Sedimentary, My Dear Watson
Ambulkar, Archis, Zeller, Stephen N., Parks & Recreation
HOW WE DID IT
How Lake Henrietta was restored to it old self.
Sediment accumulation at the bottom of waterways can potentially affect water quality, navigation, recreation, or any other intended uses. That's why sediment removal is practiced, in order to restore the original quality, nature, and appearance of a sedimented body of water. Selection of appropriate sediment removal technology depends upon various factors including costs, permits, duration, location, accessibility.
Lake Henrietta is a four-acre lake located in Doubling Gap, Pennsylvania, on the property of the Doubling Gap Center Yolijwa camp ground. The lake is part of a Christian summer camp that utilizes the lake for boating and other recreation including fishing. The lake is part of Doubling Gap Creek, a cold water fishers stream flowing through the Doubling Gap Valley. Doubling Gap state park is directly upstream from the Lake Henrietta. Over time, sediments accumulated in the upper reaches and along west side of the lake. This sediment deposition came primarily from leaf material and sand from the erosion of the local geology in the area.
Before pursuing sediment removal, the owners of the camp weighed the pros and cons of taking no action. Doing nothing would result in the deposition of 30 to 40 percent more material every 10 years into the lake. This continued deposition of sediment and leaves would most likely result in odors issues resulting in septic conditions and providing habitat for breeding of mosquitoes and other vectors. Not least, the deposited material would hinder the enjoyment by campers and camp staff of the lake.
Some of the common methods for sediment removal from lakes include draining and excavating a lake, mechanical dredging, and hydraulic dredging. While reviewing options for sediment removal, Brinjac Engineering Inc. focused on cost-effective dredging alternatives with minimum environmental impacts for sediment removal. Since this waterway was a part of high quality trout stream, minimizing impacts to the environment was critical. During review, the conventional truck-and-loâder method was compared to hydraulic dredging.
The estimated cost for hydraulic dredging work was $117,500, which included bags, pumping equipment, crews, and associated equipments for dredging, This cost was compared with the costs associated with conventional dredging of the lake by a crew of contractors with digging equipment and trucks once the lake was drained. Cost for that was estimated at $180,000. In addition, this cost for conventional dredging did not include erosion and sedimentation (E&S) that was expected to drive the cost upwards to between $100,000 and $300,000. Finally, the conventional method would create ponds as deep as seven feet from the lake dredgings. It could take months or even years to dewater and as such would be a liability to a facility that services many thousands of youths each year. Also, conventional method would take months to clean woods, build a retention area and roads and then weeks to for and loaders trucks to remove sediment and transport it to loading area for dewatering by evaporation. Hence, further evaluation of the conventional dredging alternatives was not pursued and the hydraulic dredging method was selected for sediment removal.
Discussions with the Pennsylvania's Department of Environmental Protection (DEP) indicated that due to the size of lake and drainage basin, dredging in Lake Henrietta qualified for Section 105 permit exclusion and, therefore, no permit was required. A report was still required to be submitted to DEP for this work, which was approved for a period of four to five weeks using hydraulic dredging. …