Storm water runoff is precipitation that does not soak into the ground where it falls.This is one of the greatest threats to water quality in much of the industrialized world. When water runs off yards, streets, and parking lots into storm sewers or directly into waterways, it carries with it sediments that clog streams and reduce oxygen in the water, as well as chemicals that poison aquatic ecosystems and can render water supplies undrinkable. Runoff also contributes to flooding and, because it doesn't recharge groundwater supplies, it exacerbates water shortages in many areas. As more and more people move to cities and towns, the storm water runoff problem worsens, because the flattened, impervious surfaces (paved areas) and lack of natural vegetation in these environments prevent precipitation from soaking into the ground. While runoff is a problem of immense scale, there are plenty of simple steps you can take to reduce storm water runoff on your own property.
Following are some tips to reduce run-off.
Minimize impervious surfaces on your property. In nature, most precipitation soaks into the ground where it falls. Plants absorb much of this through their roots, and some makes its way down to the water table, being purified as it gradually percolates through the soil. The "built environment," however, is characterized by impervious surfaces (surfaces that don't absorb water), so that a large portion of rainfall or snow melt becomes storm water runoff. Reducing the amount of impervious surface on your property therefore reduces the amount of runoff.
Line impervious surfaces with gravel trenches. Figure out where water runs off your driveway or patio, and then dig a small trench along the edge. Fill it with gravel to slow the runoff and allow the water to seep into the soil.
Use the water that drains off your roof. A 1,000 square foot roof can produce more than 600 gallons of runoff for every 1" of rain that falls on it. If your downspouts are connected directly to a storm drain, disconnecting them is the single most important step you can take to reduce runoff. Instead of allowing water to go directly into the sewer or to run into the street, direct your downspouts toward a vegetated area, such as your garden or lawn. Use extensions to ensure the water comes out at least 5 feet away from your foundation. Alternatively, install rain barrels or cisterns to collect the water so you can reduce the risk of soggy yards or basement flooding and save some rain for a sunny day. If you don't have any way to make good use of the stored water, consider Dutch drains, gravel-filled barrels with holes at the bottom which slow the flow of water to allow the ground to absorb it all.
Replace lawn areas with native plants. Lawns aren't particularly effective at absorbing and retaining water, especially during heavy rains. This is a problem not only because more natural precipitation runs off them, but also because they require a lot of irrigation, which in turn creates even more runoff. Native plants, such as shrubs and wildflowers, tend to develop more extensive root systems that take in and hold water much better than lawns. As an added bonus, they require less maintenance than a lawn does. If you do decide to keep your lawn, though, water it efficiently to conserve water and reduce runoff.
Add organic matter to your soil. Adding compost or mulch to your soil can make your plants happier, but it can also reduce runoff. Spread a 2-4" layer of organic material once a year.
Don't leave soil exposed. Depending on your slope and soil type, bare soil can be nearly as impervious as concrete. If you can't or don't wish to plant vegetation on an exposed patch of soil, cover it with mulch, wood chips, or gravel. This is especially important for newly landscaped yards that don't yet have established vegetation.
Plant trees and preserve existing ones. Trees' immense root systems effectively absorb water over a large area. In addition, the canopy of a tree slows the fall of rainwater so that the ground is capable of absorbing larger amounts than it otherwise would be. Plant native trees or trees which take in a lot of water and are well adapted to your environment, and take care of your existing trees. For new home constructions, leave trees in place if possible.
Don't create runoff when washing your car. Bring your car to a car wash (preferably one that recycles its water), or wash your car on your lawn. You can also wash a car without water, if you prefer.
Create a rain garden. A rain garden is a garden, planted in a slight depression in the ground, that collects water and allows it to gradually permeate into the soil. Rain gardens come in many sizes and are typically planted at the base of a slope or even at the outlet to a downspout--anywhere where water naturally flows or can be directed. Water-loving plants and a base of permeable soil enhanced with fertile loam and a topcoat of mulch allow the rain garden to quickly absorb even large amounts of water, usually in just a few hours. (more here on Rain Gardens)
Reduce the slope of your yard. If your yard has a severe slope, the soil will have a hard time absorbing even moderate rains. Consider excavating to lessen make steep slopes more gradual. In order to prevent basement flooding and foundation damage, make sure there is an adequate slope away from the house for at least 10-15 feet.
Install berms and vegetated swales. A berm is a slightly raised area, while a swale is ditch with a mild slope. Berms can be used to slow runoff on steep slopes, and swales planted with grass or other plants can direct water to a rain garden. Swales can also direct water toward a storm drain or street: since they significantly reduce the amount of runoff, very little water that enters a vegetated swale will actually make it to the street or drain.
TIPS:
- If you're building a new home, it's possible to plan your house and landscape to completely eliminate your storm water runoff. In addition to the environmental benefits, lower water bills, and the reduced risk of basement flooding, you may also qualify for tax rebates or other financial incentives. Ask your local water conservation or environmental quality agency for more information.
- Many jurisdictions offer financial incentives or free tools, such as rain barrels and downspout extensions, to homeowners who wish to reduce their runoff.
- Many roof gutter systems are too small to adequately handle heavy rains. Consider retrofitting your home with oversize gutters.
- Need to replace your roof soon? Consider installing a green roof, a roof with plantings atop it. These reduce runoff and can lower your heating and cooling bills.
- Most of the steps above require little to no modification to your property, but when excavating or installing rain gardens, berms, or swales, it's important to consider factors such as proximity to your home's foundation and your soil's infiltration rate. For example, if a swale or rain garden is installed in soil with a very low infiltration rate, you could end up with a semipermanent pond of stagnant water.
- While local regulations often favor or require steps to reduce stormwater runoff, they may also restrict the use of certain tools, such as cisterns, or require permits for certain types of landscape modifications. Information about possible permits regarding wetland impacts can be found at your local US Army Corps of Engineers website. Be sure to check regulations before you being work in a wetland area. It is best to check with your local USACE even if you do not believe wetlands to be on your property
