Zebra mussels were first discovered in Black Rock Lock (Buffalo, NY) in the late 1980s. By early 1992, all lock surfaces were covered completely by a zebra mussel infestation, which ranged from 1.5 to 4 inches thick. A monitoring program would have provided data that could have been used to develop control strategies prior to the intense infestation observed. To date, the intense infestation has caused accelerated corrosion and increased maintenance costs.
The upper end of Black Rock Lock is at Lake Erie level, with no water control structure. The channel at the lower end reenters the Niagara River. There is not a constant flow of water either through or around the lock from the channel. The lock chamber is 650 feet by 70 feet, enlarged by approximately 100 feet during pumpout with guard gates closed. The average lock lift is 5.5 feet with a draft of 21.5 feet over the sills at low water depth, and the lock is serviced by 6-feet culverts in both walls. Lateral culverts run from the main culverts into the chamber. Each operating gate has two gate valves. Actual lock lift time is 12 to 15 minutes. The lock has no gauge wells or transducers.
Water flows through the lock channel from left (upstream, Lake Erie) to right (downstream, Niagara River). Secondary culverts extend perpendicularly from the main culvert into the lock channel. Below is an overview of the upstream operational gates.
Certain areas of locks are more vulnerable to zebra mussel infestation than others. In many cases, infestation in these areas could have a significant impact on overall lock function. Thus, certain areas should be given special consideration in the design of lock monitoring programs.
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Lock Walls:
Lock walls are easy to monitor and clean mechanically. Infestation solely on the walls would cause increased turbulence, could scrape vessels, and could increase corrosion around rivets and other fixtures.
Lock Gates:
Gates provide excellent settlement surfaces and an abundance of settlement area. Miller et al. (1992) describe the following reasons for concern regarding mussel infestations on lock gates:
- Increased gate weight possibly straining hinges, warping gate leaves, and interfering with opening and closing.
- Increased metallic corrosion leading to increased maintenance or structural damage.
- Reduced clearance for fully opened gates and difficulty with fully recessing gates, increasing the potential for them to be scraped or damaged.
- Interference with gate bubbler systems could lead to bubbler clogging, thus rendering the system inoperable.
- Increased maintenance times due to the need for additional inspections, cleanings, and corrosion-related repairs.
Lock Culverts and Plumbing:
The subterranean lock culverts provide an excellent zebra mussel settlement area, which would be difficult to clean. The complex network of pipes and valves could be severely impacted by zebra mussels in terms of the overall flow rate and the symmetry of flow from one side of the lock to the other.
Recommended Monitoring Strategies for Locks:
1) Collect pumped plankton samples from an upstream station within the actual lock chamber and downstream of the lock on a regular basis as long as ambient water temperature is above 10ºC.
2) Visually inspect all exposed lock surfaces for adult zebra mussels as frequently as possible, especially when locks are dewatered.
3) Document the origins of all vessel traffic, especially those vessels from infested waters.
4) If at all possible, dry down the lock at least semiannually. During dry-down, conduct a thorough investigation of all exposed surfaces for the presence of adult zebra mussels.
If any of these monitoring strategies indicate that zebra mussels are present in the facility, begin to implement a control strategy immediately. The Management and Control section provides additional detail on both control strategies in general and the strategies which have been used successfully to date at Black Rock Lock.