By John Larrabee | Photos By Fred Orkin
This is the sloped bank behind South Cove, near the play structure. “Unplanned” paths and the trimming of brush and small trees gave way to the erosion of 6” of grass and topsoil. Once the root structure was gone, there was nothing left to keep the sand and dirt sediment from washing into the lake. Exposed, larger roots toll the death knell for these trees.
Soon after WWI, at the urging of his father, my grandfather bought a small, deeply sloped plot of land on the shore of a 550-acre lake not far from here. The lot was covered with birches, pines, raspberries and pucker brush of various sorts. After a year of weekends and after-hours carpentry, a three-bedroom “camp” built on posts emerged. Running water from a spring on the property, electricity and a fieldstone fireplace provided a humble retreat for generations. With the addition of a winding path and some stone steps, folks could get from the dirt road to the camp and onto the shore after a short climb. Never, in the 40 years until the camp burned to the ground, was there ANY stormwater erosion moving sedimentation to the water’s edge. The natural vegetation was not disturbed during construction, so it continued to protect the slope, much as it had for hundreds of years before construction.
“Armed” water bars, a simple stone barricade, a naturalized grassy bank and blueberry bushes (behind rail fence) slow the velocity of storm surges.
A rain garden, including drip-line trenches, dry wells and berms, contain stormwater long enough to be absorbed slowly.
Thirty years after the fire that destroyed the camp, my mother bought the plot from her siblings and proceeded to construct a retirement home. In order to build a cellar, garage and year-round, insulated home on the now paved road, extensive excavation, terracing, berming and perimeter draining were required. The cost of all of the erosion-preventing work was more than half the cost of the new cottage construction. Once you mess with Mother Nature, you gotta pay the price. You want a view, a paved driveway, a tennis court, a satellite sightline? You gotta pay.
This straight, long run-off ditch flows unobstructed to the lake, depositing sediment. Basins, zigzag pattern and “arming” with stone would slow the velocity and sediment deposit.
SOME BASIC FACTS
Erosion is the wearing away of the land surface by the action of wind, water, ice or gravity. Sedimentation is the deposition of eroded soils in lakes and rivers. Human activities or disturbance along Eastman Lake shoreline and throughout our watershed can bring about changes that greatly accelerate the natural erosion process, often with serious environmental or economic impacts. Erosion can lower the stability of our lake habitat and may have serious implications for property owners (property value, cost of maintenance, waste water management, health issues, etc.). Erosion is our “elephant.”
The erosion of the Eastman Lake shoreline and the resulting sediment deposit are affected by the resistance of the shore material. Shoreline material can be rock, gravel, sand, silt, clay, organic material or any combination. Each material type has a different ability to resist erosion. Rocks and gravel are heaviest and require large amounts of erosive energy to move. Good examples of this are the large boulders situated along much of the shoreline around Eastman Lake. Sand, silt and organic materials are the most easily eroded. Examples of this are our sandy beaches and some of the mulched paths along the shoreline. Clay is not very erodible because the tiny particles stick to one another. The root systems of woody
vegetation greatly augment the strength of all types of soils. This augmentation can be seen in select places along the shoreline, where brush and trees are allowed to naturalize.
At the West Cove “boat beach,” the 125” stretch of shoreline, 24-36” high, has washed into the lake. Only four blueberry bushes remain of the 2008 repair. Vegetation loss allows the sand and sediment to flow into the water.
WATER FLOW
To manage erosion properly, it is essential to understand the basic concepts of how water moves toward the lake. This has been covered in previous articles but cannot be overstated. Water velocity in our drainage channels (tributaries, ditches
and run-off streams) is mostly affected by the rate of rainfall. When a large amount of water (downpour) occurs over a short period of time, the drainage channels may not be enough to handle or slow down the increased water volume; you can see that nature, along with gravity, adds more channels. This is most easily noted after a heavy rainstorm behind the South Cove Activity Center and along the paved boat ramp.
A narrow, deep, evenly contoured section of channel is likely to have greater velocity than a section with a wide, shallow, convoluted channel. When a drainage ditch is dug straight to the water’s edge, the velocity is increased, resulting in
more erosion and sediment deposition. A smooth section of channel will have greater velocity than one with rough surfaces. Rough surfaces may be due to conditions such as a large amount of woody debris or many large boulders. “Arming” a channel with stones, rip-rap or heavy gravel can slow the velocity.
Large boulders and 3” stone protect the shoreline around much of the shoreline access road. A storm surge could wash away the stone, seen in the foreground, which will need to be replaced again in the future.
SEDIMENT
It is estimated that over 1 billion tons of sediment pollute the waters of the United States each year. Sediment is considered a pollutant when higher levels result from activities such as road and building construction, deforestation, etc. It is, by volume, the greatest water pollutant in the United States. Suspended sediment decreases the amount of sunlight that can enter the water. If sunlight is diminished, so is the productivity. This translates into fewer fish per acre. If there is enough suspended sediment, the water takes on a brown or muddy appearance. When this happens, more solar energy is absorbed compared to clearer water conditions, also resulting in increased thermal pollution. Currently, our lake is clear and clean of high amounts of sediment.
Shoreline erosion may result in the loss of shoreline vegetation, which provides aesthetic beauty and valuable habitat for wildlife. If the vegetation loss is extensive enough, the erosion rate may increase, causing more vegetation loss in a continuing and escalating cycle of degradation.
Replaced culvert pipe, “armed” with 5+ stone and rip-rap, slows run-off to the lake along the public boat ramp.
TAKING SOME BITES OF THE ELEPHANT
Here in Eastman, the maintenance team continues to meet the challenges of erosion, due to the nature of our topography: 345-acre lake basin, surrounded by hills, valleys and trails, dotted with more than 1,400 dwellings. Drainage ditches, culverts, crowning roads and forestry management all contribute to storm water erosion control.
One of the jewels in our crown is the South Cove Activity Center. During a rainstorm, thousands of gallons of water flow from its extensive roof. The soil substrate is a concretelike mixture of rock, clay and backfill that provides poor, if
any, water absorption. Some gains (elephant bites) have been made with the installation of a bermed rain garden, dry well, drip-line, infiltration trench and rain barrel by the Youth Conservation Corps. A storm surge in July, 2014 created four
washout ditches down the slope from the beach path to the dock and lagoon. Several yards of mulch were carried by the water to the wading lagoon, most of it retrieved later by volunteers. Three yards of topsoil were seeded and covered with hay to patch the washouts. A more heavy-duty solution, involving diversion of water and catch basins, will probably need to be considered to fix this busy area.
Behind South Cove, next to the play structure, is a bank that has lost all of its topsoil and grasses to erosion, baring roots of trees and shrubs and continuing to wash into the ditch and, eventually, to the lake. An adjacent ditch, which drains the
condo road and parking area, flows unimpeded into the wading lagoon. No easy fix here. Big machinery and permits will be required. This project is on a priority list.
Several bites of the elephant were taken last summer when a responsive maintenance team replaced a drainpipe and repaired a culvert adjacent to the public boat ramp, part of Cross-Country Trail #6. This year-round stream drains the
summit slope and condos and, following rains and spring thaw, overflows, carrying sediment into the lake. Upstream and below the culvert, Maintenance installed rip-rap to slow the run-off velocity and diminish sediment deposit. Natural vegetation was left in place to do its part in absorption and slowing of the water flow. A good fix.
We can thank Emil Hanslin and his fellow planners for using large boulders around most of the lakeshore bordering the access roads. Along with little or no trimming of brush and trees, this has kept sediment out of the lake. Open areas, such
as the beaches, continue to be a challenge. More than 125 feet of shoreline that was two to three feet high has washed into the lake. Three or four bushes are all that is left of a large erosion repair project that was completed five years ago. Some little nibbles of the elephant here, but several more bites to follow.
KEEP AT IT
Maintaining our beautiful, clean, clear lake is a lot like maintaining your home. It’s a constant effort, involving careful planning and the use of best management practices and common sense. Little things, like placing a few tennis ball-sized
stones under your gutter downspout, can slow down the water and the erosion. April showers might bring May flowers, but they can also erode banks, driveways and roads directly, or eventually, into Eastman Lake.
Lakes and Streams chairman John Larrabee has recently learned that there is an extensive Stormwater Management Plan for South Cove developed by Blakeman Engineering, which will address problem areas mentioned in this article. Good news, indeed.
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