Nothing has been as controversial as the idea of dredging the South Fork Rivanna Reservoir (SFRR) to regain water capacity. City Council insisted on a legitimate dredging study to compare costs and restoration potential. The proponents of the "plan" appear to fear this study as much as re-examining our future need for water. They have attempted to stop it at many levels, including convening a task force that effectively stalled the study by one year.
The Piedmont Chapter of the Sierra Club releases a new position
Rethinking Our Water Plan
The Piedmont Group of the Sierra Club believes that new information requires the Charlottesville/Albemarle Community to take a fresh look at our water needs for the decades ahead. Our community should consider a new water plan with different priorities that draws on the resources of our local watersheds. This plan should emphasize the following:
Summary of reports issued by HDR are found below.
For the full reports, click here
DREDGING FEASIBILITY STUDY SUMMARY
A Powerpoint presentation of the dredging study and conclusions.
DEWATERING PROCESSING ALTERNATIVES REPORT
This report describes the alternatives to dewater sediment material removed from the Reservoir by hydraulic dredging. The typical (and generally least cost) method for dewatering the sediment slurry is to pump the material to a confined dike facility constructed on an upland location near the waterway being dredged. HDR developed five conceptual layouts and ballpark cost estimates for constructing confined dike facilities at four sites. The storage capacity and estimated cost for each site is summarized in Table S-1 of this report.
DREDGING ALTERNATIVES REPORT
The purpose of the South Fork Rivanna Reservoir Dredging Feasibility Study is to evaluate the feasibility of restoring the water supply capacity of the South Fork Rivanna Reservoir (Reservoir) to as near its original contours and water storage volume as practical by removing accumulated sediment. This report presents a proposed two-part dredging plan for the Reservoir.
POTENTIAL BENEFICIAL REUSE OF DREDGED MATERIAL
This report describes various potential beneficial reuse applications for dredged material from the South Fork Rivanna Reservoir. The need to restore the capacity of South Fork Rivanna Reservoir and subsequent availability of valuable dredged material provides opportunity for creative partnerships to meet both environmental and economic objectives of the community.
If dredging the Reservoir moves forward, the dredged sediment would be suitable for most types of beneficial reuse.
BATHYMETRIC SURVEY OF THE RESERVOIR
HDR conducted a bathymetric survey of the Reservoir between December 14 and 18, 2009, using a dual frequency precision depth sounder deployed aboard a small, outboard-powered boat.
HDR’s volume estimate based on our 2009 bathymetric survey data shows total existing Reservoir volume is 1,389 million gallons (MG) (assuming a dam crest elevation of 382 feet). The dead storage (i.e. storage below the lowest intake elevation of 367 feet) is 401 MG.
Restoring the Reservoir to its original total volume of 1,700 MG would require dredging approximately 1,742,567 cubic yards of sediment. If only the usable volume (i.e. the volume of water above the intake) of the Reservoir is considered, the required dredging volume would be significantly less. The total dredging volume to restore the Reservoir to its original usable volume is estimated to be 918,391 cubic yards.
Sediment deposition has reduced the total capacity of the Reservoir by 22%, while the usable capacity has been reduced by 17%.
SEDIMENT CHARACTERIZATION STUDY
HDR conducted a sediment characterization study of the Reservoir to determine sediment characteristics that could affect dredging feasibility. The sediment characterization results are typical of similar riverine reservoirs and watersheds. There are no findings in the sediment characterization results that preclude or inhibit dredging the Reservoir.
The Reservoir sediments do not contain harmful levels of contaminants or metals; removing and reusing the sediment will not require special conditions or restrictions beyond those typically imposed on dredging projects.
PRE-DREDGE SURVEY REPORT
HDR conducted a pre-dredge survey of the Reservoir which evaluated natural and man-made conditions that could impede or influence future dredging activity, including in-water areas with wetlands, rock shoals, low bridges, and utility right-of-ways (ROWs), as well as publically available Reservoir access for equipment.
Observed conditions and characteristics of the Reservoir that could influence dredging activity include:
WETLANDS ASSESSMENT REPORT
Federal and state permits will be required for any dredging activity within the Reservoir. These permits will consider impacts to water quality and wetlands, as well as other environmental factors. Wetlands/waters impacts will be unavoidable if the Reservoir is to be dredged. Some wetlands/waters impacts can be avoided or reduced through establishment of wetland buffer zones where no dredging activity would occur.
The amount of wetland compensation required will be determined by the permitting agencies following submission of a permit application showing the extent of wetland impacts.
"SMALL BITES": a more practical and economical approach to dredging the SFRR by Richard Lloyd in the Hook