1. Project Title: Ecological Effects of Rubble-Mound Breakwater Construction and Channel Dredging at West Harbor, Ohio (Western Lake Erie)
2. Contact
Dr. Bruce A. Manny, Principal Investigator
National Biological Service, Great Lakes Science Center (NBS-GLSC), 1451 Green Rd., Ann Arbor, MI 48105, USA
Tel.: (313) 994-3331 ext. 255; FAX: (313) 994-8780; E-mail: (cc-mail) R8 NFRC.GL
3. Agencies Involved
U.S. Army Corps of Engineers, Washington, DC 20314-1000, USA (Under
EIRP Work
Unit 31632)
National Biological Service, Great Lakes Science Center (NBS-GLSC), 1451 Green Rd., Ann Arbor, MI 48105, USA
4. Restoration Goal
Build breakwaters on either side of the entrance to West Harbor, Ohio, and dredge channel between them to permit access to and from western Lake Erie by small water craft under all weather conditions. Assess adverse ecological impacts of breakwater construction and dredging on area biota.
5. Project Type
Modify shoreline/channel geometry at harbor entrance by construction of two breakwaters extending offshore and dredging a channel approach to the harbor between them to a uniform depth. Conduct studies of water quality and the distribution and abundance of periphyton, macrozoobenthos, and fishes in nearby habitats before, during, and after construction.
6. Background and Rationale
The study area was located in southwestern Lake Erie along a beach shoreline in shallow (0-4 m) water at the entrance to West Harbor, a natural stream channel. High-energy waves eroded parts of the beach and filled in the channel, restricting access to the harbor by sport-fishing boats. To improve access to the harbor, the U.S. Army Corps of Engineers (Corps) designed and constructed breakwaters consisting of large (0.9-2.7 tonnes) limestone boulders underlain by smaller (25-350 kg) stones on either side of the channel and dredged the channel between them to a uniform depth of 3 m. The east breakwater was connected to shore and extended 480 m offshore to water about 3.5 m deep. The west breakwater was not connected to shore (to improve water circulation) and extended offshore to water about 3 m deep. The Corps asked NBSGLSC (then the U.S. Fish and Wildlife Service, Great Lakes Fishery Laboratory) to document changes in water quality, bottom sediments, and biota before, during and after construction on the breakwaters at five transects near the harbor mouth.
7. Regulatory Considerations
The Corps was the permitting agency; they contracted with the private sector for construction and with NBS for the biological assessment. The Fish and Wildlife Coordination Act provided for project review by the U.S. Fish and Wildlife Service.
8. Criteria
Compared with site information collected prior to construction, project activities should cause no significant adverse impact on aquatic biota or their habitats in the project area and restore the area to pre-project water depths and substrate conditions.
9. Project Design
The Corps designed the breakwaters and channel dredging. NBS designed the assessment of project effects on water quality, substrates, and biota at 5 transects perpendicular to shore along a 4 km segment of the shoreline roughly centered on the harbor mouth. Three transects (II, III, and IV) were located near the proposed breakwater construction site; two (I and V) were located 0.8 km northwest and 2.0 km southeast of the harbor entrance in reference areas outside the construction site where the composition and slope of the lake bottom were similar to those in the construction site. Transect III in the channel to West Harbor assessed changes in water quality and biota occurring as a direct result of deepening and extending that channel. Water quality data collected on transects and breakwaters included bottom type, dissolved oxygen, water temperature, suspended particulate matter and turbidity. Macrozoobenthos, periphyton, and fish were identified to the lowest practical taxonomic level. Fish were collected on transects and near breakwaters with a beach seine and a 8 m semi-balloon bottom trawl.
10. Implementation
Limnological and fishery surveys were conducted on the transects using large and small research vessels in August of 1981, 1982, and 1983 and on breakwaters in April, July and September of 1982 and 1983. Breakwater construction and channel dredging were done between August 1981 and November 1882. From October 1982 to August 1983, without notifying the NBS or the Corps, the Ohio DNR constructed four offshore breakwaters southeast of the entrance to West Harbor to protect the public beach there from erosion. This activity confounded the "after" portion of the NBS assessment.
11. Degree of Environmental Intervention
Breakwaters were constructed with large dump trucks and barge-mounted cranes. Dredging with a barge-mounted hopper dredge caused significant, short-term increases in turbidity and decreases in dissolved oxygen near the construction site. Stream flow between the breakwaters was diverted and interrupted for about 2 months during channel dredging. Marked adverse changes in water quality (dissolved oxygen) were noted at the study site in 1983 following construction and dredging activities at West Harbor and during construction of offshore breakwaters by ODNR.
12. Cost
We have no estimate of the cost to design and construct the breakwaters
and dredge the channel; please contact the Corps for that information.
Costs of the NBS assessment study were about
$50 000.
13. Biological Assessment
This assessment showed that rubble-mound breakwater construction and channel dredging at the mouth of West Harbor had no detectable adverse effects on macrozoobenthos and fishes. The breakwaters provided suitable substrate for colonization by periphyton, especially Cladophora, and a more diverse assemblage of macrozoobenthos (46 taxa), including 27% Gammarus, than was found in nearby sandy substrates (36 taxa), presumably because the breakwaters offered more protection from wave action and a wider variety of habitats than the surrounding lake bottom. Breakwater construction and channelization caused fish to avoid the construction site in April and July of 1982 but had no lasting adverse effect on the distribution or abundance of fishes near the site.
14. Measures of Success
"After" aspects of the assessment in 1983 were confounded by marked decreases in dissolved oxygen at the study site that can not be ascribed with certainty to breakwater construction and channelization at the West Harbor site because the State of Ohio constructed offshore breakwaters near the study site then. Other aspects of the biological assessment were successful and showed that the breakwaters were being rapidly colonized by a wide variety of plant and animal life. Additional study would have been needed to determine when colonization of the breakwaters by periphyton, macrozoobenthos, and fish reached equilibrium.
Success Rating: 4
The project was successful as designed but would have benefited
from a longer period of
assessment.
15. Key References
All data and findings of the biological assessment by NBS are in:
Manny, B.A., Schloesser, D.W., Brown, C.L., and French, J.R.P.
1985. Ecological effects of
rubble-mound breakwater construction and channel dredging at West
Harbor, Ohio (Western Lake Erie). Technical Report EL-85-10, prepared
by U.S. Fish and Wildlife Service for the U.S. Army Corps of Engineer
Waterways Experiment Station, Vicksburg, Mississippi.
This report is presumably available from the National Technical Information Service in Washington, DC.
Correct citation for this contribution:
Manny, B.A. 1995. Ecological effects of rubble-mound breakwater construction and channel dredging at West Harbor, Ohio (Western Lake Erie), p. 263-266. In J.R.M. Kelso and J.H. Hartig [editors]. Methods of modifying habitat to benefit the Great Lakes ecosystem. CISTI (Can. Inst. Sci. Tech. Inf.) Occas. Pap. No. 1.