Onsite Stormwater Management and Homeowners

Onsite Stormwater Management and Homeowners

Rain gardens are utilized to retain and filter harmful substances found in stormwater, while adding to the neighborhood’s appearance. Credit: Tom Britt, Creative Commons.

Within the past few months, the United States has experienced several major storm events causing significant damages and losses. Analysts estimate that the economic impact of Hurricanes Harvey and Irma could reach $190 billion. Although it may be easy to imagine how the estimated 19 trillion gallons of rainwater that fell on Texas in late August resulted in its catastrophic flooding, it can be trickier to picture the amount and effects of rainwater displaced by our current land development practices during average storms. Whether in a dense urban space or sprawling suburbs, stormwater runoff produces several health- and cost-related issues due to water pollution. Unfortunately, storm sewer systems lack the design mechanisms to prevent the pollution of water sources. These effects drive demand for additional multipurpose and low-cost methods to address them. So far, the leading practice is low impact development (LID), which incorporates green infrastructure that mimics natural processes to filter, transpire, and use stormwater to protect water quality and ecosystems.

Stormwater Danger: Cause and Types

Storm sewers are designed to prevent flooding by moving excess stormwater — water from rain and snowmelt — out of developed areas through manmade drainage systems, but they create an unwanted byproduct of water pollution as untreated stormwater is carried directly to sources of water. This contamination harms ecosystems, natural amenities, and, most importantly, sources of drinking water. One type of pollution is the runoff of surface pollutants that carry pesticides and fertilizers from yards and fields, as well as dirt, chemicals, and toxins from road surfaces. A second source is sewer overflow, which is the direct discharge of untreated sewage from combined or sanitary sewer systems to nearby water sources. Combined sewer systems carry sewage, wastewater, and stormwater in one pipe,while sanitary sewer systems have a separate pipe for stormwater; however, the waste-carrying pipes of the latter can overflow and will discharge in the event of blockage, mechanical failure, or if capacity is exceeded.

Relying solely on sewer systems is problematic because increased land development requires installation of stormwater infrastructure as well as larger underground pipes to handle the added volume of water displaced from increasing impervious surface areas. Built materials that cover natural ground and effectively block the natural absorption of water create an impervious surface. This blockage forces uncovered areas to manage a larger volume of water at greater velocity. For example, a roof that is 20 feet by 30 feet will accumulate 37 gallons of water from a storm that releases only one-tenth of an inch of rain. This can potentially create problems for a single-family home, especially if it lacks effective drainage. If there are ten of these homes on a residential block, then the surrounding area has an additional 370 gallons of displaced water just from roofs alone. Other impervious surfaces such as paved driveways, walkways, patios, sidewalks, and streets displace additional water.

LID Post-Construction Practices for Homeowners

Although incorporating LID designs during the predevelopment phase of a home is an easier way to get started, effective options are also available for post-constructed homes. There are at least four recommended LID practices that can be implemented with costs that range from low ($1.50 to $3 per sq. ft.) to moderate or high ($4 to $10 per sq. ft.). These practices include: planting rain gardens, disconnecting downspouts, connecting rain barrels, and using permeable paving materials to replace impervious driveways, patios, and walkways. The purpose of these methods is to help reduce the volume and peak of stormwater runoff, improve water quality by filtering runoff, and increase the infiltration of rainfall, which they do mainly by retaining stormwater to slow its discharge into sewer systems and nearby waterways.

Rain gardens, also referred to as bioretention cells, are planted landscape depressions that retain and filter stormwater. The base of the depression consists of a soil mix and edges that are surrounded by plants adapted to water-saturated soils, with another exterior boundary of drought-resistant plants, like shrubs and trees. It is important that rain gardens use native plant species. Placement and design are also important elements that will influence effectiveness, as will the permeability of the soil and overall size of the garden. For example, during a one-inch rainfall event, a six-inch deep rain garden can store the expected 0.79 inches of runoff from an impervious area that is 7.5 times larger. For greater volume demand, the ratio can be increased with a deeper basin. Rain gardens perform important functions, and are especially effective at removing 95-98 percent of metals, 40 percent of nitrogen, and 65 percent of phosphorous found in stormwater. The landscaping of the rain garden, which can be stylized to look aesthetically pleasing, can also increase property value.

Downspouts of a home’s gutter system that are connected to a storm sewer system directly contribute to the peak water volume leading to the overflow of unfiltered stormwater. LID practices recommend disconnecting downspouts at the above-ground connections, as well as adding an elbow joint and spout extension to release the collected rainwater over pervious land areas away from the home’s foundation. Although this will contribute to more runoff water on the property, the use of a rain garden will mitigate these effects. Downspouts can also discharge into rain barrels to provide onsite water storage for later use, such as watering plants on the property. Rain barrels are usually placed in more concealed areas and must use screens over them to prevent the harboring of mosquito populations. They help conserve water, reduce discharge into storm sewers, and they provide free water for the landscape.

Using permeable paving materials to replace impervious driveways, patios, and walkways is likely to be the most expensive of the four recommended LID methods, especially if it is for a more extensive area. There are several options ranging from gravel, porous concrete, to interlocking concrete blocks. The cost of the materials may not seem steep ($4 to $10 per sq. ft.), but it should be noted that the cost and labor for deconstructing and rebuilding can add up. The reduction of displaced water from areas that can be modified is a worthwhile cause, especially when considering there are limited alternatives for reducing displaced water for most residential homes, and they tend to be very expensive. The main option is of course to lift a house, but that is an extreme choice left for homeowners in flood prone areas.

Homeowner Opportunity

Although no stormwater system in Texas could have been prepared for the colossal deluge that it experienced, our current grey infrastructure systems have difficulty addressing the present and growing demands for efficient stormwater management. The environmental damages from water pollution can impact related industry and tourism, as well as public health if water supplies are contaminated. The LID features listed above demonstrate that single-family homeowners have the ability and opportunity to effectively reduce the costs associated with stormwater management and environmental damage, which provides a savings to them, and also enhances property value.