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NOAA Technical Memorandum GLERL-119

ASSESSMENT OF IMPACTS OF INCREASED WEED GROWTH ON DETROIT

RIVER FLOWS

Cynthia E. Sellinger and Frank H. Quinn

NOAA, Great Lakes Environmental Research Laboratory, Ann Arbor, MI 48105

Great Lakes Environmental Research Laboratory

Ann Arbor, Michigan

February 2001

UNITED STATES

DEPARTMENT OF COMMERCE

Donald Evans

Secretary

NATIONAL OCEANIC AND

ATMOSPHERIC ADMINISTRATION

D. James Baker

Under Secretary for Oceans

and Atmosphere/Administrator

NAT OI NAL OCEANIC AND ATMOSPHERIC ADMINISTRAT OI N

U.S.DEPARTMENT OF COMMERCE

NATIONAL OCEANIC AND

ATMOSPHERIC ADMINISTRATION

Scott B. Gudes

Acting, Under Secretary for Ocenas

and Atmosphere/Administrator
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NOTICE

Mention of a commercial company or product does not constitute an endorsement

by the NOAA Environmental Research Laboratories. Use of information from

this publication concerning proprietary products or the tests of such products for

publicity or advertising purposes is not authorized. This is GLERL Contribution

No. 1195.

This publication is available as a PDF file and can be downloaded from GLERL’s

web site: www.glerl.noaa.gov. Hard copies can be requested from the GLERL

Publications Unit, 2205 Commonwealth Blvd., Ann Arbor, MI 48105.

pubs.glerl@noaa.gov.
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Table of Contents

Background ........................................................................................................................................ 4

Approach ............................................................................................................................................ 4

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

Results ................................................................................................................................................ 5

 Data Collection ................................................................................................................................ 5

 Data Analysis ................................................................................................................................... 6

 Water Level Analysis .................................................................................................................... 6

 Velocity Analysis.......................................................................................................................... 6

 Roughness Analysis ..................................................................................................................... 9

Conclusions ........................................................................................................................................ 9

References .......................................................................................................................................... 9

Figures

Figure 1.--Prandtl distribution fit to collected velocity data ............................................................ 5

Figure 2.--Location of the ADCP on the Detroit River .................................................................... 6

Figure 3.--Velocity data collected from 1986-1988 ......................................................................... 7

Figure 4.--Velocity data collected from 1988-1989 ......................................................................... 7

Figure 5.--Velocity data collected from 1996-1998 ......................................................................... 8

Figure 6.--Data collected from 1999-2000 ....................................................................................... 8

Figure 7.--Roughness distributions for June 87 vs. June 97 for the Upper Detroit Reach............. 10

Figure 8.--Roughness distributions for July 87 vs. 97 for the Upper Detroit Reach...................... 10

Figure 9.--Roughness comparison of 1987 vs. 1997 for the Lower Detroit Reach ....................... 11

Figure 10.--Roughness comparisons for July 1987 vs. 1997 for the Lower Reach ....................... 11

Figure 11.--Differences in water levels for months May to November - Fermi-Gibraltar ............. 12

Figure 12.--Differences in water levels for months May to November -

 St. Clair Shores-Windmill Pt....................................................................................... 12

Tables

Table 1.--Manning’s roughness values comparison (Upper Reach) .................................................. 9

Table 2.--Manning’s roughness values comparison (Lower Reach) .................................................. 9
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Assessment of Impacts of Increased Weed Growth on Detroit River Flows

Cynthia E. Sellinger

Frank H. Quinn

BACKGROUND

Detroit River flows are important to the Great Lakes water resources. Changes in these flows affect hydropower

usage, navigational activities, and shoreline profiles to name a few. The spread of zebra mussels into the Great

Lakes system led to increased clarity of the water in Lakes St. Clair and Erie and the Detroit River due to their

filter feeding habits. This increased clarity could amplify aquatic weed growth since light is able to penetrate

deeper into the water column and increase the photosynthetic process. Increased weed growth acts to increase the

hydraulic roughness of the Detroit River during the growing season, thus changing the river’s hydraulic properties. As Detroit River flows are used in a wide variety of water resource studies, it is important to quantify both

the amount and the seasonal distribution of the weeds and the increase in roughness due to the impact of the zebra

mussel.

APPROACH

The approach will be to assess changes in Manning’s roughness coefficient (Henderson, 1966) corresponding to

the zebra mussel invasion using a series of velocity measurements coupled with water level data. A time series of

velocity profiles was measured with an Acoustic Doppler Current Profiler (ADCP) deployed in the Detroit River

at Fort Wayne. The data was collected from September 1996 through September 2000. This data set is equivalent

to a set collected prior to the zebra mussel invasion at the same site from 12 November 1986 to 12 December

1989. Two reaches will be analyzed: the upper reach (Ft. Wayne to Wyandotte), and the lower reach (Wyandotte

to Gibraltar). This data will be used in conjunction with recorded water level data (NOS, 2000) along the river to

develop stage-fall-velocity equations for the upper and lower reaches. The equation’s roughness coefficients will

be analyzed to determine the change in the hydraulic flow regime due to the weed growth for both measurement

periods. These coefficients will subsequently be available for use in Detroit River stage-fall-discharge equations

and mathematical flow models.

METHODS

In order to compute an average velocity from the ADCP measured data, a curve must be fit through the measured

points. The reason for a curve fit is twofold. First, velocity measurements at the boundaries are unreliable, and

second, an integral of the curve is a better approximation of the average velocity. Each velocity measurement

consists of data collected at ten 1-meter spaced bins that were then fit to the Prandtl’s curves (Figure 1).

Average vertical velocities were calculated using the raw ADCP data. Prandtl’s equation of turbulent flow (equation 1) was applied to both data sets to produce a smooth velocity profile that includes the top and bottom of the

water column (not measurable).

UC n y

D

=× + 1 2 1 C (1)

Where U is the resultant velocity; C1 and C2

 are the slope and intercept regression coefficients; y is the roughness

length; and D is the depth at which the velocity is recorded. An averaged vertical velocity (V) will be computed

for this by evaluating V over the interval the elevation (yo) to depth of the stream (d) (equation 2).
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V C y

D

C dy

D

y

D

o

= + 



 ∫  1 2

1

ln (2)

This averaged vertical velocity is used along with water level measurements from the Fort Wayne (FW),

Wyandott (WD), and Gibraltar (GB) gages to compute Manning’s ‘n’ from Manning’s equation (3).

V

n

FW WD YM FW WD

L

V

n

WD GB YM WD GB

L

= ( ) + − 







( ) −







= ( ) + − 







( ) −







1

2

1

2

23 12

23 12

/ /

/ /

*

*

(3)

Where YM is the mean bottom elevation, L is the length of the Fort Wayne-Wyandotte and Wyandotte-Gibraltar

reaches, and the constant n is the Manning’s roughness. These roughness coefficients can then be analyzed for

variance over time.

RESULTS

Data Collection

The U.S. Army Corps of Engineers and the Great Lakes Environmental Research Laboratory (GLERL) redeployed the ADCP meter in the Detroit River on 5 September 1996. Precise locations of the meter were obtained

with a Global Positioning System (GPS) provided by the Corps. The ADCP was deployed in approximately 14

meters of water located 90 meters from shore at a latitude of 42o 17’ 88.81” and a longitude of 83o 05’ 51.74”

(Figure 2). Once deployed, the data link cable was secured to the river’s bottom with chains, then connected to a

Figure 1. Prandtl distribution

fit to collected velocity data.
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lap-top computer used for data storage and

transmission located at the National Ocean

Survey (NOS) Ft. Wayne water level gage

house.

Although the deployment went smoothly,

divers couldn’t secure the cable to the river’s

bottom with the same type of metal hooks that

were used in the past. The divers said that the

bottom was harder than before. During the first

deployment in 1986, divers secured the cable

by threading it through the metal hooks then

pushing the 35-cm long spike part into the

river’s bottom with the stomp of the foot. This

time, however, the bottom was harder, so they

used hammers to secure the hook to the bottom.

However, these hooks would not stay attached

due to the swift current, so the cable was

secured with chains.

Data has been collected since 9 September

1996. These data have been analyzed for their integrity by first ensuring that the ADCP was positioned correctly

and by comparing it with previously collected data.

Although the data is received on a 15-minute sampling period, it was averaged to a daily velocity using the

Prandtl’s nonlinear velocity equation (Equation 2). Figures 3 - 6 show daily velocities collected for the 1986-2000

period.

Data Analysis

Water Level Analysis

An analysis of water levels was conducted for the upper reach to determine the reach’s boundary. A studentstandardized t-test at a level of significance of .05 was applied to Manning’s roughness created for the reaches of

Windmill Point-Wyandotte and Fort Wayne-Wyandotte. Results of the test showed that these roughness values

have considerably different means, medians, and variances. This analysis suggests that Windmill Point levels may

not be a true representation of Detroit River levels, but may also respond to events taking place in Lake St. Clair.

Therefore, the reach of Fort Wayne and Wyandotte was used for computing roughness values for the upper reach.

Velocity Analysis

After analyzing all of the velocity data, the 1987 and 1997 data sets were selected for the final analysis. Velocity

values for 1989 represent a year of a low flow regime. A comparison of the differences in Ft. Wayne water levels

for years 1997, 1987, and 1989 indicates the data collected in 1989 is not an average water level year.

Figure 2. Location of the ADCP

on the Detroit River.
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Figure 3.--Velocity data collected from 1986-1988.

Figure 4.--Velocity data collected from 1988-1989.
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Figure 5.--Velocity data collected from 1996-1998.

Figure 6.--Data collected from 1999-present.
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Roughness Analysis

Since the objective of this study is to quantify the change in the river’s flow regime due to roughness changes,

Manning’s roughness values were compared on a monthly time scale for the upper Detroit River (Table 1) and the

lower Detroit River (Table 2) an area of prominent weed growth.

A comparison of these values using a student-standardized t-test at a level of significance of 0.05 shows that there

is a slight difference in the means and a greater difference in the population distributions (Figures 7-10) for the

months of June and July. Corroborating data, particularly for the Fermi-Gibraltar reach where there is significant

weed growth, shows a change in the water surface slope after 1988. Water level differences were computed for

two reaches (Figures 11-12) for the weed-growth months of May-November. The significant negative change in

slope at the Fermi-Gibraltar reach indicates a change in the river’s hydraulic regime that might be attributed to

increased weed growth.

CONCLUSIONS

Beginning with the presence of the zebra mussel in the late 1980’s, the hydraulic flow regime of the Detroit River

has changed. Although the amount of change is difficult to quantify, the analysis shows that different roughness

populations exist for the June and July months of 1987 and 1997. Also, the corroborative data from the slope

differences in the lower reach shows a different hydraulic regime after 1988.

REFERENCES

Henderson, F.M. Open Channel Flow. Prentice-Hall, Inc, a Simon & Shuster Company. Upper Saddle River,

New Jersey 07458 (1966).

National Ocean Service. NOS CS41, 1305 East-West Highway, Silverspring Md. 20910 (2000).

Table 1. Manning’s Roughness Values Comparison (Upper Reach).

Month Pre-zebra mussel Post zebra mussel

Manning’s Roughness Manning’s Roughness

May .0186 .0194

June .0195 .0193

July .0199 .0198

August .0199 .0203

September .0202 .0202

October .0199 .0198

November .0199 .0195

Month Pre-zebra mussel Post zebra mussel

Manning’s Roughness Manning’s Roughness

May .0278 .0274

June .0286 .0276

July .0291 .0289

August .0284 .0280

September .0288 .0284

October .0287 .0274

November .0288 .0284

Table 2. Manning’s Roughness Values Comparison (Lower Reach).
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1987

1997

YEAR

0.017

0.018

0.019

0.020

0.021

0.022

ROUGHNESS

25 20 15 10 5 0

Count

0 5 10 15 20 25

Count

June (Upper Reach)

1987

1997

YEAR

0.017

0.018

0.019

0.020

0.021

ROUGHNESS

20 15 10 5 0

Count

0 5 10 15 20

Count

July (Upper River)

Figure 7.--Roughness

distributions for June 87 vs.

June 97 for the Upper

Detroit Reach.

Figure 8.--Roughness

distributions for July 87 vs.

97 for the Upper Detroit

Reach.
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1987

1997

YEAR

0.025

0.026

0.027

0.028

0.029

0.030

0.031

ROUGHNESS

20 15 10 5 0

Count

0 5 10 15 20

Count

June (Lower River)

1987

1997

YEAR

0.024

0.025

0.026

0.027

0.028

0.029

0.030

ROUGHNESS

25 20 15 10 5 0

Count

0 5 10 15 20 25

Count

July (Lower Reach)

Figure 9.--Roughness

comparison of 1987 vs.

1997 for the Lower Detroit

Reach.

Figure 10.--Roughness

comparisons for July

1987 vs. 1997 for the

Lower Reach.
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Figure 11.--Differences in water levels for months May to November.

Figure 12.--Differences in water levels for May to November time period.