Dam Removal as a Solution to Increase Water QualityMatthew Nechvatal, Tim Granata

Department of Civil and Environmental Engineering and Geodetic Science

The Ohio State University

Background

St. John’s Dam (Figure 1) was a concrete low-head dam located on the Sandusky River in north central Ohio. The river drains approximately 3,680 km2 of the Sandusky River watershed (Figure 2) and flows north to Lake Erie. Eighty-nine percent of the watershed is located in four counties: Sandusky, Seneca, Wyandot, and Crawford, which consist of 27 major cities or villages. Table 1 shows the different types of land use designated in the watershed. Along with the St. John’s Dam, the Sandusky River has four other dams. The St. John’s dam was constructed in the 1930s to serve as a water supply for the city of Tiffin. It was originally 2.2 m high, 46 m long, and was located at River Mile (RM) 50. It was breached on March 18, 2003, by notching the dam on the west bank to 0.5 m. The dam was then removed on November 17, 2003.

Figure 1 – Breaching of St. John’s Dam (Photo by Fang Cheng)Figure 2 – Sandusky River Basin (Courtesy of Fang Cheng)

  Total Urban Ag. Shrubs Woods Water Wetlands Barren

Km2 3680 43 3090 18 465 13 41 10

% cover 100 1.2 84 0.5 12.6 0.4 1.1 0.2

Table 1 – Land use and area in the Sandusky River Watershed(Courtesy of the Sandusky River Watershed Coalition)

Objectives• Statistically determine water quality changes upstream and downstream of St.

John’s Dam after removal

• Changes in denitrification potential in the former impoundment will be studied to assess if it is a source or sink of nitrogen

• Model dam removal with a hydrodynamic model (Mike 11) to determine water quality parameters

Methodology• Nutrients (NO3

-, PO43-, NH4

+) in the river were sampled monthly at 4 locations upstream and 4 locations downstream of the dam before and after removal (Figure 3)

• Water quality YSI sonde was deployed from a canoe measuring DO, pH, temperature, ORP, specific conductivity, and turbidity at 5 Hz from 17.7 km upstream of the dam down to the dam

• Vertical profiles were taken with the YSI water quality sonde directly behind the dam measuring temperature and DO

Preliminary Results

• Pre-removal nutrient data

• In September and November nutrient concentrations increased from above the dam down to the dam then leveled off below the dam, however, in October data fluctuated

• Post-removal nutrient data

• In November nutrient concentrations increased above the former dam site and then leveled off below the former dam. This occurred approximately 8 days after removal. Nutrient data had not yet leveled off

• In December and April nutrient concentrations leveled off to similar concentrations above and below the former dam site

Figure 3 – Sample sites upstream and downstream of the dam

• Pre-removal temperature data

• In October temperature increased as you moved down the reservoir toward the dam, however, in November data fluctuated

• Post-removal temperature data

• In December temperature leveled off. There was no increase or decrease in temperature as you moved down the former impoundment toward the dam

Figure 5 – Spatial temperature profile upstream of the dam (mean subtracted from each point)

Figure 4 – Spatial nitrate distribution at eight different locations before and after dam removal upstream and downstream of St. John’s Dam

Figure 7- Sandusky River gaging station flow data before, during, and after removal

Figure 6 - Turbidity, ORP, and temperature downstream of St. John’s Dam before, during, and after removal

• YSI water quality sonde was place 200 m downstream of the dam

• Dam was removed November 17, 2003

• Turbidity increased from 32.2 NTU to 120.0 NTU in two hours following dam removal

• ORP decreased from 129 mV to 46 mV in a 70 minute duration following removal

• Temperature increased 3.93 oC over the next 2.3 days as the water from the reservoir drained downstream

• There are two gaging stations upstream of the dam

• One gaging station is approximately 33 river miles downstream from the dam

• One day after dam removal an increase of 5.7 m3/s was detected

• Three days after dam removal, a large flooding event increased the discharge by 38 m3/s

• Removing the dam was similar to a small flooding event

Acknowledgements

We would like to thank Fang Cheng and Dan Gillenwater at OSU and Bob Vargo at the Ohio DNR for the field work they have contributed to this project.

50 0 50 Kilometers

OhioSandusky River Basin

2.00

4.00

6.00

8.00

10.00

12.00

14.00

16.00

18.00

20.00

24.1 17.7 6.4 0.05 0.05 0.55 3.9 4.7

Distance from dam (km)

Nit

rate

Co

nce

ntr

atio

n (

mg

/l)

dam

downstreamupstream

12/9/03

11/25/03

10/10/03

11/11/03

9/10/03

4/23/04

post-removalpre-removal

05

101520253035404550

11/1

3/03

11/1

5/03

11/1

7/03

11/1

9/03

11/2

1/03

11/2

3/03

11/2

5/03

11/2

7/03

Time (days)

Dis

char

ge

(m^

3/s)

downstream of dam upstream of dam upstream of dam

dam removal

approximately bankfull

effects of removal

0

20

40

60

80

100

120

140

160

11/1

5/0

3

11/1

6/0

3

11/1

7/0

3

11/1

8/0

3

11/1

9/0

3

11/2

0/0

3

11/2

1/0

3

Time (days)

Tu

rbid

ity (

NT

U)

OR

P (

mV

)

0

2

4

6

8

10

12

Te

mp

era

ture

(C)

dam removal

N

EW

S

St. John's Dam

Sample Site Downstream of Dam

Sample Site Downstream of Dam

Sample Site Upstream of Dam

St. John's Dam

-2.00

-1.50

-1.00

-0.50

0.00

0.50

1.00

1.50

2.0017

.65

16.6

0

15.5

6

14.5

1

13.4

7

12.4

3

11.3

8

10.3

4

9.29

8.25

7.21

6.16

5.12

4.07

3.03

1.99

Distance from dam (km)

Devi

atio

n fro

m m

ean

11/11/03

10/24/03

12/9/03

post-removalpre-removal