Prepared in cooperation with the Wisconsin Department of Natural Resources

Effects of Best-Management Practices in Bower Creek in 

the East River Priority Watershed, Wisconsin, 1991–2009

Scientific Investigations Report 2012–5217

U.S. Department of the Interior

U.S. Geological Survey
1

2

3

4

Cover. Areas within the Bower Creek Watershed near De Pere, Wisconsin. Photographs 1 and 4 courtesy of Judy A. Horwatich 

(U.S. Geological Survey). Photographs 2 and 3 courtesy of Daniel L. Olson (U.S. Geological Survey).
Effects of Best-Management Practices 

in Bower Creek in the East River Priority 

Watershed, Wisconsin, 1991–2009

By Steven R. Corsi, Judy A. Horwatich, Troy D. Rutter, and 

Roger T. Bannerman

Prepared in cooperation with the Wisconsin Department of Natural Resources

Scientific Investigations Report 2012–5217

U.S. Department of the Interior

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

KEN SALAZAR, Secretary

U.S. Geological Survey

Marcia K. McNutt, Director

U.S. Geological Survey, Reston, Virginia: 2013

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Suggested citation:

Corsi, S.R., Horwatich, J.A., Rutter, T.D., and Bannerman, R.T., 2013, Effects of best-management practices in Bower 

Creek in the East River priority watershed, Wisconsin, 1991–2009: U.S. Geological Survey Scientific Investigations 

Report 2012–5217, 21 p., at http://pubs.usgs.gov/sir/2012/5217/.
iii

Acknowledgments

The authors thank Jon Bechle, Bill Hafs, and other staff at the Brown County Land and Water 

Conservation Department who provided land-use data, communication with land owners, and 

input on the interpretation of final results. 

The authors also thank David Graczyk, John Walker, David Housner, Daniel Olson, and other 

colleagues at the U.S. Geological Survey for contributing to the data collection, data processing, 

and data analysis phases of the project.
This page has been left blank intentionally.
v

Contents

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

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

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

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

Methods...........................................................................................................................................................2

Hydrologic and Water-Quality Data-Collection Network...............................................................2

Selection and Inventory of Watersheds ...........................................................................................6

Hydrologic Conditions During the Study Period .......................................................................................8

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

Constituent Concentrations at Base Flow ......................................................................................13

Storm Loads.........................................................................................................................................13

Effects of Best-Management Practices on Bower Creek ....................................................................16

Effects of BMPs on Water Quality ...................................................................................................16

Comparison of Results to Watershed Improvement Objectives ..........................................................18

Summary and Conclusions.........................................................................................................................20

References Cited..........................................................................................................................................20

Figures

1. Map showing location of the Bower Creek Watershed and data-collection sites in

Brown County, Wisconsin...........................................................................................................3

2. Map showing land use and land cover from 1986 in the Bower Creek Watershed,

Brown County, Wisconsin...........................................................................................................4

3. Map showing soil types in the Bower Creek Watershed, Brown County, Wisconsin......5

4. Map showing animal-waste management, streambank protection, and grass

waterways implemented during the study period in the Bower Creek Watershed,

Brown County, Wisconsin...........................................................................................................7

5. Graphs showing yearly precipitation throughout the study period and long-term

average yearly precipitation at Green Bay and Kewaunee, Wisconsin .............................8

6. Graph showing cumulative rainfall distributions for the pre- and post-BMP

(best-management practices) implementation period at Bower Creek, Brown

County, Wisconsin........................................................................................................................9

7. Graphs showing annual streamflow, base flow, and stormflow at Bower Creek,

Brown County, Wisconsin, for water years 1991–1997 and 2006–2009 .............................10

8. Graph showing average monthly distribution of streamflow and total suspended

solids, total phosphorus, and dissolved ammonia-nitrogen loads at Bower Creek,

Brown County, Wisconsin, water years 1991–1997 and 2006–2009 ...................................11

9. Graph showing average relative annual contributions of stormflow and base-flow

periods to streamflow, total suspended solids, total phosphorus, and dissolved

ammonia-nitrogen loadings at Bower Creek, Brown County, Wisconsin, for water

years 1991–1997 and 2006–2009 ...............................................................................................11

10. Graphs showing average monthly streamflow and loads of total suspended solids,

total phosphorus, and dissolved ammonia nitrogen during base-flow and stormflow

periods, expressed as a percentage of the annual total water volume and

constituent loads at Bower Creek, Brown County, Wisconsin...........................................12
vi

11. Graphs showing concentrations and water-year medians of total suspended solids,

total phosphorus, and dissolved ammonia nitrogen in base-flow samples

throughout the study period at Bower Creek, Brown County, Wisconsin ........................14

12. Photographs showingexamples of A, a dead furrow and B, an unaddressed

concentrated flow area in the Bower Creek Watershed, Brown County, Wisconsin ....19

Tables

1. Summary of targeted and implemented rural best-management practices in the 

Bower Creek Watershed, Brown County, Wisconsin.............................................................6

2. Results of Wicoxon rank-sum test for differences between constituent 

concentrations in base-flow samples from pre- and post-BMP implementation 

periods at Bower Creek, Brown County, Wisconsin.............................................................15

3. Regression results for storm loads from rainfall periods at Bower 

Creek, Wisconsin........................................................................................................................15

4. Median and mean rainfall-period storm loads and results of the Wilcoxon 

rank-sum test comparing storm-load residuals for pre- and post-BMP periods 

at Bower Creek, Wisconsin ......................................................................................................16

Conversion Factors and Datum

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) 

ton per day (ton/d) 0.9072 metric ton per day

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

Concentrations of chemical constituents in water are given in milligrams per liter (mg/L)

A water year is defined as the 12-month period from October 1 for any given year, through 

September 30 of the following year. The water year is designated by the calendar year in which 

it ends.
vii

Abbreviations

BMP best-management practices

EI erosivity index 

GIS geographic information system 

NOAA National Oceanic and Atmospheric Administration

USGS U. S. Geological Survey

USLE Universal Soil Loss Equation

WDNR Wisconsin Department of Natural Resources
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Effects of Best-Management Practices in Bower Creek in 

the East River Priority Watershed, Wisconsin, 1991–2009

By Steven R. Corsi,1 Judy A. Horwatich,1 Troy D. Rutter,1 and Roger T. Bannerman2

Abstract

Hydrologic and water-quality data were collected at 

Bower Creek during the periods before best-management 

practices (BMPs), and after BMPs were installed for 

evaluation of water-quality improvements. The monitoring 

was done between 1990 and 2009 with the pre-BMP period 

ending in July 1994 and the post-BMP period beginning 

in October 2006. BMPs installed in this basin included 

streambank protection and fencing, stream crossings, grade 

stabilization, buffer strips, various barnyard-runoff controls, 

nutrient management, and a low degree of upland BMPs. 

Water-quality evaluations included base-flow concentrations 

and storm loads for total suspended solids, total phosphorus, 

and ammonia nitrogen. The only reductions detected between 

the base-flow samples of the pre- and post-BMP periods were 

in median concentrations of total phosphorus from baseflow samples, but not for total suspended solids or dissolved 

ammonia nitrogen. Differences in storm loads for the three 

water-quality constituents monitored were not observed during 

the study period.

Introduction

Nonpoint-source contamination is a primary contributor 

to water resource quality problems in Wisconsin. In 

recognition of the importance of nonpoint sources, the 

Wisconsin Nonpoint Source Water Pollution Abatement 

Program (Nonpoint Program) was enacted in 1978 (Wisconsin 

Department of Natural Resources, 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 best-management 

practices (BMPs)—were available for funding support 

through the Nonpoint Program. For example, practices in 

rural areas included conservation tillage, contour stripcropping, streambank protection, and various barnyard-runoff 

controls. The Nonpoint Program provided matching funds to 

landowners for voluntary implementation of various BMPs 

using priority watersheds as a preference for consideration.

Until the late 1980s, little data existed to demonstrate 

the effectiveness of BMPs for improving water quality in 

Wisconsin’s priority watersheds. The Wisconsin Department 

of Natural Resources (WDNR) and U. S. Geological 

Survey (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 evaluationmonitoring program includes biological and stream-habitat 

monitoring by the WDNR and water-quality monitoring by 

the USGS. Eight watersheds were chosen for the evaluationmonitoring program. These watersheds were chosen because 

WDNR and Land County Conservation District personnel 

felt that a potential for substantial improvement existed and 

because BMPs were scheduled to be installed within the 

project timeframe. Results from five of these watersheds, 

which included Brewery and Garfoot creeks in the Black 

Earth Creek Watershed (Graczyk and others, 2003), Otter 

Creek in the Sheboygan River Watershed (Corsi and others, 

2005) and Joos Valley and Eagle Creeks in the Waumundee 

River Watershed (Graczyk and others, 2012) were 

published previously.

This report presents results from Bower Creek, the sixth 

watershed where evaluation monitoring has been completed. 

The Bower Creek Watershed is a subbasin of the East River 

located in eastern Wisconsin near DePere, Wisconsin. The 

monitoring for Bower Creek occurred from September 1990 

through January 1995, April 1996 through June 1997, and 

October 2006 through September 2009. Streamflow and 

water-quality data were collected continuously at one station 

approximately 7 miles (mi) upstream from the confluence with 

the East River.

1

U.S. Geological Survey

2

Wisconsin Department of Natural Resources
2 Effects of Best-Management Practices in Bower Creek in the East River Priority Watershed, Wisconsin, 1991–2009

Purpose and Scope

The overall objective of the WDNR and USGS 

evaluation-monitoring program was to evaluate BMP 

effectiveness in several small watersheds located in 

geographically and hydrologically diverse areas of Wisconsin.

This report summarizes the results of a study on 

effectiveness of watershed-management practices for 

controlling nonpoint-source contamination in the Bower 

Creek Watershed. Concentrations of total suspended solids, 

total phosphorus, and dissolved ammonia nitrogen in samples 

collected at base flow before BMP installation (pre-BMP) 

are compared and contrasted to those for the period after 

BMP installation (post-BMP). Pre-BMP storm loads of total 

suspended solids, total phosphorus, and dissolved ammonia 

nitrogen from sampled rainfall periods are compared and 

contrasted to the post-BMP storm loads.

Data-collection periods were from September 1990 

through March 1995, April 1996 through June 1997, and 

October 2006 through September 2009. Installation of 

BMPs began in 1996. To satisfy statistical requirements to 

keep the number of data points in the pre- and post-BMP 

implementation periods similar, July 1994 was used as the 

end of the pre-BMP implementation period. In October, 2006, 

most of the BMP installation that was planned for this program 

was complete in the watershed. Monitoring after this time was 

considered to be the post-BMP period. For the purpose of this 

study, the post-BMP period is considered to be October 2006 

through September 2009.

Physical Setting and Land Use

Bower Creek is a tributary to the East River in Brown 

County about 5 mi east of the city of DePere, Wisconsin 

(Wis.) (fig. 1). Bower Creek has been classified by the 

WDNR as a warm-water forage stream that has the potential 

to maintain a forage fish population capable of supporting an 

abundant, diverse community of forage fish and other aquatic 

life (Wisconsin Department of Natural Resources, 1993). 

Bower Creek drains 14.8 square miles (mi2

) upstream from 

the stream-gaging station, and the total stream channel length, 

which is all intermittent, is 37.1 mi from the station to the 

stream headwaters. The watershed contains several small lakes 

and ponds.

Total land use and land cover for Bower Creek in the 

beginning of the study is shown in figure 2. In the Bower 

Creek Watershed, cropland (83.1 percent) dominated the 

land use and land cover, with woodlots (6 percent) being the 

next greatest land use and land cover. In all, 115 farms were 

included or partially included in the Bower Creek Watershed. 

The average farm size was 120 acres. There were 41 barnyards 

in the watershed with an average herd size of 118 animals, of 

which 97 percent are dairy cows (Rappold and others, 1997). 

According to Brown County Land and Water Conservation 

Department, the number of livestock in the watershed and 

the cropland percentage has not changed substantially 

throughout the monitoring period, but exact numbers were not 

available. Data collected by Brown County indicate the soil 

phosphorus levels to be 50 to more than 100 parts per million 

for several fields in the Bower Creek Watershed (Kelling and 

others, 2003).

The overall channel slope of Bower Creek is 11 feet per 

mile (ft/mi). The bed material consists mainly of sand, silt, and 

clay with gravel and bedrock in riffle areas. The soil types in 

the Bower Creek watershed vary spatially and consist mainly 

of soil categories from silt loams to silty clay loams (fig. 3). 

These soils are poorly drained unless a tile system is used 

(Link and others, 1974).

Methods

Watersheds can be affected in numerous ways by changes 

in land use and land management brought about by BMP 

installation. A suite of different variables were considered in 

an attempt to understand these effects. Hydrologic, waterquality, and land-use data were the chosen areas of study 

considered to be important for this evaluation. Not only 

are the areas of study important in this evaluation, but the 

exact methods of data collection and analysis are essential 

in detecting changes resulting from BMP installation. A 

description of data collection and analysis methods for each of 

these areas of study are included in this section.

Hydrologic and Water-Quality Data-Collection 

Network

A stream-gaging station equipped for continuous 

recording of data was installed in September 1990 at 

Bower Creek (fig. 1). Stage was measured with a bubblertype pressure transducer every 5 minutes during periods 

of increased runoff and every hour otherwise. Streamflow 

measurements were made according to standard USGS 

methods (Rantz and others, 1982) every 4 to 6 weeks, 

and more frequently during high flows, to define the 

stage-streamflow relation used to compute continuous 

streamflow record.

The stream-gaging station was equipped with a stageactivated refrigerated water sampler for automatic collection 

of water samples during periods of increased runoff from 

rainfall or snowmelt. The data logger was programmed to 

initiate sampling once the stream stage reached an initial 

sampling threshold. As stage increased, samples were 

collected with each 0.2-foot (ft) increase in stage; as stage 

decreased, samples were collected with each 0.3-ft decrease 

in stage. The sampling strategy was designed to collect more 

samples during increasing stage, when the concentration of the 

constituents of interest would likely be changing most rapidly. 

After a sampling event, the samples were collected from the 

gaging station, chilled on ice in coolers, processed at the 
Methods 3

Bower Creek

Bower Creek

#

#

#

44°22'30"

87°59'30"

44°24'30"

87°56'30"

WISCONSIN

EXPLANATION

Basin boundary

# Water quality

*#

Rainfall

0

0

1 MILE

1 KILOMETER

BROWN 

COUNTY

Bower Creek

watershed

Green Bay

De Pere

Kewaunee

Base modified from U.S. Geological Survey

Bellevue, 1973, 1:24,000

De Pere, 1973, 1:24,000

Green Leaf, 1973, 1:24,000

Morrison, 1973, 1:24,000

Figure 1. Location of the Bower Creek Watershed and data-collection sites in Brown County, Wisconsin.
4 Effects of Best-Management Practices in Bower Creek in the East River Priority Watershed, Wisconsin, 1991–2009

Bower Creek

Bower Creek

Cropland 

(83.10)

Woodlot (6.00)

Percentage of total land use and land cover

Road (3.20)

Farmstead (3.30)

Other* (4.40)

*Includes pasture, grassland, grazed woodlot, 

 open water, wetland, and residential categories

Cropland

Pasture

Grassland

Woodlot

Grazed woodlot

Open water

Wetland

Farmstead

Residential

Road

Basin boundary

Land use and land cover type

EXPLANATION

0

0

1 MILE

1 KILOMETER

Land use and land cover interpreted 

from Brown County, 1986, 1:4,800 

orthophotos

44°22'30"

87°59'30"

44°24'30"

87°56'30"

Figure 2. Land use and land cover from 1986 in the Bower Creek Watershed, Brown County, Wisconsin.
Methods 5

EXPLANATION

Soil type

Kewaunee silt loam

Kewaunee-Manawa complex

Manawa silty clay loam

Other

Poygan silty clay loam

Basin boundary

Streams

Kewaunee-Manawa 

complex, 21 percent

Manawa

silty clayloam, 

21 percent

Poygan silty clay loam,

6 percent 

Other, 

4 percent

Kewaunee silt loam,

62 percent 

44°22'30"

87°59'30"

44°24'30"

87°56'30"

0

0

1 MILE

1 KILOMETER

Soil information from the Digital General Soil Map of the United States

U.S. Department of Agriculture, Natural Resources Conservation Service, 2006

Figure 3. Soil types in the Bower Creek Watershed, Brown County, Wisconsin.
6 Effects of Best-Management Practices in Bower Creek in the East River Priority Watershed, Wisconsin, 1991–2009

USGS field office, and then transported to the Wisconsin State 

Laboratory of Hygiene to be analyzed for total suspended 

solids, total phosphorus, and dissolved ammonia nitrogen as 

nitrogen using standard methods (Wisconsin State Laboratory 

of Hygiene, 1992; American Public Health Association, 1989, 

1992). Values for TSS and ammonia-nitrogen were censored 

based on the analytical detection levels. The detection levels 

for TSS were 2 mg/L before September 1994, and 5 mg/L after 

September 1994. The detection levels for ammonia-nitrogen 

were 0.027 mg/L before 1998 and 0.015 mg/L after 1998. 

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. The fixed interval during 

the sampling periods was 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 also were analyzed for total 

suspended solids, total phosphorus, and dissolved ammonia 

nitrogen.

Rainfall was measured throughout the study period at 

three locations within the watershed (fig. 1). One rain gage 

was at the stream-gage location, and 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 rainfall 

was computed as a weighted average using the Thiessen 

polygon areas as the weighting factor (Viessman and others, 

1977). Rainfall was collected in an 8-inches (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. Rain gages were calibrated annually.

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 contained the land-use and BMP 

inventories. Watershed boundaries, hydrography, roads, 

streams, woodlots, rain gages, and BMPs were digitized from 

1:24,000 topographic maps. Farm-field and parcel mapping 

was done by the USGS staff by digitizing orthophotos. 

Detailed descriptions of each watershed and the BMP program 

were reported in Rappold and others (1997), and Wierl and 

others (1996).

Wisconsin’s administrative rules to address the control 

of polluted runoff from rural areas are specified in the 

Wisconsin administrative code for natural resources, chapter 

NR120, “The Priority Watershed and Priority Lake Program.” 

(Wisconsin Department of Natural Resources, 1978). The 

rules identify the most effective BMPs to control nonpoint 

pollutants. The state of Wisconsin could cost-share as 

much as 70 percent of the practices identified. The Priority 

Watersheds Program selected, assessed, and approved the 

East River project between 1985 and 1991. Bower Creek is 

in the East River Watershed and was administered under the 

East River Priority Watershed project. The voluntary signup 

period for BMPs started in March 1991 and lasted until 

February 2006. Monitoring of the post-BMP implementation 

began on October 1, 2006, after most practices were installed 

and operational.

Targeted and implemented BMPs for the Bower Creek 

Watershed are summarized in table 1. The initial BMP targets 

were determined by Brown County based on an assessment 

on potential water-quality effect in Bower Creek. Annual 

updates of practices— animal-waste management, streambank 

protection, and upland management—were obtained by 

contacting the Brown County Land Conservation Department. 

Animal-waste management systems are installed to reduce the 

amount of organic matter reaching the stream by improving 

the cattle lots and adding filter strips. Streambank protection 

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. Riparian buffer strips reduce erosion from the 

Table 1. Summary of targeted and implemented rural bestmanagement practices in the Bower Creek Watershed, Brown 

County, Wisconsin.

[BMP, best-management practice]

Management 

practice Targeted Implemented

Animal-waste management

Manure storage (facilities) 9 1

7

Barnyard-runoff control systems 

(facilities)

32 16

Milkhouse wastewater treatment 

(facilities)

2 2

Streambank protection

Stream shaping, seeding and riprap 

(feet)

2,320 2,013

Fencing (feet) 625 625

Stream crossing (numbers of crossings) 1 1

Grade stablization (structures) 0 1

Buffer strips (acres) 0 16.4

Upland management2

Nutrient management (acres) 4,020 1,939

Upland BMPs (acres) 4,480 1,564

1

There were 17 other manure storage facilities implemented by previous 

farm programs.

2

Upland BMPs include change in crop rotation, reduced tillage, critical 

area stabilization, grass waterways, and pasture management.
Methods 7

land surface near the stream by limiting agricultural activities, 

providing more natural vegetation within a 25–35 foot buffer 

from the streambank. Upland-management practices are 

designed to reduce the amount of sediment and nutrients 

delivered with runoff or subsurface drainage by cropland, 

manure, and fertilizer management. Upland-sediment and 

runoff control practices include change in crop rotation, 

reduced tillage, critical area stabilization, grass waterways, 

and pasture management.

In 2006, most of the BMP installation goals set by the 

WDNR and local Land Conservation Department had been 

achieved in the Bower Creek Watershed. Additional practices 

could be implemented for several years, but it was felt that 

many sources of nonpoint pollution had been controlled by 

the practices that had been implemented and there were no 

immediate plans to implement more BMPs for sources that 

were not controlled. The land-use tracking was discontinued in 

2007 when the post-BMP monitoring phase ended. The status 

of barnyard and streambank protection practices as of 2009 is 

shown in figure 4. The barnyard installations from before the 

study period and during the study period are distinguished by 

different symbols on this figure.

0

0

1 MILE

1 KILOMETER

!

!

!

!

!

!

!

!

!

!

!

!

!

!

!

!

!

"

"

"

"

"

"

"

"

Bower Creek

Bower Creek

EXPLANATION

Grassed waterway

Streambank protection Barnyard control system

Previously installed barnyard practices

Manure storage

Basin boundary

Base modified from U.S. Geological Survey

Bellevue, 1973, 1:24,000

De Pere, 1973, 1:24,000

Green Leaf, 1973, 1:24,000

44°22'30"

87°59'30"

44°24'30"

87°56'30"

Figure 4. Animal-waste management, streambank protection, and grass 

waterways implemented during the study period in the Bower Creek Watershed, 

Brown County, Wisconsin.
8 Effects of Best-Management Practices in Bower Creek in the East River Priority Watershed, Wisconsin, 1991–2009

Hydrologic Conditions During the 

Study Period

Precipitation: The 30-year normal annual precipitation 

is 29.19 in. at the National Oceanic and Atmospheric 

Administration (NOAA) weather station in Green Bay, Wis., 

and 31.9 in. at the NOAA weather station in Kewaunee, Wis. 

(National Oceanic and Atmospheric Administration, 2010). 

Long-term averages from 1862 through 2009 are 31.8 in. at 

Green Bay (1886 through 2009) and 30.3 in. at Kewaunee 

(National Oceanic and Atmospheric Administration, 2010). 

Data collected at the NOAA gages indicate that precipitation 

during the study period was less than the long-term average 

for 2 of 3 years during the pre-implementation phase and 1 

of 3 years during the post-implementation phase of the study 

(fig. 5). The largest deviation between annual precipitation 

and the long-term average was in calendar year 1993, when 

the precipitation was 36.51 in. at Green Bay and 38.03 in. at 

Kewaunee.

Monitored storms during the study period ranged in 

rainfall depth from 0.19 to 3.23 in. The median depth of 

rainfall of 0.79 in. from the monitored storms was less during 

the pre-BMP implementation period than 0.93 in. observed 

during the post-BMP implementation period. The distribution 

of rainfall depth from monitored storms during the preBMP implementation period indicates that the pre-BMP 

implementation-period storm depths were slightly less than 

those from the post-BMP implementation period (fig. 6).

Streamflow: Streamflow data were collected continuously 

during the study period and published each year in “Water 

Resources Data, Wisconsin” for water years 1991 through 

1997 and 2007 through 2009 (Holmstrom and others, 

1992–1998; U.S. Geological Survey, 2008–10). These data 

0

5

10

15

20

25

30

35

40

Precipitation, in inches

Green Bay

Kewaunee Kewaunee long-term average 

(29.44 inches) Green Bay long-term average

(28.97 inches)

1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009

EXPLANATION

Year

Figure 5. Yearly precipitation throughout the study period and long-term average yearly precipitation at Green Bay and 

Kewaunee, Wisconsin.
Hydrologic Conditions During the Study Period 9

0

0.20

0.40

0.60

0.80

1.00

0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

Cumulative frequency

Rainfall, in inches

Pre-best-management practice (BMP)

Post-best-management practice 

EXPLANATION

Figure 6. Cumulative rainfall distributions for the pre- and postBMP (best-management practices) implementation period at 

Bower Creek, Brown County, Wisconsin.

were used to determine streamflow characteristics and to 

compute nutrient and total suspended solids loads. In addition, 

daily mean base-flow contributions were separated from 

the daily mean streamflows (White and Sloto, 1990), and 

overland runoff (stormflow) was determined by computing 

the difference between daily mean streamflow and daily 

mean base flow. The mean annual streamflow at Bower Creek 

during the study period was 7.90 ft3

/s, of which 36 percent 

was base flow (figs.7–9). The mean flow for the pre-BMP 

implementation period was 10.6 ft3

/s (37 percent base flow) 

and for the post-BMP implementation period was 6.1 ft3

/s 

(34 percent base flow). The greatest mean overall streamflow 

and base flow occurred in 1993.

Seasonal and Hydrologic Distribution of Loads: 

Daily mass loads were computed for total suspended solids, 

total phosphorus, and dissolved ammonia nitrogen for the 

monitoring period. These values were used to compute mean 

monthly loads to understand how the loads were distributed 

throughout the year (fig. 8). Additionally, streamflow and 

loads were separated into annual (fig. 9) and monthly (fig. 10) 

base-flow and stormflow contributions.

Overall, the largest contributions of streamflow and 

loadings occur in March, April, June, and July, but there 

is some variability in this conclusion among different 

constituents. A summary of the main seasonal and hydrologic 

patterns observed in these data are as follows:

• Streamflow: Total streamflow contributions during 

March, April, and June accounted for 68 percent of 

annual streamflow, 54 percent of which was in March 

and April. Streamflow was lowest from August through 

October. Average annual stormflow contribution was 

nearly double that from base-flow periods. Average 

monthly stormflow contributions were greater than 

or nearly the same as those from base-flow periods 

for all months. The peaks of base-flow and stormflow 

volumes occurred in March and April with a secondary 

peak in June.

• Total suspended solids loadings: Total suspended solids 

loadings during April were 29 percent, and June and 

July accounted for 55 percent of the annual loadings. 

Average annual total suspended solids loadings 

were dominated by stormflow periods (92 percent) 

as compared to base-flow periods. Average monthly 

contributions of total suspended solids loads were 

greater during stormflow periods than during baseflow periods in all months except January. The greatest 

stormflow contributions occurred during March, April, 

June, and July. 

• Total phosphorus loadings: Total phosphorus from 

March, April, and June accounted for 72 percent of 

annual loadings, of which 56 percent was in March and 

April. Average annual total phosphorus loadings were 

greater during stormflow periods (79 percent) than 

during base-flow periods. Average monthly loads were 

greater during stormflow periods than during base-flow 

periods for all months.

• Dissolved ammonia nitrogen loadings: Dissolved 

ammonia nitrogen from March and April accounted 

for 68 percent of annual loadings. Average annual 

dissolved ammonia-nitrogen loadings were greater 

during stormflow periods (68 percent) than during 

base-flow periods. Average monthly loadings were 

dominated by the months of March and April, with 

base-flow contributions of 28 percent and stormflow 

contributions of 40 percent of the mean annual load 

during those 2 months. Stormflow loadings were also 

greater during all other months of the year as well.

The distribution of average monthly loads and average 

annual loads suggests that different constituents exhibit 

different behaviors depending on their particulate and 

dissolved fractions. Total suspended solids consists of 

100 percent particulate matter, total phosphorus is comprised 

of particulate and dissolved fractions, and dissolved ammonia 

nitrogen is completely in solution. Total suspended solids 

loads are dominated by stormflow; total phosphorus loads are 

greater in stormflow, but base flow is more influential than for 

total suspended solids; and dissolved ammonia-nitrogen loads 

are greater in stormflow, but still more affected by base flow 

than total phosphorus. These data suggest that the loadings for 

constituents containing particulate fractions are greater during 

stormflow, and loadings for constituents containing dissolved 

fractions have increased loadings during base flow. With this 

information and the monthly load data, it is apparent that the 

transport mechanisms and sources of these three constituents 

vary to some degree. Two primary pathways from sources 

to the stream are through surface runoff and groundwater 

discharge. The pathway of total suspended solids would 

be limited mainly to surface runoff, whereas the dissolved 

fractions of total phosphorus and ammonia nitrogen can also 

be transported through the shallow groundwater system and 
10 Effects of Best-Management Practices in Bower Creek in the East River Priority Watershed, Wisconsin, 1991–2009

50

504540353025201510

Percent baseflow

76543210

Annual average daily mean base flow

Full yearPartial year

86420

201816141210

Streamflow, in cubic feet per second

86420

141210

Streamflow, in cubic feet per second

Base flow, in cubic feet per second

1991 1992 1993 1994 1995 1996 1997 2007 2008 2009 1998–

2006

1991 1992 1993 1994 1995 1996 1997 2007 2008 2009 1998–

2006

No flow collected from 1998–2006 No flow collected from 1998–2006

No flow collected from 1998–2006 No flow collected from 1998–2006

EXPLANATION

Base flow as a percentage of total annual flow

Annual average daily mean flow

Pre-best-management practice (BMP)

Post-best-management 

practice

Annual average daily mean stormflow (total flow–base flow)

Pre-best-management practice (BMP)

Post-best-management 

practice

Year Year

Figure 7.

Annual streamflow, base flow, and stormflow at Bower Creek, Brown County, Wisconsin, for water years 1991–1997 and 2006–2009.
Hydrologic Conditions During the Study Period 11

0

5

10

15

20

25

30

35

40

45

50

Percentage of annual total

Streamflow

Total suspended solids

Total phosphorus

Dissolved ammonia nitrogen

EXPLANATION

January February March April May June July August September October November December

Year

Figure 8. Average monthly distribution of streamflow and total suspended solids, total phosphorus, and dissolved ammonianitrogen loads at Bower Creek, Brown County, Wisconsin, water years 1991–1997 and 2006–2009.

discharged to the stream in base flow. Solids tend to settle out 

more during base-flow periods because stream velocities are 

less during these periods than during storms.

Higher concentrations and loads of dissolved ammonia 

nitrogen in winter could have several contributing factors. 

Winter spreading of manure on crop lands may result in 

greater concentrations and loads because infiltration and 

movement in the soil would be reduced on frozen ground, 

microbial organisms needed for oxidation of ammonium 

would not be as active in cold winter and spring temperatures, 

and contact with soils that have the potential to remove 

ammonium from the manure-affected runoff while it migrates 

into groundwater or to drain tiles would be reduced. In 

general, the applied manure is more likely to reach the 

stream because of these conditions during stormflow periods 

for runoff. Loads and flows are also greatest for base-flow 

periods in March and April. Soils are typically at a high level 

of saturation during these months, leading to increased base 

flow levels that would also generate increased loadings of 

ammonia nitrogen.

The implications of this information on identifying 

sources of individual constituents are as follows: Total 

suspended solids contributions would be greatest from areas 

of active surface runoff; land uses that promote infiltration 

would decrease total suspended solids loads. Total phosphorus 

and dissolved ammonia nitrogen would be greatest from 

areas of active surface runoff, but the dissolved fraction could 

also enter the stream through infiltration and subsequent 

groundwater subsurface drainage transport such as tiles to 

the stream; land uses that promote infiltration would reduce 

the phosphorus and dissolved ammonia-nitrogen load 

during surface-runoff periods but may or may not change 

the total phosphorus and dissolved ammonia-nitrogen load 

during base-flow periods. In addition, dissolved phosphorus 

may be introduced by desorption from sediments in the 

stream channel.

These results are not unique in this region of Wisconsin. 

Data collected in a companion project at Otter Creek in 

Sheboygan Co., Wis., resulted in similar conclusions regarding 

seasonal distribution of loads (Corsi and others, 2005). The 

largest contributions of all three constituents in Otter Creek 

were from February through April with a secondary peak 

of total suspended solids and total phosphorus in June and 

July. Contributions from storm periods were greater than that 

from base-flow periods for total suspended solids and total 

phosphorus, but base-flow and stormflow contributions for 

Stormflow

Base flow

EXPLANATION

0

10

20

30

40

50

60

70

80

90

100

Streamflow Total suspended

solids

Total phosphorus Dissolved ammonia

Percent of total

Constituent

Figure 9. Average relative annual contributions of stormflow 

and base-flow periods to streamflow, total suspended solids, total 

phosphorus, and dissolved ammonia-nitrogen loadings at Bower 

Creek, Brown County, Wisconsin, for water years 1991–1997 and 

2006–2009.
12 Effects of Best-Management Practices in Bower Creek in the East River Priority Watershed, Wisconsin, 1991–2009

0

5

10

15

20

25

30

Percent of annual load

Total phosphorus

0

2

4

6

8

10

12

14

16

18

20

Percent annual water volume 

Streamflow

Base flow

Stormflow

0

5

10

15

20

25

30

35

40

Total suspended solids

January February March April May June July August September October November December

January February March April May June July August September October November December

EXPLANATION

Base flow

Stormflow

EXPLANATION

Base flow

Stormflow

EXPLANATION

Year

Year

Figure 10. Average monthly streamflow and loads of total suspended solids, total phosphorus, and 

dissolved ammonia nitrogen during base-flow and stormflow periods, expressed as a percentage of the 

annual total water volume and constituent loads at Bower Creek, Brown County, Wisconsin.
Water Quality Before and After Installation of Best-Management Practices 13

dissolved ammonia nitrogen were nearly equal. A broader 

study of small watersheds throughout Wisconsin included 

examination of total suspended solids and total phosphorus 

loads in different ecoregions (Danz and others, 2010). Results 

were more variable than Otter and Bower Creek, but still 

indicated that load contributions were greatest from late winter 

to early summer except for August–September peaks of total 

suspended solids in the Northern lakes and Forests/North 

Central Hardwoods region. Similar to Otter Creek and Bower 

Creek, stormflow contributions exceeded that of base-flow 

contributions of total suspended solids and total phosphorus.

Water Quality Before and After 

Installation of Best-Management 

Practices

The primary objective of this study was to evaluate 

overall BMP effectiveness at the watershed scale. BMPs 

installed in the Bower Creek Watershed over the course 

of the study can potentially affect the stream in numerous 

different ways. Changes in water chemistry were evaluated 

using results from base-flow sampling and also by evaluating 

storm loads from rainfall periods. Land-use data were used to 

interpret results from these analyses and to help understand the 

effects of individual BMP types.

Constituent Concentrations at Base Flow

Base flow in Bower Creek consists of groundwater 

contributions, including that from drain tiles. Water-quality 

sample results from base-flow concentrations, therefore, will 

reflect groundwater discharges, and direct surface effect and 

in-stream processes. Consequently, base-flow water quality 

may be affected by some land-use practices in the watershed 

that affect direct surface influences (such as streambank 

protection) and others that affect infiltration to ground water 

(such as filter strips).

Fixed-interval water-quality samples were collected 

throughout the pre- and post-BMP implementation periods. 

Base-flow samples were separated from the fixed-interval 

samples for use in subsequent data analysis. Base-flow 

samples were identified by use of a combination of techniques. 

First, daily mean streamflow was separated into base-flow 

and overland-runoff components. For any given fixed-interval 

sample, if the ratio of instantaneous discharge to daily mean 

base flow was less than or equal to 0.95, that sample was 

considered to be a potential base-flow sample. In addition, an 

estimation of the time lag for overland runoff in the watershed 

was computed as the drainage area in square miles raised to 

the exponent 0.2 (Viessman and others, 1977). The overlandrunoff time lag was estimated to be 1.7 days for Bower Creek, 

so potential base-flow samples that were collected within 

1.7 days of the peak of a hydrograph were not considered to be 

base-flow samples.

During the study, a total of 56 samples for total 

suspended solids, 56 samples for total phosphorus, and 

53 samples for dissolved ammonia nitrogen were collected 

during conditions that qualified as base flow (fig. 11).

Statistical analyses (Wilcoxon rank-sum test) were 

used to test for significant differences between base-flow 

results from samples collected during the pre- and post-BMP 

implementation periods (Helsel and Hirsch, 1992). Results of 

the Wilcoxon rank-sum nonparametric test indicate significant 

differences at the 95-percent confidence level between preand post-BMP base-flow concentrations for total phosphorus 

but not for total suspended solids and dissolved ammonia 

nitrogen (table 2).

The lack of significant change in ammonia-nitrogen 

concentrations during base flow in Bower Creek is similar to 

results from all but one (Garfoot Creek) of the other Whole 

Stream Monitoring watersheds. 

Storm Loads

Because much of the annual total suspended-solids 

and nutrient transport occurs during storms, fixed-interval 

sampling—particularly at a monthly frequency—may not 

indicate changes resulting from BMP implementation (Walker, 

1993). Consequently, mass transport resulting from individual 

rainfall storms was analyzed. Stream water was sampled 

numerous times per storm for each storm used in the analysis 

(average of 10 samples per storm, minimum of 2 samples per 

storm, and maximum of 32 samples per storm). Instantaneous 

mass transport of a particular constituent was 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 within a storm period were 

kept to a minimum.

Variability in storm loads caused by differences in 

rainfall, temporal land surface variability, and other processes 

can be large enough to mask potential differences in the 

pre- and post-BMP implementation periods. In addition, 

because the pre- and post-BMP implementation 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 
14 Effects of Best-Management Practices in Bower Creek in the East River Priority Watershed, Wisconsin, 1991–2009

2

5

10

20

50

Total suspended solids, 

in milligrams per liter

Measured value 

Censored value

Annual median

0.1

0.2

0.5

1.0

Total phosphorus, 

in milligrams per liter

Dissolved ammonia-nitrogen, 

in milligrams per liter

1991 1993 1995 1997 1999 2001 2003 2005 2007 2009

0.02

0.05

0.10

0.20

0.50

1.00

EXPLANATION

Measured value 

Censored value

Annual median

EXPLANATION

Measured value 

Censored value

Annual median

EXPLANATION

Pre best-management practice 

(BMP)

Post best-management 

practice

Year

Figure 11. Concentrations and water-year medians of total suspended solids, total phosphorus, and dissolved ammonia nitrogen in 

base-flow samples throughout the study period at Bower Creek, Brown County, Wisconsin.
Water Quality Before and After Installation of Best-Management Practices 15

Table 2. Results of Wilcoxon rank-sum test for differences between constituent concentrations in baseflow samples from pre- and post-best management practice implementation periods at Bower Creek, 

Brown County, Wisconsin.

[BMP, best-management practice; mg/L, milligrams per liter; bold text indicates a statistically significant change in concentration between pre- and post-BMP implementation periods]

Response variable

Number of 

samples for 

pre-/postBMP periods

Median concentration (mg/L)

Pre-BMP Post-BMP Significance

level

Total suspended solids 29/15 10.0 10.0 0.691

Total phosphorus as P 29/15 0.340 0.235 0.026

Dissolved ammonia nitrogen as N 29/12 0.139 0.149 0.398

solution is to perform regressions relating the storm loads 

to variables representing climatic and seasonal conditions. 

If the explanatory variables remove variability representing 

the natural climatologic and seasonal conditions, then the 

variability remaining in the regression residuals represents 

the combination of changes induced by the BMPs and 

model error. Because the regression, by design, reduces the 

variability in the data, it should theoretically be possible to 

detect smaller differences between the pre- and post-BMP 

implementation periods than to detect differences by using the 

storm loads directly.

Several explanatory variables were selected for use 

in the regressions, most of which were based on various 

measures of rainfall or antecedent watershed conditions for 

each distinct rainstorm. These included total rainfall (P), the 

15- and 30-minute maximum intensities (I15 and I30), and 

the Universal Soil Loss Equation (USLE) erosivity index 

(EI) (Wischmeier and Smith, 1978). Additional rainfallbased measures included the 1-, 3-, and 5-day antecedent 

rainfall (API1, API3, and API5), which is computed as the 

total rainfall for the 1, 3, and 5 days before the beginning 

of each storm, respectively. For this, terms combining total 

rainfall and the antecedent rainfall also were considered 

(for example, P+API1). Antecedent base flow (base flow on 

the day before the storm) was used as another measure of 

watershed condition preceding the storm. Finally, two seasonal 

terms were included to allow for variations arising solely on 

the basis of the time of year. The seasonal terms were based 

on the serial date of the storm (T), using a period of 1 year, 

and sine and cosine terms to allow for amplitude and phaseshift 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 this would 

result in erroneous conclusions when comparing pre- and 

post-BMP implementation periods, the final regressions were 

based on a logarithmic transformation of the storm loads, thus 

assuring that negative loads cannot be predicted.

For each constituent, stepwise regressions were done 

on the explanatory variables described above (table 3). For 

each regression, additional variables were considered if the 

improvement in the resulting regression was considered 

large enough to warrant their use (a coefficient significantly 

different from zero at the 95-percent confidence level). In 

addition, various regression plots were examined to verify 

that the underlying assumptions of regression analysis were 

not violated.

Previous watersheds evaluated for BMP effectiveness 

through this program indicated that statistically significant 

differences of the median storm load could be detected at 

reduction levels of 28–89 percent (Graczyk and others, 

2012; Corsi and others, 2005; and Graczyk and others, 

2003). In addition, differences in median storm loads were 

observed between 18 and 73 percent that were not statistically 

significant. For Bower Creek, an evaluation of detectable 

change was determined to be between 37 and 76 percent based 

on evaluation of pre-BMP period data (Walker and others, 

1995). The ability to detect changes that are significant relies 

Table 3. Regression results for storm loads from rainfall periods from 1990–1997 and 2006–2009 at Bower Creek, Wisconsin.

[R2, fraction of the variance of response variables explained by the explanatory variables for the model; Lbf, natural log of base flow on the previous day; API1, 

sum of rainfall for 24 hours preceding the event; API3, sum of rainfall for 3 days preceding the event; T, serial date of the storm; P, total precipitation; LEi, 

natural log of the Universal Soil Loss Equation erosivity index] 

Response variable Explanatory variables Sample 

size

Adjusted 

R2 Standard error Standard error (percent)

Total suspended solids Lbf, API1, API3, sin(T), P+API1, P+API3 34 0.63 1.36 182

Total phosphorus as P Lbf, API1, API3, P+API1, P+API3 34 0.63 1.02 120

Dissolved ammonia nitrogen as N Lbf, P+API1, LEi 32 0.462 1.37 184
16 Effects of Best-Management Practices in Bower Creek in the East River Priority Watershed, Wisconsin, 1991–2009

on the magnitude of change as well as variability in the storm 

load residuals after regressions have been applied.

The regression residuals were tested for differences 

between the pre- and post-BMP implementation periods 

(table 4). The median storm loads from rainfall periods 

for all three constituents for the pre-BMP and post-BMP 

implementation periods are also listed in table 4. Regression 

residuals for the two periods were compared statistically by 

means of the Wilcoxon rank- sum test, as described previously 

in the section Water Quality Before and After Installation of 

Best-Management Practices. 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 total suspended solids and total phosphorus, a 

decrease was observed in median storm loads from rainfall 

periods. For dissolved ammonia nitrogen, an increase was 

observed. Testing the storm-load residuals demonstrates that 

these changes were not statistically significant for any of 

the constituents at the 95-percent confidence level (table 4). 

Therefore, the differences in pre- and post-BMP conditions 

are likely not due to the BMPs installed, but more likely 

to be due to natural variability from variable hydrologic or 

seasonal conditions.

Effects of Best-Management Practices 

on Bower Creek

A substantial number of BMPs were implemented in 

the three primary categories targeted in the Bower Creek 

watershed (table 1). For the animal-waste category, about 

70 percent of the targeted manure storage and barnyardrunoff control systems were implemented. Installation of the 

barnyard-runoff control systems provided the extra benefit of 

controlling most of the animal access to the stream channels, 

because the Bower Creek stream channel was previously 

accessed by livestock in or adjacent to the feedlots. All 

targeted stream bank fencing, shaping, and seeding listed 

under the stream bank protection category was completed 

during the project period. A new county ordinance requiring 

20- to 35-foot riparian buffer strips resulted in over 16 acres 

of riparian buffer strips. Implementation of BMPs in the 

upland management category included preparation of nutrient 

management plans for most of the farms and almost 50 percent 

of the upland BMPs implemented. A description of individual 

BMPs and their potential effects on water quality has been 

previously published (Graczyk and others, 2003).

Effects of BMPs on Water Quality

Despite the implementation of many BMPs in the Bower 

Creek Watershed, the sampling results indicate no substantial 

improvement in most measures of water quality.

Base-flow concentrations were significantly reduced 

for total phosphorus, but not for total suspended solids and 

dissolved ammonia nitrogen. Storm loads observed after 

implementation of BMPs were not significantly different than 

those observed before implementation began. Significant 

improvements in water quality have been observed at other 

Whole Stream Monitoring projects (Graczyk, 2003; Corsi, 

2005; Graczyk, 2012). At 4 of the 5 other streams included in 

the Whole Stream Monitoring projects, a significant reduction 

was observed in pollutant concentrations during base flow and 

storm loadings.

Understanding the effects of specific pollutant sources in 

a watershed is a complex task. Important factors include the 

land use, topography, condition of the land, proximity to the 

stream, likelihood of runoff from each area to reach the stream 

under different conditions, BMPs installed, effectiveness of the 

BMPs, human actions that affect drainage, and other factors. 

To keep a detailed inventory of all of these factors requires 

personnel resources that are often not available to watershed 

managers. Without a detailed inventory, a substantial amount 

of uncertainty exists in evaluation of source effects on water 

quality. Given this uncertainty and the expected benefits of 

each BMP to the overall quality of a stream, it is difficult 

to explain why this level of BMP implementation did not 

do more to improve the water quality in Bower Creek. For 

the purpose of improving BMP implementation efforts in 

the future, it is important to explore potential reasons that 

improvements in base-flow concentrations and storm loads 

were not observed for Bower Creek Watershed.

Base-flow Concentrations: Results from other monitoring 

projects in Wisconsin agricultural watersheds might help 

Table 4. Median and mean rainfall-period storm loads and results of the Wilcoxon rank-sum test comparing storm-load 

residuals for pre- and post-best management practice implementation periods at Bower Creek, Wisconsin.

[BMP, best-management practice; lbs, pounds]

Variable

Median storm loads Mean storm loads Storm-load residuals

Pre-BMP Post-BMP Pre-BMP Post-BMP Significance level

Total suspended solids (tons) 18.98 9.51 151 103 0.551

Total phosphorus as P (lbs) 228 185 790 533 0.91

Dissolved ammonia nitrogen as N (lbs) 59 145 261 163 0.61
Effects of Best-Management Practices on Bower Creek 17

explain the lack of response in the base-flow concentrations 

of ammonia nitrogen and total suspended solids. A reduction 

in total phosphorus base-flow concentrations indicate some 

benefit of the BMPs, such as limiting cattle access to the 

stream and nutrient management, but the post-BMP median 

base-flow concentration of 0.24 milligrams per liter (mg/L) 

is still much higher than the 0.075 mg/L targeted for streams 

of this size (Robertson and others, 2006). Results from the 

three other Whole Stream Monitoring projects indicated that 

median total phosphorus concentrations during pre-BMP base 

flow were from 0.07 to 0.09 mg/L compared to a much higher 

median of 0.34 mg/L at Bower Creek (Graczyk, 2003: Corsi, 

2005; Graczyk, 2012). A large number of drain tiles have 

been installed in the Bower Creek Watershed (Jon Bechle, 

Brown County Land and Water Conservation Department, oral 

commun. 2012), which could be an important delivery system 

of total phosphorus to Bower Creek during non-event periods. 

Results from monitoring of drain tiles for the Discovery 

Farm program in Wisconsin indicated that drain tiles can 

flow all year long, and contribute substantial amounts of total 

phosphorus and ammonia nitrogen to the receiving streams 

(Discovery Farms, 2010). BMP implementation in the Bower 

Creek watershed did not focus on reduction of non-event flows 

from drain tiles (Jon Bechle, Brown County Land and Water 

Conservation Department, oral commun. 2012).

Total suspended solids concentrations measured during 

base-flow conditions for the three other Whole Stream 

Monitoring projects indicate a significant reduction in the total 

suspended solids concentration. This result was attributed 

to a large pre-BMP concentration followed by a large 

reduction in the number of cows with access to the stream 

(Graczyk, 2003: Corsi, 2005; Graczyk, 2012). A reduction 

in the base-flow concentration of total suspended solids in 

Bower Creek might be expected, because most of the cow 

access to the stream was reduced. This benefit might not have 

been observed, because of the low median pre-BMP total 

suspended solids concentration of 10 mg/L and the fact the 

drain tiles can contribute total suspended solids to the stream 

most of the year (Discovery Farms, 2010). In comparison, 

pre-BMP median base-flow concentrations for five other 

streams evaluated previously ranged from 9 mg/L to 62 mg/L 

(Graczyk and others, 2003; Corsi and others, 2005, Graczyk 

and others, 2012).

Storm Loads: Unlike base-flow concentrations, storm 

loads are more a consequence of sources activated by runoff 

events. These sources include upland areas, barnyards, and 

woodlots as well as eroding stream banks and drain tiles that 

were previously discussed as contributing to elevated baseflow concentrations. Woodlots are 6 percent of the watershed 

and not considered to be a critical source of contaminants, 

but storm loads generated by the rest of sources in the Bower 

Creek watershed are considered high. Results from monitoring 

small watersheds in the Southeastern Wisconsin Till Plains 

ecoregion indicated that Bower Creek had the second largest 

annual median total suspended solids (of 14 sites) and total 

phosphorus (of 12 sites) unit area loads at 131 tons/mi2

 and 

685 pounds per square mile respectively (Corsi and others, 

1997). In the present study, storm loads accounted for 

92 percent of total suspended solids loads, 79 percent of total 

phosphorus loads, and 64 percent of ammonia nitrogen loads 

(fig. 9). Such high storm loads would seem to make it easier to 

observe some reduction as a result of BMPs, but emphasis on 

storm loads also means targeting the sources with the largest 

storm load potential is important. All of the above sources 

must be considered when evaluating the potential reasons the 

management practices did not significantly reduce the storm 

loads in the Bower Creek watershed.

Two potential reasons the storm loads were not reduced 

are (1) changes in productivity for the population of milk 

cows in the watershed and (2) the existing BMPs do not 

address all the sources. In the approximate time frame of 

the monitoring activities (1981 to 2008) there was only a 

small increase in the number of cows in Brown County, 

but the average milk production grew from 13,200 to 

22,300 pounds per cow per year which is also thought to 

reflect changes in milk production from the pre-BMP to the 

post-BMP implementation periods (Bechle, oral commun. 

2012). Because milk production increased so substantially, 

manure production also increased (U.S. Department of 

Agriculture, Natural Resources Conservation Service, 2009); 

therefore, field applications of manure increased through the 

study period. In the same time frame, the number of herds 

in Brown County declined from 1,348 to 239, indicating 

that manure was concentrated in fewer places. According to 

Brown County records, this information was also indicative 

of the situation in Bower Creek; therefore, with little change 

in the number of cows in Bower Creek, manure production 

increased, and became more concentrated at fewer farms in 

the watershed throughout the study period. Because of the 

manure distribution systems in place, these circumstances led 

to a greater amount of manure applied to the fields in the postBMP implementation period.

In addition, changes in cropping practices resulted in less 

erosion protection that resulted in less ground cover over the 

winter. The changes in cropping practices included (1) more 

land in soybeans, corn, and wheat; (2) less land in hay and 

other cover crops; (3) less conservation tillage; (4) oats 

eliminated as a crop; and (5) more land in corn silage (Bechle, 

oral commun. 2012). Between 1981 and 2008, the land used 

for growing soybeans in Brown County increased from 200 

to 22,400 acres and the land used for growing hay declined 

from 74,000 to 61,000 acres. With these increases in manure 

production and changes in cropping practices, one may have 

expected storm loads to increase during the monitoring period, 

but no significant change in the storm loads over the study 

period was observed.

Collectively, all of this manure production and cropping 

information may indicate that the implemented BMPs, such 

as animal-waste management and upland management, did 

benefit the watershed by preventing an increase in pollutant 

loadings in Bower Creek. More data would be needed to 

support definitive conclusions on this topic.
18 Effects of Best-Management Practices in Bower Creek in the East River Priority Watershed, Wisconsin, 1991–2009

Given the water quality observed during this study, 

it seems that more BMPs are needed to achieve stormload reduction goals for the existing agricultural activities. 

Results from other Whole Stream Monitoring projects 

indicate sufficient BMPs can be implemented in a watershed 

to reduce the storm loads (Corsi, 2005; Graczyk, 2012). 

Previous management efforts achieved a high level of 

implementation of animal-waste management BMPs, but 

50 percent of the targeted barnyard-runoff control measures 

were not implemented. In addition, there are still substantial 

targeted areas remaining for future implementation of 

upland management BMPs (table 1). Soil test phosphorus 

values (50 to more than 100 ppm) for a number of fields in 

Bower Creek Watershed pose an increased likelihood for 

phosphorus loading contributions to Bower Creek from upland 

erosion (Kelling and others, 2005). Brown County staff have 

recommended more grassed waterways and buffer strips be 

installed in an attempt to reduce sediment and phosphorus 

delivery (Bechle, oral commun. 2012). A large number of 

farms have nutrient management plans in place, but some have 

not been fully implemented because of remaining unaddressed 

concentrated flow areas, such as dead furrows (plowed 

trenches meant to help drain fields more efficiently) and fields 

without grassed waterways (fig. 12). The Brown County staff 

suggests that it may be beneficial to review how well these 

nutrient management plans are being implemented.

An upland pollutant transport system that likely needs 

more consideration and management is the robust network 

of drain tiles within the watershed. This drainage system 

enhances efficiency of runoff and allows farmers access to 

work in fields earlier than without the drain tiles, but it also 

provides an efficient pollutant transport system directly to the 

stream. Previous monitoring of agricultural drain tiles through 

Wisconsin’s Discovery Farms program in Kewaunee County 

determined that 34% of the annual total phosphorus load and 

25% of the sediment load from the monitored fields were 

delivered through the drain tiles (Discovery Farms, 2010). 

Ammonia loads were substantial during periods of frozen 

ground. Installation of runoff management for drain tiles is not 

a BMP category considered for the Bower Creek Watershed, 

but this information from Discovery Farms monitoring results 

indicates that substantial reductions may be possible in Bower 

Creek with management of drain tile runoff.

Comparison of Results to Watershed 

Improvement Objectives

In the Nonpoint Source Control Plan for the East River 

Priority Watershed Project (Wisconsin Department of Natural 

Resources, 1993), the specific objectives for the Bower Creek 

Watershed are the following:

1. Restore wetlands and maintain existing wetlands for 

preservation of wildlife and habitat,

2. Improve the aquatic habitat for the resident 

fish population,

3. Reduce phosphorus delivered to Bower Creek and 

its tributaries,

4. Reduce nutrients delivered to Bower Creek and its 

tributaries, and

5. Reduce sediment delivered to Bower Creek and 

its tributaries.

Preliminary pollutant-reduction goals to help achieve 

these objectives were set at a 50-percent reduction of 

sediment loads and a 70-percent reduction of phosphorus 

loads. Data resulting from this project indicate that the 

water quality generally did not improve. The level of BMP 

implementation was high for all types of targeted areas 

except upland management and barnyard-runoff control 

systems. Considering that an estimated 97 percent of the 

total suspended solids that reaches Bower Creek originates 

from eroding cropland (Wisconsin Department of Natural 

Resources, 1993), additional upland management could 

potentially reduce pollutant loads substantially more.

In comparison to specific objectives of the Nonpoint 

Source Control Plan, the success of the project in meeting 

each individual objective varied. Specific objectives are 

addressed as follows:

1. Because wetlands were not monitored during this project, 

there is no assessment of restoration of wetlands for the 

Bower Creek Watershed.

2. Habitat and biology populations were not monitored 

for this project because flows during some periods were 

non-existent.

3. Median total phosphorus during base-flow periods 

was reduced from 0.34 mg/L in the pre BMP period to 

0.24 mg/L in the post-BMP period, but storm loadings did 

not change.

4. Dissolved ammonia-nitrogen loadings were not reduced 

during the study period.

5. Total suspended sediment loadings were not reduced 

during the study period.
Comparison of Results to Watershed Improvement Objectives 19

A

B

Figure 12. Examples of A, a dead furrow and B, an unaddressed concentrated flow area in the Bower Creek Watershed, 

Brown County, Wisconsin.
20 Effects of Best-Management Practices in Bower Creek in the East River Priority Watershed, Wisconsin, 1991–2009

Summary and Conclusions

The U.S. Geological Survey and the Wisconsin 

Department of Natural Resources began a comprehensive 

evaluation-monitoring program in 1989 to assess the 

effectiveness of best-management practices (BMPs), funded 

through the Wisconsin Nonpoint Source Program. Hydrologic 

and water-quality data were collected at Bower Creek from 

1990 to 2009 with the pre-BMP period ending in July 1994 

and the post-BMP period beginning in October 2006. BMPs 

installed in this watershed included streambank protection and 

fencing, stream crossings, grade stabilization, buffer strips, 

various barnyard-runoff controls, nutrient management, and a 

small amount of upland management.

Water-quality samples were collected during base 

flow and storms for the pre- and post-BMP implementation 

periods. Samples were analyzed for total suspended 

solids, total phosphorus, and dissolved ammonia nitrogen. 

Statistically significant differences between pre- and postBMP implementation periods were detected in median 

concentrations of total phosphorus, but not in total suspended 

solids and dissolved ammonia nitrogen in base-flow samples.

The median storm loads for total suspended solids, total 

phosphorus, and dissolved ammonia nitrogen during rainfall 

periods were compared statistically by means of the Wilcoxon 

rank-sum test. This test was also applied to regression 

residuals to test for differences between the pre- and postBMP implementation periods. Regression equations were 

constructed to remove some of the variability due to natural 

factors; a difference in the regression residuals is more likely 

to indicate a difference in water quality because of the BMPs 

than would a test of differences with the raw storm-load data. 

Differences between the pre- and post-BMP storm loads from 

rainfall periods were not observed for total suspended solids, 

total phosphorus, or dissolved ammonia nitrogen.

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Science Publishing Network, Columbus, Pembroke, and 

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For more information concerning the research in this report, 

please contact:

Center Director

U.S. Geological Survey

Wisconsin Water Science Center

8505 Research Way

Middleton, Wi 53562

http://wi.water.usgs.gov/
Corsi and others—Effects of Best-Management Practices in Bower Creek, 1991–2009—Scientific Investigations Report 2012–5217