Soil Erosion from Two Small Construction Sites, Dane County, Wisconsin

U.S. Department of the Interior

U.S. Geological Survey

USGS Fact Sheet FS-109-00

August 2000

Introduction

Soil erosion from construction sites has long been identified as a significant

source of sediment and other suspended solids in runoff in many parts of the

United States (Hagman and others, 1980; Yorke and Herb, 1976; Becker and

others, 1974). In some states, such as Wisconsin, sediment has been identified

as the number one pollutant (by volume) of surface waters (Wisconsin Department of Natural Resources, 1994). Because numerous water-quality problems

in streams are associated with excessive sedimentation, Federal and state

regulations requiring erosion-control measures at construction sites larger than

5 acres have been developed and implemented from the 1970’s to the present.

During the 1990’s, excessive erosion and sediment production associated with

small residential and commercial sites of less than 5 acres has been increasingly

recognized for its effects on streams—not only erosion from individual sites but

also erosion from discontinuous groups of sites within a stream basin.

Currently, most Federal, state, and local construction regulations require

some type of erosion control plan for sites disturbing more than 5 acres. On sites

less than 5 acres, minimal erosion control measures are required. In most

instances, only perimeter controls (silt fences and straw bails) and tracking pads

(crushed stone or gravel at vehicle access points) are required as erosion control

practices. In the U.S. Environmental Protection Agency Phase II Stormwater

Rules, erosion control will be required on sites less than 5 acres (small

construction sites) beginning in 2003. The purpose of the project was to evaluate

the significance of erosion on construction sites less than 5 acres as a source of

sediment to surface waters.

Why study small construction sites?

Water-quality impacts

When left uncontrolled, large amounts of soil and other small particles—

collectively called sediment—can move off of construction sites along with

other attached pollutants. By volume, sediment is the greatest pollutant entering

our surface waters, and causes multiple problems. Sediment buries plant and

animal habitat critical to healthy streams, lakes, and wetlands. Loss of habitat

reduces the number, diversity, and productivity of plants and animals living in

aquatic environments. Sediment that remains suspended in the water column

reduces water clarity, inhibits aquatic plant growth, lowers the esthetic and

recreational values of water resources, and makes it difficult for some fish to

find food. Suspended sediment increases the solar heating of water, scours

aquatic life in streams, and clogs the gills of fish and aquatic insects. Warm

water holds less oxygen than cooler water (oxygen is vital to aquatic animals)

and increased water temperatures are stressful to coldwater fish such as trout.

Particulate-bound nutrients, such as phosphorus delivered to surface waters by

eroded soils, often causes algal blooms and alterations in the food chains, which

further reduces the quality of these water resources.

Number of construction sites in Dane County, Wisconsin

Hundreds of small and potentially problematic construction sites are being

built upon in Dane County, Wisconsin, as urban and suburban development

rapidly expands into the surrounding rural areas. For example, residential

building permits issued in Dane County increased 15 percent in a single year,

from 1,489 in 1997 to 1,709 in 1998 (Rosenberg, 1999). As urban sprawl

continues in Dane County and in many other rapidly developing areas of the

United States, erosion control at small construction sites will become an

increasingly important issue as the water quality of streams, rivers, and lakes

becomes degraded by sediment.

Cumulative effect of small construction sites

The cumulative effect of construction activities on a small site can be

significant when compared to the platting (installation of roads, sewers, and

utilities) of the subdivision. Several reasons exist:

• Paved roads, curbs and gutters, and storm sewers effectively convey runoff

water and associated sediment away from the sites.

• More equipment and vehicles are taken on and off the small construction sites

per unit area than for platting; this causes mud and debris to be tracked from

the site and also causes increased soil compaction, which reduces infiltration

Overview

Numerous studies have shown that the amount of sediment transported by stormwater runoff from large construction sites (greater

than 5 acres) with no erosion control practices in place is significantly

greater than from sites with erosion controls (U.S. Environmental

Protection Agency, 1999). This Fact Sheet evaluates water-quality

data collected by the U.S. Geological Survey (USGS) and the Dane

County Land Conservation Department from June 1998 to July 1999

from two small construction sites (less than 5 acres)—one residential

and one commercial—in Dane County, Wisconsin (fig. 1). Study data

characterizing the magnitude of erosion from these two typical small

construction sites will be used in the formulation of U.S. Environmental

Protection Agency’s National Pollution Discharge Elimination System

(NPDES), regulations requiring erosion control practices on construction sites that disturb less than 5 acres.

Results of this USGS/Dane County Land Conservation study indicated that small construction sites are potential sources of large

amounts of sediment erosion. Sediment loads from the two monitored

construction sites were 10 times larger than typical loads from rural

and urban land uses in Wisconsin. Total and suspended solids concentrations data indicate the active construction phase produced concentrations that were orders of magnitude higher than pre- and postconstruction periods. Furthermore, these concentrations were dramatically reduced when the site was seeded and mulched. These

results support the need to design and implement erosion control

plans.

Figure 1. Location of study sites in Dane County.

Cities, towns, and villages

Commercial construction site

Residential construction site

0 5 10 MILES

0 5 10 KILOMETERS

EXPLANATION

WISCONSIN

DANE COUNTY
and increases runoff volume. The tracked mud and debris is deposited on the

roads, which are usually connected to the stormwater drainage system.

• Erosion rates caused by construction activities have the potential to be higher

than erosion rates from platting because of the steep, uncovered high-slope

soil piles that are created when topsoil is stripped and when basements or

foundations are excavated.

How and when were the Dane County sites studied?

Site selection

Two small construction sites in Dane County, one residential and one

commercial, were selected to represent typical construction activity on sites less

than 5 acres in size (fig. 1). The residential lot was 0.34 acres with an average

slope of 8 percent, and the commercial office development lot was approximately 1.72 acres with an average slope of 4 percent.

Sites were selected on the basis of five criteria:

1. The site had to be stabilized or without construction activity for a sufficient

period to allow for pre-construction monitoring of water quantity and water

quality.

2. The site had to accommodate small wing walls or other structures that would

direct discharge from a significant area of the site to a single discharge point.

3. The site had to be smaller than 5 acres.

4. Construction on the site had to be completed by September 1998.*

5. The builder had to agree to the proposed monitoring plan.

*Note: Some changes in scheduling occurred after site selections were made.

Site monitoring

Because the objective of the study was to quantify the movement of soil

during construction activity, erosion control practices were not evaluated as

part of this study. At both the commercial site and the residential site, erosion

controls were placed downstream from the monitoring equipment. The monitoring equipment installed at each site is shown and described in figure 2.

Data were recorded hourly during dry periods. Rainfall and flume water

Table 1. Summary table for the sampled runoff events for (A) the commercial construction site, and (B) the residential construction site [Precip.,

precipitation; lbs, pounds; mg/L, milligrams per liter]

Photo 2. Residential

construction site after

monitoring equipment

was installed in June

1998.

Photo 1. Water-quality samples from

the commercial construction site.

levels were recorded every minute during periods of rainfall and runoff.

Collection of individual water-quality samples was triggered by the datalogger

during runoff by using time pacing (for example, 5 minutes between samples).

This time pacing could be adjusted to ensure that the samples were representative of the entire storm, particularly the period of increasing runoff in the

beginning.

Samples were split and processed for analysis. Processed samples were

taken to the Wisconsin State Laboratory of Hygiene for determination of the

concentrations of total and suspended solids (the measures used to represent

sediment).

Load computation

Solids loads were computed by multiplying runoff volume, solids concentration, and a constant for unit conversion. The loads, rainfall, and runoff

A. Tipping-bucket raingage to measure

rainfall depth and intensity;

B. Datalogger to record data from the

sensors, trigger the collection of

samples, and alert USGS personnel

about rainfall and runoff;

C. Modem to retrieve data and to monitor

sites during rainfall and runoff;

D. Automatic water-quality sampler to

collect samples during storms;

E. Pressure transducer and flume to

measure water level and estimate

runoff volume; and

F. Plywood wingwalls to funnel runoff

from the site to a single discharge

point.

Figure 2. Monitoring equipment installed at construction sites.

Monitoring equipment includes:

D

F

E

A

B, C

Active construction samples

Pre-construction

sample

Commercial construction site

Sampled runoff event

Storm

information

Event mean

Average solids loads concentration (EMC)

B-1

B-2

B-3

B-4

B-5

B-6

B-8

B-10

B-12

B-13

B-14

B-15

B-16

B-17

B-18A,B

B-19

B-20

6/27/98 

7/3/98

7/6/98

7/7/98 

7/19/98 

7/20/98

8/4/98

8/23/98

10/5/98

10/17/98

11/9/98

4/21/99

5/16/99

5/23/99

6/1/99

6/4/99

6/6/99

0.3

901

25

528

325

342

136

1579

100

399

107

87

318

18.1

7.9

3.5

24

Total

solids

(lbs) Number Start

date

Pre

Active

Active

Active

Active

Active

Active

Active

Active

Transition

Transition

Transition

Transition

Post

Post

Post

Post

Construction

phase

1.92

0.72

0.26

0.32

0.80

0.61

0.50

0.96

0.45

0.80

0.72

0.46

1.49

0.42

0.67

0.27

1.01

Precip.

depth

(inches)

Runoff

volume

(cubic feet)

0.2

931

26

581

327

272

129

1479

91

389

96

81

288

12.5

5.3

2.4

20

Suspended

solids

(lbs)

94

22,285

16,216

17,700

22,176

19,939

2,574

14,803

1,925

3,211

1,134

1,364

2,237

255

76

86

159

Suspended

solids

(mg/L)

138

21,580

15,605

16,086

22,032

25,065

2,721

15,803

2,117

3,296

1,263

1,462

2,475

368

114

124

193

Total

solids

(mg/L)

A

32

669

26

526

236

219

803

1,601

756

1,940

1,351

952

2,059

788

1,112

455

1,983

Residential construction site

SH-1

SH-2

SH-4

SH-5

SH-6

SH-7

SH-8

SH-9

SH-10

SH-11

SH-12

SH-13

SH-14

SH-15

Pre

Pre

Pre

Pre

Pre

Pre

Pre

Pre

Active

Active

Active

Post

Post

Post

14,029

1,408

837

523

1,079

149

336

168

2,999

3,576

1,789

85

150

161

14,074

1,298

740

414

986

84

249

71

2,587

3,074

1,503

19

69

57

Sampled runoff event

Storm

information

Event mean

Average solids loads concentration (EMC)

314

11.3

4.07

5.45

26.5

0.924

2.97

0.407

57.8

39.7

7.70

0.602

0.655

0.568

Total

solids

(lbs) Number

6/27/98

7/20/98

8/4/98

8/4/98

8/24/98

9/14/98

10/5/98

10/17/98

11/9/98

4/8/99

4/21/99

7/17/99

7/19/99

7/20/99

Start

date

Construction

phase

0.81

1.07

0.69

0.48

0.70

2.10

0.98

0.99

1.72

1.95

1.07

1.60

0.40

0.53

Precip.

depth

(inches)

Runoff

volume

(cubic feet)

315

10.5

3.60

4.31

24.2

0.519

2.20

0.172

49.9

34.2

6.47

0.135

0.303

0.202

Suspended

solids

(lbs)

Suspended

solids

(mg/L)

Total

solids

(mg/L)

B

359

129

78

167

394

99

142

39

309

178

69

113

70

57
summaries are presented in tables 1A and 1B. Event-mean concentrations

(EMC’s) were computed by dividing the average load by the runoff volume and

a unit conversion factor. Regression models were developed for the EMC’s for

each phase of construction (pre-construction, active construction, transition and

post-construction) for each construction site using 5-minute maximum intensity and total precipitation depth. This regression model was used to estimate

loads for the nonsampled storms so that an annual load could be computed. Total

solids analysis quantifies the suspended and dissolved solids in a sample. In

general, values for total solids should be greater than those for suspended solids,

but analysis errors can cause values for suspended solids to be greater than those

for total solids.

Construction and monitoring timelines

Commercial site

Pre-construction-phase monitoring began on June 20, 1998. A storm on June

27, 1998 was the only pre-construction storm that produced runoff. Despite a

1.92-inch rainfall, only 0.2 pounds of suspended solids were measured in runoff

(table 1A and photo 1). This was the largest storm during the study, yet it

represented the smallest amount of suspended solids discharged in runoff.

Active construction began the first week of July 1998 and continued through

the storm on October 17, 1998. This timing was critical because it occurred

during the summer months when the highest rainfall intensities occurred.

Landscaping and site stabilization (transition phase) began in November

1998 and was completed in May 1999. Suspended-solids loads measured in

storm runoff decreased substantially during this phase, coincident with stabilization of soil at the site.

Residential site

Pre-construction-phase monitoring began on the residential site in June

1998. Initial sediment concentrations and loads from the first monitored storm

(June 27, 1998), (SH-1, table 1B) were significantly higher than the events

sampled later. This was because the site had very little vegetative cover, making

it susceptible to erosion (photo 2). The site was seeded with annual rye grass to

help prevent erosion. Suspended solids loads in runoff during subsequent

storms dropped dramatically after the grass cover was established. This reinforced the importance of proper seeding and mulching to reduce runoff.

Active construction began in November 1998 and was completed in May

1999. Three storms were monitored during the active construction phase.

Because most of the construction took place during the winter months when the

ground was frozen, few storms produced runoff. Those storms, however, did

show that residential development could be a significant source of suspended

solids.

Post-construction monitoring resumed after the site was considered stable.

Three events were monitored during July 1999; all sampling results indicated

very low suspended-solids loads.

What were the results?

Construction phase producing the most sediment

A summary of the data collected during runoff events at the two sites (tables

1A and 1B and fig. 3 show that during active construction, the average EMC of

solids increased dramatically when compared to pre-construction and postconstruction EMC’s. This finding indicates that the active construction phase

is the most important phase to control.

Factors affecting sediment production

Several factors contributed to increased erosion during active construction.

First, the vegetative cover is removed from the site. Vegetative cover reduces

raindrop energy, and plant roots hold the soil in place. When vegetation is

removed, the protective cover is removed. Seeding and site stabilization

substantially reduce the concentration of solids in the runoff. A dramatic

reduction in EMC for both sites after stabilization is depicted in figure 3.

Second, heavy equipment compacts the soil, resulting in increased runoff

volume. This is demonstrated by sampled events B-1 and B-2 (table 1A). A

1.92-inch, high-intensity rainfall on June 27, 1998, produced a runoff volume

of 32 cubic feet, whereas a 0.72-inch rainfall on July 3, 1998 just after the soil

was stripped produced 670 cubic feet of runoff.

Differences between event mean concentrations of solids

The primary reason for between-site differences in EMC’s was the time of

active construction. Construction at the commercial site was completed during

the summer, when short, but high-intensity rainfalls are common; in contrast,

the residential active construction was completed during the winter, when rain

tends to fall at low intensity in protracted periods. Evidence indicates that the

EMC’s at the residential site would be as high as those of the commercial site

if the active construction period occurred during the summer months. The first

sampled storm at the residential site was monitored when the site was similar

to an active construction site. Much of the ground had little or no cover (photo

2). The EMC for that storm (SH-1) was 14,000 mg/L, which was similar to that

for several storms monitored at the commercial site.

Application of Universal Soil Loss Equation

The Universal Soil Loss Equation (USLE) (Wischmeier and Smith, 1978)

predicted a soil loss of 8.8 tons for the commercial site and 1.7 tons for the

residential site over the construction period. As is evident from figure 4,

agreement between predicted soil loss and actual sediment load is closer for the

commercial site.

Several factors explain the difference between the sum of the monitored and

estimated loads and the predicted loads at the residential site. The first is that

Figure 4. Predicted (by USLE), monitored, and estimated total and suspended solids loads for the commercial and residential construction sites.

Figure 3. Average event mean concentrations for total and suspended

solids for the commercial and residential construction sites. 2,800 140 2,100 200640

0

100

130

2,000

140

550

2,400

0

50

15,000 15,000

0

2,000

4,000

6,000

8,000

10,000

12,000

14,000

16,000

Pre-construction

Active construction

Transition

Post-construction

Pre-construction

(Does not include SH-1 storm)

Active construction

Transition

Post-construction

SOLIDS CONCENTRATION, IN MILLIGRAMS PER LITER

Total solids

Suspended solids

Commercial site Residential site

CONSTRUCTION PHASE

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

Total

solids

Suspended

solids

Predicted

solids

SEDIMENT LOAD, IN TONS

Residential site

1

0

2

3

4

5

6

7

8

9

10

Total

solids

Suspended

solids

Predicted

solids

Commercial site

Predicted

Monitored

Estimated

for unsampled

runoff events

Predicted

Monitored

Estimated

for unsampled

runoff events
Information

For information on this study or on other USGS programs in Wisconsin,

contact:

District Chief

U.S. Geological Survey

8505 Research Way

Middleton, WI 53562

(608) 828-9901

http://wi.water.usgs.gov/

Authors: David W. Owens1, Peter Jopke2, David W. Hall1,

Jeremy Balousek2, and Aicardo Roa2

1

U.S. Geological Survey, Middleton, Wis.

2

Dane County Land Conservation Department, Madison, Wis.

Printed on recycled paper

active construction took place during the winter months, when the monitoring

equipment was deactivated. A second reason is that the USLE predicts soil

erosion, not sediment yield. Soil erosion is the process of soil particles being

detached from the soil surface. Sediment yield, on the other hand, is the process

of detached soil being transported from a specific area. Not all soil that is eroded

will leave the site; therefore, the sediment yield should be lower than the amount

of soil that is eroded. The monitoring results indicate the amount of soil that is

leaving the construction site, which is sediment yield.

Comparison of unit-area loads

Comparisons of sediment yield from various land uses can be made if the

yields are expressed as unit-area loads, which are defined as the mass of a

particular constituent transported by a stream, divided by the drainage area of

the watershed (Corsi and others,1997). For this study, the loads from the two

construction sites were converted to pounds per acre. Data from the construction sites were based on one year of monitoring and represent the total load

estimated for that given year. The unit-area loads for other land-use categories

(fig. 5) reflect the median load from multiple years of data. The relative

significance of construction is evident in figure 5.

References Cited

Becker, B.C., Nawrocki, M.A., and Sitek, G.M., 1974, An executive summary of

three EPA demonstration programs in erosion and sediment control: Washington,

D.C., U.S. Environmental Protection Agency Report EPA-660/2-74-073

Corsi, S.R., Graczyk, D.J., Owens, D.W., and Bannerman, R.T., 1997, Unit-area

loads of suspended sediment, suspended solids, and total phosphorus from small

watersheds in Wisconsin: U.S. Geological Survey Fact Sheet FS-195-97, 4 p.

Hagman, B.B., Konrad, J.G., and Madison, F.W., 1980, Methods for controlling

erosion and sedimentation from residential construction activities, in National

Conference on Urban Erosion and Sediment Control—Institutions and Technology, October 10-12, 1979, St. Paul, Minnesota: U.S. Environmental Protection

Agency Report EPA-905/9-80-002, January, 1980.,p. 99–105

Rosenberg, S., Madison Area Builders Association, March 30, 1999, personal

communication

U.S. Environmental Protection Agency, 1999, National Pollution Discharge Elimination System - Storm Water Phase II, Federal Register, Vol. 64, No. 235,

December 8, 1999, Rules and Regulations.

Wischmeier, W.H. and Smith, D.D., 1978, Predicting rainfall erosion losses—a

guide to conservation planning: Washington, D.C., U.S. Department of Agriculture

Wisconsin Department of Natural Resources, 1994, The Wisconsin Water Quality

Assessment Report to Congress, PUBL-WR 254-94-REV, Wisconsin Department of Natural Resources, Madison, Wis.

Yorke, T.H., and Herb, W.J., 1976, Urban-area sediment yield effects of construction site conditions and sediment control methods, Proceedings of the Third

Federal Inter-Agency Sedimentation Conference, 1976, Denver, Colorado, March

22-25, 1976: Water Resources Council, Sedimentation Committee, p. 2-52

through 2-64

Acknowledgments

We would like to thank the Dane County Lakes and Watersheds Commission

for providing printing costs. We would also like to thank the Blettner Group and

homeowners Ron and Karen Blawusch for cooperating and providing access to

their property.

Figure 5. Unit-area solids loads for residential and commercial construction

sites, compared with state summaries for urban and rural land uses.

Rainfall during study period

The rainfall during the monitoring period was close to the 30-year long-term

average for Madison, Wis. (fig. 6). The exception was April 1999, when the

rainfall was nearly double the long-term average for that month.

First flush phenomenon

The data do not show a direct correlation between sediment yield and the first

rainfall (first flush) during the active construction phase. Discrete concentrations of total and suspended solids were related more to rainfall intensity than

the first flush.

Application of results to other areas

The project results show the magnitude of the erosion problem for small

construction sites. Soil type, site slope, type of erosion control practices

installed, rainfall depth and intensity, and other factors play a large role in

erosion and transport of sediment off the site. This project serves as an indicator

that small construction sites are a significant contributor of sediment loading to

surface waters if proper erosion controls are not implemented.

Figure 6. Normal (30-year) monthly precipitation and monitored precipitation at the commercial and residential construction sites.

350

410

6,750

1,650

0 2,000 4,000 6,000 8,000

SUSPENDED SOLIDS, IN POUNDS PER ACRE

State summary (rural)

State summary (urban)

Commercial construction site

(summer construction)

Residential construction site

(winter construction)

0

1

2

3

4

5

6

7

Jul. Aug. Sep. Oct. Nov. Dec. Jan. Feb. Mar. Apr. May Jun. Jul.

Normal monthly precipitation,

1961–90

Monitored precipitation at the

commercial construction site

Monitored precipitation at the

residential construction site

PRECIPITATION, IN INCHES