Prepared in cooperation with the Michigan Department of Environmental Quality

Comparison of Streamflow and Water-Quality Data 

Collection Techniques for the Saginaw River, Michigan

Scientific Investigations Report 2012–5150

U.S. Department of the Interior

U.S. Geological Survey
Cover: The Saginaw River at Bay City, Michigan. (Cover photograph courtesy of Aaron Toth)
Comparison of Streamflow and WaterQuality Data Collection Techniques for the 

Saginaw River, Michigan

By C.J. Hoard, D.J. Holtschlag, J.W. Duris, D.A. James, and D.J. Obenauer

Prepared in cooperation with the Michigan Department of Environmental Quality

Scientific Investigations Report 2012–5150

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: 2012

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Suggested citation:

Hoard, C.J., Holtschlag, D.J., Duris, J.W., James, D.A., and Obenauer, D.J., 2012, Comparison of streamflow and 

water-quality data collection techniques for the Saginaw River, Michigan: U.S. Geological Survey Scientific Investigation Report 2012–5150, 28 p.
iii

Contents

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

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

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

Saginaw River Watershed...................................................................................................................2

Techniques for Monitoring Streamflow ............................................................................................2

Techniques for Collecting Water-Quality Samples .........................................................................4

Techniques for Collecting Discrete Samples of Suspended Sediment ......................................5

Gaged-Flow Comparison ..............................................................................................................................7

Water Quality Results..................................................................................................................................10

Suspended Sediment and Acoustic Backscatter Results ...........................................................14

Detecting Vertical Variations in Point Measurements of Suspended Sediment 

Concentrations with Down-Looking Acoustic Backscatter Data ........................14

Detecting Temporal Variations in Composite Suspended Sediment Concentrations 

with Side-Looking Acoustic Backscatter Data .......................................................22

Summary........................................................................................................................................................26

References Cited..........................................................................................................................................27

Figures

1. Map showing location of the Saginaw River study area and the surrounding 

area in Michigan...........................................................................................................................3

2. Plot showing channel cross-section and grab- and depth integrating multiple 

vertical sampling locations in the channel of the Saginaw River, Michigan......................4

3. Map showing discrete suspended-sediment sampling locations near 

station 04157061, Saginaw River at Bay City, Michigan.........................................................6

4. Graphs showing daily mean and unit flows at A, station 04157000, 

Saginaw River at Saginaw, and B, station 04157061, Saginaw River at 

Bay City, Michigan from April to September 2009...................................................................8

5. Graphs showing A, residual for daily mean flows between stations 04157000, 

Saginaw River at Saginaw, and 04157061, Saginaw River at Bay City, 

Michigan, and B, the relative percent difference of daily mean flows for 

the two stations.............................................................................................................................9

6. Graphs showing water levels and flows at station 04157061, Saginaw River 

at Bay City, Michigan during suspended-sediment sampling on 

A, July 30, 2009, and B, August 12, 2009..................................................................................17

7. Backscatter contour plot showing locations of suspended-sediment 

concentration measurements along two vertical profiles sampled on 

July 30, 2009, from 11:01 to 11:05 a.m. at station 04157061, Saginaw River 

at Bay City, Michigan .................................................................................................................18

8. Backscatter contour plot showing locations of suspended-sediment 

concentration measurements along two vertical profiles sampled on 

August 12, 2009 from 11:03 to 11:07 a.m. at station 04157061, Saginaw River 

at Bay City, Michigan .................................................................................................................19
iv

9 Graph showing relation between acoustic backscatter and suspendedsediment concentrations from samples along two vertical profiles in July 

and August 2009 at station 04157061, Saginaw River at Bay City, Michigan....................20

10. Graph showing frequency of flow reversals in the Saginaw River at 

Bay City, Michigan in May and August 2009..........................................................................23

11. Graph showing cumulative frequency distribution of integrated flow 

velocities in the Saginaw River at Bay City, Michigan from April to 

September 2009...........................................................................................................................23

12. Graph showing relation between signal amplitude and signal-to-noise ratio 

from Argonaut 500 SL with distance to width bin at the Saginaw River at 

Bay City, Michigan, from April to September 2009................................................................25

13. Graph showing composite suspended-sediment concentration measurements 

and contemporaneous measurements of acoustic amplitude and signal-tonoise ratios from a side-looking acoustic Doppler current profiler in the 

Saginaw River at Bay City, Michigan in 2009.........................................................................25

Tables

1. Physical parameters measured at stations 04156999, Saginaw River at 

Saginaw, and 04157061, Saginaw River at Bay City, Michigan...........................................10

2. Summary of nutrient and sediment concentrations measured at 

station 04156999, Saginaw River at Saginaw, Michigan......................................................11

3. Summary of nutrient and sediment concentrations measured at 

station 04157061, Saginaw River at Bay City, Michigan.......................................................12

4. Results of use of the Wilcoxon two-sided signed-ranks test to compare 

paired depth integrated multiple vertical and surface-grab samples for 

selected constituents collected at collected at station 04156999, 

Saginaw River at Saginaw, and 04157061,Saginaw River at Bay City, 

Michigan and for both stations combined..............................................................................12

5. Median relative percent difference for selected constituents in depth 

integrated multiple vertical and surface-grab samples collected at stations 

04156999, Saginaw River at Saginaw, and 04157061, Saginaw River at 

Bay City, Michigan and for both stations combined.............................................................13

6. Suspended-sediment concentrations and acoustic-backscatter and 

velocity data from measurements at vertical profiles at station 0415761, 

Saginaw River at Bay City, Michigan ......................................................................................15

7. Analysis of variance and parameter estimates for simple linear regression 

relating suspended-sediment concentrations with acoustic backscatter for 

two profiles sampled in July and August 2009 at station 04157061, 

Saginaw River at Bay City, Michigan ......................................................................................21

8. One-way analysis of covariance and parameter estimates relating 

suspended-sediment concentrations with depth by profile and sample month 

at station 04157061, Saginaw River at Bay City, Michigan...................................................21

9. Analysis of covariance and parameter estimates for linear regression relating 

suspended-sediment concentrations with acoustic backscatter for 

two profiles sampled in July and August 2009 at station 04157061, 

Saginaw River at Bay City, Michigan ......................................................................................22
v

Conversion Factors, Abbreviations, and 

Datum Information

Inch/Pound to SI

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

square mile (mi2) 2.590 square kilometer (km2) 

Volume

gallon (gal) 3.785 liter (L) 

Flow rate

foot per second (ft/s) 0.3048 meter per second (m/s)

cubic foot per second (ft3/s) 0.02832 cubic meter per second (m3/s)

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

°F=(1.8×°C)+32

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

°C=(°F-32)/1.8

Vertical coordinate information is referenced to National Geodetic Vertical Datum of 1929 

(NGVD 29).

Horizontal coordinate information is referenced to North American Datum of 1983 (NAD 83).

Altitude, as used in this report, refers to distance above the vertical datum.

Specific conductance is given in microsiemens per centimeter at 25 degrees Celsius 

(μS/cm at 25 °C).

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

dB Decibel

DIMV Depth Integrating Multiple Vertical

EWI Equal Width Interval

kHz Kilohertz

NTRU Nephelometric Turbidity Ratio Unit 
vi

Acknowledgement

The authors wish to thank the Andrew LeBaron and Dawn Roush of Michigan Department of 

Environmental Quality for providing water use information along the Saginaw River. In addition, the authors thank Peter Cinotto and Bonnie Gray of the USGS for technical reviews of this 

manuscript. Elizabeth Ciganovich provided the editorial review and formatted this manuscript 

for publication.
Comparison of Streamflow and Water-Quality Data 

Collection Techniques for the Saginaw River, Michigan

By C.J. Hoard, D.J. Holtschlag, J.W. Duris, D.A. James, and D.J. Obenauer 

Abstract

In 2009, the Michigan Department of Environmental 

Quality and the U.S. Geological Survey developed a plan to 

compare the effect of various streamgaging and water-quality 

collection techniques on streamflow and stream water-quality 

data for the Saginaw River, Michigan. The Saginaw River 

is the primary contributor of surface runoff to Saginaw 

Bay, Lake Huron, draining approximately 70 percent of the 

Saginaw Bay watershed. The U.S. Environmental Protection 

Agency has listed the Saginaw Bay system as an “Area of 

Concern” due to many factors, including excessive sediment 

and nutrient concentrations in the water. Current efforts to 

estimate loading of sediment and nutrients to Saginaw Bay 

utilize water-quality samples collected using a surface-grab 

technique and flow data that are uncertain during specific 

conditions. Comparisons of current flow and water-quality 

sampling techniques to alternative techniques were assessed 

between April 2009 and September 2009 at two locations in 

the Saginaw River. Streamflow estimated using acoustic Doppler current profiling technology was compared to a traditional 

stage-discharge technique. Complex conditions resulting from 

the influence of Saginaw Bay on the Saginaw River were 

able to be captured using the acoustic technology, while the 

traditional stage-discharge technique failed to quantify these 

effects. Water-quality samples were collected at two locations 

and on eight different dates, utilizing both surface-grab and 

depth-integrating multiple-vertical techniques. Sixteen paired 

samples were collected and analyzed for suspended sediment, 

turbidity, total phosphorus, total nitrogen, orthophosphate, 

nitrite, nitrate, and ammonia. Results indicate that concentrations of constituents associated with suspended material, such 

as suspended sediment, turbidity, and total phosphorus, are 

underestimated when samples are collected using the surfacegrab technique. The median magnitude of the relative percent 

difference in concentration based on sampling technique was 

37 percent for suspended sediment, 26 percent for turbidity, 

and 9.7 percent for total phosphorus samples collected at both.

Acoustic techniques were also used to assist in the determination of the effectiveness of using acoustic-backscatter 

information for estimating the suspended-sediment concentration of the river water. Backscatter data was collected by 

use of an acoustic Doppler current profiler, and a Van Dorn 

manual sampler was simultaneously used to collect discrete 

water samples at 10 depths (3.5, 7.5, 11, 14, 15.5, 17.5, 19.5, 

20.5, 22, and 24.5 ft below the water surface) along two vertical profiles near the center of the Saginaw River near Bay 

City. The Van Dorn samples were analyzed for suspendedsediment concentrations, and these data were then used to 

develop a relationship between acoustic-backscatter data. 

Acoustic-backscatter data was strongly correlated to sediment 

concentrations and, by using a linear regression, was able to 

explain 89 percent of the variability. Although this regression technique showed promise for using acoustic backscatter 

to estimate suspended-sediment concentration, attempts to 

compare suspended-sediment concentrations to the acoustic 

signal-to-noise ratio estimates, recorded at the fixed acoustic 

streamflow-gaging station near Bay City (04157061), resulted 

in a poor correlation.

Introduction

The Saginaw Bay watershed is Michigan’s largest watershed and drains approximately 15 percent of Michigan’s total 

land area. The Saginaw River accounts for approximately 70 

percent of the total drainage to Saginaw Bay, Lake Huron, 

and is, thus, a major contributor to the overall water quality of 

Saginaw Bay (Michigan Department of Environmental Quality, 2006). The U.S. Environmental Protection Agency (EPA) 

lists the Saginaw Bay system as an “Area of Concern” (AOC) 

owing to impairment of fisheries and loss of recreational value 

resulting from high amounts of sediment and nutrients (phosphorus and nitrogen) that enter the system (Environmental 

Protection Agency, 2009).

As indicated in the current Lake Huron Binational Partnership 2008–2010 Action Plan (Environmental Protection 

Agency, 2009) one of the major efforts that will be conducted 

by the National Oceanographic and Atmospheric Administration (NOAA), the Michigan Department of Environmental 

Quality (MDEQ), and the Michigan Department of Natural 

Resources (MDNR) will be “Managing the Impact of Multiple 

Stressors in Saginaw Bay.” This effort is focused on understanding the combined effects of nutrients, sediments, and 
2 Comparison of Streamflow and Water-Quality Data Collection Techniques for the Saginaw River, Michigan

other stressors in the Saginaw Bay watershed, with the goal of 

identifying management actions that will improve the health 

of the Bay (Environmental Protection Agency, 2009). Because 

this effort is intended to focus on the specific effects that the 

Saginaw River could be having on Saginaw Bay, having the 

most accurate data will be important for understanding basic 

river discharge and constituent loading to Saginaw Bay. 

Currently, most sampling efforts conducted by the 

MDEQ and NOAA rely on a single or three-point grab sample 

from 1 to 3.3 ft below the surface. This sample is intended to 

represent the roughly 490-ft-wide river that ranges in depth 

from less than 3.3 ft at the banks to approximately 30 ft in 

the central shipping channel. In 2009, streamflow was measured by the U.S. Geological Survey (USGS) on the Saginaw 

River using gage height- or stage- to-river discharge relations. 

Although river-stage measurements themselves are typically 

accurate, at certain times conditions can affect the accuracy of 

the computed discharge from the rating curve, which relates 

stage to discharge. The conditions that may cause the actual 

flow to deviate from the expected stage-discharge relation can 

include, but are not limited to, ice formations, certain atmospheric pressure conditions, and wind conditions. Computation 

of loads of particular constituents based on nonrepresentative 

samples or stream discharge values could cause a potential 

bias in our understanding of the nutrient and sediment inputs 

from the Saginaw River to Saginaw Bay. 

During the spring and summer of 2009, the USGS developed a sampling program to evaluate various water-quality 

and streamflow data-collection techniques on the Saginaw 

River. The objectives of this program were to 1) compare 

samples collected by a discrete surface-grab technique to 

samples collected through the depth-integrating multiplevertical technique (DIMV), 2) compare discharge estimates 

for the Saginaw River collected using a fixed “side-looking” 

acoustic Doppler current profiler (ADCP) gage to estimates 

derived from a standard gage using a stage-discharge relation, 

3) compare constituent load estimates for nutrients and sediment to Saginaw Bay utilizing the various flow and waterquality data available, and 4) explore the relation between 

acoustic backscatter collected from ADCP measurements to 

sediment concentration.

Purpose and Scope

The purpose of this report is to describe 1) the evaluation 

of different collection techniques for water-quality and streamflow data on the Saginaw River and 2) the relation between 

acoustic backscatter and suspended-sediment concentration for 

the Saginaw River. Water-quality samples were collected eight 

times at two sites on the Saginaw River between April 21 and 

September 8, 2009. During each sampling event at each site, a 

discrete sample was collected by the surface-grab technique in 

conjunction with a sample collected by the DIMV technique. 

Each sample was analyzed for eight constituents in addition 

to physical parameters measured at the site. Nonparametric 

statistics were used to evaluate differences in constituent concentration based on the water-quality sampling technique used. 

Streamflow was monitored at each sampling site; a traditional 

gage-height recorder was used upstream and a side-looking 

ADCP gage was used downstream of the site. Forty discrete 

suspended-sediment samples were collected at various depths 

in conjunction with vertical ADCP measurements. Acoustic 

backscatter recorded by the ADCP was related to suspendedsediment concentration.

Saginaw River Watershed

The Saginaw River watershed is located in the eastcentral portion of Michigan (fig. 1). The Saginaw River is 

a 22.2-mi-long river (U.S. Geological Survey, 2010) that 

begins at the confluence of the Shiawassee and Tittabawassee Rivers and ultimately discharges to Saginaw Bay (fig. 1). 

The river generally flows from the southwest to northeast. 

Four major tributaries contribute flow to the Saginaw River; 

the Cass, Flint, Shiawassee, and Tittabawassee Rivers. These 

rivers combine to drain an area of roughly 6,300 mi2, or 

approximately 70 percent of the entire Saginaw Bay watershed (fig. 1). Land-use characteristics compiled in the 2001 

National Land Cover Dataset (Multi-Resolution Land Characteristics Consortium, 2008) indicate that 45 percent of land use 

in the Saginaw River watershed is agricultural. The remaining area is classified as undeveloped forest and grassland 

(27 percent), wetland (14 percent), developed (13 percent), 

and open water (1 percent). The mean annual discharge for 

the Saginaw River at station 04157000 (fig. 1) for the period 

from 1992 to 2009 (period of continuous record) is 4,375 ft3/s 

(U.S. Geological Survey, 2010). The 30-year average (1971–

2000) minimum and maximum annual temperatures for the 

watershed are 36.3 °F and 56.8 °F respectively (PRISM Climate Group, 2008). The 30-year average annual precipitation 

for the watershed is 31.4 in. (PRISM Climate Group, 2008).

Techniques for Monitoring Streamflow

Discharge in the Saginaw River was monitored using a 

combination of discrete flow measurements and data from two 

USGS streamflow-gaging stations. Discrete discharge measurements were collected near two streamflow-gaging stations 

using an ADCP. These discrete flow measurements were also 

collected in conjunction with water-quality sampling events.

Flow in the Saginaw River was continuously monitored 

at two USGS streamflow-gaging stations. The gage at Saginaw, station 04157000 (fig. 1), measured the altitude of the 

water surface in the river; this is also known as the stage of 

the river. To estimate discharge in the river, a stage-discharge 

relation was developed. This stage-discharge relation was 

developed by directly measuring the flow of the river over a 

wide range of river stages. A model is then developed to relate 

river stage to discharge such that for a given river stage, the 

discharge in the river can be estimated. 
0 2.5 5 10 MILES

0 2.5 5 10 KILOMETERS

EXPLANATION

Saginaw River watershed

 Saginaw Bay watershed

 River

 Water-quality station

 Water-quality and discharge station

 Discharge station

 Climate station

 Saginaw

Bay City

Essexville

Tittabawassee River

Shiawassee River

Flint River

Cass River

Saginaw River

43°21'

43°28'

43°35'

43°41'

−83°59' −83°32' −84°6'

04157000 207222

04156999

04157061 202631

Saginaw Bay

46°30'

45°00'

46°30'

42°00'

−85°30' −84°00' −82°30'























Introduction 3

Figure 1. Location of the Saginaw River study area and the surrounding area in Michigan.
EXPLANATION

 Vertical sample transect

 Surface grab location

4 Comparison of Streamflow and Water-Quality Data Collection Techniques for the Saginaw River, Michigan

Figure 2. Channel crosssection and grab- and 

depth integrating multiple 

vertical sampling locations 

in the channel of the 

Saginaw River, Michigan.

In addition to streamflow-gaging station 04157000, a 

new gage 04157061 (fig. 1) was installed further downstream 

at Bay City between the Liberty and Independence Bridges. 

Station 04157061 utilized acoustic Doppler technology to 

measure the velocity of the water for a section of the river. 

Estimating flow at this gage required the development of an 

index-velocity rating (Morlock and others, 2001). Once the 

process for developing the index-velocity rating was complete, 

the discharge in the river could be estimated.

Techniques for Collecting Water-Quality 

Samples

Prior to collecting samples for water-quality assessment, 

field measurements of physical parameters of the river were 

collected using a multiparameter water-quality sonde. Standard USGS calibration and measurement procedures (Gibs 

and others, 2007) for multiparameter instruments were used 

to collect pH, water temperature, specific conductance, and 

dissolved oxygen. These physical parameters were measured 

at the midpoints of the left, center, and right thirds of the river, 

and the median values of those measurements were recorded. 

Following the measurement of the physical parameters of the 

river, samples for water quality were collected.

Water-quality samples were collected from two locations on the Saginaw River for comparison of surface-grab 

and DIMV techniques. The first water-quality station, number 

04156999, was approximately 1 mi upstream from USGS 

streamflow-gaging station 0415700 (fig. 1). The second 

water-quality station was at USGS streamflow-gaging station 04157061. At each water-quality station (04156999 and 

04157061), eight sets of paired-grab and integrated samples 

were collected between April 21 and September 9, 2009. Six 

samples were collected as part of a routine schedule targeted 

at the middle of the month, and two samples were event driven 

and were aimed at collecting samples during high-flow events. 

During the period of sampling, however, there was a lack of 

high flow-events, so the event-driven samples were collected 

during low-flow events in the river that reflect potential backwater conditions from seiche activity on Saginaw Bay. 

The surface-grab technique requires the deployment of 

a 1-L high-density polyethylene (HDPE) sample bottle into 

the river at approximately 1– 3.3 ft depth. The sample bottle 

was deployed at three points across the width of the channel at 

the approximate midpoints of the left, center, and right thirds 

of the channel (fig. 2). These three points correspond roughly 

with where the physical parameter readings were collected. 

The water from these three points was then composited into 

a 3-L HDPE bottle. The water in the 3-L bottle was mixed 

by shaking the bottle and then was decanted into individual 

sample bottles. Sample bottles were then processed, stored, 

and shipped according to USGS protocols (Wilde, 2006).

In addition to the grab sample, a DIMV sample was also 

collected. Initially, sample collection using the equal-widthinterval (EWI) technique (Wilde, 2006) was attempted, but 

the river conditions did not meet the criteria for isokinetic 

collection of a sample. As a result, DIMV samples were collected according to standard USGS protocols (Wilde, 2006). 

Ten vertical transects were selected at equal widths across the 
Introduction 5

channel (fig. 2). For the first sampling event on April 21, 2009, 

a USGS DH–2 sampler (Davis, 2005) equipped with a 5/16-in. 

inner diameter nozzle was lowered at each transect at a rate 

of 0.5 ft/s. It was determined that the DH–2 sampler was not 

necessary because of the low velocity (< 2.0 ft/sec) of the river 

so, for subsequent events, a USGS DH–95 sampler (Davis, 

2005) was used. A DH–95 sampler equipped with a 5/16-in. 

inner diameter nozzle was deployed from a boat-mounted 

crane, lowered at a constant rate to the bottom of the channel, 

and then raised to the surface at the same rate. Water collected 

in the sampler was composited in a 14-L HDPE churn. After 

all 10 sections had been sampled and composited in the churn, 

the churn was mixed using the churn paddle and continuously 

churned while water was decanted into individual sample 

bottles. As with the grab sample, the samples were then 

processed, stored, and shipped according to USGS protocols 

(Wilde, 2006).

Samples collected from both the surface-grab and DIMV 

techniques were analyzed for ammonia, nitrite, nitrite plus 

nitrate, total nitrogen, orthophosphate, and total phosphorus by 

the USGS National Water Quality Laboratory with methods 

described in Fishman (1993). Samples were also analyzed for 

total suspended sediment by the USGS Sediment Laboratory 

(Louisville, Kentucky) using standard methods described by 

Guy (1969). Turbidity of the two different samples was also 

analyzed onsite using an optical turbidimeter. Each turbidity sample was measured five times and the median value 

was recorded. 

Techniques for Collecting Discrete Samples of 

Suspended Sediment 

During the July 30, 2009, and August 12, 2009, sampling 

events, discrete sampling of the water column for suspended 

sediment was performed in conjunction with ADCP backscatter measurements. A Van Dorn sampler was used to collect 

discrete water samples at 10 depths (3.5, 7.5, 11, 14, 15.5, 

17.5, 19.5, 20.5, 22, and 24.5 ft below the water surface) 

along two vertical profiles near the center of the Saginaw 

River near station 04157061 (fig. 3). The left profile (looking 

downstream) is located at about 43o 36’ 33.6” north latitude 

and 83o 53’ 11.7” west longitude; the right profile is located 

at about 43o 36’ 32.8” north latitude and 83o 53’ 10.9” west 

longitude. The Van Dorn sampler was field-rinsed with river 

water prior to, and in between, discrete water samples. Sample 

water collected from the Van Dorn sampler was shaken to 

homogenize the sample and then decanted directly into a 

suspended-sediment sample bottle. All sediment bottles were 

then processed, stored, and shipped according to USGS protocols (Wilde, 2006). 
EXPLANATION

 Gage 04157061

 Vertical sample profile

43°36'40''

43°36'35''

43°36'30''

43°36'25''

Left bank

Right bank

Down-looker track

SonTek side-looker beam

Flow direction

Saginaw River

0 250 500 1,000 FEET

0 50 100 200 METERS

83°53'15'' 83°53'10'' 83°53'5''

6 Comparison of Streamflow and Water-Quality Data Collection Techniques for the Saginaw River, Michigan

Figure 3. Discrete suspended-sediment sampling locations near station 04157061, Saginaw River at 

Bay City, Michigan.
Gaged-Flow Comparison 7

Gaged-Flow Comparison

The gaged flows for the Saginaw River at Saginaw 

(04157000) and at Bay City (04157061) display similar characteristics from April 20, 2009 to September 9, 2009. Figure 

4 illustrates the daily mean flow values for both gages as well 

as the underlying unit flow values (instantaneous flow values 

recorded at every 15 or fewer minute intervals) that were used 

to compute the daily mean flow value. The daily mean flow 

value was computed as the average of all unit flow values 

recorded in 1 day. Precipitation data collected at National 

Weather Service (NWS) Cooperative Observer Program stations in Saginaw, Mich. (station 207222, fig. 1) and Essexville, 

Mich. (station 202631, fig. 1) are also included (National 

Oceanic and Atmospheric Administration, 2010). The general 

magnitude and distribution of the daily mean flow values at 

both stations match relatively well, indicating the flows are 

generally associated with precipitation events; this can be 

seen for the events in early May, mid-June, and early August 

of 2009. There are periods of time where the daily mean flow 

at Saginaw is estimated (grey background on fig. 4) in which 

there are substantial differences in daily mean flow between 

the two gages. 

Comparison of the daily mean flow values between the 

Saginaw and Bay City gages indicates that the flows at Saginaw are generally higher than the flows measured in Bay City. 

Figure 5 illustrates the residual of the daily mean flow between 

the two gages (daily mean flow value at Saginaw minus the 

daily mean flow value at Bay City) through the period when 

both sites were gaged. Ninety-nine of the 139 coincident daily 

mean flow values were higher at Saginaw than Bay City. 

Presenting the residuals as a relative percent difference of the 

flow (absolute value of the residual divided by the average of 

the flow at Saginaw and Bay City gages) shows that the percent difference in flow is greatest during periods of low flows. 

Although this is expected because the residual is larger relative 

to the total flow during low flow, it suggests that the greatest 

disagreement in flows between the two gages is during low 

flows. As a whole, the median and mean relative percent differences were 13.7 and 18.4 percent respectively (fig. 5).

The decrease in flow from the upstream gage to the 

downstream gage was not expected, because some small 

tributaries between Saginaw and Bay City contribute flow to 

the Saginaw River. Investigation into whether water withdrawals from the Saginaw River accounted for this flow reduction 

revealed that more water was discharged to the river as a 

result of various manufacturing and water treatment processes 

than was withdrawn from the river (Andrew LeBaron and 

Dawn Roush, Michigan Department of Natural Resources 

and Environment, written commun., 2010). Return flow to 

the river from various manufacturing and treatment facilities 

ranged from less than 1 percent to almost 7 percent of the 

daily mean flow at Saginaw and averaged 1.2 percent from 

April 20 to September 9, 2010. This water use information 

further confounded the results of the comparison of the gages. 

Upon closer inspection of the unit values, it became clear that 

significant backwater and, in some cases, reverse flow was 

occurring at the streamflow-gaging stations; however, this 

complex flow was not able to be resolved by the traditional 

stage-discharge technique utilized at the upstream station at 

Saginaw (fig. 4). 

The ability to record backwater and reverse-flow conditions at the Bay City gage but not at the Saginaw gage was 

a result of the different technologies used for gaging at each 

site. The ADCP gage at Bay City instantaneously measured 

both the magnitude and direction of the water velocity in the 

river. By using the index-velocity relation developed for that 

gage, a discharge value could be estimated. During periods of 

backwater or reverse flow, the index velocity allowed for the 

estimation of a negative discharge to be estimated as seen on 

figure 4. 

At the gage in Saginaw, only the instantaneous river stage 

was being measured. The instantaneous stage was then used to 

estimate the flow by using the stage-discharge relation developed for that gage. The nature of the stage-discharge relation 

was such that a negative flow could not be computed. Therefore, when the measured instantaneous stage was affected 

by backwater or reverse-flow conditions, a flow of zero was 

recorded. If a flow of zero was recorded for a unit value, then 

the daily mean flow value was not computed from the unit 

values but was estimated (fig. 4, shaded gray) as the combined 

flow of the four major tributaries (Cass, Flint, Shiawassee and 

Tittabawassee Rivers) to the Saginaw River. These flows come 

from gages that are upstream of the Saginaw gage, which 

contributes to the uncertainty associated with the flow estimate 

at Saginaw.

The complex flow dynamics of the Saginaw River pose 

problems for gaging stations utilizing traditional stage-discharge monitoring techniques. Conversely, gaging stations that 

use acoustic technology are able to estimate flow under the 

range of conditions observed on the Saginaw River because 

river velocity is directly measured at these stations. Converting gaging stations on the Saginaw River from stage-discharge 

stations to acoustic stations would likely improve the flow 

estimates along the river. In turn, because constituent loads to 

Saginaw Bay are calculated using Saginaw River flow data 

from station 04157000, the constituent load estimates would 

likely be improved as well.
MAY

EXPLANATION

Precipitation at Saginaw

 Estimated daily value Positive unit value 0 or negative unit value Daily mean value

EXPLANATION

Precipitation at Essexville

 Positive unit value 0 or negative unit value Daily mean value

May Aug. 

2009

July

May Aug. 

2009

A. Streamflow-gaging station 04157000B. Streamflow-gaging station 04157061

JuneJune

-10,000

0

10,00020,00030,00040,00050,000

Discharge, in cubic feet per second 

-10,000

0

10,00020,00030,00040,00050,000

Discharge, in cubic feet per second 

July

Figure 4. Daily mean and unit flows at A, station 04157000, Saginaw River at Saginaw, and 

B, station 04157061, Saginaw River at Bay City, Michigan 

September 2009.
Discharge, in cubic feet per second

Relative difference, in percent

A. Residual of published daily values

B. Relative percent difference

May June July Aug. Sept.

2009

−5,000

−2,500

0

2,500

5,000

Mean=18.4 percent

Median=13.7 percent

0

25

50

75

100

May June July Aug. Sept.

2009

EXPLANATION

Flow estimated at 04157000

Flow computed at 04157000

Gaged-Flow Comparison 9

Figure 5. A, residual for daily mean flows between stations 04157000, Saginaw River at Saginaw, and 04157061, Saginaw River at 

Bay City, Michigan, and B, the relative percent difference of daily mean flows for the two stations.
10 Comparison of Streamflow and Water-Quality Data Collection Techniques for the Saginaw River, Michigan

Table 1. Physical parameters measured at stations 04156999, Saginaw River at Saginaw, and 

04157061, Saginaw River at Bay City, Michigan.

[ft3/s, cubic feet per second; mg/L, milligrams per liter; μS/cm, microsiemens per centimeter; C°, degrees Celsius; 

NA, not available]

Date Flow 

(ft3

/s)

Dissolved 

oxygen

(mg/L)

pH

Specific

 conductance 

(μS/cm)

Water 

temperature 

(C°)

Station 04156999

Apr. 21, 2009 NA 10.7 8.1 619 9.7

May 18, 2009 6,940 8.9 8.2 615 15.9

June 16, 2009 3,500 8.1 8.0 668 21.5

July 14, 2009 3,960 10.7 8.4 748 23.6

July 30, 2009 2,060 7.5 8.0 691 24.2

Aug. 12, 2009 6,530 6.2 7.5 540 24.9

Sept. 2, 2009 814 9.8 6.8 689 19.7

Sept. 8, 2009 1,030 12.1 8.3 731 23.0

Station 04157061

Apr. 21, 2009 8,700 9.5 8.2 664 10.8

May 18, 2009 8,460 8.4 8.1 558 15.1

June 16, 2009 1,340 7.6 7.8 616 20.6

July 14, 2009 -247 7.8 8.1 676 22.5

July 30, 2009 2,130 7.7 8.0 670 23.5

Aug. 12, 2009 8,260 5.4 6.8 484 24.5

Sept. 2, 2009 -40.1 7.7 8.0 671 20.7

Sept. 8, 2009 4,440 10.0 8.1 691 21.8

Water Quality Results

In total, 16 paired surface grab and DIMV samples were 

collected on the Saginaw River. The results of the physical 

and chemical analyses for these samples are illustrated in 

tables 1–3. 

Differences in concentrations of the paired samples 

resulting from sampling technique were tested for using the 

Wilcoxon signed-rank test (Helsel and Hirsch, 2002). This test 

was selected because it was not sensitive to the distribution of 

the data, which was not normally distributed. Standard parametric tests, such as the paired t-test, require a normal distribution to detect true differences in the means of two sample 

populations (Helsel and Hirsch 2002). The null hypothesis 

was that the median constituent concentration for each sample 

population (grab and integrated) was the same. The Wilcoxon 

signed-rank test was applied to each site individually as well 

as for both sites combined. All differences in medians with 

levels of significance at 5 percent or lower (p < 0.05) were 

considered statistically significant. In the event a constituent 

concentration was censored, a value of one-half the censoring 

level was substituted for the censored value for the purpose of 

performing the test. 

Statistical differences in paired-sample median concentrations were detected for four different constituents (table 4). 

Nitrite plus nitrate, suspended sediment, total phosphorus, and 

turbidity were statistically different on the basis of sampling 

technique at station number 04156999 (upstream). Suspended 

sediment, total phosphorus, and turbidity were also statistically different at station number 04157061 (downstream) as 

well as when data from both sites were combined (table 4). 

In general, the constituent concentrations that were 

significantly different were greater in the DIMV samples than 

in the surface-grab samples. Previous studies have shown 

suspended-sediment, turbidity, and constituent concentrations 

associated with suspended material, such as total phosphorus, 

are affected by the sampling technique employed to collect 
Water Quality Results 11

Table 2. Summary of nutrient and sediment concentrations measured at station 04156999, Saginaw River at Saginaw, Michigan. 

[DIMV, Depth Integrated Multiple Vertical; NTRU, Nephelometric Turbidity Ratio Unit; mg/L, milligrams per liter; N, Nitrogen; P, Phosphorus; <, value censored at minimum reporting level; E, value estimated above method detection level but below minimum reporting level; <, less than]

Date Sample 

type

Turbidity

(NTRU)

Ammonia 

(mg/L as N)

Nitrite + 

nitrate

(mg/L as N)

Nitrite

 (mg/L as N)

Orthophosphate

(mg/L as P)

Total 

phosphorus

 (mg/L as P)

Total 

nitrogen

(mg/L as N)

Suspended 

sediment 

(mg/L)

Apr. 21, 2009 DIMV 32.4 0.068 1.32 0.012 E0.009 0.098 2.15 46.0

Apr. 21, 2009 Grab 33.8 .081 1.30 .012 .010 .095 2.02 39.0

May 18, 2009 DIMV 21.7 .023 1.20 .014 .016 .077 1.99 26.0

May 18, 2009 Grab 17.9 .118 1.17 <.002 .017 .069 1.96 22.0

June 16, 2009 DIMV 13.5 <.020 2.14 .029 .016 .065 2.75 26.0

June 16, 2009 Grab 9.29 <.020 2.12 .028 .015 .053 2.79 8.0

July 14, 2009 DIMV 21.1 <.020 .929 .011 E.006 .069 1.60 25.0

July 14, 2009 Grab 14.6 <.020 .893 .011 E.006 .057 1.57 14.0

July 30, 2009 DIMV 15.6 <.020 1.03 .015 .024 .074 1.62 16.0

July 30, 2009 Grab 13.1 <.020 1.00 .014 .024 .073 1.66 13.0

Aug. 12, 2009 DIMV 30.2 E.020 .950 .022 .032 .111 1.61 36.0

Aug. 12, 2009 Grab 24.9 .025 .968 .022 .033 .098 1.59 28.0

Sept. 2, 2009 DIMV 19.8 <.020 .562 .007 .012 .060 1.04 21.0

Sept. 2, 2009 Grab 7.54 <.020 .487 .007 .012 .045 .975 6.0

Sept. 8, 2009 DIMV 20.0 <.020 .393 .008 <.024 .066 1.10 20.0

Sept. 8, 2009 Grab 17.5 <.020 .393 .009 <.024 .071 1.14 15.0

a sample (Horowitz and others, 1990; Martin and others, 

1992; Harmel and others, 2010). Median values of the relative 

percent difference for constituent concentration on the basis 

of sampling technique are shown in table 5. As expected, 

suspended-sediment concentrations showed the highest variability between surface-grab and DIMV sampling techniques. 

The median relative percent difference ranged from 27 percent 

at station 04156999 to 40 percent at station 04157061. The 

median relative percent difference when combining data from 

both stations was 37 percent (table 5). Turbidity also had high 

variability between the sampling techniques, with median 

relative percent differences ranging from 19 percent at station 

04156999 to 28 percent at station 04157061 and 26 percent 

when combined (table 5). Variability in total phosphorus 

concentration was smaller, with median relative percent differences ranging from 7.4 at station 04157061 to 12 at station 

04156999 and 9.7 percent when combined. 

The statistically significant difference between nitrite 

plus nitrate concentrations due to sampling technique at 

station 04156999 was unexpected. Variability in nitrite plus 

nitrate concentration was small, with median relative percent 

differences ranging from 0.8 percent at station 04157061 to 

2.3 percent at station 04156999 and 1 percent when combined. 

However, results by Harmel and others (2010) indicate that 

dissolved species like nitrite plus nitrate may vary across a 

channel. It is uncertain in this case why the significant difference in concentration is occurring at this station. Nitrite values 

are nearly identical for both sampling techniques (table 2), 

which indicates that the nitrate component is contributing to 

the variation in concentration due to the sampling technique 

used. Possible explanations for the variation include nearby 

point sources of nitrate discharge that have not fully mixed 

within the channel or algal activity in the photic zone of the 

channel. Algae may be utilizing nitrate in the upper portion of 

the channel that is targeted by surface-grab sampling, causing nitrate concentrations to be lower there than in deeper 

parts of the channel, although other dissolved nutrient constituents commonly utilized for algal growth did not exhibit 

this distribution.

Generally, concentrations of suspended material were 

lower at station 04157061 than at station 04156999 (table 2 

and 3). Although constituent concentrations were lower at station 04157061, the variability in constituent concentration as a 

result of the sampling technique used was greater than at station 04156999 (table 5). The greater median relative percent 

difference at the station 04157061 indicates that the system 
12 Comparison of Streamflow and Water-Quality Data Collection Techniques for the Saginaw River, Michigan

Table 3. Summary of nutrient and sediment concentrations measured at station 04157061, Saginaw River at Bay City, Michigan. 

[DIMV, Depth Integrated Multiple Vertical; NTRU, Nephelometric Turbidity Ratio Unit; mg/L, milligrams per liter; N, Nitrogen; P, Phosphorus; E, value estimated above method detection level but below method reporting level]

Date Sample 

type

Turbidity 

(NTRU)

Ammonia 

(mg/L as N)

Nitrite + 

nitrate

 (mg/L as N)

Nitrite 

(mg/L as N)

Orthophosphate 

(mg/L as P)

Total 

phosphorus 

(mg/L as P)

Total 

nitrogen 

(mg/L as N)

Suspended 

sediment 

(mg/L)

Apr. 21, 2009 DIMV 22.4 0.092 1.25 0.013 0.010 0.076 1.94 22.0

Apr. 21, 2009 Grab 19.0 .104 1.24 .013 .011 .068 1.83 18.0

May 18, 2009 DIMV 20.1 .039 1.19 .017 .017 .075 2.02 23.0

May 18, 2009 Grab 17.3 .040 1.20 .017 .018 .072 1.96 18.0

June 16, 2009 DIMV 15.5 .031 2.78 .053 .009 .071 3.65 15.0

June 16, 2009 Grab 11.1 E.016 2.80 .053 .008 .066 3.72 10.0

July 14, 2009 DIMV 25.5 .083 .922 .022 .016 .085 1.68 29.0

July 14, 2009 Grab 12.3 .067 .922 .022 .014 .070 1.72 10.0

July 30, 2009 DIMV 14.1 E.011 .938 .027 .011 .075 1.63 16.0

July 30, 2009 Grab 10.7 E.015 .953 .027 .012 .074 1.65 9.00

Aug. 12, 2009 DIMV 20.2 .040 .848 .024 .039 .113 1.48 21.0

Aug. 12, 2009 Grab 15.9 .034 .840 .025 .038 .104 1.45 14.0

Sept. 2, 2009 DIMV 16.2 .061 .718 .021 .020 .077 1.32 16.0

Sept. 2, 2009 Grab 11.5 .054 .716 .022 .020 .067 1.36 10.0

Sept. 8, 2009 DIMV 13.5 .073 .471 .015 .036 .065 1.17 14.0

Sept. 8, 2009 Grab 10.1 .069 .467 .015 E.014 .061 1.11 10.0

Table 4. Results of use of the Wilcoxon two-sided signed-ranks test to compare paired depth 

integrated multiple vertical and surface-grab samples for selected constituents collected at 

collected at station 04156999, Saginaw River at Saginaw, and 04157061,Saginaw River at Bay City, 

Michigan and for both stations combined.

Constituent

p-value

Station 04156999 Station 04157061 Both stations

Ammonia 1

0.10 0.25 10.92

Nitrite .46 .94 .46

Nitrite plus nitrate .035 .67 .097

Orthophosphate 1

.26 .25 .80

Suspended sediment .0078 .014 .0005

Total nitrogen .74 .74 .53

Total phosphorus .039 .0078 .0004

Turbidity .021 .014 .0006

1. 10 percent or more values are censored.
Water Quality Results 13

may not be well mixed. The complex interaction of the Saginaw River and Saginaw Bay, near station 04157061, likely 

leads to velocity variations that affect the concentrations of 

suspended material. As a result, the DIMV sampling technique 

was better able to characterize the suspended-material concentration than the grab sampling technique, because the DIMV 

technique allows river water to be composited both laterally 

and vertically to account for velocity variations throughout the 

channel.

Total phosphorus concentrations did not exhibit the same 

characteristics as the other suspended-material constituents. 

Even though there was statistically significant variation in the 

total phosphorus concentration as a result of sampling technique (table 4), the median relative percent difference was less 

at station 04157061 (7.4 percent) than at station 04156999 

(12 percent). In addition, the median total phosphorus concentration of DIMV samples was higher at station 04157061 

(0.075 mg/L) than at station 04156999 (0.071 mg/L). This 

may indicate that the dissolved species of phosphorus were a 

larger percentage of the total phosphorous at station 04157061 

than at station 04156999. To explore that possibility, the percentage of total phosphorus that was dissolved was estimated 

by dividing the concentration of orthophosphate by the total 

phosphorous concentration. The mean percentage of orthophosphate for station 04156999 was 20 percent whereas the 

mean for station 04157061 was 25 percent. This is a slight 

increase that does not take into account all dissolved species 

of phosphorous, so some uncertainty remains as to whether 

differences in the amount of dissolved phosphorus between 

sites is leading to the variability between sites.

In sum, variations in constituent concentration were 

detected as a result of the sampling technique used at two 

stations on the Saginaw River. DIMV samples better characterized suspended constituents that are heterogeneously 

distributed laterally and vertically throughout the river channel 

and, in some cases, dissolved constituents than surface-grab 

samples. Ideally, more samples would have been collected 

over a larger suite of flows and a larger time period. This 

would have improved sample size for the statistical tests, 

demonstrated how large-magnitude flows may affect heterogeneity of constituent concentrations in the river channel, and 

improved understanding of the temporal distribution of constituent concentrations in the river. Even so, the variability in 

constituent concentration due to sampling technique has implications for the estimation of loads to Saginaw Bay, specifically 

for constituents associated with particulate material in the 

river like suspended sediment and total phosphorous. Discrete 

surface-grab sampling may introduce bias that underestimates 

the concentrations of sediment between 27 and 40 percent and 

total phosphorus between 7.4 and 12 percent. Therefore load 

estimates based on constituent concentrations that are biased 

low will also be biased low.

Table 5. Median relative percent difference for selected constituents in depth integrated multiple 

vertical and surface-grab samples collected at stations 04156999, Saginaw River at Saginaw, and 

04157061, Saginaw River at Bay City, Michigan and for both stations combined.

Constituent Station 04156999 Station 04157061 Both stations

Ammonia 10 15 113

Nitrite 1.9 0.3 1.2

Nitrite plus nitrate 2.3 0.8 1.0

Orthophosphate 12.7 9.4 3.4

Suspended sediment 27 40 37

Total nitrogen 2.0 2.5 2.2

Total phosphorus 12 7.4 9.7

Turbidity 19 28 26

1. 10 percent or more values are censored.
14 Comparison of Streamflow and Water-Quality Data Collection Techniques for the Saginaw River, Michigan

Suspended Sediment and Acoustic Backscatter 

Results

An ADCP measures water velocity using the Doppler 

principal (Simpson, 2001). While it is submerged in water, an 

ADCP emits an ultrasonic (acoustic frequencies greater than 

20 kHz) pulse through two or more transducers. The same 

transducers are then used to detect the returning sound waves 

that have bounced off suspended-sediment particles, plankton, 

or other pulse-reflecting bodies or backscatterers moving with 

the water. The slight shift in frequency or phase between the 

emitted and returned signal is used to compute water velocity 

in two or more dimensions. 

The returning acoustic signal is commonly discretized 

over time to compute water velocities at varying distance 

intervals (bins of uniform size) from the ADCP. If the ADCP 

transducers are oriented vertically downward from a point 

near the water surface, this discretization will provide velocity 

information with increasing depth at that point. If the ADCP 

is oriented horizontally in the water column, the discretization 

will provide velocity information at that depth for increasing distances across a river. The maximum distance from the 

ADCP for which velocity data can be obtained may be limited 

by the distance to the channel bottom or to the opposite channel bank or by the strength of the returning acoustic signal. 

The strength of the returning signal is reduced with distance 

between the ADCP and the bin and when fewer backscatterers 

are in the water. 

In addition to water-velocity data, Deines (1999) 

describes calibration procedures for the use of vertical 

profiles of acoustic-backscatter data to estimate suspended 

plankton and sediment concentrations in water. Thorne and 

others (1991) conclude that acoustic-backscatter techniques 

are potentially powerful tools for examining the structure of 

suspended-sediment concentration profiles near the sea bed. 

Gartner (2004) describes successfully estimating suspendedsolids concentrations from acoustic-backscatter intensity 

measured by ADCP in San Francisco Bay, California. 

Preliminary assessments of the potential utility of 

acoustic backscatter as an indicator of suspended-sediment 

concentrations were conducted on the Saginaw River near 

streamflow-gaging station 04157061 (fig. 3). In the first 

assessment, detection of the variation of suspended-sediment 

concentrations with depth by use of acoustic backscatter was 

investigated. A down-looking boat-mounted ADCP unit was 

held, approximately stationary over two vertical profiles while 

water samples were collected at various depths and subsequently measured for suspended-sediment concentrations. 

In the second assessment, a side-looking (horizontal) ADCP 

(HADCP) unit was used to track temporal variations in flow 

velocity and backscatter across the river from April 21 to 

September 8, 2009. Preliminary results for both investigations 

are provided below. 

Detecting Vertical Variations in Point 

Measurements of Suspended Sediment 

Concentrations with Down-Looking Acoustic 

Backscatter Data

Suspended sediment concentrations were measured in 

water samples taken at 10 depths along two vertical profiles 

near the center of the Saginaw River at streamflow-gaging 

station 04157061 (fig. 3). The left profile (looking downstream) is located at about 43o

 36’ 33.6” north latitude and 

83o 53’ 11.7” west longitude; the right profile is located at 

about 43o 36’ 32.8” north latitude and 83o 53’ 10.9” west 

longitude. Sediment-sampling events occurred on July 30, and 

August 12, 2009. 

A downward-facing RD Instruments Workhorse Rio 

Grande ADCP, operating at 600 kHz with four beams, was 

used to measure water velocity at 1-second intervals during 

both sampling events. For each 1.6 ft-depth bin, water-velocity 

and backscatter values were averaged over periods when samples for suspended-sediment analysis were obtained at each 

profile. These periods were less than 10 minutes long. Binaverage velocity and backscatter data were linearly interpolated from depth bin centers to points of suspended-sediment 

sample collection. The deepest suspended-sediment samples 

were matched with the average velocity and backscatter data 

from the deepest ADCP bin. The results provide water-velocity 

and acoustic-backscatter data for comparison with suspendedsediment concentrations measured in water samples (table 6).

Substantial changes in flow magnitude and direction can 

occur over short periods of time at station 04157061, because 

of the low hydraulic gradient of the river and the proximity of 

the streamflow-gaging station to Saginaw Bay, where water 

levels are sensitive to changes in wind velocity. Particularly 

during the summer months, changes in flow near the station 

are more commonly associated with wind effects and variable backwater conditions from the bay, compounded by large 

conveyance characteristics of Saginaw River, rather than 

changes in runoff conditions in the watershed. Major tributaries to Saginaw River were considered at base flow conditions 

shortly before and during the sampling events. Ancillary measurements of flow were taken at a transect just downstream 

from the two profiles, labeled “Down-looker track” in figure 

3. Continuous measurements of water levels taken at station 

04157061 also show hydrodynamic variations at the time of 

sample collection (fig. 6). 

Sampling depths and acoustic-backscatter characteristics along the transect through the sampling profiles for the 

July and August sampling events are shown on figure 7 and 

figure 8. Note that the depth bins for the July 30, 2009 transect 

taken from 11:01 to 11:05 a.m. (fig. 7) were 0.33 ft in height, 

whereas the depth bins for the Aug. 12, 2009 transect taken 

from 11:03 to 11:07 a.m. (fig. 8) were 1.6 ft in height. Depth 

bins during suspended-sediment sampling were 1.6 ft, however, during both sampling events.
Water Quality Results 15

Table 6. Suspended-sediment concentrations and acoustic-backscatter and velocity data from measurements at vertical profiles at 

station 0415761, Saginaw River at Bay City, Michigan.—Continued

Eastern Standard Time Transect

Sample depth below the 

water surface, 

in feet

Suspended-sediment 

concentration, 

in milligrams per liter

Interpolated acoustic 

backscatter, 

in decibels

Interpolated velocity, 

in feet per second

July 30, 2009

10:15 a.m. Right 24.5 16.0 74.8 0.11

10:16 a.m. 22.0 16.0 74.8 .11

10:17 a.m. 20.5 15.0 74.6 .11

10:18 a.m. 19.5 14.0 74.2 .11

10:19 a.m. 17.5 14.0 74.0 .11

10:20 a.m. 15.5 13.0 73.4 .12

10:21 a.m. 14.0 13.0 73.0 .13

10:22 a.m. 11.0 12.0 72.9 .18

10:23 a.m. 7.5 10.0 73.8 .23

10:24 a.m. 3.5 10.0 72.2 .30

10:37 a.m. Left 24.5 21.0 78.3 .10

10:38 a.m. 22.0 16.0 77.6 .10

10:39 a.m. 20.5 17.0 76.5 .09

10:40 a.m. 19.5 15.0 76.2 .09

10:41 a.m. 17.5 14.0 75.3 .14

10:42 a.m. 15.5 12.0 74.1 .16

10:43 a.m. 14.0 13.0 73.4 .17

10:44 a.m. 11.0 13.0 72.2 .18

10:45 a.m. 7.5 11.0 71.9 .24

10:46 a.m. 3.5 10.0 71.6 .34

August 12, 2009

11:28 a.m. Right 24.5 1

40.0 80.7 0.82

11:29 a.m. 22.0 23.0 81.3 .78

11:30 a.m. 20.5 24.0 81.6 .76

11:31 a.m. 19.5 26.0 81.4 .77

11:32 a.m. 17.5 23.0 81.1 .78

11:33 a.m. 15.5 20.0 80.8 .79

11:34 a.m. 14.0 21.0 80.5 .80

11:35 a.m. 11.0 20.0 80.2 .82

11:36 a.m. 7.5 23.0 80.0 .81

11:37 a.m. 3.5 17.0 76.7 .81
16 Comparison of Streamflow and Water-Quality Data Collection Techniques for the Saginaw River, Michigan

Table 6. Suspended-sediment concentrations and acoustic-backscatter and velocity data from measurements at vertical profiles at 

station 0415761, Saginaw River at Bay City, Michigan.—Continued

Eastern Standard Time Transect

Sample depth below the 

water surface, 

in feet

Suspended-sediment 

concentration, 

in milligrams per liter

Interpolated acoustic 

backscatter, 

in decibels

Interpolated velocity, 

in feet per second

11:48 a.m. Left 24.5 24.0 83.3 .78

11:49 a.m. 22.0 26.0 83.0 .81

11:50 a.m. 20.5 25.0 82.4 .86

11:51 a.m. 19.5 23.0 82.1 .88

11:52 a.m. 17.5 21.0 81.6 .91

11:53 a.m. 15.5 26.0 81.2 .93

11:54 a.m. 14.0 21.0 81.0 .94

11:55 a.m. 11.0 25.0 80.7 .95

11:56 a.m. 7.5 19.0 80.2 .95

11:57 a.m. 3.5 14.0 77.2 .93

1

 Suspended sediment concentration considered an outlier in linear regression with backscatter as the explanatory variable. 

Suspended sediment concentrations from water samples 

obtained during the July sampling event were approximately 

normally distributed with mean and standard deviation of 13.8 

and 2.71 mg/L, respectively. In particular, the Lilliefors test 

(Conover, 1980) did not reject the null hypothesis of normality at the 5-percent level of significance (p-value 0.0500). In 

contrast, normality of suspended-sediment concentrations 

in water samples collected in profiles on Aug. 12, 2009, 

(August sampling event) was rejected (p-value 0.0066). If 

the maximum concentration of 40 mg/L measured in water 

sampled at 24.5 ft below the water surface in the right profile 

were excluded, however, the hypothesis of normality was not 

rejected (p-value 0.0939). 

The mean and standard deviations of the 19 nonexcluded suspended-sediment concentrations measured in 

water obtained during the August sampling event were 22.2 

and 3.22 mg/L, respectively. With or without the excluded 

August concentration of 40.0 mg/L, the equality of the median 

suspended-sediment concentrations from the July sampling 

(13.5 mg/L) and August sampling (23.0 mg/L) was rejected 

(p-value < 0.0001). No significant differences were found in 

median suspended-sediment concentrations between profiles 

during the July sampling event (p-value = 0.6472) or the 

August sampling event (p-value = 0.7605). 

Because of the relation of suspended sediment to streamflow, time series of suspended-sediment concentration data 

tend to be asymmetrically (commonly log-normally) distributed, rather than normally distributed. Less information is 

available about the probability distribution of spatial series of 

suspended-sediment concentrations along vertical profiles. The 

normality of suspended-sediment concentration distributions 

was accepted for the limited range of sediment concentrations 

available for the analysis described in this report.

Adjusting acoustic-backscatter measurements to relate 

to suspended-sediment concentrations is not a straightforward 

process (Gartner, 2004). In particular, acoustic-backscatter 

values are affected by numerous factors other than suspended 

particles including transmission losses. These losses are 

associated with sound absorption by water and suspended 

particles, and beam spreading along the acoustic path. These 

effects depend on environmental characteristics including the 

distance between the acoustic signal and the sediment particles, temperature, pressure, and instrument characteristics 

including power, transducer size, and frequency. 

Algorithms within the WinRiver II software (Teledyne 

RD Instruments, 2011), were used to convert the Received 

Signal Strength Indicator (RSSI), in counts (labeled as 

Intensity in WinRiver II), to a relative backscatter in decibels 

(labeled as Backscatter in WinRiver II). The relative backscatter estimated by the WinRiver II software provides an indication of local (bin) acoustic backscatterers by providing an 

adjustment for transmission losses. In this report, backscatter 

will refer to this adjusted backscatter component labeled as 

Backscatter in WinRiver II. 

As with suspended-sediment concentrations, median 

backscatter and flow velocity varied between the July and 

August 2009 sampling events. In July, the median backscatter 

(in the two profiles) was 74.1 decibels, and the median backscatter in August 2009 was 81.1, or about 9.4 percent higher. 

Similarly, the median velocity in July 2009 was 0.13 ft/s, and 

the median velocity in August 2009 was 0.82 ft/s. 
EXPLANATION

Water level Sampling right profile 

 Flow Sampling left profile

A.

B.

Water level, in feet above NGVD29 

Flow, in cubic feet per second Flow, in cubic feet per second

Time, in hours on August 12, 2009

0:00 4:00 8:00 12:00 16:00 20:00 0:00

Time, in hours on July 30, 2009

0:00 4:00 8:00 12:00 16:00 20:00 0:00

11.0

10.8

10.6

10.4

10.8

10.6

10.4

10.2

2,800

2,400

2,000

1,600

1,200

7,920

7,910

7,900

7,890

7,880

7,870

7,860

Water level, in feet above NGVD29 

Water Quality Results 17

Figure 6. Water levels and flows at station 04157061, Saginaw River at Bay City, Michigan during suspended-sediment sampling on 

A, July 30, 2009, and B, August 12, 2009.
EXPLANATION

Backscatter, in decibels

Sediment collection points

River bottom 24

20

16

12

8

4

0

28

Depth below water surface, in feet

-10 70 150 230 310 390 470 550 630

Distance from left bank, in feet

Top ADCP bin

Bottom ADCP bin

18 Comparison of Streamflow and Water-Quality Data Collection Techniques for the Saginaw River, Michigan

Figure 7. Locations of suspended-sediment concentration measurements along two vertical profiles sampled on July 30, 2009, 

from 11:01 to 11:05 a.m. at station 04157061, Saginaw River at Bay City, Michigan. (ADCP, acoustic Doppler current profiler)

Based on a Kruskal-Wallis test (Conover, 1980), no 

significant differences in median backscatter were detected 

between profiles during the July sampling event (p-value 

= 0.4961) or during the August sampling event (p-value = 

0.1413). No significant differences were found in median 

velocities between profiles during the July sampling event 

(p-value = 0.8796). In the August sampling event, however, 

the median velocity of 0.92 ft/s in the left profile was somewhat higher than the median velocity of 0.79 ft/s in the right 

profile (p-value = 0.0043). 

Simple linear regression was used to statistically 

relate acoustic backscatter as the explanatory variate with 

suspended-sediment concentrations measured from water 

samples taken along two vertical profiles on Saginaw River at 
EXPLANATION

Backscatter, in decibels

Sediment collection points

Bottom ADCP bin

Top ADCP bin

River bottom

Distance from left bank, in feet

600 500 400 300 200 100 0

Depth below water surface, in feet

28

24

20

16

12

8

4

0

Water Quality Results 19

Figure 8. Locations of suspended-sediment concentration measurements along two vertical profiles sampled on August 12, 2009 

from 11:03 to 11:07 a.m. at station 04157061, Saginaw River at Bay City, Michigan. (ADCP, acoustic Doppler current profiler)

Bay City (fig. 9). In an initial regression analysis using all 40 

suspended-sediment concentration measurements, the Aug. 12, 

2009, suspended-sediment concentration of 40.0 mg/L from 

water in the right profile at a depth of 24.5 ft below the water 

surface was identified as an outlier based on a studentized 

residual of 5.325. The root mean square error (RMSE) of this 

relation was 3.307 and the coefficient of determination (r2) 

was 0.7145. With this outlier removed, the RMSE decreased 

to 1.688 while the r2 increased to 0.8933. In this second 

regression, the studentized residual with the largest magnitude 

was -2.1, providing no substantial evidence of additional outliers. All subsequent regressions discussed in this report omitted 

the August concentration considered to be an outlier. 

Multiple linear regression equations were considered 

as an alternative to the simple linear regression. In separate 

regression analyses, parameters were estimated for flow 

velocity and sample depth with backscatter retained as a 

covariate. Results indicate that neither estimated parameter 
EXPLANATION

 Regression prediction

► August data—right profile

◄ August data—left profile

► July data—right profile

◄ July data—left profile

Acoustic backscatter, in decibels

Suspended-sediment concentration, in milligrams per liter

70 72 74 76 78 80 82 84

8

12

16

20

24

28

20 Comparison of Streamflow and Water-Quality Data Collection Techniques for the Saginaw River, Michigan

Figure 9 Relation between 

acoustic backscatter 

and suspended-sediment 

concentrations from samples 

along two vertical profiles in 

July and August 2009 at station 

04157061, Saginaw River at 

Bay City, Michigan.

was significantly different than zero given that backscatter data was included, with p-values of 0.2975 and 0.0804, 

respectively. 

A one-way analysis of covariance was used to investigate 

the relation between suspended-sediment concentration and 

depth by a group of variables formed from the four possible 

profile and sample month combinations. Results indicate that 

a parallel-lines model is appropriate, with each group member 

having a unique intercept but common relation to depth (slope 

term) (table 8). A simultaneous multiple comparison test by 

Scheffe (Stapleton, 1995), was used to determine which of 

the six possible pairwise comparisons of intercept terms were 

statistically different at the 5-percent level of significance. 

The six possible comparisons are: [JR-JL, JR-AR*, JR-AL*, 

JL-AR*, JL-AL*, AR-AL], where J indicates July, A indicates 

August, R indicates the right profile, and L indicates the left 

profile. Thus, JR-JL compares the intercept term between the 

right and left profiles in July. Pairs of intercept terms followed 

by an asterisk in the bracketed term above are significantly 

different. Essentially, no significant differences were detected 

between intercept terms for profiles within the same sample 

months at the 5 percent level of significance. 

A one-way analysis of covariance also was conducted 

to assess whether the relation between backscatter and 

suspended-sediment concentration was effected by the month 

of the sampling events. Results indicate that neither the mean 

response (intercept term) nor the relation of backscatter to 

sediment concentration (slope term) differs significantly 

between July and August (table 9). Thus, the simple linear 

regression equation described in table 7 is considered adequate 

to model the available data. Given the limited data available to 

develop this equation, however, the utility of the corresponding relation also is limited.
Water Quality Results 21

Table 7. Analysis of variance and parameter estimates for simple linear regression relating suspended-sediment concentrations with 

acoustic backscatter for two profiles sampled in July and August 2009 at station 04157061, Saginaw River at Bay City, Michigan.

[<, less than; —, no data]

Source Degrees of freedom Sum of squares Mean square F Value Probability of great F statistic

Model 1 909.6 909.6 319.2 <0.0001

Error 37 105.4 2.850 — —

Variable Degrees of freedom Parameter estimate Standard error t Value Probability of a greater |t| statistic

Intercept 1 –82.625 5.6299 –14.68 <0.0001

Backscatter 1 1.297 .07259 17.87 < .0001

Table 8. One-way analysis of covariance and parameter estimates relating suspended-sediment concentrations with depth by profile 

and sample month at station 04157061, Saginaw River at Bay City, Michigan.

[<, less than ;--, no data]

Source Degrees of freedom Sum of squares Mean square F Value Probability of great F statistic

Month-profile 3 721.19 240.397 74.78 <0.0001

Depth 1 211.687 211.687 65.85 <.0001

Error 34 109.302 3.215 — —

Variable Month-profile 

combination Parameter estimate Standard error t Value Probability of a greater |t| statistic

Intercept Average 12.2103 0.76317 16.00 <0.0001

July—right –4.7404 .49343 –9.61 <.0001

July—left –3.8404 .49343 –7.78 <.0001

August—right 4.2213 .51224 8.24 <.0001

August—left 4.3596 .49343 8.84 <.0001

Depth All .3749 .04620 8.11 <.0001
22 Comparison of Streamflow and Water-Quality Data Collection Techniques for the Saginaw River, Michigan

Table 9. Analysis of covariance and parameter estimates for linear regression relating suspended-sediment concentrations with 

acoustic backscatter for two profiles sampled in July and August 2009 at station 04157061, Saginaw River at Bay City, Michigan.

[<, less than; --, no data]

Source Degrees of freedom Sum of squares Mean square F Value Probability of great F statistic

Month 1 1.524 1.524 0.53 0.4727

Backscatter 1 222.36 222.36 76.9 <.0001

Backscatter X 

month 1 2.707 2.707 .94 .3399

Error 35 101.20 2.892 — —

Variable Month Parameter estimate Standard error t Value Probability of a greater |t| statistic

Intercept Average –92.843 12.596 –7.37 <0.0001

July 12.606 12.595 1.00 .3238

August –12.606 12.596 –1.00 .3238

Backscatter Average 1.422 .1613 8.82 <.0001

July –.156 .1613 –.97 .3399

August .156 .1613 .97 .3399

Detecting Temporal Variations in Composite 

Suspended Sediment Concentrations with 

Side-Looking Acoustic Backscatter Data

A SonTek Argonaut-SL 500 (side-looking, 500 kHz) 

two-beam horizontal ADCP (HADCP) was mounted near 

the water-level gaging station at the Saginaw River at Bay 

City (fig. 3). The HADCP was located at approximately 

43o 36’ 35.3” north latitude and 83o 53’ 11.2” west longitude. 

It was operated from April 21, 2009, until it was removed on 

Sept. 8, 2009. A third vertical beam on the ADCP measured 

the heights of water above the instrument (depths) during this 

period, which varied from 8.5 to 11.5 ft with an average of 

about 10.5 ft. 

The centerline of the 25-degree separation angle between 

the two slanted horizontal beams was directed approximately 

normal to the channel at an azimuth of about 135 degrees 

clockwise from true north. Along this azimuth, the acoustic 

signal was subdivided into 10 bins, each having a width of 

26 ft and starting 33 ft from the ADCP. No valid data could 

be obtained in the 33 ft closest to the instrument, referred 

to as the blanking distance, because this distance (time) is 

required for the transducers to receive a signal following a 

transmission. Velocity, signal amplitude of backscatter, and 

noise characteristics are measured for each bin. In addition, 

an integrated velocity cell, beginning 33 ft and ending 295 ft 

from the instrument, provided average characteristics. 

This HADCP monitored flow velocities (ft/s), raw signal 

strengths as signal amplitudes (in counts), and instrument 

noise levels (in counts) at generally 15-minute intervals, with 

measurements averaged over 1-minute intervals. Flow direction is reported with respect to the beam azimuth, with downstream flow in the range of 0 to 180 degrees and upstream 

flow in the range of 180 to 360 degrees. During the monitoring 

period, reversals in flow direction were common, particularly 

in the summer months (fig. 10), although upstream (negative) 

flow velocities at Saginaw River at Bay City, Mich. (fig. 11) 

greater than 1 ft/s were uncommon.
Upstream flow 

direction

Downstream flow direction

Flow direction normal to transect, in degrees

Relative frequency

0 30 30 90 120 150 180 210 240 270 300 330 360 0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

EXPLANATION

 May 2009

 August 2009

Figure 10. Frequency of flow 

reversals in the Saginaw River 

at Bay City, Michigan in May 

and August 2009.

Flow velocity, in feet per second

Cumulative frequency

–2 –1 0 1 2 3 4 5

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

1.0

0.8

0.9

Upstream flow Downstream flow

Water Quality Results 23

Figure 11. Cumulative 

frequency distribution of 

integrated flow velocities 

in the Saginaw River at 

Bay City, Michigan from April 

to September 2009.
24 Comparison of Streamflow and Water-Quality Data Collection Techniques for the Saginaw River, Michigan

The acoustic backscatter described by the returning 

signal amplitude is affected by transmission losses that occur 

as the signal traverses the river. Thus for Saginaw River, the 

returned signal amplitude generally decreased with transmission distance across the river (fig. 12). Transmission losses 

that account for beam spreading and absorption by water 

are the primary components of these losses (Gartner, 2004), 

which vary strictly with distance to the bin centers. Distances 

to the bin centers, however, did not vary during the monitoring period. Thus, adjusting the returned signal amplitudes for 

these transmission losses would vary only the mean returning 

signal amplitude by a constant. Adding a constant to the mean 

signal amplitudes would not affect their statistical relation 

with mean suspended-sediment concentration in the cross 

section. Therefore, the mean returning signal amplitudes were 

left unadjusted in this comparison with suspended-sediment 

concentrations. 

Noise is an unwanted acoustic signal that obscures the 

measurement of water velocities and backscatterers. The 

noise level for the Argonaut SL 500 is typically 30–35 counts 

(SonTek YSI Incorporated, 2009). This noise level also can be 

affected by the presence of electric motors or other electronic 

devices. During the monitoring interval, the median measured 

signal noise was 30.5 counts and ranged from 28 to 36 counts. 

Signal amplitudes and noise levels were used to compute 

the signal-to-noise ratio (SNR) as:

SNR decibels

counts = Signal Amplitude Signal Noise c ⋅ ( ) − ⋅ 0 4. 3 ounts

where: 

SNR signal-to-noise ratio in decibels, 

Signal Amplitude magnitude of the reflected acoustic signal, 

which varies with the amount and 

type of suspended material, and the 

distance from the transducer. The signal 

amplitude is attenuated with distance as 

a result of beam spreading and sound 

absorption. Signal amplitude is reported 

in logarithmic units of counts, and

Signal Noise measured acoustic return when no 

acoustic pulse has been transmitted, and 

represents the ambient electronic noise. 

Signal noise is reported in logarithmic 

units of counts.

An SNR of 3 decibels is the minimum in which it is possible to interpret velocity and backscatter characteristics, and 

an SNR of 10 decibels is considered reasonably high. By this 

convention, velocity data in all bins across the river may be 

interpretable (fig. 12).

In 2009, eight DIMV suspended-sediment samples were 

obtained along a transect at the Saginaw River at Bay City. 

The suspended-sediment concentrations in the DIMV samples 

ranged from 14.0 to 29.0 mg/L with an average concentration 

of 19.5 mg/L. No relation between these measured concentrations and signal amplitudes or signal-to-noise ratios (fig. 13) 

could readily be discerned from this limited dataset. Given the 

limited range of suspended-sediment concentration measurements and the difficulty of representing average transect 

concentrations from non-isokinetically collected sediment 

samples, the available data is considered inadequate to support 

an evaluation of the utility of the SonTek SL–500 for continuous monitoring of suspended-sediment concentrations.
EXPLANATION

 ▲ Average signal amplitude

 ● Average signal-to-noise ratio

Distance from horizontal ADCP to bin, in feet

Signal amplitude, in counts

0 50 100 150 200 250 300

80

100

120

140

160

Signal amplitude, in decibels

20

35

40

45

50

30

25

Figure 12. Relation 

between signal amplitude 

and signal-to-noise ratio 

from Argonaut 500 SL with 

distance to width bin at the 

Saginaw River at Bay City, 

Michigan, from April to 

September 2009. (ADCP, 

acoustic Doppler current 

profiler)

EXPLANATION

● Sediment concentration

▲ Signal amplitude

 Signal-to-noise ratio

1 Apr. 1 May 1 June 1 July 1 Aug. 1 Sept. 1 Oct.

 2009

Suspended-sediment concentration, in milligrams per liter

12

16

20

24

28

32

80

90

95

100

105

110

85

Signal amplitude, in countsSignal amplitude, in counts

30

20

40

Water Quality Results 25

Figure 13. Composite 

suspended-sediment 

concentration measurements 

and contemporaneous 

measurements of acoustic 

amplitude and signal-to-noise 

ratios from a side-looking 

acoustic Doppler current 

profiler in the Saginaw River 

at Bay City, Michigan in 2009.
26 Comparison of Streamflow and Water-Quality Data Collection Techniques for the Saginaw River, Michigan

Summary

The Michigan Department of Environmental Quality and 

the U.S. Geological Survey (USGS) developed a plan in 2009 

to compare the effect of various streamflow and water-quality 

measurement techniques on streamflow and water-quality data 

for the Saginaw River, Michigan. The Saginaw River was 

selected for this research because it is the primary contributor of surface runoff to Saginaw Bay, Lake Huron, draining 

approximately 70 percent of the Saginaw Bay watershed. The 

Environmental Protection Agency lists the Saginaw River and 

Saginaw Bay system as an “Area of Concern” based, in part, 

on excessive sediment and nutrient loading to the system. 

Efforts to determine the load of sediment and nutrients to 

Saginaw Bay rely on streamflow and nutrient constituent concentrations collected in the Saginaw River. Current estimates 

of sediment and nutrient loads to this system use water-quality 

samples collected using grab techniques and flow data that are 

uncertain during some specific conditions. Results of these 

flow and water-quality sampling techniques were compared to 

results from alternative techniques between April and September 2009 at two locations in the Saginaw River. 

Streamflow measurements were collected at Saginaw 

(04157000) and Bay City (04157061). Streamflow gaging 

using acoustic Doppler current profiling technology at Bay 

City was compared to traditional stage-discharge gaging 

techniques at Saginaw. In general, flow at station 04157061 

was less than at the upstream station at Saginaw (04157000). 

Conditions resulting from the influence of Saginaw Bay on 

the Saginaw River made streamflow gaging problematic at the 

upstream location using traditional slope/stage techniques, as 

indicated by the large number of daily mean flow values listed 

as estimated. The acoustic gage technology used at Bay City 

was able to capture the velocity variability that resulted from 

the interactions of the Saginaw River and Saginaw Bay.

Water-quality samples were collected at two locations, 

on eight different dates, by the use of both surface-grab and 

DIMV sampling techniques. Sixteen paired samples were 

collected and analyzed for suspended sediment, turbidity, total 

phosphorus, total nitrogen, orthophosphate, nitrite, nitrate, 

and ammonia. Results indicate that concentrations of constituents associated with particulate material such as suspended 

sediment, turbidity, and total phosphorus collected through 

a DIMV sampling technique are statistically different than 

those collected through a surface-grab technique. In addition, 

the dissolved concentration of nitrite plus nitrate, was shown 

to be statistically different on the basis of sampling technique 

at the Saginaw water-quality station (04156999). Variability 

in constituent concentration attributed to sampling technique 

was greatest for suspended sediment followed by turbidity and 

total phosphorus, with median relative percent differences of 

37, 26 and 9.7 percent respectively.

Statistical methods were used to assess the feasibility of 

acoustic-backscatter information collected during flow measurements for estimating the suspended-sediment concentration of the river water. Discrete water samples were collected 

using a Van Dorn sampler at 10 depths (3.5, 7.5, 11, 14, 15.5, 

17.5, 19.5, 20.5, 22, and 24.5 ft below the water surface) along 

two vertical profiles near the center of the Saginaw River near 

Bay City. Samples were analyzed for suspended-sediment 

concentrations, and the data were then related through linear 

regression to acoustic-backscatter data that was collected 

simultaneously. Acoustic backscatter was strongly correlated 

to suspended-sediment concentrations, describing 89 percent 

of the variability through use of a linear regression. This correlation indicates potential for using acoustic-backscatter data 

to estimate suspended-sediment concentrations in the Saginaw River. Attempts to correlate DIMV suspended-sediment 

samples collected at eight separate times, to signal-to-noise 

ratio estimates recorded at the fixed acoustic gage deployed 

near Bay City resulted in poor correlation.

Results of the method comparison for two streamflowgaging and water-quality data-collection techniques indicate 

that uncertainty in constituent concentration and streamflow 

magnitude likely lead to uncertainty in nutrient- and sedimentload estimates for Saginaw Bay. Efforts to quantify phosphorus cycling in the Saginaw River and Saginaw Bay system 

may benefit from employing channel-integrating sampling 

strategies, like DIMV or EWI, to better characterize phosphorus inputs into Saginaw Bay. Grab sampling may be underpredicting phosphorus concentrations between 7.4 and 12 

percent. In general, dissolved species concentrations, such as 

most nitrogen species, were not statistically different between 

DIMV and grab-sampling techniques. Therefore concentrations of nitrogen species are likely not biased low as a result 

of surface-grab techniques used. Additionally, streamflow 

gaging using acoustic gage technology would reduce uncertainty in flow estimates that arise from interactions between 

the Saginaw River and Saginaw Bay. Improved flow estimates 

would likely lead to improved constituent-load estimates for 

Saginaw Bay.
References Cited 27

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—Comparison of Streamflow and Water-Quality Data Collection Techniques for the Saginaw River, Michigan— SIR 2012–5150