Permanent BMP Awareness
When a new neighborhood, commercial development or office building is constructed, the natural flow of the land is disturbed. Most of the trees, natural grass and soil are destroyed and replaced with concrete, pavement, sidewalks and other unnatural structures. The topography of the land is likely altered and the former natural flow of water has now been dramatically changed. The direct result of all these changes is that rainwater that used to be soaked up by the ground will now flow off the developed land at a much faster rate and the amount of water flowing out of gutters, down driveways, streets and parking lots is much larger than the land can handle. In order to handle the rapid rate and volume of water runoff, both residential and commercial properties may be required to establish and maintain retention or detention basins. Basins are storm water Best Management Practices (BMPs) designed to reduce the impacts of pollutants and increased storm water runoff on local streams caused by development. They are an essential part of the City of Bartlett's efforts to improve the quality of our streams, rivers and lakes. All basins will collect and fill with rain water or storm water runoff during and after rain events. Understanding the type of basin you have will help to better plan for its maintenance needs.
Types of Basins
Detention basins are dry and have mowed turf grass in the bottom of them. You may hear these types of basins referred to as dry basins. Many are constructed with a concrete channel or swale for low volume water flow from the inlet to the outlet structure. Detention basins are primarily used to detain storm water that discharges into streams to prevent scouring and channelization as well as downstream flooding that could result from the increased volume and rate of water from developed property.
Retention basins are designed to have a permanent pool of water and are commonly referred to as wet basins. Retention basins store water throughout the year, but also fill with storm water after rain events. The advantages of a retention basin over a detention basin are higher pollutant removal efficiencies and less chance that pollutants will be re-suspended during a storm. Retention basins can also serve as an aesthetic or recreational amenity as well as habitat for some wildlife.
Maintaining Your Basin
All basins need periodic maintenance. In the City of Bartlett, the Homeowners Associations (HOA's), property management companies and property owners are required to maintain basins to ensure that all rainwater on any given property is collected in a manner that does not disturb the surrounding land. A consistent maintenance program is the best way to ensure that a basin will continue to perform its water quality and flood control functions. In general, a maintenance program should contain:
Inspect the head wall, the weir, the exhaust and other key components of the basin on a regular basis to ensure the pond is operating as intended. Inlet and outlet pipes should be checked for structural integrity to ensure they aren't crumbling or broken. If the basin has rip-rap, it should be replaced when it becomes clogged with sediment and debris.
Many basins rely on vegetation to filter sediment from storm water before it reaches the outlet of the basin and to prevent erosion of the banks and bottom of the basin. Turf grass is the most common ground cover. Grass should be cut at regular intervals and be maintained at a height not to exceed nine inches but should not be cut shorter than three inches. Excessive vegetation such as willows or other large trees and shrubs should be removed unless they serve some part of your treatment plan. For retention basins, a "no-mow" zone should be established along portions of the banks to help prevent bank erosion and to act as a filter for storm water runoff entering the basin across the ground.
Embankment and Outlet Stabilization
Keep the earth and dam around basins in good order. The velocity of water entering and exiting some basins can be great enough to cause scouring. Make sure the basin's banks, bottom and outlet are stable. There should be no active erosion which could add to stream pollution as well as cause failure of the basin.
Debris and Litter Control
Inspect for trash or other debris that may be blocking the inlet or outlet pipes as well as the emergency spillway. Remove any trash or debris from the basin. Trash is considered a storm water pollutant and should be disposed of properly.
It's important to clean out sediment that might be restricting water flow. Remove accumulated sediment with a shovel and wheelbarrow if it's blocking water flow. Small amounts of removed sediment can be spread evenly on upland areas and seeded with natural vegetation.
Additional hints to a healthy basin
Do not use pesticides, herbicides or fertilizers in your basin. These products will leach from the basin and pollute our streams and rivers. In addition, these chemicals are harmful to wildlife, including frogs, toads, fish, dragonflies, etc. that may exist in the basin.
If you must use fertilizers, only use low-phosphorus, slow release varieties. Follow the manufacturer's directions for application. Keep fertilizer on the lawn and not on paved or other impervious surfaces.
Make sure the basin is draining properly. Detention basins are designed to release storm water slowly, not hold the water permanently. Improperly maintained basins can become a breeding area for mosquitoes and reduce the storage volume of the pond.
Do not place yard waste such as leaves, grass clippings or brush in basins or in the storm drains located in the streets. Items like grass clippings and other various organic materials that find their way down the storm drains release excess nutrients that cause algae to grow at much faster rates in retention basins and increases the maintenance needed to keep the pond in working order. If these materials pass through detention basins, they can cause excessive algae growth in our streams and rivers. Algae deplete the oxygen that aquatic life depends upon to live.
The green space created by basins is an ideal location for people to walk pets. Pet waste should be picked up and disposed of properly. Pet waste contains pathogens that are not only harmful to the environment but also harmful to human health.
Communicate with the homeowners in your neighborhood or the tenants in your commercial space and make sure everyone understands the importance of reducing the chemicals, pollutants and waste products that make their way down the storm drains in the neighborhood or office park.
It's Your Basin
Taking great care of your retention and detention basin ensures that the water we are returning to our streams and rivers is cleaner than it would have been had it just passed over a greasy pavement. If we educate people on the roll these basins are playing in their neighborhood or office park, people will be more careful the next time they are blowing their grass clippings or sending their pet waste down the closest storm drain.