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Stormwater Management

By Donna Dawson
6/24/2013 9:40:27 AM

"Small, simple changes in the way we manage our properties can have a big impact and help protect the waterbodies that we play in and depend on." This quote from the Homeowner's Guide to Stormwater Management, from the New Hampshire Department of Environmental Services, summarizes the details of this 66-page publication. In it you'll learn why this is an issue to be concerned with in our home landscape design and practices, and details of nine do-it-yourself steps for a positive impact.

In natural areas such as forests, heavy rains seep into the soil. In human-built landscapes, water often runs from impervious surfaces such as roofs, walks and drives, not into the soil, but into our waterways. This is "stormwater" which can impact our watersheds-surface water such as rivers and lakes and groundwater from which many of us get our drinking water.

This impact on our watershed is often negative in several ways. Stormwater can:

--change hydrology, or how water flows over and through the land. Examples are flooding, streambank erosion and lowered groundwater tables.

--wash sediment into surface waters, making water cloudy. This, in turn, can make it hard for fish to live but better for invasive plants such as purple loosestrife to take root and grow.

--wash nutrients from fertilizers and pet wastes into watersheds. This speeds up algal growth, which can not only be a nuisance for swimming and boating, but harmful to animals, humans and particularly fish.

--wash bacteria from pet wastes into water, making humans and pets sick, and closing beaches.

--wash chlorides from road salt into waterways. High salt concentrations kill off freshwater plants, stress aquatic life and may contaminate drinking water, including private wells.

--wash toxic contaminants into waterways, such as oil and gasoline from drives and roads, or pesticides and herbicides. Many of these are quite toxic to aquatic life, and can harm other animals and humans.

--increase thermal pollution as water runs over hot paved surfaces. Such warm water has less oxygen than cool, so this makes it harder for fish to breathe and survive.

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To minimize such negative impacts of your landscape on our watersheds, consider these nine practices or changes to your landscape. Specific construction details are in the above guide.

--Dripline infiltration trench. This is simply a trench, about 18-inches wide and about 8-inches deep, with crushed stone of various sizes in layers, under the roof dripline. It captures heavy roof runoff, allowing it to seep into the soil naturally. It works best in sandy or well-drained soils; otherwise, you may need to install a perforated PVC pipe as well in the trench.

--Driveway infiltration trench. This is a trench similar to the above dripline one, only along a driveway or walk.

--Dry well. Similar to the dripline trench, this is a pit with gravel to collect heavy water runoff from downspouts and roof valleys, allowing it to then seep into the soil naturally. Typically they are about 3 feet on each side, and deep, the size varying with amount of water to collect.

--Infiltration steps. These gentle wide steps up moderate slopes allow water infiltration, define walking paths and reduce erosion. They work on moderate slopes under 45 degrees, and are typically of wood timbers or stone pavers as the step risers, with crushed stone for the deep steps between each rise.

--Pervious walkways and patios. While such solid, paved walks are seen sometimes in public spaces (a good example being the main walk in the St. Albans, Vt., park), you can make these at home with space between bricks, flagstones, or other pavers. Water can soak between pavers into a stone reservoir underneath. You can find pervious pavers for drives too.

--Rain barrels. Place these large drums, often plastic and of a 55-gallon capacity or similar, under downspouts to collect water for later use in watering plants. Make sure to empty between rains, and have enough to capture runoff from large storms. Cisterns are larger capacity versions.

--Rain gardens. These bowl-shaped gardens utilize soil, mulch and plants to absorb runoff and allow it to then seep into the soil naturally. Not just any plants can be used, since they need to withstand dry periods, then being in water for short durations. You can find more on such gardens in The Vermont Rain Garden Manual (www.vermontconservation.org).

--Vegetated Swale. Picture this as a long rain garden, a shallow channel with plants that takes water runoff from paved surfaces and directs it slowly to an area where it can infiltrate the soil. The plants help trap sediment, remove pollutants and prevent erosion. Swales are often about 2 to 3 feet deep, with gently sloping sides. If the soil is compacted or clay, remove a foot or two from the bottom and add some sand to create a sandy loam.

--Water bar. If you have a moderately steep path, drive or walk, consider adding one of these. Bury a 6- or 8-inch wide rot-resistant timber across the path at an angle, with a trench of similar depth on the upward side, lined with geotextile (like weed barrier) fabric and filled with crushed stone. As water flows down the slope it will soak into the trench, then the timber directs it to the side where it can infiltrate.

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