Dam Removal as a Solution to Increase Water Quality

1
Dam Removal as a Solution to Increase Water
Quality Matthew Nechvatal, Tim Granata Department
of Civil and Environmental Engineering and
Geodetic Science The Ohio State University
Preliminary Results
Background St. Johns 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. Johns Dam, the Sandusky River
has four other dams. The St. Johns 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 4 Spatial nitrate distribution at eight
different locations before and after dam removal
upstream and downstream of St. Johns Dam
Figure 6 - Turbidity, ORP, and temperature
downstream of St. Johns Dam before, during, and
after removal
Figure 2 Sandusky River Basin (Courtesy of Fang
Cheng)

• 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

Figure 1 Breaching of St. Johns Dam (Photo by
Fang Cheng)

• 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

  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. Johns 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

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

• 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

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

• 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

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.
Figure 3 Sample sites upstream and downstream
of the dam