LAKEPORT — The county could be close to beginning a suction-dredging program to mechanically remove hydrilla tubers from Clear Lake.
The Community Development Department on Wednesday adopted a mitigated negative declaration and associated mitigation monitoring plan for a proposed county program to physically remove the tubers during the course of five years.
Community Development Director Richard Coel made the decision after closing the public hearing on the issue Wednesday. The public hearing had been continued to Wednesday following an earlier discussion on April 6.
The state requires eradication of hydrilla from water bodies, and the proposed mechanical removal program would be an additional tool the county could use to address the plants.
If not controlled, the hydrilla plants could cover the lake within seven or eight years because of fast growth and rapid reproduction, according to Carolyn Ruttan, invasive species program coordinator for the Lake County Department of Water Resources (DWR).
The suction dredging could provide a long-term solution rather than short-term results, as seen with chemical treatments, Coel said.
Since 2007, 356 hydrilla plants have been located in Clear Lake, Ruttan said. The county currently treats visible hydrilla plants with herbicides, but chemicals still have to be applied to those areas yearly, even if the plant appears dead on the lakebed, because the tubers can lay dormant for up to nine years, Ruttan said.
The dredging program proposes to use an Aquamog, which acts like a vacuum cleaner, to remove the top 12 inches of sediment in areas where hydrilla plants are known to grow.
The project would occur around the lake”s perimeter at a distance of up to 1,800 feet from the shoreline and a depth of up to 15 feet.
The removed lakebed contents, estimated to include 90 percent water and 10 percent sediment and tubers, would be sucked through a 20-foot hose onto a barge.
A quarter-inch screen on the discharge end of the pump (on the barge) would catch potentially cultural, archeological, or otherwise significant items. A representative from DWR would be stationed on the barge to monitor the discharge end at all times. Tubers caught by the screen would be removed and sorted with the others.
The dredged materials would be unloaded at the nearest public dock into a covered dumpster, and then transported to an upland location for dewatering.
The program would be a coordinated effort between DWR and the California Department of Food and Agriculture. The tasks related to suction-dredging equipment use would be contracted out, according to Ruttan.
If the program is approved, DWR would actively search the lake for hydrilla growths and then employ the suction dredging in those areas, provided the locations are not deemed sensitive, Ruttan said.
The suction dredging would be directed only at those sites where plants have been found, according to Ruttan. The physical removal could be successful in removing a vast majority of the tubers, and the remaining few plants would be treated with herbicides, she said.
County staff developed a series of mitigation measures in order to avoid or minimize the potential environmental impacts of the project, as required by law. Topic areas for mitigation measures include air quality, biological or cultural resources, geology, noise and hazardous materials.
Local scientists, environmental advocates, tribal representatives and other concerned citizens discussed their opinions with county staff during the public hearing.
County staff amended portions of the monitoring plan after the April 6 meeting, adding mitigation measures regarding water quality sampling and dredging near culturally sensitive areas.
Coel directed staff to add a measure regarding replanting of tules in the case of accidental damage, which Ruttan said would be highly unlikely with the proposed removal system.
Ruttan said DWR hopes to complete a trial run this year. Before a trial occurs, the project would need approval from four outside agencies: Army Corps of Engineers, Central Valley Regional Water Quality Control Board, California Department of Fish and Game and California State Lands Commission.
The county has begun the permitting application processes required by those agencies, Ruttan said.
Contact Jeremy Walsh at jwalsh@record-bee.com or call him at 263-5636, ext. 37.
