Dredging Lake Adger estimated to cost $2.5-$5 million

Published 11:11 pm Thursday, June 4, 2015

Aerial photo of Lake Adger in 2010 showing sedimentation.

Aerial photo of Lake Adger in 2010 showing sedimentation.

By Leah Justice


Polk County Commissioners heard this week that dredging Lake Adger is estimated to cost between $2.5-$5.1 million.

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Commissioners met Monday, June 1 and heard from Stu Ryman, with Altamont Engineering, who reviewed the results of a feasibility study recently done on dredging the lake.

Ryman said the study evaluated the extent of sediment in the lake, the quantity of sediment that could be removed, methods of removing the sediment and estimate costs of removal.

Ryman showed aerial photos of Lake Adger near the marina in 2010 compared to the same aerial view in 2013, saying it can be seen there is quite a bit of sediment accumulation over the three-year period.

Aerial photo of Lake Adger in 2013 showing increased sedimentation.

Aerial photo of Lake Adger in 2013 showing increased sedimentation.

Ryman said his firm went through the lake to determine what depth the water was and determined now there are some sections near the Green River that are less than six inches deep. Some areas were less than one foot deep and the portion of the lake furthest from the marina got to 10 ft. The majority of the west section of the lake is less than one foot and five feet deep, he said.

How much to dredge

Ryman said commissioners will have to decide how much the county wants to dredge the lake. He said if the county wants to dredge for an average depth of five feet, it would require removing 150,000 cubic yards of sediment.

If the county wants to dredge to an average of 10 ft. deep, 450,000 cubic yards of sediment will have to be removed.

Dredging the Green River one mile upstream would add another 20,000 cubic yards needed for removal, said Ryman.

Costs to dredge

Costs to dredge range from $15-$30 per cubic yard, Ryman said so if the county wants to dredge the lake to an average depth of five feet the cost would be between $2,550,000 and $5,100,000.

Ryman said there is grant funding available that could pay up to 50 percent of the costs. He later said a state grant for dredging is fairly new and has only been funded $150,000 per year so far.

The money the county spends on studies, permitting or land costs for sediment disposal could be counted as the county’s match if a grant is acquired.

Disposal of sediment

The study determined that the sediment in the lake is not of any value. Sediment taken from the Green River before it reaches the riverbed would be of value, however.

The county will need to find a place to store the sediment, preferably as close to the lake as possible to cut down on trucking costs, Ryman said.

Ryman said the desired method for disposal is to find an offsite location where the material will be trucked. He suggested no less than 10 acres and preferably 20-30 acres.

Dredging methods

Options for removing sediment include hydraulic dredging and mechanical excavation, according to Ryman. Hydraulic dredging is usually done in larger areas such as inlets and much larger bodies of water, so mechanical excavation is being recommended for Lake Adger.

Ryman said contractors Altamont talked to recommended lowering the lake level and using excavators and dump trucks to haul it to the offsite location.

The future

Ryman said sediment is going to continue to accumulate in the future unless something is done on the Green River to remove sedimentation before it reaches the lake. He said Lake Lure is currently being dredged every other year at a cost of $400,000-$500,000 each dredging year. Ryman recommended Polk County facilitate a sand and gravel dredging operation on the Green River for ongoing removal of sediment. There was formerly a company that removed sediment from the Green River but that operation stopped many years ago.

Ryman also said the dredging has to be permitted and the N.C. Wildlife Resources Commission has indicated there is an endangered fresh water mussel on the Green River which could create a sand and gravel permitting hurdle. He said the county will have to figure out where the mussel occurs to know where a sand and gravel operation could be set up on the Green River.

Commissioner Keith Holbert said if Polk County cannot find a sand and gravel operation for the Green River, dredging the lake would be a waste of money.

Commissioner Ray Gasperson said Polk County government along with citizens need to have a strategic plan and decide its priorities. A sand and gravel operation needs to be the first step, Gasperson said.

Commissioner chair Tom Pack said if a grant is only funded $150,000 a year state-wide, Polk County is going to have to look at funding the majority of the dredging itself.

Ryman said one of the contractors Altamont spoke to runs a sand and gravel operation downstream of Lake Lure and is interested in a second operation.

Commissioners decided to continue discussions on the dredging of Lake Adger during its July meeting.