Archive for the ‘Bottom Barriers’ Category

Milfoil Treatment Update – September 2012

Sunday, September 30th, 2012

[ What follows are the notes from the divers submitted after their visit of September 11-13. ]

We extracted a total of 31 panels (est. just over 18,000 sf) and associated metal from sites shown in red. The only remaining panels that I am aware of are at the Middle Brook site (site 14 on this map).

Additionally, we hand harvested a total of 3,138 plants from 8 sites.
We did not visit (DNV) several of the sites in the south basin, but it is expected that there is growth at those sites.


Of the sites/areas we did work, milfoil growth does seem to be increasing. As examples consider the following observations:

Site 6 yielded over 1000 plants and these were noted to be spread throughout the bay, as deep as 15′ generally mixed among dense growth of native species.

Site 15, originally just the boat launch at Aloha Hive, is now spread a bit South and well East of the launch scattered to moderate all the way to the southernmost portion of the swim docks transitioning from flat silty bottom to moderately steep and rocky area.

Site 5 was not fully cleared, but plants are moderately scattered from the swim platform off the point northward a full three properties (to the large yellow house with white trim (which also has a very loud Chocolate Lab)). We worked the northernmost reach of that site off of the yellow and white house.

And while it is not noted on my map, there are also scattered milfoil plants just outside of the public boat launch.. primarily on the northern bit in the shallow rocky area just outside of the launch itself.

In general, it seems that milfoil is again starting to grow/spread faster than we are clearing it… though that conclusion is necessarily tentative. Once the full survey is conducted this week we’ll be able to put together a game plan for 2013. I would anticipate however that the 2013 plan include more robust harvesting 2-3 times throughout the summer (i.e., perhaps as much as a concentrated week-long efforts instead of spreading out 2-day visits). We’ll revisit this idea once the survey/maps are completed.


Some Bottom Barriers Will Be Used this Year

Thursday, July 28th, 2011

On july 23rd and 24th weekend divers from Lycott came to remove the milfoil growth that had been identified in June.  They located and hand pulled individual plants from locations near Camp Aloha Hive and Camp Lochearn.  They also identified an area or about 2500 square feet near where Middle Brook flows into the lake where the milfoil growth is dense enough to warrant using bottom barriers.  After determining that this would be the most cost effective way to proceed,  we engaged Lycott to install bottom barriers to completely cover this patch.

Lycott has prepared and submitted a permit application to the State, and will send notifications to abutting landowners as required.  Once we receive approval from the State, Lycott’s divers will perform the work, probably in the first half of August.  We are still planning to have them return again nearer the end of the summer.  Then they will swim the entire perimeter looking for milfoil and removing any they find.

The following satellite photo shows the portion of the lake near the mouth of Middle Brook.

The area of milfoil to be treated is indicated in red.  Above it you can see the mouth of Middle Brook, which meanders down from the top of the photo.  Camp Billings is at the lower left, the Horizons docks stick into the lake right of center, and the state fishing access is at the wide part of the paved road to the right.  Click on the photo for a larger image.

[if you look closely you can see that Camp Billings has mowed their initials into their field on the northwest side of the road — perhaps for the benefit of the frequent balloons that fly over from the Post Mills Airport]

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The following enlargement shows the shape and extent of the milfoil patch more clearly.  It is about 33 feet by 80 feet.  The Lycott divers use software which collects their GPS locations and maps them onto Google Earth, which then shows the area in context.  If you are so inclined you can download the KML data here.

Getting the Bottom Barriers Up

Wednesday, September 8th, 2010

Pursuant to our contract with the State, this week a dive crew from Lycott arrived and began removing the two acres of bottom barriers that were still deployed in various locations in the lake.

Rolling up sheets of heavy plastic on the Aloha Hive field

We will keep these sheets in storage, against the possibility that we will need to use them again.

Bottom Barrier – Final Inspection

Thursday, November 6th, 2008

We are required by our Bottom Barrier permit to inspect the barriers we have in place through the end of October each year.  This year our final inspection took place on an unusually warm day in early November.  The air was almost 60F.  The water was much colder.

The purpose of the inspection is to find and fix what our permit calls “billowing.”  The sheets of “fish grade polyvinyl chloride fabricated liner” are held down along their length by “weighting devices” that are epoxy coated pieces of steel “rebar.”  For a variety of reasons gas can collect under the sheets.  The most common cause is the decomposition of decaying milfoil.   Our diver swims along over each sheet and removes any billowing, straightening the sheets and replacing the rebar weights as necessary.



Our bottom barriers are currently placed at bottom depths varying between about eight and fifteen feet.  There are about 200 sheets, each 6 feet by 100 feet, covering about two acres.  (the sheets overlap by about a third, if you are checking my math)

Here is AJ trying to warm up after a stretch under water.  He said that although one can begin to get used to the cold, his fingers get numb after a while.  Also he would want me to mention that our divers’ “dry” suits really aren’t.

Bottom Barriers

Friday, September 28th, 2007


One of the strategies we use to control the rampant spread of Eurasian Milfoil in Lake Fairlee is the deployment of bottom barriers. These are sheets of heavy black PVC plastic, which are spread on the bottom of the lake. Each sheet is 6 feet by 100 feet. We have about 200 of them. They are held down with epoxy coated “rebar” bars and hooks. The sheets keep the sunlight from reaching the plants, which kills them and prevents new growth.

Our permit from the Vermont Department of Environmental Conservation allows us to place up to three acres of bottom barrier at a time. We are required to use only qualified professionals to install it. Because the decaying plants release methane, which collects in large bubbles under the sheets and can dislodge them, the installed bottom barriers must be inspected regularly. The sheets cannot be installed before June 22nd, in deference to the spawning season of the resident fish. And no area of the lake can be covered for more than 28 months.

In fact we are only able to cover about two acres at any one time. We generally use the last five or six weeks of each season to remove all of our bottom barriers and move them to a new location. It takes our full crew, four divers and a boat person, that long to do the job. Our finances are stretched to the limit, and we want to keep the suction harvester operating as long as possible. Also, we have found that the most effective way to deploy the sheets we have is to overlap them 12 to 18 inches.

preparing to removeWe use the same pontoon boat for the bottom barrier operation as for suction harvesting. divers in the water remove the rebar from a section, and bring the end up to the waiting boat.

hooked to the boat There are hooks on the front of the pontoons to which the end of the sheet is attached. then the boat backs carefully over the sheet, peeling it gently off the bottom until it streams our behind.

hauling-out-sheets-1-2.JPGThen the crew on the boat pulls the sheet up onto the deck, folding it back and forth. You cannot tell from the picture how dirty a job this part is, nor how bad it smells.

stacking sheets Here they are stacking the folded sheets. Note (especially in the large picture at the top) how low in the water the boat is floating. In previous years we have pulled al the sheets, storing them on the shoreline, then done all the installing. This year, because many of the moves were not a long way, we filled the boat one day and put it all down the next, when possible.

laying sheetsIt is harder to show the process of laying down the sheets. Most of the activity takes place under the water. There are three divers working, one at each end and one in the middle, making sure that the sheets get situated properly. where the milfoil is thick, or where the water is deep, the job gets harder. Wind can also create problems, making it nearly impossible to get the sheets into position. Then each sheet is weighted with coated rebar, and hooked in place with J-hooks.

This year the largest area of bottom barrier is just east of Treasure Island — the island, not the beach. A new patch of milfoil erupted there this summer and we are trying to gain some control of it before it spreads. Some of this patch is rooted in water deeper than fifteen feet, which is very unusual. Because of financial constraints we had to let the divers go a week earlier this year, and were therefore unable to move all the bottom barrier we intended to.