PROGRAMS:
Watershed Surveys
A watershed is all the land that surrounds a lake, which drains or sheds its water into the lake through tributaries, ditches, directly over the land or by ground water. Thompson Lake sprawls across four towns - Oxford, Poland, Casco and Otisfield. It has a surface area of 4,255 acres and a watershed of 22,400 acres (see the map on the right).
In an undeveloped, forested watershed, storm water runoff, consisting of rain and snowmelt, is slowed and filtered by trees and shrubs and soaks into the forest floor. But in a developed watershed, the velocity of storm water runoff increases on impervious surfaces like rooftops, compacted and bare soil, gravel roads and pavement.
If eroding soil carries too much phosphorus into a lake, algae growth can explode and cover the lake with a thick mat of slimy green plant matter. Such algae "blooms" have already occurred in lakes around Lewiston and Augusta. Once they occur, they are enormously expensive to fix. Restoring a lake's clarity may take decades. That's why minimizing soil erosion is so important.
But in order to fix erosion problems you first need to find out where they are. That's where the watershed survey comes in. The purpose of the survey is to:
- raise public awareness about the significant impact of polluted
runoff, and the connection between land use and water quality.
- encourage people to become responsible and active stewards of the
watershed and the lake.
- identify existing soil erosion sites in the watershed and prioritize
them.
- use the survey information to make recommendations to the town and
private land owners on solving erosion problems.
- identify projects for TLEA's Youth Conservation Corps. CLICK HERE
Teams of volunteers and technical staff conduct surveys. The day chosen
for the survey begins with environmental experts training the volunteers on
the mechanics of surveying and how to identify and prioritize the erosion
sites. For the remainder of the day, survey teams document erosion on roads,
the shoreline, residential properties, construction sites and foot trails
using cameras, GPS units, and standardized forms.
Survey teams work together throughout the next month to complete their
sector. Sites are ranked by degree of impact and estimated cost to repair.
Examples of polluted runoff on Thompson Lake are shown on the right and
below. Phase one was a survey of the Thompson Lake Watershed in Otisfield
and was completed in 2008 (CLICK
HERE to read the entire report). Phase two, covering Casco and
Poland, was completed in 2009. The third sector has been surveyed in 2010.
It includes Oxford, the rest of Otisfield, and a small piece of Norway.
The three-year round of surveys updates and replaces older surveys which
TLEA conducted in 1994 and 1999. The 2008 survey, covering most of Otisfield,
was funded entirely by TLEA. The Department of Environmental Protection
awarded TLEA a grant to support the 2009 survey of the Casco and Poland
sectors. TLEA provided most of the funding for the final 2010 survey, but
will also be able to use DEP grant funds left over from 2009.
To learn what private landowners can do to minimize soil erosion, please
refer to: The Benefits of Buffers
CLICK HERE
Thompson Lake Watershed Survey – Southern Section, 2009.
In 2009 TLEA received a $16,190 grant from the Maine
Department of Environmental Protection to conduct a survey of the southern
section of the Thompson Lake watershed. This section constituted the entire
watershed in the towns of Casco and Poland. The grant was matched by
donations of cash and volunteer labor from the towns, TLEA, and residents.
The 2009 survey was the second in a series of three recent surveys of
Thompson Lake: The first, covering most of Otisfield, was completed in 2008.
The third and last will take place in the spring of 2010.
In April, a month before the actual survey, landowner permission letters
were mailed. On May 2, 2009, representatives of TLEA and the DEP met 24
volunteers at the Casco Fire Station for a training session. The volunteers
learned how to document erosion problems using survey forms, cameras, and
GPS units. At the completion of the training period, the group divided into
nine teams, each led by a technical expert. Each team was assigned a
specific geographic area indicated on maps. The task of each team was to
spot and examine erosion sites, each of which was identified on a printed
form, with photographs and GPS locations recorded. The team members also
estimated the severity of the site and the costs of mitigation. In addition
to looking at private residential properties, the teams also examined
private and town roads which can often constitute the most serious erosion
spots.
Surveyors found 106 individual erosion sites in Casco and Poland, including
roads (town and private), residential, boat and beach access points,
driveways, and paths. TLEA has already met with the towns and several
individual residents to discuss survey results and plan remedial work. TLEA
also plans to contact the private road associations involved in order to
promote erosion control.
Summary fact sheets will be distributed at the Casco and Poland town
offices and at other locations throughout the towns. They will also be
posted on this website. At the conclusion of the Oxford/Norway watershed
survey in 2010, a full report summarizing the findings from all four towns
will be issued.
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"2009 Casco/Poland Survey, Photo by Kathy Cain"
