2016-10-14 / In the Know

Science of stormwater maintenance

By Michael Shaw Special to the Leader

Scarborough is a large community with a stormwater drainage system to match.

There are 56 miles of storm drain pipes ranging in diameter from 4 inches to 48 inches.

Along with the pipe, there are 2,438 catch basin structures collecting rain runoff. When you factor in the 76 miles of ditches in town you start to understand the size and complexity of the system.

These three systems are located in the road or the road shoulder within the town right of way.

A less noticed component of a comprehensive drainage system are the outlet control structures which are a way to control the runoff from the ditches and pipes.

Out of the right of way, these structures control the rate and quality of the storm water runoff from developed areas. Because water flows more quickly over hard surfaces such as roads, driveways and roofs there has to be a way to control the rate of flow so that property downstream is not impacted.

The goal of stormwater design is to make sure that the flow rate of run off is no greater post development than it was pre development.

In more recent years another goal of these structures is to improve the quality of the water being released into streams. By holding the water from run off in a pond or a specially manufactured basin suspended solids are allowed to settle to the bottom where they can be removed once they build up to a certain level.

Currently the town has 95 ponds of which 51 are the maintenance responsibility of the town. The remaining 44 ponds are maintained by homeowner associations.

It is common for a pond to not require maintenance for the first 15 to 20 years of its life. It is important to note that when these detention basins are filled in by illicit dumping of leaves and grass clippings the functional lifespan of the pond is decreased dramatically.

This summer, public works crews have focused attention on removing sediment from a number of town owned detention ponds.

By removing silt we provide more capacity for additional silt to be filtered out during future storm events. The material that settles in the ponds comes from everyday activities such as sand and gravel hauling, leaves falling from trees and even sand from winter operations that is not collected by sweeping operations.

Typically, detention ponds are on private property. When a subdivision is dedicated an easement is granted to the town for the purpose of access to perform maintenance and repair.

When we identify a pond for maintenance we will reach out to the home owner who has the easement to notify them of our plans.

Any damage done to lawns due to equipment travel is repaired when we leave. As a home owner it is a good idea to know if you have such an easement because most easement language does not allow planting or building in the easement area.

If you have such an easement it will be spelled out in your property deed.

If you have any questions about stormwater or stormwater infrastructure, please visit the town website and click onto the GIS page.

You can also call Public Works at 730-4400 Monday through Friday and we will answer your questions.

Another helpful resource is the www.thinkbluemaine.org website.

Michael Show is public works director for Scarborough.

Return to top