If you have been to meetings about the management of Chautauqua Lake’s plants or algae in the last 30 years, then you’ve likely heard someone proclaim the need to “dredge the lake” or “dredge the outlet.”
The Chautauqua Lake Outlet was dredged over 100 years ago for steamboat navigation. Canals leading to the lake have also been dredged. Streams produce deltas – sand and gravel bars where the current slows and where the stream drops its coarse sediment loads. Dredging navigation channels for marinas and boat access at creek mouths has happened routinely through the years on this lake. Municipalities have dredged the bars at the mouth of various streams. In a natural stream system, those sediment “crescents” act as dams and slow water upstream, causing it to flood its floodplain and drop debris and sediments upstream, with less going into the lake.
Many owners of creekfront properties want creek mouths dredged to reduce the incidence of flooding and property damage. Some with boats in creeks upstream want the mouths of the creeks dredged so they can motor in and out of the lake. Some delta deposits, such as at Dutch Hollow Creek, can extend so far into the lake that they can be navigational hazards to unaware night boaters. The removal of sediment crescents at creek mouths can have negative impacts though, such as allowing the stream to push sediments faster and further into the lake and accelerating bottom erosion in the stream, resulting in even more sediment and nutrients flowing into the lake. Dredging deltas can also remove important fish spawning and nesting habitat.
Presently, some people are suggesting dredging organic sediments on a scale large enough to try to reduce internal phosphorus loading to the lake, while others suggest dredging shallow vegetated areas such as Burtis Bay from 3-5 feet down to 11 feet or more to make it difficult for plants to grow to the surface and interfere with boating. In 2012, Chautauqua County hired Ecologic to undertake a dredging feasibility study for several creek mouths and Burtis Bay. The resulting 2013 Dredging Feasibility Report projected that it would cost roughly $3.97 million to dredge 7.4 acres of Burtis Bay down a depth of 2.5 feet, which is not deep enough to make that area free of plant growth. Due to the presence of arsenic in Burtis Bay sediments, it was determined at that time that sediments dredged from this bay would not be able to be used as land cover and, instead, would have to go to a secure landfill such as the Chautauqua County Landfill, with significantly higher cost. Estimates were also made for dredging 4 acres at Bemus Creek, 1 acre at Dutch Hollow Creek, 6.5 acres at Goose Creek, and 7.5 acres at Mud Creek. These estimates, plus the Burtis Bay estimate, totaled $8,977,000, with additional costs for purchasing land for staging and dewatering sediments and for special treatment of arsenic contaminated sediments, etc. The rough total figure came to nearly $10 million to dredge just over 26 acres. The report concluded that, “the dredging of nearshore areas of this lake is feasible, but costly.” It went on to say, “Dredging can help mitigate past sediment deposits, but effective control measures must be in place to reduce the rate of future sediment deposition.” This report can be found at the Chautauqua Lake and Watershed Management Alliance website at chautauqualakealliance.org.
In reviewing this report, one may conclude that small-scale channel maintenance dredging for marina access and creek mooring is likely to be economically feasible to continue, but large-scale, high-volume dredging to increase depth to below the zone where light powers plant growth would seem to be very expensive and cost prohibitive. For now, the best we can do is take effective regulatory and voluntary actions to capture and infiltrate stormwater and to control erosion from the watershed, shoreline, and lake bottom.
Article by John Jablonski III, Special Projects Coordinator for Chautauqua Watershed Conservancy | Photo source: Dredging Feasibility Report Chautauqua Lake, 2013