Pond Restoration: Dealing with Duckweed & Bamboo | Chappaqua, NYMarch 27, 2019
All landscapes are considered ‘disturbed’ compared to a natural environment. Some more than others.
The challenge is to reverse the eutrophication process in this man-made Earth pond with a half-moon dam. This shallow, half-acre pond was constructed in the mid-19th century by damming the outlet with a poured concrete wall and spillway which discharged into a brook which was buried and piped during early stages of development of housing lots.
We assume that the original hydrology and storm water fed and recharged the pond from surface sheet flow primarily. Subsequent development drained the surface and ground water bypassing the envelope of the pond on both sides of the property.
Over time the concrete became cracked and porous and the pond level dropped while correspondingly silt and vegetation choked the pond. The pond is surrounded on the back and both sides by large, aggressive bamboo, which provided some shade but contributed a tremendous amount of unwanted organic debris into the aquatic zone. Poor land-use practices, including mowing and fertilizing to the water’s edge contributed to the nutrient loading as well as the asphalt roadway which was uphill, draining towards the pond.
Two main issues were the low water level due to leakage at the outflow, and lack of oxygen, stagnation coupled with the nutrient loading, created an ideal environment for duck weed. Without a proper inflow and outflow, mosquito breeding was a possible public health hazard and the pond was unattractive and uninviting.
This landscape was ecologically poor, lacked ecosystem service function, or aesthetic appeal. First step to correct, address, or improve any of these issues, we develop a plan with specifications including reinforcement of the concrete dam with an impervious clay ramp within the pond, bottom aeration provided by diffusers, and extensive wetland biofiltration planting extending form the terrestrial to establishing a littoral shelf and marginal bog filter to naturally improve water quality.
Just before work was commenced on the project, the landscaper employed by the client cut the bamboo stalks/shoots down to 6” above ground, more critically important is the cut was made at an angle, thus weaponizing and creating a serious liability and threat.
Part of the project involved de-watering and hand-dredging significant amounts of organic material, mainly brush, bamboo, trees, vegetation etc. This is necessary to install the aeration disks, and add biologicals (MuckAway) to increase the dissolved oxygen and healthy bacteria to reduce the sludge and sedimentation as much as possible.
While the de-watering process was performed with diesel pumps discharging to a containment area constructed of geotextile fabric, hay bales and fence post, cracks were repaired on both sides of the now exposed concrete dam to limit leakage.
Wetland systems are the lifeblood of our landscape and freshwater is a precious natural resource not unlike the complicated systems which make up the human body, a landscape environment should be treated holistically in terms of design, development and land use management/maintenance practices.
We suggest identifying the flow paths and issues critically important to the client while being a sensitive and responsible steward of the ecology of the water shed for the greater community.
Landscape Ecologist, President