U.S. Department of the Interior

U.S. Geological Survey

Water-Resources Investigations Report 03-4163

In cooperation with the Wisconsin Department of Natural Resources

Effects of Best-Management Practices in the Black 

Earth Creek Priority Watershed, Wisconsin, 1984–98
Effects of Best-Management Practices 

in the Black Earth Creek Priority 

Watershed, Wisconsin, 1984–98

By D.J. Graczyk1, J.F. Walker1, J.A. Horwatich1, and R.T. Bannerman2

In cooperation with the Wisconsin Department of Natural Resources

1

U.S. Geological Survey, 2Wisconsin Department of Natural Resources

Water-Resources Investigations Report 03–4163

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

Gale A. Norton, Secretary

U.S. Geological Survey

Charles G. Groat, Director

U.S. Geological Survey, Reston, Virginia: 2003

For sale by U.S. Geological Survey, Information Services

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Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply 

endorsement by the U.S. Government.
iii

Contents

Abstract.................................................................................................................................................. 1

Introduction ........................................................................................................................................... 1

Purpose and Scope ..................................................................................................................... 2

Physical Setting and Land Use.................................................................................................. 2

Methods ................................................................................................................................................. 4

Data-Collection Network............................................................................................................ 4

Selection and Inventory of Watersheds .................................................................................. 5

Hydrologic Conditions During the Study Period .............................................................................. 7

Precipitation ................................................................................................................................. 7

Streamflow.................................................................................................................................. 10

Water Quality Before and After Installation of Best-Management Practices ......................... 13

Nutrient and Sediment Concentrations at Base Flow ......................................................... 13

Storm Loads................................................................................................................................ 17

Effects of Specific Management Practices ................................................................................... 19

Summary and Conclusions................................................................................................................ 22

References Cited ................................................................................................................................ 23

Figures

 1. Map showing the location of the Black Earth Creek watershed in 

Dane County, Wis., and data-collection sites................................................................. 3

 2. Pie charts showing percentage of total land use and land cover for 

Brewery and Garfoot Creek watersheds, Dane County, Wis....................................... 4

 3. Map showing eligible and implemented best-management practices 

(BMPs), Brewery and Garfoot Creek watersheds, Dane County, Wis. ...................... 6

 4–12. Graphs showing:

 4. Yearly precipitation at Brewery and Garfoot Creeks and 1961–90 

 normal precipitation at Madison, Wis....................................................................... 7

 5. Histograms of precipitation events at Brewery Creek, Dane County, 

 Wis., for which storm loads were calculated.......................................................... 8

 6. Histograms of precipitation events at Garfoot Creek, Dane County, 

 Wis., for which storm loads were calculated.......................................................... 9

 7. Streamflow characteristics for Brewery Creek, Dane County, Wis. ................. 10

 8. Streamflow characteristics for Garfoot Creek, Dane County, Wis. ................... 12

 9. Streamflow characteristics for Black Earth Creek, Dane County, Wis............. 13

 10. Annual streamflow and base flow with 3-year moving average for 

 Black Earth Creek, Dane County, Wis., 1955–98 water years ............................. 14

 11. Concentrations and water-year medians of suspended sediment 

 and nutrients in base-flow samples during the data-collection 

 period at Brewery Creek, Dane County, Wis. ........................................................ 15

 12. Concentrations and water-year medians of suspended sediment 

 and nutrients in base-flow samples during the data-collection 

 period at Garfoot Creek, Dane County, Wis. .......................................................... 16
iv

Tables

 1. Summary of eligible and implemented rural best-management 

practices in the Brewery and Garfoot Creek watersheds, Wis................................... 5

 2. Summary of streamflow characteristics for Brewery, Garfoot, 

and Black Earth Creeks, Wis., for pre-and post-BMP periods .................................. 11

 3. Peak streamflow and selected recurrence intervals for Black 

Earth Creek,Wis., 1954–98 ................................................................................................ 11

 4. Results of the Kendall test of trend in streamflow characteristics, 

Black Earth Creek near Black Earth, Wis., water years 1954–98 .............................. 12

 5. Results of the Wilcoxon rank-sum test on the median concentrations 

of suspended sediments and nutrients at base flow, pre- and post-BMP 

periods, Brewery and Garfoot Creeks, Wis................................................................... 17

 6. Regression results for storm loads at Brewery and Garfoot Creeks, Wis. .............. 18

 7. Results of the Wilcoxon rank-sum test comparing storm loads and 

storm-load residuals for pre- and post-BMP periods at Brewery and 

Garfoot Creeks, Wis. ......................................................................................................... 19

 8. Matrix of interactions between BMPs and different aspects of water 

quality, with statistical test results from comparing pre-to post-BMP 

periods for a generalized watershed, at Brewery and Garfoot Creek 

watersheds, Wis. ............................................................................................................... 20
v

Conversion Factors and Abbreviations

Multiply By To obtain

Length

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

acre 0.4047 square hectometer (hm2

) 

square mile (mi2

) 2.590 square kilometer (km2) 

Flow rate

cubic foot per second (ft3

/s) 0.02832 cubic meter per second (m3/s)

Mass

pound, avoirdupois (lb) 0.4536 kilogram (kg) 

Hydraulic gradient

foot per mile (ft/mi) 0.1894 meter per kilometer (m/km)

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as 

follows:

 °F=(1.8×°C)+32

Abbreviated water-quality units used in this report: Chemical concentrations and water 

temperature are given in metric units. Chemical concentration is given in milligrams 

per liter (mg/L), micrograms per liter (μg/L). Milligrams per liter is a unit expressing the 

concentration of chemical constituents in solution as weight (milligrams) of solute per 

unit volume (liter) of water. One-thousand micrograms per liter is equivalent to 1 milligram 

per liter. For concentrations less than 7,000 mg/L, the numerical value is the same as for 

concentrations in parts per million.

Water year: Water year in USGS reports dealing with surface-water supply is the 12-month 

period October 1 through September 30. The water year is designated by the calendar year 

in which it ends and includes 9 of the 12 months. Thus, the year ending September 30, 1998, 

is called the “1998 water year.”
vi
Effects of Best-Management Practices in the Black 

Earth Creek Priority Watershed, Wisconsin, 1984–98

By D.J. Graczyk1, J.F. Walker1, J.A., Horwatich1, and R.T. Bannerman2

reductions between the pre- and post-BMP periods likely 

are results of the installed BMPs.

The effectiveness of the BMPs on water quality are 

watershed specific. The effectiveness of the practice will 

depend on the type, number, and location of the BMPs 

implemented.

Introduction

Nonpoint-source contamination is a major contributor 

to water-quality problems in many watersheds. In recognition of the importance of nonpoint sources, the Wisconsin 

Nonpoint Source Water Pollution Abatement Program 

(Nonpoint Program) was enacted in 1978. When first 

introduced, the Nonpoint Program identified problems 

in 130 of the 330 watersheds in Wisconsin. For a given 

watershed, various management options—termed bestmanagement practices (BMPs)—are available for funding support through the Nonpoint Program. For example, 

practices in rural areas include conservation tillage, 

contour strip-cropping, streambank protection, and various 

barnyard-runoff controls. Using priority watersheds as a 

unit for consideration, the Nonpoint Program provides 

matching funds to landowners for voluntary implementation of various BMPs.

The U.S. Geological Survey (USGS), in cooperation with the Wisconsin Department of Natural Resources 

(WDNR), studied the Black Earth Creek watershed in 

southern Wisconsin from October 1984 through September 1986 to assess the hydrology, aquatic macrophytes, 

and water quality of Black Earth Creek and its tributaries. 

Streamflow and water-quality data were collected continuously at one site on a cold-water trout stream (Garfoot 

Creek near Cross Plains) and one site on a warm-water 

stream (Brewery Creek at Cross Plains).

Abstract

The Wisconsin Department of Natural Resources 

and the U.S. Geological Survey began a comprehensive, 

multidisciplinary evaluation-monitoring program in 1989 

to assess the effectiveness of the Wisconsin Nonpoint 

Source Program. Hydrologic and water-quality data were 

collected at Brewery and Garfoot Creeks in 1984 and 1985 

(pre-best-management practices (BMPs) period) and 1997 

and 1998 (post-BMP period). In rural areas, best-management practices may include conservation tillage, contour 

strip-cropping, streambank protection, and various barnyard-runoff controls. Water-quality samples were collected 

during base flow and storms. 

At Brewery Creek, no statistically significant differences in the median base flow water-quality concentrations 

between the pre- and post-BMP periods. At Garfoot Creek, 

the median suspended-sediment concentration at base flow 

decreased by 41 percent between the pre- and post-BMP 

periods and the median ammonia nitrogen concentration 

decreased by 67 percent. Both of these differences were 

statistically significant at the 0.05 (probability) level.

For both Brewery and Garfoot Creeks, the median 

storm loads for suspended sediment, total phosphorus, and 

ammonia nitrogen were compared statistically by means of 

the Wilcoxon rank-sum test. This test also was applied to 

regression residuals for differences between the preand post-BMP periods. For Garfoot Creek, only the 

median load for ammonia nitrogen shows a statistically 

significant difference between the pre-and post-BMP periods. None of the median storm loads for Brewery Creek 

were statistically significant at the 0.05 level. The decrease 

of the regression residuals between the pre- and post-BMP 

periods for ammonia nitrogen at Brewery Creek and for 

total phosphorus and ammonia nitrogen at Garfoot Creek 

all were statistically significant at the 0.05 level. These 

1

U.S. Geological Survey, 2Wisconsin Department of Natural Resources
2 Effects of Best-Management Practices in the Black Earth Creek Priority Watershed, Wisconsin, 1984–98

The information presented in a report from that study 

included determination of (1) streamflow, (2) aquatic 

macrophyte species and biomass, (3) suspended-sediment, 

total phosphorus, and total nitrogen loads, (4) miscellaneous water-quality characteristics, (5) water temperatures, 

and (6) concentrations of dissolved oxygen (Field and 

Graczyk, 1990). Data from that study were used to develop 

a plan for the control of nonpoint-source pollution and 

related resource management in the Black Earth Creek 

watershed (Wisconsin Department of Natural Resources, 

1989).

By the mid-1980s, it was clear that little data were 

available to demonstrate the effectiveness of using BMPs 

to improve water quality in Wisconsin’s priority watersheds. The WDNR and USGS developed and began a 

comprehensive, multidisciplinary evaluation-monitoring 

program in water year 1989 to assess the effectiveness of 

the Wisconsin Nonpoint Source Program (Wierl and others, 1996). This evaluation-monitoring program includes 

biological and stream-habitat monitoring by the WDNR 

and water-quality monitoring by USGS. Brewery and Garfoot Creeks were the first watersheds monitored for water 

quality. These watersheds were chosen because data prior 

to BMP implementation already were collected and 

BMPs were scheduled to be installed immediately after 

monitoring began. 

Purpose and Scope

This report summarizes the results of a study on 

effectiveness of watershed-management practices for controlling nonpoint-source contamination in the Brewery and 

Garfoot Creek watersheds. Concentrations of phosphorus, 

nitrogen, and suspended sediment at base flow before 

BMP installation (pre-BMP) are compared and contrasted 

to those for the period after BMP installation (post-BMP). 

In addition, pre-BMP storm loads are compared and 

contrasted to the storm loads post-BMP.

During October 1984 through September 1986, no 

BMPs were installed in either watershed. Installation of 

BMPs began in 1989 and was completed in 2001. Data 

collection was reinitiated in October 1989 and continued 

until September 1998. In October 1996, sufficient BMPs 

were installed in each watershed to consider the subsequent period to be the post-implementation period. For 

Brewery Creek, the pre-BMP period is from October 1984 

through September 1986. For Garfoot Creek, a sufficient 

number of pre-BMP storms had not been obtained prior 

to resumption of data collection; therefore, the pre-BMP 

period was extended and consists of October 1984 through 

April 1990. The post-BMP for Brewery Creek period is 

from October 1996 through September 1998 and for 

Garfoot Creek from April 1997 through September 1998.

Physical Setting and Land Use

Garfoot and Brewery Creeks, tributaries to Black 

Earth Creek, are in northwestern Dane County (fig. 1). 

Garfoot Creek has been classified by the WDNR as a class 

II trout stream; that is, a stream in which some natural 

trout reproduction occurs but artificial propagation is 

needed to maintain a trout fishery. Brewery Creek is a 

warm-water stream that has the potential to maintain a 

forage fish population (Wisconsin Department of Natural 

Resources, 1989). 

Garfoot Creek drains 5.39 mi2

 upstream from the 

streamflow-gaging station near Cross Plains (fig. 1), and 

the stream channel is 3.9 mi long from the station to the 

stream headwaters. The overall channel slope is 97 ft/mi, 

and the channel slope between the 10- and 85-percent 

points of the main channel is 47 ft/mi. The bed material consists mainly of sand, silt, and clay with gravel in 

riffle areas. Garfoot Creek flows along a wide valley floor 

flanked by steep valley walls. The valley floor of Garfoot 

Creek is mainly outwash and alluvium composed of sand, 

gravel, and clay (Cline, 1963). The valley walls are soilcovered sandstone, shale, and dolomite bedrock. The soils 

of Garfoot Creek are primarily silt loams; some of the silt 

loams are poorly drained, and water can pond in depressions (Glocker and Patzer, 1978.)

Brewery Creek drains 10.5 mi2

 upstream from the 

streamflow-gaging station near Cross Plains, which 

includes 2.82 mi2 of noncontributing area. The stream 

channel is 6.1 mi long from the station to the stream headwaters and has been channelized in some parts. The mainchannel slope is 40 ft/mi, and the channel slope between 

the 10- and 85-percent points of the main channel is 35 

ft/mi. The bed material of the stream channel is mostly 

soft silt and clay. Brewery Creek flows through outwash 

and alluvium composed of sandstone with some shale; 

most of the bedrock in the watershed is dolomite. The soils 

of the Brewery Creek watershed are silt loams that are 

poorly drained in valley bottoms and highly erodible in the 

uplands (Glocker and Patzer, 1978).

Total land use and land cover for Garfoot and Brewery Creeks are shown in figure 2. As of 1987, cropland 

and woodlot dominated the land use and land cover in the 

two watersheds. In the Brewery Creek watershed, cropland 
43 10'

89 40'

43 05'

89 35'

WISCONSIN

Watershed location in Dane County

0 1 MILE

0 1 KILOMETER

EXPLANATION

Stream-gaging station

Water-quality station

Rain gage

Watershed boundary

Subwatershed boundary

Black Earth

Cross

Plains

Rain gage 1

Rain gage 2

Rain gage 3

Rain gage 1

Rain gage

2

Rain gage 3

Black

Earth

Creek

Garfoot Creek

Brewery

Creek

Base from U.S. Geological Survey

Dane County base map, 1980

Figure 1. Location of the Black Earth Creek watershed in Dane County, Wis., and data-collection sites.

Introduction 3
4 Effects of Best-Management Practices in the Black Earth Creek Priority Watershed, Wisconsin, 1984–98

(57 percent) was the dominant land use and land cover, 

with woodlot (22 percent) being the next greatest land use 

and land cover. In the Garfoot Creek watershed, woodlot 

(50 percent) dominated the land use and land cover, with 

cropland (26 percent) being the next greatest land use 

and land cover. Other land use and land cover in Brewery 

Creek included grassland (5 percent), pasture (4 percent), 

and residential (3 percent). The area just upstream from 

the data-collection site was a residential area. There was 

more pasture (10 percent) and grassland (8 percent) in 

the Garfoot Creek watershed than in the Brewery Creek 

watershed (4 and 5 percent, respectively). The area just 

upstream from the data-collection site at Brewery Creek 

was a residential area. Residential development in the 

Garfoot Creek watershed, which typically was singlefamily homes on large lots, was minimal.

Methods

Data-Collection Network

Streamflow-gaging stations equipped for continuous 

recording of data were installed in October 1989 at Garfoot and Brewery Creeks at the same locations as gaging 

stations from the previous study (fig. 1). Measurements of 

streamflow were made according to standard USGS methods (Rantz and others, 1982). Streamflow measurements 

were made every 4 to 6 weeks, and more frequently during 

high flows, to define a stage-streamflow relation 

for each site.

Each gaging station was equipped with a stage-activated refrigerated water sampler for automatic collection 

of water samples representing high flows. A data logger 

was programmed to collect a sample with each 0.2- ft 

increase in stage once the stream stage reached an initial 

sampling threshold. After the stream stage peaked, a sample was collected with each 0.4-ft decrease in stage. The 

sampling strategy was designed to collect most samples 

during increasing stage when the constituent concentrations of interest would be changing the most. The samples, 

which were chilled to 4o

C after collection, were analyzed 

for suspended sediment, total phosphorus, and ammonia 

nitrogen. Samples collected were selected for analysis to 

represent variation in water quality over a range of increasing and decreasing stages. 

In addition to the automated samples, manual samples 

were collected at a fixed interval approximately every 

2 weeks in the spring, summer, and fall and once a month 

in the winter. Samples were integrated over the depth 

and width of the stream by use of a hand-held sampler 

(Edwards and Glysson, 1988). The fixed-interval samples 

were analyzed for suspended sediment, total phosphorus, 

and ammonia nitrogen.

The suspended-sediment samples were analyzed by 

the USGS sediment laboratory in Iowa City, Iowa according to USGS methods (Guy, 1973). Total phosphorus and 

ammonia nitrogen were determined by the Wisconsin 

Laboratory of Hygiene according to standard methods 

(American Public Health Association, 1985; Wisconsin 

Laboratory of Hygiene, 1992). 

Precipitation during the previous study was measured at one location at the approximate centroid of each 

watershed. Precipitation was collected in an 8-in. collector, which drained into a 3-in.-inside-diameter standpipe. 

Precipitation measurements were made every 15 minutes. 

Brewery Creek

Woodlot (22) Cropland (57)

Other (5)

Grassland (5)

Road (4)

Residential (3)

Pasture (4)

Garfoot Creek

Woodlot (50)

Cropland (26)

Pasture (10)

Grassland (8)

Other (6)

Figure 2. Percentage of total land use and land cover for 

Brewery and Garfoot Creek watersheds, Dane County, Wis.
Precipitation was collected during nonfreezing periods 

only (March 1–November 30) at the two sites.

In October 1989, three rain gages were installed in 

each watershed (fig. 1). One rain gage was at the site of 

the rain gage from the previous study. The other two rain 

gages were sited by trial-and-error to result in approximately equal Thiessen polygon areas. Thiessen polygons 

represent the areas in closest proximity to each rain gage; 

the average precipitation was computed as a weighted 

average using the Thiessen polygon areas as the weighting factor (Viessman and others, 1977). Thus, because 

the Thiessen polygon areas are approximately equal, the 

arithmetic average of the precipitation at the three rain 

gages is approximately equal to the average precipitation 

for a given watershed. Precipitation was collected in an 

8-in. collector that drained into a tipping bucket rain gage. 

Each tip represented 0.01 in. of rain; all rainfall data were 

recorded every 5 minutes. 

Selection and Inventory of Watersheds

 Inventory of the rural watersheds began in 1992 

to provide information on land-use and land-treatment 

changes that may affect water quality. A geographic information system (GIS) database contains 

the land-use and BMP inventories. 

Watershed boundaries, hydrography, 

roads, streams, woodlot, rain gages 

and BMPs were digitized from 

1:24000 topographic maps. Farm-field 

and parcel mapping was done by the 

Dane County Regional Planning Commission. Detailed descriptions of each 

watershed and the BMP program are 

reported in Rappold and others (1997), 

and Wierl and others (1996).

The Priority Watersheds Program 

selected, assessed, and approved the 

Black Earth Creek project between 

1985 and 1989. Voluntary signup 

period for BMPs started in March 

1989 and ended in March 1997. Monitoring of the post-BMP implementation started when the majority of practices were installed and operational. 

The post-BMP implementation period 

began in the Brewery Creek watershed 

on October 1, 1996, and at Garfoot 

Creek watershed in April 1, 1997.

Eligible, and installed BMPs for 

Garfoot and Brewery Creek watersheds are summarized in table 1. 

Annual updates of practices—barnyard-runoff control, streambank 

protection, and upland control—were 

obtained by contacting the Dane 

County Land Conservation Office. 

Barnyard-runoff control systems are 

installed to reduce the amount of 

organic matter reaching the stream 

by improving the cattle lots and adding 

filter strips. Streambank protection 

Table 1. Summary of eligible and implemented rural best-management practices

in the Brewery and Garfoot Creek watersheds, Wis.

[ft, feet; BMP’s, best-management practices. Table contains revisions to a BMP table previously 

published in Rappold and others (1997), which are the result of changes in practices eligible or 

implemented. Data are number of sites unless otherwise noted]

Evaluation monitoring watershed

Practice Brewery Creek Garfoot Creek

Animal-waste management

Eligible barnyard-runoff control systems 20a 7a

Implemented barnyard-runoff control systems 10b 5

Streambank protection

Eligible streambank protectionc 22,000 ft 16,800 ft

Implemented streambank protectionc 19,100 ft 16,700 ft

Eligible Fencing 1,200 ft 5,475 ft

Implemented fencing 0c 5,475 ft

Contracted stream crossing 1 4

Implemented stream crossing 1 4

Contracted grade stabilization 2 2

Implemented grade stabilization 2d 2

Upland management

Eligible nutrient management 2,440 acres 590 acres

Implemented nutrient management 1,415 acres 155 acres

Eligible upland BMPse 5,170 acres 1,520 acres

Implemented upland BMPse 1,145 acres 285 acres

a Includes barnyards that no longer have livestock: Brewery = 5, Garfoot = 1.

bTotal includes a barnyard-control system installed by landowner without cost-share funding.

cThe contracts for length of streambank protection reflect the total length of each practice. 

One eroded site can include various practices, such as riprap, shoreline and streambank stabilization, and shoreline buffers. Both banks may have been eroded and/or implemented with BMPs.

dSite eligible for BMP no longer has livestock.

e Includes an individual practice or series of practices, other than nutrient management, that 

result in a reduced pollutant source, such as contour farming, contour strip cropping, field strip 

cropping, grassed waterways, and reduced tillage.

Methods 5
6 Effects of Best-Management Practices in the Black Earth Creek Priority Watershed, Wisconsin, 1984–98

0 1 2 MILES

0 1 2 KILOMETERS Brewery

Creek

43 10'

43 08'

89 37'30"

Creek

43 06'30"

89 42'30"

89 40'30"

43 04'

Garfoot

Garfoot Creek watershed

Brewery Creek watershed

EXPLANATION

Eligible barnyard runoff BMP

Installed barnyard runoff BMP

Barnyard no longer has livestock

Implemented streambank protection BMP

Stream

Base from U.S. Geological Survey 1:24,000:

Black Earth, 1962; Cross Plains, 1962;

Middleton, 1969; Springfield Corners, 1969

Figure 3. Eligible and implemented best-management practices (BMPs), Brewery and Garfoot Creek watersheds, 

Dane County, Wis.
reduces the amount of sediment reaching the stream by 

limiting cattle access and stabilizing streambanks by various practices, including fencing and installation of watering areas in the stream. Upland-control practices reduce 

the amount of sediment and 

phosphorus by cropland and manure management on 

highly erodible lands.

In 1999, a majority of the goals set by the WDNR 

and local Land Conservation Department had been 

achieved in the Garfoot and Brewery Creeks Watersheds. 

Additional practices could be implemented for several 

years, but it was felt that most sources of nonpoint pollution had been controlled by the implemented practices. 

The land-use tracking was discontinued in 1999 when the 

post-monitoring phase ended. The status of barnyard and 

streambank-protection practices as of 1999 is shown in 

figure 3.

Hydrologic Conditions During the 

Study Period

Precipitation

The 30-year normal precipitation for the study 

area was 30.88 in. at the National Oceanic Atmospheric 

Administration (NOAA) weather station at the Madison, 

Wis., airport (National Oceanic and Atmospheric Administration, 2000). Data from the rain gages in the middle of 

each watershed show that the annual rainfall was substantially above the 30-year normal (1961–90) for 3 of the 11 

years monitored at Brewery Creek (1985, 1986, and 1993) 

and 4 of the 11 years monitored at Garfoot Creek (1985, 

1986, 1993, and 1998); in both watersheds, rainfall was 

substantially below the 30-year normal during 1 year: 

1997 for Brewery Creek and 1990 for Garfoot Creek 

(fig. 4). The largest deviation between annual precipitation 

and the 30-year normal was in water year 1993 for both of 

the rain gages (fig. 4). At Brewery Creek, the annual 

1985 1986 1990 1991 1992 1993 1994 1995 1996 1997 1998

1985 1986 1990 1991 1992 1993 1994 1995 1996 1997 1998

WATER YEAR

WATER YEAR

Long-term normal precipitation (30.88 inches)

Long-term normal precipitation (30.88 inches)

0

10

20

30

40

50

0

10

20

30

40

50

PRECIPITATION AT GARFOOT CREEK

RAIN GAGE 2, IN INCHES

PRECIPITATION AT BREWERY CREEK

RAIN GAGE 2, IN INCHES

Figure 4. Yearly precipitation at Brewery and Garfoot Creeks and 1961–90 normal precipitation at Madison, Wis.

Methods 7
8 Effects of Best-Management Practices in the Black Earth Creek Priority Watershed, Wisconsin, 1984–98

precipitation was 48.6 in. in 1993, which was 17.7 in. 

above the long-term annual normal (fig. 4). At Garfoot 

Creek, the annual precipitation was 45.4 in. in water year 

1993 which was 14.5 in. above the annual long-term 

normal (fig. 4). Ninety-three and 96 percent of the above 

normal precipitation fell in 4 months at Brewery and Garfoot, respectively, in water year 1993. The largest deviation 

between monthly precipitation and the long-term normal 

for July was in 1993 (3.4 in.). At Brewery Creek, the July 

1993 total monthly rainfall was 11.2 in., which was 

7.8 in. above normal. The total monthly precipitation for 

July 1993 was 9.9 in. at Garfoot Creek, which was 6.5 in. 

above normal.

At Brewery Creek, the lowest annual precipitation 

was 27.7 in. in water year 1997, which is 3.2 in. below the 

long-term normal. The lowest annual precipitation measured at Garfoot Creek was 26.9 in. in water year 1990, 

which is 4.0 in. below the annual long-term normal. 

A Kendall test for trend (Helsel and Hirsch, 1992) 

was done for the precipitation data collected at the 

Brewery Creek and Garfoot rain gages for the 11 years of 

record. No statistically significant trend (at the 5-percent 

significance level) was found in the annual precipitation 

at either site. A Kendall test for trend also was done for 

annual precipitation for 11 years of record at the NOAA 

rain gage at the Madison airport. Again, no statistically 

significant trend was found at the 5-percent significance 

level. Annual precipitation at the NOAA rain gage for the 

1954–98 period also had no statistically significant trend. 

The 1954–98 periods corresponds to the streamflow data 

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0

STORM PRECIPITATION, IN INCHES

0

1

2

3

4

Pre-BMP (Best Management Practice) Period

NUMBER OF STORMS

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0

STORM PRECIPITATION, IN INCHES

0

1

2

3

4

5

Post-BMP (Best Management Practice) Period

NUMBER OF STORMS

Figure 5. Histograms of precipitation events at Brewery Creek, Dane County, Wis., for which storm loads were calculated.
collected at a USGS long-term gaging station at Black 

Earth Creek near Black Earth (fig.1).

Histograms are presented for rainstorms for which 

storm loads were calculated for Brewery and Garfoot 

Creeks (figs. 5 and 6). At Brewery Creek during the preBMP period (1985 and 1986 water years), 11 precipitation 

events amounting to less than 2 in. produced surface runoff 

and subsequent storm loads (fig. 5). Two precipitation 

rainstorms were in the 2- to 4-in. range, and one precipitation rainstorm was greater than 4 in. (fig. 5). During the 

post-BMP period, there were 17 rainstorms with less than 

2 in. of total rain (fig. 5). Five rainstorms were between 

2- to 4 in. range, and one rainstorm had a total rainfall 

greater than 4 in. (fig. 5). At Brewery Creek, three fewer 

rainstorms produced surface runoff and storm loads in the 

pre-BMP period than in the post-BMP period. More rainstorms in the post-BMP period had rainfall between 

2 and 4 in.

At Garfoot Creek during the pre-BMP period 

(1985–86 and 1990 water years), there were 14 rainstorms 

with less than 2 in. of total rainfall. Three rainstorms had 

a total rainfall between 2 and 4 in. and one rainstorm had 

a total precipitation greater than 4 in. (fig. 6). During the 

post-BMP period, 15 rainstorms had total rainfall of less 

than 2 in., 1 rainstorm had between 2 and 4 in., and 

1 rainstorm had total precipitation greater than 4 in. 

(fig. 6). The distributions of pre- and post-BMP rainstorms 

that produced storm runoff are similar. There was one 

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0

STORM PRECIPITATION, IN INCHES

0

1

2

3

4

Pre-BMP (Best Management Practice) Period

NUMBER OF STORMS

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0

STORM PRECIPITATION, IN INCHES

0

1

2

3

4

5

Post-BMP (Best Management Practice) Period

NUMBER OF STORMS

Figure 6. Histograms of precipitation events at Garfoot Creek, Dane County, Wis., for which storm loads were calculated.

Hydrologic Conditions During the Study Period 9
10 Effects of Best-Management Practices in the Black Earth Creek Priority Watershed, Wisconsin, 1984–98

more rainstorm in the post-BMP period with less than 

2 in. of rain compared to the pre-BMP periods. The main 

difference is that there were more rainstorms between 

2 and 4 in. in the pre-BMP period. For the most part, the 

distributions for rainstorms that produced surface runoff 

and storm loads were similar in the pre- and post-BMP 

periods for both Brewery and Garfoot Creeks. 

Streamflow

At Brewery Creek, the mean annual streamflow 

for the study period was 2.4 ft3/s (table 2); the minimum 

annual streamflow was 0.58 ft3/s in water year 1991, and 

the maximum annual streamflow was 4.3 ft3/s in water 

year 1993 (fig. 7). At Garfoot Creek, the mean annual 

streamflow for the study period was 5.2 ft3

/s (table 2); the 

maximum annual streamflow was 7.7 ft3/s in water year 

1993, and the minimum annual streamflow was 3.2 ft3/s 

in water year 1990 (fig. 8). The mean annual streamflow at 

Black Earth Creek near Black Earth for water years 1954–

98 was 35 ft3/s (table 2); the minimum annual streamflow 

was 27 ft3/s in water year 1990 (fig. 9), and the maximum 

annual streamflow was 61 ft3/s in water year 1993 

(fig. 9). At Brewery Creek, the mean annual streamflow 

for the pre-BMP period was 3.1 ft3

/s, whereas the mean 

annual streamflow for the post-BMP period was 

2.2 ft3/s. At Garfoot Creek, the mean annual streamflow 

for the pre- and post-BMP periods were 4.9 ft3/s and 

5.8 ft3/s, respectively (table 2).

Streamflow data collected as part of this study were 

used to determine the streamflow characteristics at the 

Garfoot, Brewery, and Black Earth Creek gaging stations 

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

1985 1986 1990 1991 1992 1993 1994 1995 1996 1997 1998

0

1

2

3

4

5

6

7

8

BASE FLOW ,

IN CUBIC FEET PER SECOND

ANNUAL STREAMFLOW,

IN CUBIC FEET PER SECOND OVERLAND RUNOFF, IN INCHES

7-DAY MINIMUM FLOW,

IN CUBIC FEET PER SECOND

WATER YEAR

1985 1986 1990 1991 1992 1993 1994 1995 1996 1997 1998

WATER YEAR

1985 1986 1990 1991 1992 1993 1994 1995 1996 1997 1998

WATER YEAR

1985 1986 1990 1991 1992 1993 1994 1995 1996 1997 1998

WATER YEAR

POSTBMPPREBMPPOSTBMPPREBMP

POSTBMPPREBMPPOSTBMPPREBMP

[BMP, Best Management Practice]

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

Figure 7. Streamflow characteristics for Brewery Creek, Dane County, Wis. 
(fig. 1). In addition, the streamflow data were needed to 

determine the nutrient and sediment loads at the Brewery 

and Garfoot Creek gaging stations. Base flow represents 

ground-water discharge to the stream channel. Base flow 

was separated from the daily mean streamflows over the 

period of study (1984–98) by methods described in White 

and Sloto (1990). Overland runoff—the difference between 

the annual mean discharge and base flow—is water 

that flows over the land surface and enters the stream. 

Daily streamflow data for the gaging stations for all the 

water years of the study period are published in “Water 

Resources Data, Wisconsin, Water Years 1985–1998” 

(Holmstrom and others, 1986, 1987, 1990–99). 

The highest annual streamflow at all three stations 

was in water year 1993. The annual streamflow at Black 

Earth Creek in 1993 was 175 percent of the mean for the 

period of record (44 years) and was the highest annual 

streamflow ever recorded at the station. This streamflow 

corresponds to the greatest annual precipitation measured 

at the study-site rain gages and the greatest annual precipitation measured at the NOAA weather station at Madison 

for the period of data collection. The minimum annual 

streamflow occurred in water year 1991 at Brewery Creek 

and in water year 1990 at Garfoot Creek and Black Earth 

Creek (figs. 7, 8, and 9). At Brewery Creek in water year 

1991, the 7-day mean low flow was zero (fig. 7). 

A frequency analysis of annual peak at streamflows 

at Black Earth Creek near Black Earth for 1954–98 was 

done using the log-Pearson Type III procedure following 

Bulletin 17-B guidelines for annual peaks (Interagency 

Advisory Committee on Water Data, 1982). The estimated 

peak streamflows for selected frequencies are presented in 

table 3. The peak streamflows (1,320 ft3

/s) for the period 

of record at Black Earth Creek occurred in 1993. This 

flood peak was between the 25- and 50-year recurrence 

interval (table 3).

A Kendall test for trend was done for all of the 

streamflow characteristics for the study period at Brewery, 

Garfoot, and Black Earth Creeks. None of the streamflow 

characteristics had a statistically significant trend for the 

study period. The Kendall test for trend also was done for 

Black Earth Creek for annual streamflow, base flow, and 

overland runoff for 1954–98. A statistically significant 

upward trend was found for annual streamflow and base 

flow but not for overland runoff for Black Earth Creek 

near Black Earth (table 4). Because annual streamflow 

is the sum of annualized base flow and overland runoff, 

the increase in annual streamflow may be caused by the 

increase in base flow.

Table 2. Summary of streamflow characteristics for Brewery, Garfoot, and Black Earth Creeks, Wis., pre- and post-BMP periods

[BMP, best-management practice; WY, water year]

Brewery Creek Garfoot Creek Black Earth Creek

Streamflow 

characteristic

(cubic feet 

per second, 

unless noted)

Pre-BMP

10/84–9/86

Post-BMP

10/96–9/98

Period 

of

record

Pre-BMPa

10/84–4/90

Post-BMP

4/96–9/98

Period 

of

record

Pre-BMP

WY 85–86

Post-BMP

WY 97–98

Period 

of record

WY 54–98

Mean annual

 streamflow

 3.08 2.25 2.43 4.93 5.76 5.23 50.8 41.7 34.9

Minimum 7-day

 low flow

 .93 1.1 0 1.8 2.60 1.8 29.0 23.0 13

Mean base flow 2.30 1.70 1.72 4.19 4.90 4.42 43.6 35.4 29.6

Mean base flowb 73 76 67 84 85 85 86 84 85

a Includes all of 1990 water year.

b

As a percentage of mean annual streamflow.

Hydrologic Conditions During the Study Period 11

Table 3. Peak streamflow and selected recurrence intervals 

for Black Earth Creek, Wis., 1954–98

[ft3/s, cubic feet per second]

Recurrence interval 

(years)

Peak streamflow

(ft3

/s)

 1.25 251 

 2 432

 5 725

 10 939

 25 1,226

 50 1,450
12 Effects of Best-Management Practices in the Black Earth Creek Priority Watershed, Wisconsin, 1984–98

Table 4. Results of the Kendall test of trend in streamflow 

characteristics, Black Earth Creek near Black Earth, Wis., 

water years 1954–98

[ft3/s, cubic foot per second; <, less than]

Streamflow

characteristic

Kendall 

Tau

Trend slope 

estimate

(ft3

/s)

Significance 

level

Annual streamflow 0.36 0.3766 <0.01

Base flow .11 .3502 <.01

Overland runoff .11 .0267 .28

Since 1960, there have been three periods of apparently increasing annual streamflow and base flow for the 

Black Earth Creek area near Black Earth, Wis. (fig. 10). 

The first increase was in the mid-1970s, the second during the mid-1980s, and the last from about 1992 to 1995 

(fig. 10). As noted previously, no statistically significant 

trend was found in annual precipitation at the Madison 

airport rain gage. The increase in the annual streamflow, 

which likely is related to base flow (ground-waterseepage to the stream) of Black Earth Creek corresponds 

to increasing snowfall. Krohelski and others (2002) found 

a good correlation between increasing snowfall and 

periods of increasing base flow of Black Earth Creek in 

south-central Wisconsin. Snowfall is one of the sources 

1985 1986 1990 1991 1992 1993 1994 1995 1996 1997 1998

WATER YEAR

POSTBMPPREBMP

1985 1986 1990 1991 1992 1993 1994 1995 1996 1997 1998

WATER YEAR

POSTBMPPREBMP

NO DATANO DATA

NO DATANO DATA

0

1

2

3

4

5

6

7

8

9

0

5

10

15

20

25

BASE FLOW,

IN CUBIC FEET PER SECOND

ANNUAL STREAMFLOW,

IN CUBIC FEET PER SECOND OVERLAND RUNOFF, IN INCHES

7-DAY MEAN LOW FLOW,

IN CUBIC FEET PER SECOND

1985 1986 1990 1991 1992 1993 1994 1995 1996 1997 1998

WATER YEAR

POSTBMPPREBMP

1985 1986 1990 1991 1992 1993 1994 1995 1996 1997 1998

WATER YEAR

POSTBMPPREBMP

[BMP, Best Management Practice]

0

1

2

3

4

5

6

7

8

9

0

1

2

3

4

5

6

7

8

9

Figure 8. Streamflow characteristics for Garfoot Creek, Dane County, Wis.
of recharge to the ground-water system in south-central 

Wisconsin. In addition, changing land practices in the 

watershed may have increased the infiltration rate and 

hence increased base flow. Gebert and Krug (1996) found 

similar trends in other sites in southwestern Wisconsin. 

Even though an increase is apparent in annual streamflow 

and base flow in the latter part of the study period (fig. 10), 

no statistically significant trend was found. This result may 

be due more to the short time period (11 years) than to 

absence of a trend. Although the annual streamflows and 

base flows indicate a cyclical pattern (fig. 10), the overall 

flows appear to be increasing.

Water Quality Before and After 

Installation of Best-Management 

Practices

Nutrient and Sediment Concentrations at 

Base Flow

Because base flow of a stream consists of groundwater discharge to the stream, base-flow water quality 

generally reflects ground-water quality. Consequently, 

base-flow water quality may be affected by land-use 

practices in the watershed that affect ground water. 

Concentrations of nutrients, for example, may become 

1985 1986 1990 1991 1992 1993 1994 1995 1996 1997 1998

WATER YEAR

POSTBMPPREBMP

1985 1986 1990 1991 1992 1993 1994 1995 1996 1997 1998

WATER YEAR

POSTBMPPREBMP

1985 1986 1990 1991 1992 1993 1994 1995 1996 1997 1998

WATER YEAR

POSTBMPPREBMP

1985 1986 1990 1991 1992 1993 1994 1995 1996 1997 1998

WATER YEAR

POSTBMPPREBMP

0

10

20

30

40

50

60

70

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

BASE FLOW,

IN CUBIC FEET PER SECOND

ANNUAL STREAMFLOW,

IN CUBIC FEET PER SECOND OVERLAND RUNOFF, IN INCHES

7-DAY MINIMUM FLOW,

IN CUBIC FEET PER SECOND

0

10

20

30

40

50

60

70

0

10

20

30

40

50

60

70

[BMP, Best Management Practice]

Figure 9. Streamflow characteristics for Black Earth Creek, Dane County, Wis.

Hydrologic Conditions During the Study Period 13
14 Effects of Best-Management Practices in the Black Earth Creek Priority Watershed, Wisconsin, 1984–98

elevated above background concentrations in ground 

water as a result of agricultural activities.

Comparisons of base-flow water quality concentrations during the pre- and post-BMP periods may indicate 

changes due to BMPs. A nonparametric Wilcoxon ranksum test can be used to determine whether significant 

differences are present between two independent periods 

(pre- and post-BMP). The null hypothesis is that median 

of selected constituents at base flow during the pre-BMP 

period are the same as those in the post-BMP period. The 

alternative hypothesis is that the median concentrations 

at base flow in the post-BMP period are less than those 

during the pre-BMP period. If the alternative hypothesis 

appears to be true, then the reduction may be a result of 

changing land-use practices in the watershed. 

Water-quality samples were collected at base flow 

during the pre- and post-BMP periods. Daily mean 

streamflows were separated into overland flow and base 

flow to determine whether a sample collected was during 

a base-flow period, the ratio of instantaneous streamflow 

and daily mean base flow was calculated. If the ratio of 

instantaneous discharge to daily mean base flow was less 

than or equal to 0.95, then a sample collected on this day 

was considered to be a potential base-flow sample. In addition, an overland-flow time lag was calculated. The time 

lag was equal to the drainage area raised to the 0.2 power 

and rounded up to the next day (Viessman and others, 

1977). The overland- flow time lag was determined to 

be 2 days for both Garfoot and Brewery Creeks. If a potential base-flow sample was collected within 2 days of the 

peak of a hydrograph rise, this sample was not considered 

to be a base-flow sample. The remaining potential baseflow samples then were evaluated on the basis of their 

hydrograph position relative to preceding storms. 

The Wilcoxon rank-sum nonparametric test of the 

median (MathSoft, 2000) was applied to the pre-BMP 

and post-BMP concentrations for the base-flow samples. 

Results of the Wilcoxon rank-sum test can be found 

in table 5. Concentration of the base-flow samples for 

Brewery and Garfoot Creeks are shown in figures 11 and 

12. Also shown on these figures is the median for each 

constituent by water year.

0

10

20

30

40

50

60

70

1955 1960 1965 1970 1975 1980 1985 1990 1995

3-year moving average

0.0

10.0

20.0

30.0

40.0

50.0

1955 1960 1965 1970 1975 1980 1985 1990 1995

WATER YEAR

WATER YEAR

3-year moving average

BASE FLOW,

IN CUBIC FEET PER SECOND

ANNUAL STREAMFLOW,

IN CUBIC FEET PER SECOND

POSTBMPPREBMP

POSTBMPPREBMP

[BMP, Best Management Practice]

Figure 10. Annual streamflow and base flow with 3-year moving average for Black Earth Creek, Dane County, Wis., 1955–98 

water years.
Base-flow sample

Water-year median

Pre-BMP Period

Post-BMP Period

1.0000.1000.0100.001

10.000

1.000.100.01

10.00

1

10

100

1000

SUSPENDED SEDIMENT,

IN MILLIGRAMS PER LITER

TOTAL PHOSPHORUS,

IN MILLIGRAMS PER LITER

AMMONIA NITROGEN,

IN MILLIGRAMS PER LITER

[BMP, Best Management Practice]

1985 1986 1987 1988 1989 1990 1991 1991 1992 1993 1994 1995 1996 1997 19981985 1986 1987 1988 1989 1990 1991 1991 1992 1993 1994 1995 1996 1997 19981985 1986 1987 1988 1989 1990 1991 1991 1992 1993 1994 1995 1996 1997 1998

Figure 11. Concentrations and water-year medians of suspended sediment and nutrients in base-flow samples during the data-collection period at Brewery Creek, 

Dane County, Wis.

Water Quality Before and After Installation of Best-Management Practices 15
16 Effects of Best-Management Practices in the Black Earth Creek Priority Watershed, Wisconsin, 1984–98 1.00 0.10 0.01 1.00 0.10 0.01

1

10

100

1000

SUSPENDED SEDIMENT,

IN MILLIGRAMS PER LITER

TOTAL PHOSPHORUS,

IN MILLIGRAMS PER LITER

AMMONIA NITROGEN,

IN MILLIGRAMS PER LITER

Base-flow sampleWater-year median

Pre-BMP Period

Post-BMP Period

[BMP, Best Management Practice]

1985 1986 1987 1988 1989 1990 1991 1991 1992 1993 1994 1995 1996 1997 19981985 1986 1987 1988 1989 1990 1991 1991 1992 1993 1994 1995 1996 1997 19981985 1986 1987 1988 1989 1990 1991 1991 1992 1993 1994 1995 1996 1997 1998

Figure 12. Concentrations and water-year medians of suspended sediment and nutrients in base-flow samples during the data-collection period at Garfoot Creek, 

Dane County, Wis.
For Brewery Creek, none of the differences in the 

median water-quality concentrations for the pre- and postBMP periods were statistically significant at the 0.05 level 

(table 5; values less than 0.05 are significant). For Garfoot 

Creek, the 41-percent decrease in the median suspended 

sediment concentration between the pre- and post-BMP 

periods is statistically significant at the 0.05 level (table 

5). The 67-percent decrease in ammonia nitrogen median 

concentration between the pre- and post-BMP periods also 

was statistically significant at the 0.05 level (table 5). The 

slight decrease in total phosphorus median concentration 

between the pre-and post-BMP periods was not statistically significant at the 0.05 level (table 5).

Storm Loads

Because a great deal of the annual sediment and nutrient transport occurs during storms, fixed-interval sampling, 

particularly at a monthly frequency, may not show changes 

resulting from BMP implementation (Walker, 1993). Consequently, mass transport resulting from individual storms 

was analyzed. Instantaneous mass transport of a particular 

constituent is determined by multiplying streamflow by 

the concentration of the constituent and a conversion factor 

(Porterfield, 1972). The integration method was then used 

to determine the mass transport of each constituent for 

each storm (Porterfield, 1972), expressed as a storm load. 

Concentration at the beginning of a storm was estimated 

from samples collected during previous base-flow periods 

between storms. Concentration at the end of the storm 

was estimated from samples collected immediately after 

the end of the storm. Some concentration 

data for individual storms were estimated 

by the relation between concentration and 

streamflow. Estimated data samples within 

a storm period were kept to a minimum.

In many cases, the variability in the 

storm loads is large enough to mask potential differences in the pre- and post-BMP 

periods. In addition, because the pre- and 

post-BMP periods arise from different 

hydrologic conditions, differences in the 

hydrologic conditions could result in 

differences that are not a result of the management practices. For these reasons, one 

solution is to perform regressions relating 

the storm loads to variables representing 

climatic and seasonal conditions. If the 

independent variables represent the natural 

climatologic and seasonal conditions, then 

the variability remaining in the regression residuals represents the combination of lack-of-fit for 

the regression model and changes induced by the BMPs. 

Because the regression, by design, reduces the variability 

in the data, in theory it should be possible to detect smaller 

differences between the pre- and post-BMP periods compared to detecting differences in the storm loads.

A number of independent variables were selected, 

most of which were based on various measures of precipitation for each distinct rainstorm. These variables included 

total rainfall (P), the 15- and 30-minute maximum intensities (I15 and I30), and the Universal Soil Less Equation 

(USLE) erosivity index (EI; Wischmeier and Smith, 1978). 

Additional precipitation-based measures included the 

1-, 3- and 5-day antecedent precipitation (API1, API3 and 

API5

), which is computed as the total rainfall for the 1, 3, 

and 5 days prior to the beginning of each storm, respectively. Terms combining total rainfall and the antecedent 

precipitation also were considered (for example, P+API1). 

Finally, two seasonal terms were included to allow for 

variations arising solely based on the time of year. The seasonal terms were based on the serial date of the storm (T), 

using a period of 1 year and both sine and cosine terms to 

allow for amplitude and phase-shift estimation.

Preliminary regression results indicated that for many 

of the constituents and storms, simple linear regressions 

resulted in the prediction of negative storm loads. Because 

these negative loads would result in erroneous conclusions 

when comparing pre- and post-BMP periods, the final 

regressions were based on a logarithmic transformation of 

the storm loads, thus assuring that negative loads cannot be 

Table 5. Results of the Wilcoxon rank-sum test on the median concentrations of suspended sediments and nutrients at base flow, pre- and post-BMP 

periods, Brewery and Garfoot Creeks, Wis.

[mg/L, milligrams per liter; BMP, best-management practice]

Median concentration, mg/L

Dependent variable Pre-BMP Post-BMP Significance level

Brewery Creek

Suspended sediment 62.0 54.6 0.127

Total phosphorus .15 .12 .105

Ammonia nitrogen .03 .064 .872

Garfoot Creek

Suspended sediment 37.5 22.0 .016

Total phosphorus .09 .08 .166

Ammonia nitrogen .06 .020 .001

Water Quality Before and After Installation of Best-Management Practices 17
18 Effects of Best-Management Practices in the Black Earth Creek Priority Watershed, Wisconsin, 1984–98

predicted. For each creek and constituent, stepwise regressions were done using the independent variables described 

above (table 6). For each regression, additional variables 

were considered if the improvement in the resulting regression was considered large enough to warrant the use of 

additional variables. In addition, various regression plots 

were examined to verify that the underlying assumptions 

of regression analysis were not violated.

For both Brewery and Garfoot Creeks, the median 

storm loads for all three constituents for the pre-BMP and 

post-BMP periods are listed in table 7. The two periods 

were compared statistically by means of the Wilcoxon 

rank-sum test as described previously. Along with the test 

applied to the storm loads, the regression residuals also 

were tested for differences between the pre- and post-BMP 

periods (table 7). If the regressions represent the variability 

due to natural factors, a difference in the regression residuals could be attributed directly to a difference due to the 

BMPs.

For Brewery Creek, ammonia nitrogen was the only 

median storm load that decreased, and the decrease was 

not statistically significant at the 0.05 level (table 7). 

There are three potential reasons that the differences are 

not statistically significant. First, the difference may be 

due entirely to chance, so the difference is not a result of 

the BMPs. Second, differences in the underlying natural 

conditions (precipitation amount and intensity, seasonal 

distribution of storms, and so forth) between the pre- and 

post-BMP periods may be obscuring a real difference. 

Third, the variability in the data may be large enough to 

obscure a real difference. For the first two reasons, there is 

no way to determine whether a nonsignificant difference 

is due to chance or differences in the underlying conditions. Because the regression residuals will have a smaller 

variability (the regression removes some of the variability 

through the relation with the independent variables), testing the regression residuals could reduce the variability 

enough to reveal a true difference between the two periods. 

For Brewery Creek, this result appears to be the case for 

ammonia nitrogen, where the difference in storm load 

residuals between the pre- and post-BMP periods is statistically significant at the 0.05 level (table 7). Therefore, for 

ammonia nitrogen, the difference in pre- and post-BMP 

conditions is likely due to the BMPs installed.

For Garfoot Creek, only the median storm load for 

ammonia nitrogen shows a statistically significant difference between the pre- and post-BMP periods (table 7). 

The decrease in ammonia nitrogen was 66 percent. The 

test applied to the regression residuals shows that the 

differences in load residuals for both total phosphorus 

and ammonia nitrogen are statistically significant at the 

0.05 level (table 7). Therefore, the reduction in pre- and 

post-BMP conditions for total phosphorus and ammonia 

nitrogen is likely due to the BMPs installed.

Table 6. Regression results for storm loads at Brewery and Garfoot Creeks, Wis.

[P, total rainfall; EI, Universal Soil Loss Equation Erosivity Index; APIn, antecedent rainfall n days before the storm; In, n-minute maximum precipitation 

intensity; T, starting date of streamflow period, in years since 1904; cos( ), trigonometric cosine function; sin( ), trigonometric sine function; R2

, fraction 

of variation explained by the regression]

Dependent variable

Independent 

variables Sample size Adjusted R2 Standard error

Standard error,

percent

Brewery Creek

Suspended sediment P+API1, I15, cos(T), 

sin(T)

 29 0.829 0.733 34

Total phosphorus P+API1

, I15, cos(T), 

sin(T)

 26 .790 .672 16

Ammonia nitrogen EI, cos(T), sin(T) 24 .635 .946 31

Garfoot Creek

Suspended sediment P+API3

, I30, cos(T), 

sin(T)

 31 .651 .737 28

Total phosphorus P+API1

, cos(T), 

sin(T)

 33 .594 .748 17

Ammonia nitrogen P+API3

, cos(T), 

sin(T)

 31 .642 .613 20
Effects of Specific Management 

Practices

Concentrations of nutrients and sediment observed 

during base-flow conditions and storms can be reduced 

by BMPs. For the purpose of discussion, BMPs can be 

divided into five main categories: animal-wastemanagement systems, fencing, streambank protection, 

nutrient management, and upland-control practices 

(University of Wisconsin Extension, 1998). Because each 

watershed is affected by a mixture of BMPs and each BMP 

has varying success in controlling different aspects of 

water quality, it is useful to consider a matrix of interactions between the BMPs and the potential water-quality 

change caused by BMPs. In this matrix (table 8), the 

direction of each arrow indicates whether the water quality 

is likely to improve (downward indicating a decrease in 

concentration) or degrade (upward indicating an increase 

in concentration). The size of each arrow indicates how 

likely the BMPs would be to change the water quality of 

the stream. A small arrow indicates some effect on the 

water quality but may not cause a significant change. A 

large arrow indicates likelihood of significant change in 

water quality. A horizontal bar indicates that the BMP may 

have little effect or an unknown effect on the stream-water 

quality. A separate matrix for a generalized watershed, for 

the Brewery Creek watershed and for the Garfoot Creek 

watershed, is included in table 8. The last row under each 

of the matrices indicates the observed effect for Brewery 

Creek and Garfoot Creek watersheds of the implementation of BMPs in the watershed.

Animal-waste-management systems are used to control phosphorus and ammonia nitrogen loading to a stream. 

BMPs for controlling barnyard wastes include directing 

clean surface water around the barnyard, constructing settling basins or filter walls, and establishing vegetated filter 

strips (University of Wisconsin Extension, 1998). Controlling animal wastes should have a noticeable effect on 

storm loads of phosphorus and ammonia nitrogen by eliminating the direct runoff of manure and urine (table 8). The 

effect on the base-flow water quality may be less. Streams 

that flow through a barnyard or that are directly connected 

to a barnyard by a ditch or pipe can achieve reductions in 

the base-flow concentration of phosphorus and ammonia 

nitrogen by eliminating this waste stream. On the other 

hand, animal-waste systems that emphasize infiltration into 

the ground-water-flow system may increase the base-flow 

concentrations of phosphorus. Animal-waste-management 

systems should have little or no effect on the suspended-sediment concentration or suspended sediment load (table 8).

By restricting access of cattle, streambank fencing 

allows vegetative stabilization of the streambank. This 

stabilization should reduce bank erosion during high flows 

and should lead to lower suspended-sediment and totalphosphorus loads. Base-flow suspended-sediment 

concentrations also should be reduced if cattle access 

Table 7. Results of the Wilcoxon rank-sum test comparing storm loads and storm-load residuals for pre- and post-BMP 

periods at Brewery and Garfoot Creeks, Wis.

[BMP, best management practice]

Median storm loads, pounds1 Storm load residuals

Dependent variable Pre-BMP Post-BMP Direction 

of change

Significance 

level

Direction 

of change

Significance 

level

Brewery Creek

Suspended sediment 3.4 4.9 Increase 0.244 Increase 0.930

Total phosphorus 46.6 55.1 Increase .696 Increase .959

Ammonia nitrogen 29.8 9.0 Decrease .292 Decrease .026

Garfoot Creek

Suspended sediment 16.6 6.6 Decrease .149 Decrease .280

Total phosphorus 114 38.8 Decrease .066 Decrease .044

Ammonia nitrogen 36.6 12.5 Decrease .006 Decrease .005

1

Suspended-sediment loads are in tons

Effects of Specific Management Practices 19
20 Effects of Best-Management Practices in the Black Earth Creek Priority Watershed, Wisconsin, 1984–98

Table 8. Matrix of interactions between BMPs and different aspects of water quality, with statistical tests results from comparing

pre- to post-BMP periods for a generalized watershed, and Brewery and Garfoot Creek Watersheds, Wis.

[BMP, best-management practices; N/C, no change; %, percent; --, no expected affect on water quality]

Sediment Phosphorus Ammonia nitrogen

Best management practices Base flo

Best management

practices

Best management

practices

w Storm Base flow Storm Base flow Storm

Generalized Watershed

Animal-waste-management systems -- --

Fencing --

Streambank protection -- --

Nutrient management -- --

Upland-control practices -- -- --

Brewery Creek Watershed

Sediment Phosphorus Ammonia nitrogen

Status

(%) Base flow Storm Base flow Storm Base flow Storm

Animal-waste-management

systems

75 -- --

Fencing 0 -- -- -- -- -- --

Streambank protection 90 -- -- -- --

Nutrient management 50 -- -- -- --

Upland-control practices 20 -- -- --

Observed effect N/C N/C N/C N/C N/C

Garfoot Creek Watershed

Sediment Phosphorus Ammonia nitrogen

Status

(%) Base flow Storm Base flow Storm Base flow Storm

Animal-waste-management

systems

70 --

Fencing 100 -- --

Streambank protection 100 --

Nutrient management 30 -- -- -- --

Upland-control practices 20 -- -- --

Observed effect N/C N/C

Statistically significant improvement in water quality expected

Improvement in water quality expected

Water quality could either improve or degrade

Degradation of water quality expected
to the channel and streambank is restricted. Base-flow 

concentrations of ammonia nitrogen and total phosphorus 

from animal waste could be reduced by not allowing cattle 

direct access to the stream.

Streambank-protection practices include stabilizing 

shoreline, shaping and seeding streambanks, and rehabilitating fishery habitat (University of Wisconsin Extension, 1998). Streambank-protection systems typically will 

reduce erosion by restricting cattle access and stabilizing eroded streambanks. By protecting the streambanks, 

sedimentation and nutrient delivery to the stream (that 

is, phosphorus attached to soil particles) will be reduced. 

Base-flow sediment concentration and sediment storms 

loads should be reduced after implementation of streambank protection (table 8). Phosphorus base-flow concentration and storm loads may be reduced by implementation of streambank protection, but the effect will be less 

than the effect on suspended-sediment concentration and 

storm load (table 8). Ammonia nitrogen concentration in 

base-flow streamflow and storm loads should be affected 

minimally by streambank protection (table 8). 

Nutrient-management practices (University of Wisonsin–Extension, 1998), which include use of recommended 

fertilizer and manure application rates, should reduce 

phosphorus and ammonia nitrogen concentration and loads 

during both base-flow and storm conditions (table 8). 

Nutrient management should have no effect on suspended 

sediment.

Upland-protection practices, which are designed to 

prevent and control sheet and rill erosion, include changes 

in crop rotation, change of permanent cover, minimum or 

reduced tillage, contour and strip cropping, and grassed 

waterways. The main effect on streamwater quality from 

upland protection will be to reduce suspended-sediment 

concentration and loads during storms (table 8). Phosphorus storm loads also will be reduced if the soil-attached 

phosphorus is a major contributor to the stream phosphorus load. Because upland-protection practices encourage 

infiltration, they potentially could increase concentrations 

of phosphorus in the ground-water system, which could 

increase base-flow concentrations.

In Brewery Creek, 80–95 percent of the suspended 

sediment reaching Brewery Creek was estimated to be 

from eroding cropland (Wisconsin Department of Natural 

Resources, 1989). Because the level of upland protection was low (20 percent) of the potential land area, the 

expected effects from these practices would be diminished 

(table 8). For this watershed, only ammonia nitrogen 

during storms showed a statistically significant decrease 

between the pre- and post-BMP periods (table 8). The 

source of ammonia nitrogen to the stream is likely from 

animal waste. The sources of total phosphorus load to the 

stream are barnyards and soil with attached phosphorus. 

Even though 70 percent of the barnyards were controlled 

by runoff-control systems and removal of livestock, the 

potential improvement in total-phosphorus loads are 

likely being masked by a continuing supply of phosphorus 

attached to sediment from upland erosion of croplands. 

Benefits of the BMPs also may be masked by location of 

controlled barnyards. These barnyards are off the main 

stem of Brewery Creek, so the effects of the controls may 

not be apparent at the gaging station and watershed outlet.

 An estimated 90 percent of sediment reaching 

Garfoot Creek was from eroding croplands (Wisconsin 

Department of Natural Resources, 1989). Only 20 percent 

of upland protection was implemented in the watershed. 

With this low level of upland protection implemented, a 

decrease in suspended-sediment loads during storms is 

expected (table 8). Yet, for this watershed, both suspendedsediment and ammonia nitrogen concentrations in base 

flow decreased significantly between the pre- and postBMP periods. A major source of ammonia nitrogen to the 

stream is from animal waste (Wisconsin Department of 

Natural Resources, 1989). Barnyard-runoff controls were 

implemented at five of seven eligible barnyards. Garfoot 

Creek flowed through two of these barnyards, and a third 

drained directly to the creek (fig. 3). After the barnyard 

controls were implemented, this source of ammonia nitrogen during base-flow periods was eliminated, and the postBMP ammonia nitrogen was less than the pre-BMP period.

Suspended-sediment concentration also was reduced, 

as indicated by comparing pre- and post-BMP implementation low-flow periods. One of the management practices 

implemented was fencing. Approximately 1 mile of fencing was installed along Garfoot Creek (table 1 and table 8), 

most of it along the main stem. The watershed plan 

(Wisconsin Department of Natural Resources, 1989) indicated that streambank erosion along Garfoot Creek was 

minimal but cattle had access to two sites with eroding and 

trampled banks and one site controlled by fencing. Fencing also is a component of barnyard controls. A barnyard 

directly upstream from the gage was controlled, and animals were excluded from the stream except at a watering 

area. Fencing the stream prevents animals from wading 

in the stream and resuspending sediment that would be 

transported downstream during base flow.

Total-phosphorus and ammonia-nitrogen loads during 

storms in the Garfoot Creek watershed showed a statistically significant decrease between the pre- and post-BMP 

periods. An important source of total phosphorus and 

Effects of Specific Management Practices 21
22 Effects of Best-Management Practices in the Black Earth Creek Priority Watershed, Wisconsin, 1984–98

ammonia nitrogen in the Garfoot Creek watershed is animal waste (Wisconsin Department of Natural Resources, 

1989). In the Garfoot Creek watershed, five of seven 

barnyards had runoff-control systems implemented. These 

five barnyards all were along the main stem of Garfoot 

Creek (fig. 3), and two of these had the highest estimated 

barnyard phosphorus loads in the watershed (Wisconsin 

Department of Natural Resources, 1989). Controlling these 

barnyards resulted in a significant reduction of nutrient 

loads in the streams.

In contrast, the barnyard BMPs that were installed in 

the Brewery Creek watershed were effective in reducing 

the storm loads of ammonia nitrogen but were not effective in reducing the total phosphorus loads. The source of 

total phosphorus in the Brewery Creek watershed is from 

animal waste and phosphorus that is attached to sediment. 

The suspended sediment in the Brewery Creek watershed 

is fine (silt and clay) and has a greater capacity to bind 

total phosphorus than the coarse-grained sediments (sand) 

that predominate in the Garfoot Creek watershed. The 

installed barnyard-control systems have reduced the total 

phosphorus loads from animal waste but would not have 

controlled the total phosphorus load that is transported to 

the creek from upland erosion. Therefore, the Brewery 

Creek watershed likely will continue to be a source of 

phosphorus, either as direct overland transport or from 

resuspended sediment in the channel.

Suspended-sediment loads during storms did not 

show a significant decrease between the pre-and post-BMP 

periods at either the Brewery Creek or Garfoot Creek 

watershed. At Garfoot Creek, there was a statistically significant decrease in the suspended-sediment concentration 

during base-flow periods. At high flows, the suspended 

sediment that has been deposited in the channel previously (years of deposition) probably is being resuspended. 

To detect a significant difference between the pre-and 

post-BMP periods, suspended-sediment monitoring likely 

would have to continue for years in the future.

The effects of the BMPs on water quality are watershed specific. The effectiveness of the BMPs will depend 

on the type, number, and location of the controls implemented. In addition, the sources of the contaminants to 

the watershed will determine whether the practices are 

effective. If the soil substrate is sandy and barnyards are 

numerous, then the source of total phosphorus will be from 

animal wastes, and barnyard controls may be highly effective (Garfoot Creek). If the soils are transported easily and 

the source of phosphorus is from phosphorus attached to 

soil particles, then barnyard controls may not be as effective (Brewery Creek).

Summary and Conclusions

The U.S. Geological Survey, in cooperation with 

the Wisconsin Department of Natural Resources, began a 

comprehensive, multi-disciplinary evaluation-monitoring 

program in 1989 to assess the effectiveness of the Wisconsin Nonpoint Source Program. Hydrologic and water-quality data were collected at Brewery and Garfoot Creeks in 

1984 and 985 (pre-BMP period) and 1997 and 1998 (postBMP period). BMPs installed in these two basins included 

conservation tillage, contour strip-cropping, streambank 

protection, and various barnyard-runoff controls.

Water-quality samples were collected during baseflow and storm conditions for two periods: pre- and postBMP implementation. Samples were analyzed for suspended sediment, total phosphorus, and ammonia nitrogen. 

At Brewery Creek, no statistically significant differences 

were found in the median concentrations of the waterquality constituents at base flow between pre- and postBMP periods. At Garfoot Creek, the median suspendedsediment concentrations between the pre- and post-BMP 

periods decreased by 41 percent, and the difference is 

statistically significant at the 0.05 level. The median 

ammonia nitrogen concentrations of base-flow samples 

between the pre- and post-BMP periods decreased by 

67 percent, and the difference was statistically significant 

at the 0.05 level. No statistically significant difference in 

the median total phosphorus concentrations was found at 

base flow between the pre- and post-BMP periods.

For both Brewery and Garfoot Creeks, the median 

storm loads for suspended sediment, total phosphorus, and 

ammonia nitrogen were compared statistically by means 

of the Wilcoxon rank-sum test. This test was also applied 

to the regression residuals for differences between the 

pre- and post-BMP periods. The regression represented the 

variability due to natural factors; a difference in the regression residuals could be attributed directly to a difference 

due to the BMPs.

For Brewery Creek, differences between the pre- and 

post-BMP median storm loads were not statistically significant at the 0.05 level for any of the three constituents 

described above. There was a decrease, however, in the 

regression residuals for ammonia nitrogen between the 

pre- and post-BMP periods that was statistically significant 

at the 0.05 level. This difference is likely attributed to the 

installed BMPs. For Garfoot Creek, only the median load 

for ammonia nitrogen showed a statistically significant 

difference between the pre- and post-BMP periods. 

Significant differences also were observed in the 
storm-load residuals for both total phosphorus and ammonia nitrogen. It appears that the implementation of BMPs 

in the Garfoot Creek watershed is improving the water 

quality of that stream. The reduction in the pre- and postBMP periods is likely due to the installed BMPs.

The overall results for the effectiveness of BMPs are 

mixed. In this study, the Garfoot Creek watershed showed 

more improvement in water quality than the Brewery 

Creek watershed. The Garfoot Creek watershed was fenced 

extensively, and most of the planned barnyard practices 

were installed. Fencing the stream corridor may have the 

greatest effect on constituent concentrations at base flow. 

Keeping animals out of the stream will allow banks to 

revegetate, and bank erosion will be reduced; stream-bottom sediments will not be resuspended, and animal waste 

will not be deposited directly in the stream. Fewer BMPs 

were installed in the Brewery Creek watershed, which may 

account for less improvement in water quality. 

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