- How do you redirect runoff water?
Runoff water in urban environments can be redirected using dry streams, grassed swales, French drains, and in certain cases, berms or other artificial structures. Runoff water should be diverted to low impact infrastructures such as swales, rain gardens, and detention or retention basins. In farm environments, tile drainage systems and collection ditches can be used to direct agricultural runoff to wetlands, bioreactors, saturated buffers, and similar treatment elements.
- How does a rain barrel or cistern help control runoff water?
Rain barrels and cisterns can be used on individual structures to capture and direct precipitation that falls on roofs. Depending on the roof material, they can effectively divert runoff into containers that store the water for future use. Most rain barrels hold around 50 gallons of water and are a convenient size for individual homes. For large commercial buildings, a cistern holding hundreds or even thousands of gallons offer larger opportunities for reuse. This saved (and free) water is great for uses such as landscape irrigation, vehicle washing stations, and even water for flushing toilets. In some communities, commercial buildings may qualify for reductions in stormwater fees by installing control measures like these.
- How does a rain garden reduce runoff problems?
Rain gardens are heavily planted installations located in the path of established runoff flow within a landscape. They’re used to good effect in private yards, in parks, and along lightly traveled urban streets. Rain gardens require permeable soil, since they’re designed to collect runoff and allow it to pool within the garden and allow it to slowly soak into the soil. This filters the water of pollutants like excess fertilizer, weedkillers, and animal waste before it reaches groundwater. Rain gardens can be very small or quite extensive, depending on the volume of runoff they’re expected to manage. To minimize the footprint of large rain gardens, they can be built somewhat deeper while still managing relatively large amounts of runoff.
- How can a dry well help?
Dry wells, or infiltration trenches are essentially underground storage areas for stormwater runoff. They’re particularly useful in instances when water is being dumped from a downspout or pipe at high speed. Water enters the gravel-filled storage area and infiltrates slowly into the ground or through an underdrain. The dry well slows down incoming water, reducing its erosive power and may even filter out some larger suspended particles. Dry wells and infiltration trenches are covered with soil so they can be treated as an uninterrupted part of the landscape. In these structures, it’s important to line the sides of the storage area (not the bottom) with a geotextile material that provides support for the walls. Woven geotextiles used for erosion control, and even in road construction, are excellent for this purpose. Woven options that are designed for permeability can also be used on the top of the dry well to prevent soil from infiltrating the gravel layer.
- How do you manage runoff on steep slopes?
High, or even moderate volume runoff traveling down steep slopes present significant risk of erosion. This could lead to anything from heavily silted runoff to deadly bank collapses or landslides. Regardless of the size of the slope, the same management strategies apply. Well ahead of the slope, construct berms or swales to divert the water to a less hazardous area for detention or controlled movement. Installing swales and maintaining natural areas filled with trees, bushes, and native vegetation, backed by berms make an excellent choice because they encourage runoff to spread out, slow down, and soak into the soil, rather than concentrating the power of the flowing water. On the slope itself, protect existing vegetation and plant additional cover to anchor the soil in place and avoid loss of supporting structure. In extreme situations, other stabilization tools may be necessary, including geogrids and geotextiles, both to minimize erosion and restrict and control the movement of hazards like landslides and falling rocks. Another strategy to use on-slope, to reduce speeds and minimize erosive action, is to construct water bars made of logs or rocks situated in a trench on the slope itself. The bars should be built on an oblique angle to the direction of flow and direct flowing water into a stable, vegetated area.
- Should I build levees to protect my property from flooding when the stream rises?
Floodplains, or relatively low-lying land that borders streams and rivers are critical elements for natural mitigation of floods. They provide a place for water to spread out and slow down without extending beyond the floodplain itself, essentially acting as temporary storage and reducing downstream flooding. Using berms, levees, and high banks along rivers and streams to keep water within its low water boundaries eliminates the protection a floodplain provides. Erosion and bank collapse is a common result, as well as even more significant downstream flooding. Embracing the natural control of a floodplain will provide better protection, which can be enhanced by establishing natural, native plantings in the low-lying area, which also provides valuable habitat for wildlife, not to mention a much more attractive view.
- How can I prevent stream banks from eroding because of runoff water?
In the long run, natural methods provide much more effective protection against erosion due to runoff water. The first line of defense is to preserve and even increase a variety of natural vegetation near streams and lakes. The root systems of grasses, shrubs, trees all anchor the soil in place, while the surface structures of the plants slow the speed of the runoff. For more extreme situations, the addition of saturated buffers and infiltration trenches along the direction of flow can be very effective in reducing the incoming volume.
It’s important not to disturb channels or streambanks, even to “clean up” the stream. Removing trash is helpful for maintaining a healthy habitat, but natural litter like leaves, branches, and even logs are a natural part of the stream system. They provide nutrients as they decay and even provide habitats to creatures within the ecosystem. Similarly, vegetation along banks shouldn’t be altered.
- Where does most stormwater runoff eventually end up?
Most stormwater will flow into nearby surface water, like creeks and streams, while some flows into any nearby body of water. Like nearly all natural surface waters, it will eventually flow down within a watershed to larger rivers, lakes, and eventually the ocean. If there are no slopes to lead water downhill, stormwater will simply pool in place, which can lead to destructive flooding around buildings, sidewalks, and streets.
In developed areas, both urban and rural, stormwater runoff inevitably becomes polluted with silt, animal waste, chemicals, nutrients, and even the remains of dead animals. This polluted water can quickly destroy valuable aquatic ecosystems and contaminate drinking water sources. Eventually, this polluted water travels all the way to the ocean and can cause enormous dead zones where there is not enough oxygen to support marine life, like the devastating seasonal dead zones in the Gulf of Mexico.
- What causes stormwater runoff to become polluted?
In urban environments, stormwater runoff traveling across private yards and commercial landscaping installations can pick up excess fertilizer and weedkillers, while water traveling closer to homes and commercial buildings is likely to pick up a variety of pesticides and insecticides. Detergents from activities like car washing, soil from gardens, and even lightweight mulches can contaminate stormwater when it’s pulled along to nearby surface waters. When these pollutants settle to the bottom of streams and ponds, or their larger cousins, they can disturb or seriously damage aquatic and surrounding habitats.
