Dredging Update for Lake Braddock and Blackburn Pond
August 5, 2011
A lot of progress has been made on the dredging project in the past weeks. As discussed in earlier updates, LBCA retained GKY & Associates to guide us through the permitting and field work process. They have completed a number of tasks so far:
- Surveying around Lake Braddock and Blackburn Pond (these were where the tags around a number of trees came from; note that it is very unlikely we’d need to remove any trees—this is just for marking purposes)
- Research for any historic resources or threatened and endangered species at our site
- Delineation of existing wetlands
- Conducting a bathymetric survey (using depth finders and push poles to find out where the current lake bottom is)
So far, everything is on track, on schedule, and on budget!
On July 13th, we met with GKY to review where we stand and to make some decisions about how to move forward. Based on the bathymetric survey, GKY provided estimated volumes of sediment that could be removed from each cove in the lake and from the pond. They provided several options, using different slopes and depths, but we ultimately agreed with their recommendation to remove as much sediment as possible (i.e., to dig down to the original lake bottom). This is by far the most cost-effective option and will buy us the most time until the next dredging project.
The other important bit of information we learned relates to costs. Once you know how much sediment is to be removed, you can get a ballpark estimate of what the total project costs will be. Using recent data from Burke Centre’s dredging projects, we can estimate that the field work component of dredging will cost approximately $241,000, which when combined with the permitting and engineering support from GKY totals $331,000, well within the budgeted amount of approximately $370,000 in the reserve study. With this bit of great news, we should be able to address any unexpected line-item tasks that might be identified during the course of the dredging project (e.g., rehabilitation of the rock weirs, should they need it). In addition, the Lake and Pond Committee will explore using its own funding (separate from the dredging funds) for other projects that will take advantage of the lowered lake level and be much simpler to accomplish (e.g., finally getting the lily pads under control).
The information from this meeting was discussed in meetings with the Lake and Pond and Finance Committees and then presented to the Board. GKY is now proceeding with development of additional reports.
April 20, 2011
GKY will be on site later this week (Friday) or early next week (Monday or Tuesday) using a Trimble GPS to locate some site features that we will incorporate into our plan submission to the county. We will not be putting ribbons on the site or disturbing the anything around the lake in any fashion. I will continue to let you know a couple in advance of our site visit.
The trees with white and yellow ribbons on them are not going to be removed. The surveyors flagged those trees to help them track what trees have been surveyed. The pink ribbons indicate the outer limits of the lake and streams on site. Having the pink ribbons in place around the lake and stream will help the Army Corps of Engineers representative confirm the boundaries.
April 11, 2011
GKY will be coming out to the project site on Wednesday of this week to start the wetland delineation field work.
April 5, 2011
Lake Braddock and Blackburn Pond were designed to function (among other things) as urban stormwater ponds, controlling flooding during heavy rains and removing sediments and other pollutants. As a result, we must periodically remove the accumulated sediment to maintain the desired level of biological and aesthetic functions that we have all come to expect.
Lake Braddock has been dredged on at least two occasions since the community was built. Once was in the 1980s and again in the mid-1990s. During the second dredging, LBCA installed rock weirs in both of the northwest and northeast forebays (where the two main streams enter the lake). Rock weirs are basically low walls of loose rock that act to slow incoming water, allowing sediment to drop out. Weirs also help to contain sediment, making future dredging easier. Blackburn Pond has never been dredged and has no weir.
As you have probably noticed, sediment has accumulated in the northwest forebay (between Lighthouse Lane and Ulysses Court) to the point that it rises above the lake level on most days. This is a sign that the forebay is nearly full and that dredging is needed; reports from two consultants agreed.
LBCA, through the Board and the Lake and Pond Committee, has started the process of acquiring the appropriate permits and hiring a dredging contractor. Since these activities require a great deal of expertise that we do not have in-house, LBCA divided the task into two parts: 1) hire a contractor to assist us with acquiring the relevant permits, developing a request for proposals from dredging contractors, and supervising the field work and 2) hire an experienced field contractor to perform the actual dredging and hauling of sediment.
After soliciting bids from a number of contractors, LBCA selected GKY & Associates of Chantilly to lead us through the initial permitting phase. GKY has significant experience in permitting, planning, and in working with Fairfax County. They currently are managing the dredging of several ponds in neighboring Burke Center. LBCA and GKY recently held a kickoff meeting to begin the dredging planning process.
While many of the specific details are under development, GKY has already begun work and has developed a conceptual plan for the dredging project. The permitting process requires several field studies and surveys, permit applications with county, state, and federal agencies, and significant geotechnical design work. Residents can expect to see field teams onsite, and, when possible, LBCA and GKY will post notice on the webpage when these activities will take place.
The general plan for dredging is to lower the water level, allowing the sediment to be removed to dry out. This will permit the use of mechanized equipment (such as a backhoe), and it is generally far less expensive than hydraulic dredging like that done at Lake Accotink. The spoil will be allowed to dry for a short period. Then trucks will be brought to the three sites and haul the sediment to an offsite location identified by GKY. Note that we will not be using the old "mulch site" on Burke Road to deposit the material. The mulch site was likely to face more significant permitting hurdles, thereby driving up the cost of the effort. To access the northwest and pond sites, temporary access roads will need to be developed. This may cause a temporary disruption of some existing activities (such as use of the playground equipment near the northwest inlet).
A common question is: "How much will the dredging cost?" At this point, that is a difficult question to answer. The upcoming field surveys will determine the volume of material that needs to be removed, and this is the primary driver for the costs. In general, we can expect dredging to cost roughly $300,000 to $350,000. LBCA's 2006-2010 reserve study set aside reserve funds to dredge the lake and pond. This funding has been moved to the 2011-2015 reserve plan.
Overall, the permitting process is expected to take approximately nine months. Towards the end of the process, LBCA and GKY can begin to develop solicitations for the second phase (the actual dredging), which would likely take place in the following months. As a result, we can tentatively expect to begin dredging next spring. Note that this is a VERY rough schedule and can change due to weather, permitting delays, budget implications, and a number of other factors.
LBCA and the Lake and Pond Committee will post periodic updates as we navigate the process. | 
