

12 Clive

13 Coralville

14 Council Bluffs

15 Davenport

16 Des Moines

17 Dubuque

18 Elk Run Heights

19 Evansdale

20 Fort Madison

21 Grimes

22 Hiawatha

23 Iowa City

24 Johnston

25 Le Claire

26 Marion

27 Marshalltown

28 North Liberty

29 Norwalk

30 Ottumwa

31 Panorama Park

32 Pleasant Hill

33 Raymond

34 Riverdale

35 Robins

36 Sergeant Bluff

37 Sioux City

38 Storm Lake

39 University Heights

40 Urbandale

41 Waterloo

42 Waukee

43 West Des Moines

44 Windsor Heights

5
Every construction project that will

disturb one acre of land or more is

subject to NPDES permit requirements. Rules mandate that a

NPDES permit from the Iowa

Department of Natural Resources

(DNR) must be obtained. Each site

greater than one acre must also

have a Storm Water Pollution

Prevention Plan (SWPPP) to

obtain a permit. The key component of pollution prevention plans

is to identify practices that reduce

erosion and prevent sediment loss

from construction sites. 

Planning is the key to implementing and maintaining an effective

SWPPP during construction activities. How erosion will be minimized and how sediment will be

contained on site should be considered from the very beginning of

new development designs. The first

priority should be to maximize erosion control. Sediment control will

be more effective when erosion is

minimized. 

Your local NRCS field office can

provide assistance in developing

and implementing effective pollution prevention plans.

Storm Water Pollution Prevention Planning

( S W P P P )

6

• Minimize clearing and grading.

• Phase essential grading to limit

soil exposure.

• Immediately stabilize exposed

soils.

• Protect steep slopes and cuts.

• Protect and stabilize drainageways.

• Install perimeter controls to

keep sediments on-site.

• Train contractors on SWPPP

implementation.

• Inspect SWPPP practices after

storms and perform needed

maintenance.

• Adjust the plan once construction has started, if needed.

Elements of an Effective Storm Water Pollution

Prevention Plan (SWPPP):
Erosion is a three-step process

involving the detachment, transport, and deposition of soil particles. There are many kinds of erosion. Sheet and rill erosion, gully

erosion, stream bank erosion and

wind erosion are a few primary

concerns. Each of these types of

erosion involves the detachment

and transport of soil and downstream/downwind deposition of

sediment.

Sheet & Rill Erosion: Sheet erosion is

the uniform movement of a thin layer of soil

from sloping, bare, unprotected land. Falling

raindrops detach soil particles which go into

solution as runoff occurs. Detached particles are

transported down slope to a point of deposition.

Rills form with longer, harder rains when runoff

volumes accelerate.

Gully Erosion: Rill erosion evolves into

gully erosion as runoff increases, from one heavy

rain or a series of storms over time. A gully is

generally defined as a scoured out area that is not

crossable with tillage or grading equipment.

Stream Bank Erosion: This type of

erosion is the scouring away of stream banks.

Degrading or downcutting streambeds and/or

repeated high flows of extended duration cause

bank erosion. Stream bank erosion is a significant

contributor of sediment loads.

Wind Erosion: Wind erosion is similar to

sheet erosion in that detachment, transport, and

deposition of soil particles occur, except that

wind is the transportation mechanism rather than

water.

Types of Erosion

Soil Erosion

7
Understanding the erosion process

is essential to the design and

implementation of effective 

erosion control plans. The key to 

erosion control is preventing the

detachment of soil particles and

reducing the volume of runoff.

Erosion control is achieved by

minimizing land disturbing activities, maintaining vegetative cover,

mulching, applying a compost

blanket, or installing rolled erosion

control products (mats or blankets).

Erosion Control

Erosion Control Practices

Erosion control practices discussed and examined in this section:

t Compost Blankets

t Vegetative Establishment

t Mulching

t Rolled Erosion Control Products

t Grading Strategies

A compost blanket protects against erosion until vegetation is established on this storm water

detention basin retrofit project at North High School in Davenport, Iowa. The darker color of the

compost is due to its high organic matter content.

8
Compost Blankets . . . an erosion control and

soil quality enhancement practice. Compost blankets provide a soil

amendment consisting of decomposed organic waste with a consistency similar to high quality topsoil but a much higher organic matter

content. The high organic matter content of compost absorbs the

impact of raindrops, which prevents detachment of soil part i c l e s .

Organic matter also retains water on site to reduce runoff and potential transportation of sediment or o t h e r p o l l u t a n t s .

Design Techniques

• Compost can be applied to a depth

specified for site conditions using

manure spreaders, bulldozers, end

loaders, or pneumatic blower

trucks. Generally, a two inch minimum blanket depth is recomm e n d e d .

• Compost blankets are effective as

temporary site stabilization while

vegetation is established.

• Seeding is completed after the

compost blanket has been

installed or as the blanket is being

installed with a blower truck.

• Compost amended soils contribute

to rapid establishment of vegetative cover and water retention.

C h a l l e n g e s / L i m i t a t i o n s

• Compost blankets should not be

used in areas of concentrated

water flow.

• Access to composting facilities

and adequate supplies of compost

may limit use of compost blankets

in some locations.

Applying compost and seed with a 

pneumatic blower truck.

Early Spring

Early Summer

According to research on compost

blankets by Dr. Tom Glanville and his

team of Iowa State University

researchers, compost-treated slopes

produced significantly less runoff (50-

80 percent less) than slopes with bare

soil. They also found that even at

rainfall intensities of nearly four inches

per hour, the water absorbing capacity

of the compost blankets reduced erosion by 98 percent.

To learn more about ISU research on

compost blankets, visit

www.eng.iastate.edu/compost.

ISU Research on Compost Blankets

Pneumatic blower trucks are a new tool for

compost-based erosion control practices.

9

Compost blankets control erosion until 

seeding is adequately established. 
Grading Strategies . . . designing developments to fit the existing landscape minimizes the amount of

required grading. This reduces the amount of land exposed to erosion and saves money. Some grading will always be needed.

Coordinate essential grading to minimize erosion potentials.

Design Techniques

• Phased grading is recommended.

Phasing divides essential grading

into distinct portions. Grading of

each phase is started and completed in sequence.

• Generally, it is best to start grading activities at the top of a

site first and then move

down the gradient. Try to

maintain vegetative cover

(buffer strips) as the site

progresses.

• Phased grading maintains

strategic vegetative cover

and minimizes the amount

of disturbed land at any

given time to reduce erosion. 

• Deep tillage should be done

as the final step of grading

activity to reduce soil compaction. This increases infiltration and decreases runoff.

C h a l l e n g e s/L i m i t a t i o n s

• Each grading phase needs to be

planned carefully to assure time

and cost efficiencies are realized.

Minimize the amount of land exposed to erosive rain

and wind with phased grading.

10
Mulching . . . applying vegetative residue to protect the

soil surface from the impact of raindrops or the erosive forces of

wind until vegetative cover is established. Mulching conserves moist u re for seedlings and protects them from temperature extre m e s .

Mulching limits soil erosion, lessens the need to contain sediment and

enhances water q u a l i t y. Mulches most often used include straw, fiber

o r wood chips.

Design Techniques

• Straw mulches do not bond to the

soil. They will blow off the site or

be carried away by water if they

are not tacked in by disking. T h e y

can also be held in place by

spraying on a tackifier (glue) or

fiber mulch to hold the straw in

place. 

• Straw mulch is usually applied at

a rate of 1-2 tons per acre.

• Fiber mulches are chopped up

paper or wood fiber and are typically sprayed on as a slurry along

with seed.

• Wood chip mulches are rarely

used on larger sites because of the

expense. They can be a good

solution, though, for smaller critical areas.

• Mulching is one of the best ways

to provide instant erosion control

on a bare site to protect it until

vegetation can be established.

C h a l l e n g e s / L i m i t a t i o n s

• Mulches can be used on most sites

and are generally only limited by

severe slopes. On steeper slopes,

rolled erosion control products

should be used. 

• Mulch is not effective at stabilizing channels or other areas of concentrated flows. A rolled erosion

control product is recommended

for areas of concentrated flow.

• Too much mulch or uneven distribution of mulch can smother new

grass seedlings.

Applying Straw Mulch

Straw mulch was disked in where vegetative

cover is starting to establish. The mulch blew

off the bare ground to the right because it was

not tacked in by disking.

11
Rolled Erosion Control Products

(RECP’s) . . . mats or blankets of organic or synthetic

materials applied to the soil surface to protect disturbed areas from

erosion until vegetative cover is established. Rolled erosion control

products are especially effective at controlling erosion on severe

slopes or areas of concentrated flows.

Design Techniques • Proper selection and installation

of RECP’s is critical to successful

use of these products. 

• Trenching, overlapping, and stapling must be completed according to manufacturer’s recommend a t i o n s .

• Seeding is done prior to blanket

installation (some blankets have

seed embedded). 

• R E C P ’s are highly recommended

for protecting areas of concentrated flows.

C h a l l e n g e s / L i m i t a t i o n s

• RECP’s may not be cost-effective for flat grades.

This roll of coconut fiber matting will

be used to provide cover until 

vegetation is established.

“I have never seen a rolled

erosion control product fail.

When problems occur, it is

always improper product

selection or installation

errors to blame.”

-Dwayne Stenlund, CPESC

Erosion Control Specialist 

Minnesota DOT

12
Vegetative Establishment . . . establishing vegetative cover is the best way to control erosion. Temporary

vegetation with fast-growing annual species is an economical way to

stabilize a construction site until permanent vegetation is established. Mulching or compost blankets should always be used with

temporary or permanent seeding.

Design Techniques • Two options available for establishing permanent vegetation are s e e di n g and s o d d i n g.

• Sodding can be applied at any

time, but regular watering is

required until root systems are

e s t a b l i s h e d .

• Seeding is usually less expensive

than sodding, but is typically

restricted to Spring (March 1-May

15) or Fall (August 1-September

15). Seeding periods can be

extended when mixtures of native

(prairie) species are seeded.

• When seeding, always include

mulch, compost blankets or rolled

erosion control products to control

erosion, improve seed germination

and enhance establishment of vegetative cover.

• Use a mix of native grasses and

forbs (flowering species) when

possible to increase infiltration,

reduce maintenance costs, increase

wildlife habitat, improve soil quality and protect water quality.

• Temporary vegetative cover can be

established by broadcasting oats,

C h a l l e n g e s / L i m i t a t i o n s

• The two greatest challenges to

establishing vegetation are the climate at the time of seeding and

poor soil conditions.

• Poor soil conditions found at many

construction sites can make establishing vegetation challenging. Soil

amendments such as organic matter (compost), fertilizer, and lime

often need to be added. (See Soil

Quality Restoration, page 30)

• Compaction of soils on construction sites inhibits plant growth and

the land’s ability to absorb rainfall.

To relieve compaction, a deep

tillage operation will be necessary.

• Success of seed establishment is

influenced by the weather (including temperature and rainfall conditions) making supplemental practices essential (compost

b l a n k e t s / m u l c h i n g / R E C P ’s ) .

A two week old seeding applied with a compost blanket protects this slope. Note

the problems with establishing vegetative cover in the area of concentrated flow.

Compost socks were added as a remedial measure after gullying had occurred.

wheat or rye. Temporary seeding

should be used to provide cover

until the next permanent seeding

p e r i o d .

13
Sediment Control

Sediment Control Practices

Sediment control practices discussed and examined in this section:

t Rock Check Dams

t Compost Socks

t Compost Filter Berms

t Inlet Protection Devices

t Sediment Control Basins

t Filter Strips

Sediment control, which is often

confused with erosion control, is

trapping detached soil particles that

are already moving in the erosion

process. Slowing the velocity of

runoff and providing vegetative filtering helps trap sediment on-site,

but typically sediment control is

achieved by temporarily impounding flows to allow sediment to settle out. Sediment is the number one

pollutant of Iowa’s surface waters.

It is critical that effective sediment

control practices be installed and

maintained when soil is exposed to

the erosive force of rain and wind.

t Silt Fences 

t GeoRidgeTM

The rock check dam shown above adds water quality protection to a traditional storm water deten -

tion basin by temporarily impounding runoff from frequent, low intensity rainfalls. A traditional

detention basin only controls large storms to reduce flooding.

14
Compost Filter Berms . . . small triangular

structure made of biologically active composted material that slows

and filters water to capture sediment and degrade pollutants. In

addition to providing sediment control, compost filter berms

improve water quality by absorbing pollutants such as hydrocarbons, nutrients and bacteria.

Design Techniques

• Compost filter berms are small

triangular structures of specified

blends of composted organic

materials installed perpendicular

to sheet flows of runoff. 

• The width of the berm at its base

should be twice that of its height.

• Using a commercially available

berm forming device is highly

recommended to ensure uniform

installation.

• Slope gradient perpendicular to

the berm should be five percent

or less.

• Drainage areas should be limited

to 1/4 acre per 100 lineal foot of

berm length, which can be

achieved by spacing berms no

more than 100 feet apart on a

slope.

• Because of compost’s ability to

absorb pollutants, berms are recommended around water bodies

where protecting and improving

water quality is a priority.

C h a l l e n g e s / L i m i t a t i o n s

• Compost berms should not be

used to control concentrated

flows.

• Success is contingent upon the

right composition of materials

being specific and installed. 

• If installed with a pneumatic

blower truck, compost filter

berms can be installed on any

terrain, including rocky or hilly

ground, and in difficult soil conditions such as frozen or wet

ground.

• Compost filter berms do not have

to be removed once construction

is complete. They can be seeded

during installation to become

part of the permanent landscape

or can be spread out and used a

second time as a soil amendment.

• Compost filter berms are most

effective if used in conjunction

with compost blankets.

15
Compost Socks . . . mesh tubes filled with biologically active composted material that slow and filter water to capture and degrade pollutants transported by runoff. Like compost

berms, socks filled with compost are placed at the top of slopes and

on the contour across slopes to intercept and treat sheet flows.

Design Techniques

• Compost socks are mesh-like

textile tubes that come in multiple diameters, ranging from 8 to

24 inches.

• Compost socks are filled by

pneumatic blower trucks.

• They may be staked at 8 foot

intervals for added stability.

• Install socks on the contour no

more than 100 feet apart going

down the slope.

• Flare the ends uphill to temporarily impound water.

• Compost socks injected with

seed can be used to stabilize

severe slopes or stream banks.

• Compost socks can be installed

on concrete or asphalt for inlet

protection.

C h a l l e n g es/ L i m i t a t i o n s

• Spacing compost socks too far

apart or not placing them on the

contour will reduce eff e c t i v e n e s s .

• Uneven ground may cause leakage

under compost socks. Blowing

compost into the joint of the sock

and the ground on the uphill side

of the sock will help prevent leaks.

Stakes should be installed to hold compost

socks in place to prevent movement.

16

Compost socks with a compost 

blanket protect this slope.
Filter Strips . . . strips of vegetation left as a buffer

between construction sites and stream corridors. Filter strips

reduce the velocity of runoff leaving a construction site, filter sediment and enhance infiltration of runoff. Filter strips should be

maintained as permanent buffers to protect urban streams, ponds

and wetlands after construction is completed.

Design Techniques

• Filter strips are buffer zones of

grasses along the edges of

streams. They absorb runoff, stabilize the soil and trap pollutants.

Trees and shrubs can be strategically planted for habitat value. 

• Surface runoff should be evenly

distributed and enter the filter

strip as a sheet flow.

• Areas of existing vegetation can

be maintained or new vegetation

can be established prior to the

onset of land disturbing activities.

• Many communities are

encouraging or requiring

ponds and stream buffers.

Installing or maintaining

buffers is a storm water management practice that helps

communities protect water

quality and comply with

Phase I and II of NPDES regulations.

C h a l l e n g e s / L i m i t a t i o n s

• Private ownership in stream corridors can prevent the installation

and maintenance of a comprehensive filter strip system.

• Dedicated linear green space is

needed to buffer urban streams.

Trails can be installed to provide

a community amenity.

• When planting new filter strips,

use native vegetation to build soil

quality and enhance infiltration.

Iowa farmers have installed 18,223 miles of filter

strips along rural streams. Urban filter strips are

increasingly being installed to buffer urban streams.

17

Buffering urban stream corridors protects water quality,

stabilizes stream banks and provides linear green

space for recreational activities.
GeoRidgeTM. . . low profile, porous berms installed 

perpendicular to the direction of flow. The GeoRidgeTM system is

designed to complement the performance of erosion control blankets in channel and slope applications.

Design Techniques • Recommended spacing of

G e o R i d g eTM is directly related to

the channel grade. The steeper the

grade, the closer the spacing.

• Prepare the channel by forming

the shape and grade of the channel. Install the erosion control

blankets before installing the

G e o R i d g eTM s y s t e m .

• Place GeoRidgeTM berms perpendicular to the direction of the

f l o w. Overlap panels by a minimum of 2 inches. Cut a slot in the

crest of the overlapping berm to

allow contact between the foot of

the berm and the soil.

• Secure berms with pins or staples.

The pin/staple spacing across the

width of the panel should be ten

inches on center for the upstream

leg and 20 inches on center for

the downstream leg.

• G e o R i d g eTM can be removed after

the site is stabilized and used over

a g a i n .

C h a l l e n g e s / L i m i t a t i o n s

• Silt deposited behind GeoRidgeTM

must be removed periodically to

maintain permeability.

• Allowing excessive sediment to

build up behind the berm will create a non-porous check structure

which causes overflow and scouring on the downhill side of the

structure. This can lead to failure

of the system. 

A GeoRidgeTM system complements erosion con -

trol blankets to protect areas of concentrated

flow on this site in Iowa’s fragile Loess Hills

r e g i o n .

18

This GeoRidgeTM system has trapped

sediment. Maintenance should be

performed to maintain its effectiveness.
Inlet Protection . . . traps and filters sediment

from runoff before it enters storm sewer inlets. Inlet protection

serves as a last line of defense for keeping sediment on site.

Construction sites will always generate some sediment-laden runoff,

making inlet protection an important practice. A variety of products and techniques are available to provide inlet protection.

Design Techniques

• Inlet protection techniques can

vary from covering inlets with

geotextile (above) to placing silt

fence, compost socks or rock filter dams around the inlet. A h o s t

of other options are available. 

• The key is to install a protective

device that filters storm water

r u n o ff one last time before it

enters the storm sewer.

• Traditional flood control detention basins can be retrofitted with

an inlet protection system to provide water quality benefits while

maintaining flood control funct i o n s .

C h a l l e n g e s / L i m i t a t i o n s

• Since inlet protection devices

impede the direct flow into the

storm drain, streets may become

temporarily flooded or covered

with deposited sediment.

• Designers should provide a plan

for dealing with impounded

w a t e r. Deposited sediment should

be cleaned promptly. Sediment

can also clog the filtering medium, requiring regular maintenance to prevent extended ponding of runoff water. 

• Inlet protection techniques should

not be subjected to large sediment

loads. The vast majority of sediment should be trapped upland

from inlets. Inlet protection

should provide a final filtering of

r u n o ff, after other components of

a pollution prevention plan have

done their job.

A geotextile fabric is installed beneath the

grate of this storm sewer inlet. Runoff will

receive one last filtering before moving off-site.

A rock check dam serves as an inlet 

protection device on this site.

19
Rock Check Dams . . . rip rap grade stone

placed perpendicular to concentrated flows in ditches or swales.

Rock check dams serve as sediment trapping structures by slowing

flows and allowing sediment to drop out of runoff. This practice is

used to prevent gully erosion from scour caused by concentrated

flows. 

Design Techniques

• Maximum height of rock check

dams should be three feet. The

top of the rock check dam

should be a minimum of one

foot below the top of the ditch or

swale to prevent out or bank

flows.

• Front and back slopes should

extend three feet out for every

foot of height (3:1 slopes).

• Temporary ponding must not

cause damage to adjacent areas

or structures.

• The top of the dam should be

level across the entire length to

provide a “level spreader” affect,

should the dam overtop.

C h a l l e n g e s / L i m i t a t i o n s

• Trapped sediment needs to be

removed after every erosive rain

to maintain the capacity of the

structure until vegetation is

established. 

• Dams are typically not removed

after a site is stabilized, which

could cause problems with future

maintenance, such as mowing.

• Pores between rocks can become

plugged, reducing the filtering

ability of the structure.

These rock check dams complement RECP’s

and trap sediment in concentrated flows.

20
Sediment Control Basins . . . basins are

commonly used on construction sites to retain sediment by

impounding and slowly releasing runoff. Sediment settles out of

standing water, so maximizing the time water is impounded incre a ses the amount of sediment retained on site. Basin outlets can be

wrapped in geotextile or bedded in gravel to enhance trap eff i c i e n c y. 

C h a l l e n g e s / L i m i t a t i o n s

• Trapped sediment should be

cleaned out regularly to maintain

storage capacity and maximize

time of impoundment.

• Sediment basins are not trap eff icient for very fine silts and clay

sized soil particles that stay in

suspension for extended periods.

• Bed outlets in gravel or wrap

them with geotextile to help trap

fine particles. Coagulating agents

are also available, which cause

fine particles to clump together

and fall out of suspension.

Design Techniques

• Basins can be placed strategically

throughout the construction site

and be temporary in nature. For

instance, a basin can be installed

as part of a phased grading plan

and removed as one phase is

completed. 

• Often, a large basin is installed as

a perimeter protection practice.

L a rge volumes of water can be

captured and retained with this

approach. 

• Perimeter basins can be removed

and the site landscaped after

grading is completed and the site

is stabilized. 

• In many cases, sediment basins

can be multi-functional. They can

serve as sediment traps during

construction and as water features that helps manage storm

water after development is comp l e t e d .

Basin 

Outlet

21
Silt Fences . . . t e m p o r a rysediment barriers of geotextile fabric anchored in the ground and supported by posts on the

d o w n s t ream side of the fabric. Silt fences temporarily impound

r u n o ff and retain sediment on-site, often as perimeter c o n t rol. T h e y

a re most effective when designed to provide comprehensive water

and sediment control throughout a construction site and if used in

conjunction with erosion control practices.

Design Te chnique s • Silt fences can be sliced or

trenched into the ground. Slicing

normally creates a more secure

system as the ground can be

compacted more fully to prevent

undercutting of the fence.

• Install silt fences on the contour,

and no more than 100 feet apart

going down a slope.

• Flare the ends of silt fence runs

uphill to temporarily impound

w a t e r.

• Silt fence should always be used

with rolled erosion control products when used as ditch checks to

control concentrated flows.

Space silt fence so that the elevation at the bottom of an upstream

fence is equal to the elevation of

the top of the next fence downstream, creating a stair- s t e p

e ff e c t .

• Inspect and clean out or replace

silt fence after every one-half

inch rain. (This is the most crucial and difficult aspect of an

e ffective silt fence system.)

• Silt fence systems must be

removed after a site is stabilized.

C h a l l e n g e s / L i m i t a t i o n s

Conditions that limit the effectiveness of silt fences include:

• Not placing on the contour 

• Spacing too far apart

• Ends not curved uphill, allowing

water to bypass the fence

• Not entrenching deeply enough

to prevent undercutting

• Not maintained/cleaned out after

a storm event

• Used as perimeter control

devices or ditch checks without

supporting practices

A series of silt fence ditch checks. Note how

concentrated flows have caused gullying

between the checks. A rolled erosion control

product is recommended to enhance the effec -

tiveness of silt fence checks. 

22
Low Impact Development (LID)

Traditionally, storm water management has involved the rapid conveyance of water via storm sewers to surface waters. Where storm

water management is required, it has focused on flood control, but

not water quality protection. Low Impact Development is a different approach that retains and infiltrates rainfall on-site.

Infiltration-based storm water management practices associated

with LID may include the following:

t Soil Quality Restoration

t Bioretention Cells

t Bioswales

t Infiltration Trenches

t Native Landscaping

t Permeable Paving Alternatives

t Rain Gardens

Bioretention cells manage runoff from

impervious surfaces that dominate com -

mercial, institutional and industrial sites.

Land development can have profound impacts on surface and

ground water resources. Roads,

parking lots, rooftops and compacted turf areas inhibit water from

infiltrating the ground and recharging streams with slowly released

g r o u n d w a t e r. Rainwater flows off

impervious and compacted surfaces

into storm drains which discharg e

into streams, wetlands, rivers or

lakes, polluting these receiving

waters. Low Impact Development

(LID) is an ecologically friendly

approach to land development and

storm water management. The goal

of the LID approach is to mitigate

d e v e l o p m e n t ’s impacts on land,

water and air. The LID approach

emphasizes site design and planning

techniques that retain water on-site

and mimic the natural infiltrationbased, ground water-drive hydrology of our historic landscape. Low

Impact Development infiltrates

more rain and sheds less runoff, to

protect water quality and reduce

flood peeks.

Storm Water Management

23
Bioretention Cells . . . s h a l l o w, landscaped

d e p ressions that can handle large volumes of water f rom extensive

impervious surfaces found in commercial, institutional, industrial or

residential settings. Bioretention cells generally have an engineere d

substratum, due to altered and compacted soil conditions.

C h a l l e n g e s / L i m i t a t i o n s

• There is potential for fine particles to accumulate in the surface

layer of bioretention cells, which

could impede the percolation of

water through the soil profile. 

• Maintain a mowed turf border

around the perimeter of the cell

to trap fine particles and prevent

this potential problem.

Design Techniques

• The subgrade of a bioretention

cell will usually include a tile

drain bedded in gravel and a soil

matrix that is amended with sand

and compost to ensure at least 40

percent pore space is maintained.

• Bioretention cell size can be up

to 30 percent of the square

footage of the impervious surface draining to the cell, but usually will be less than ten percent.

The depth of the amended subgrade affects the surface area of

the bioretention cell. 

• Native trees and shrubs can be

planted to provide shading for

parking surfaces.

• Bioretention cells should be

strategically located to capture

roof runoff or segment impervious surfaces to intercept runoff

before the volume becomes too

large. 

• The underlying tile drain should

be below frost lines to keep the

soil matrix drained.

A turfed island was converted into a bioreten -

tion cell at this site. Curb cuts allow runoff to

enter the bio-cell for pollutant removal. Large

runoff events can still enter storm sewers. 

24
Bioswales . . . vegetated conveyance systems that provide an alternative to storm sewers. They incorporate some of the

design features of rain gardens and bioretention cells that facilitate

infiltration. Bioswales convey large runoff events to storm sewer

inlets or d i rectly to surface waters, infiltrating the first flush of

r u n o ff and providing vegetative filtering to flows that cannot be infiltrated. 

Design Techniques

• Bioswales allow frequent, low

intensity rains that account for

the majority of annual precipitation to infiltrate. The infiltrated

water from bioswales helps

recharge groundwater.

Recharging groundwater will

supply receiving waters with a

slow, purified seep rather than

surges of polluted surface runoff.

• Infiltration trenches, subgrade

drains and amended soils may be

needed to facilitate infiltration.

• Bioswales will safely convey

large storm flows that exceed

infiltration capacity.

• Enhance and utilize existing natural drainage swales whenever

possible to absorb and convey

storm water runoff.

C h a l l e n g e s / L i m i t a t i o n s

• Compacted soil conditions usually require subgrade enhancement

to facilitate infiltration.

• Ordinances often require curbs

and gutters on urban streets,

making it necessary to obtain

variances to use swales in conveying road runoff in urban areas

(as shown above).

A bioswale featuring native vegetation show -

ing its fall colors.

25
Infiltration Trenches . . . excavated trenches

backfilled with a coarse stone aggregate and biologically active

organic matter. Infiltration trenches allow temporary storage of

runoff in the void space between the aggregate and help surface

runoff infiltrate into the surrounding soil.

Design Techniques • D i fferent design techniques will be

needed for different site conditions.

Deep, narrow trenches work well

in parking lots (above). Wi d e r,

more shallow trenches (below)

work on the perimeter of a site or

down the center line of a swale.

• Trenches should be lined with geotextile fabric before placing gravel.

• The grated trench shown above has

a layer of granular material covering the folded fabric. This top layer

of granular material will need to be

replaced periodically as fines accumulate.

• Fabric will be folded over to cover

the top of the trench (shown at

right) to prevent fines from migrating into pore space of the gravel.

Cover the trench with compost

amended soil and plant native vege t a t i o n .

• An underdrain may be needed to

decant water that is unable to percolate into the soil profile.

C h a l l e n g e s / L i m i t a t i o n s

• The trench should be inspected

after the first few runoff events

and then at least annually therea f t e r. An observation port can be

installed to monitor percolation

rates. 

• Clogging of trenches could occur

over time due to accumulation of

fine particles. If an infiltration

trench becomes clogged, replace

the top layer of the trench where

fines have concentrated.

26
Native Landscaping . . . native plants have a

tremendous root architecture that builds soil quality and increases

organic matter content. High organic matter content helps soil hold

water like a sponge and infiltrate most rain. Native landscaping is a

key component of infiltration-based storm water management practices.

Design Techniques • Use native plants in landscaping

designs in conjunction with other

soil quality restoration techniques

(i.e. addressing compaction,

enhancing organic matter content).

• Devote at least 30 percent of green

space (yards, parks, campuses) to

native landscaping and direct

r u n o ff toward native landscaped

a r e a s .

• Always maintain a mowed turf

border around native landscape in

an urban setting to enhance aest h e t i c s .

• Design plantings to provide

season long

color displays.

• Some native

plants grow as

tall as 8 feet

high. Selecting

lower growing

species (3-4

feet) may provide the best

design for

urban sites.

C h a l l e n g e s / L i m i t a t i o n s

• Weed ordinances could make

native landscaping “illegal” in

some communities, as some ordinances place limitations on the

maximum height vegetative cover

can be. Variances can usually be

o b t a i n e d .

• A strong bias exists for mowed

turf and a well-groomed appearance. Perceptions of native landscaping as “wild” or “unkept”

have caused problems.

• Develop an educational campaign

to help people understand that

native lands c a p i n g

helps create

h y d r o l o g ically functional landscapes. 

A mix of native grasses and forbs are featured around

the perimeter of Coral Ridge Mall in Coralville, Iowa.

Summer Colors

Fall Colors

27
Permeable Paving Alternatives . . . p a v e r blocks, geoweb re i n f o rced gravel and grassed surfaces are permeable paving surfaces. All of these options provide the support of

traditional impervious parking surfaces while allowing water to infiltrate. Subgrade can be designed to hold varying storm sizes.

Subdrains can be used to facilitate water movement through these

systems. 

Design Techniques • Permeable paving systems can be

designed to infiltrate virtually any

design storm, including the 100-

year storm. 

• Permeable systems can be used

strategically with impervious surfaces to capture the high frequency-lower intensity storms and the

first flush of large storms. 

• Potential sites for these paving

alternatives include: parking lots,

fire lanes, off-street parking

aprons in residential neighborhoods, camping area parking

pads, driveways, bike paths and

private roads.

C h a l l e n g e s / L i m i t a t i o n s

• This practice should be used with

caution in areas underlain with

highly permeable soils (i.e., sandy

soils) where infiltrated pollutants

may reach groundwater without

the opportunity for adequate filtering and processing of pollutants. 

• The grassed paver alternatives

should not be used for high volume traffic areas. These systems

are best suited to fire lanes, overflow parking areas, or for infrequently used facilities that require

l a rge parking capacity (i.e.

churches, stadiums, malls).

Grass as a permeable paving alternative. Sub-structure of grass paving.

28
Rain Gardens . . . p o p u l a r, new perennial gardens

featuring native vegetation strategically located to capture runoff

f rom impervious surfaces such as roofs, driveways, and patios. Rain

gardens are landscaping features used by homeowners to cre a t e

beautiful yards able to absorb water, reduce runoff, protect water

q u a l i t y, and prevent flooding. They perform essentially the same

function as bioretention cells.

Design Techniques • Determine soil quality and percolation rates with a soil investigat i o n .

• Designs can be as simple as a

shallow excavation and org a n i c

matter enhancement, if good soil

quality exists. Detailed engineering of the substrate may be necess a r y, depending on soil quality

and site conditions.

• Choose a location that is at least

ten feet, but preferably 30-40 feet,

from the house. Utilize natural

depressions, if possible.

• If poor soil quality exists, soil

should be excavated and amended

with compost (and possibly sand).

• If a high water table and/or poor

percolation rates exist, a subdrain

tile should be installed. The tile

will lower the water table and

allow water to percolate through

the amended soil profile.

• Plant with colorful native flowers

and grasses. Native plants

improve soil quality to help

restore infiltration capacity.

• The surface should be 5-10 percent the size of impervious surfaces that drain into them.

• Rain gardens create functional

C h a l l e n g e s / L i m i t a t i o n s

• Urban soils are often extensively

altered and heavily compacted

during development. Compacted

soils should be excavated and

replaced with a mixture of 30

percent sand/30 percent compost/40 percent soil.

• In some cases, outlets for a drain

tile may not be easily accessible.

• French drains (holes drilled

through compacted layers and

filled with porous material) can

sometimes substitute for drain

t i l e s .

For more information about rain gardens,

visit:

www.mninter.net/~stack/rain/

www.raingardens.org

landscapes by infiltrating rainwater and by processing pollutants.

Deep rooted natives can also “dewater” the soil profile by “breathing” water vapor into the atmosp h e r e .

• Rain barrels can store rainfall for

watering rain garden plants until

they are established. Rain barrel

overflows should be directed to

rain gardens.

29
Soil Quality Restoration . . . key to restoring soil quality is reducing soil compaction and increasing organic

matter content. In urban communities the soils are often disturbed

and severely compacted. Topsoil is generally thin with low organic

matter.

Design Techniques • Restoring soil quality is a water

quality management practice. A

healthy soil profile has high

o rganic matter content and 50 percent pore space. High org a n i c

matter content allows water to be

absorbed and infiltrated. A d e q u a t e

pore space in the soil profile

allows water to be stored on-site.

• Compacted soils lack pore space

which prevents infiltration and

storage of water. Minimize land

disturbing activities to prevent

c o m p a c t i o n .

• Where compaction can’t be avoided, perform deep tillage before

establishing vegetative cover (see

photo at right).

• Add compost to

achieve higher

o rganic matter

content. Org a n i c

matter a b s o r b s

rainfall and facilitates infiltration.

C h a l l e n g e s / L i m i t a t i o n s

• Soil quality restoration needs to be

recognized as a viable component

of a storm water management system. Enhancing soil quality

reduces the amount of runoff that

is shed and improves water quality

by absorbing and processing pollutants moving in the first flush of

any runoff event.

• Compaction is generally widespread in urban areas due to grading activities associated with

development. Compaction is the

most difficult challenge when

attempting to restore soil quality.

• Performing deep tillage can be

challenging in

constrained settings.

30

Utilize One-Call to locate all utilities prior to

performing deep tillage. 

“I think the biggest problem caused by construction is com -

paction. If planners were to develop pre-plans that address con -

trolling traffic and unnecessary soil disturbance, runoff would

be reduced.” -Mike Sucik, State Soil Scientist, Iowa NRCS
Final Thoughts

Helpful Websites:

www.ia.nrcs.usda.gov

www.iamu.org

www.urbanwaterquality.org

www.epa.gov

www.stormh2o.com

www.cwp.org

www.lowimpactdevelopment.org

w w w. s t o r m wa t e r c e n t e r. n e t

w w w. g r e e n i n f ra s t r u c t u r e. n e t

w w w. r m i . o r g

Photos & Content Provided By:

Lynn Betts, NRCS

Randy Cooney, IDALS-DSC

Express Blower, Inc.

Iowa Department of Natural Resources

ISU Extension Service

Jason Johnson, NRCS

Stacie Johnson, Iowa Mulch

Rich Maaske, IDALS-DSC

Dan Mays, Scott Co. Master Gardener

Paul Miller, NRCS

Mark Muller, Down To Earth Graphics

Jim Patchett, CDF, Inc.

Wayne Petersen, NRCS

Jay Riggs, Dakota SWCD

Dick Tremain, NRCS

Jennifer Welch, URBAN

Conservation for urbanizing landscapes is a rapidly evolving field.

New techniques are emerging and

new products are constantly being

developed. It is imperative that conservationists, developers, engineers,

and municipal officials stay flexible

and stay abreast of the changes that

will continue to unfold. 

This brochure provides a snapshot

of the industry as of 2004. Not all

practices or products are included

in this brochure. However, the most

common, effective, and most promising practices are highlighted. 

Some of the newest practices may

not have design standards and specifications developed yet. NRCS is

partnering with a number of entities

to update the erosion and sediment

control chapter and the storm water

management chapter of Iowa’s

Statewide Urban Design and

Specifications (SUDAS) manual.

The SUDAS manual will be

reviewed annually and include standards and specifications for the

newest practices. This manual will

give design professionals the tools

needed to help communities comply with water quality regulations. 

Many different options are available when deciding on a system of

practices to enhance construction

site erosion and sediment control

and improve storm water management. NRCS can provide planning

and technical assistance to help

meet conservation needs in the

urbanizing areas of Iowa. 

31

 ̈
Developed in cooperation with:

• Environmental Protection Agency (EPA)

• Iowa Association of Municipal Utilities (IAMU)

• Iowa Department of Agriculture and Land

Stewardship (IDALS)

• Iowa Department of Natural Resources (DNR)

• Iowa State University Extension Service

• Urban Resources & Borderland Alliance Network

(URBAN)

The U.S. Department of Agriculture (USDA)

prohibits discrimination in all its programs and

activities on the basis of race, color, national

origin, gender, religion, age, disability, political beliefs, sexual orientation, and marital or

family status. (Not all prohibited bases apply

to all programs.) Persons with disabilities who

require alternative means for communication

of program information (Braille, large print,

audiotape, etc.) should contact USDA’s TARGET Center at 202-720-2600 (voice and

TDD). 

To file a complaint of discrimination, write

USDA, Director, Office of Civil Rights, Room

326W, Whitten Building, 14th and

Independence Ave., SW, Washington, DC

20250-9410 or call (202) 720-5964 (voice or

TDD). USDA is an equal opportunity provider

and employer.