STREAMBANK
STABILIZATION PROJECT – NATICK, MA
TIMOTHY D. DESCHAMPS, Executive Director
Central Mass. Mosquito Control Project
111 Otis Street Northborough, Massachusetts 01532
(508) 393-3055 ● deschamps@cmmcp.org
Wetlands
restoration and ditch maintenance are integral parts of the Integrated Pest
Management Program performed by the Central Mass. Mosquito Control Project
(CMMCP). CMMCP currently works in 39 cities and towns in Massachusetts, and
last year alone cleaned over 145,000 feet of ditches. One of our projects that has not quite performed to our expectations due to continued
streambank failure is the subject of this article.
At
the subject site, located in Natick, Massachusetts, we cleaned the ditch system
for the first time in 1993 using a low ground pressure excavator.
Work
crews were out several times since that time as part of our stream maintenance
program using hand tools to keep the system free from obstructions. By 2004 the
downstream section had degraded again to a point where it breached its banks
and flooded over the resident’s driveway.
Each
time the excavator was called to action, the downstream area required removal
of accumulated silt due to the failure of the streambank upstream. In our work
in this system, we did not touch the 75 foot area closest to the culvert mouth
due to concerns from the homeowner that he will lose additional sections of his
lawn. This bank has failed due to poor slope (1:1) and increased pressure from
people and yard maintenance personnel.
In
an effort to correct this problem and as a long term solution, Northeast
Environmental Solutions (www.northeastenvironmentalsolutions.com)
was contacted to give their opinion on the site and to see if a solution could
be worked out. NES is based in Amherst, Massachusetts and they provide erosion
control, sediment control, vegetated substrates and customized materials
delivery to their customers using the newest and most efficient technologies
available to them.
At
the request of CMMCP Wetland Project Coordinator Amanda Hope, Ed Severance from
NES came out to the project area in early 2007 and gave us a site evaluation
and a cost proposal. As a state agency, CMMCP does not usually subcontract any
of our services, but this type of program was new for us and the CMMCP
Commission voted to cost share this project with homeowner as a pilot program,
in the hopes CMMCP personnel may be able to do similar work like this in the
future.
NES
required two days to do this work, and in early May the weather forecast for
the next few days would be perfect. The compost to be used is made from
recycled organic materials and completely inert, free of unwanted seeds and is
guaranteed against invasive weed intrusion. The pneumatic, injection system
used by NES has a very low impact on the area, since the injection operation is
controlled using a remote system, and the only equipment necessary for
installation is a technician carrying the hose. The truck that transports the
compost is specially designed, and has a moving floor that carries the compost
(or other material like mulch stone, etc.) into an auger system that is then
forced into the hose using high pressure air.
This
truck can be refilled during the project to allow constant operation, and is
parked up to several hundred feet from the restoration site.
The
first order of business was to create a stable platform for the compost socks.
A
layer of gravel was blown into the streambank and then leveled, and wooden
stakes were pounded into the embankment to further anchor the compost socks.
A
layer of geogrid was placed on the streambank, and then the first sock was filled
with the gravel mixture. The remainder of the socks would then be filled with
the compost mixture, and the top layers would have a grass seed mixed in also.
Filling
the socks required the sock to be placed over the spray hose, using an adapter
at the bottom of the hose to stretch out the sock to the correct diameter,
about twelve inches. Then a knot is tied at the end of the sock.
As
the truck delivers the compost to the sock, the hose is pulled back.
Once
the first sock was in place, it was flattened slightly, and the geogrid was pulled
up over the sock and anchored in the streambank with large wire staples.
The
remainder of the socks, now filled with compost, can be placed over this
foundation, with a slight taper to the back. As each new sock is placed,
compost is used as a backfill to create a flat, stable surface for the next
sock.
After
two layers, one side of the geogrid is wrapped around the socks, and the final
sock will have the top of the geogrid wrapped over it and secured with the wire
staples.
A
compost/seed mixture used in the final socks is sprayed on top to blend in the
repair with the existing surface. One side required 3 full socks, with another
one running half way down. Total height is about four feet.
The
other side required two full socks, with one running about three quarters the
distance, for a total height about 2 and a half feet.
NES
claims over a period of about ten years the geogrid and sock casing with break
down by the sun’s ultraviolet radiation. By then the streambank has become
stable.
After
about 10 hours of work, the job was complete. The only thing to do now was to
monitor the site and determine if it will be a viable long term solution. The
site was visited twice a month until August, then once a month thereafter.
Massachusetts
went though a rather lengthy period of drought last summer, and one failure
noted was a lack of germination of the grass seed, especially in the sock face.
It was also necessary to place a barrier around the area for a short time to
alert the grounds crews to stay away and let the area stabilize. NES reseeded the
site two times, June and October, and in October noted a small area of
undercutting that was fixed using a few stones from the area. The second seed
mixture used was a rice cut grass which was recommended by NES. The site has
now filled in nicely, with the sock faces the only areas left to be reseeded.
Other options for the sock face included wetland plants like red stem dogwood,
etc.
We
are confident that this work will be a long term solution to a problem area, and
will not require maintenance to such a degree as in the past.
The author would like to
acknowledge the following people:
CMMCP Board of Commission
Francis Lynch, homeowner
Amanda Hope, CMMCP Wetland
Project Coordinator
Ed Severance & crew,
Northeast Environmental Solutions
