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Ten Tips for Reducing and Preventing Floods

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Ten Tips for Reducing and Preventing Floods Ten Tips for Reducing and Preventing Floods As the rain falls, many municipalities across Pennsylvania will worry about the very real possibility of flooding and the associated infrastructure damage that comes with it. According to the Environmental Protection Agency (EPA), heavy downpours have increased in frequency and intensity over the last 50 years in the United States and are expected to become even more intense as a result of climate change. This raises the likelihood of flooding. The EPA also notes that the average 100-year floodplain is projected to grow by 45 percent by 2100, and the annual damages from flooding may increase by as much as $750 million.i As bleak as that may sound, thankfully there are steps municipalities can take to reduce the number and intensity of floods through simple changes in the way a municipality manages stormwater and how it treats its floodplains. Before we get to the top ten list of flood prevention tips, let’s define what green infrastructure is and what it does. What is Green Infrastructure? Green infrastructure is the use of plants and absorption techniques to capture and transport precipitation and stormwater runoff. It is the opposite of traditional grey infrastructure, which uses drains, pipes, and ditches to take stormwater to a treatment plant or outfall in a stream. Green infrastructure includes rain gardens, vegetated swales, rain barrels, porous pavement, and other techniques – some of which will be described later. A good source to learn about these different technologies can be found at https://www.epa.gov/green-infrastructure/what-green- infrastructure. How Can Green Infrastructure Manage Floodwater? There are two main types of flooding: localized and riverine. Riverine flooding happens when precipitation overwhelms the capacity of the river\stream channel, and the water flows over the river banks. Localized flooding occurs when precipitation overwhelms the storm drain system, causing stormwater to back-out of the system and into streets, basements, and parking lots. Green infrastructure can manage both types of flooding. Curb bump-outs like these absorb stormwater, slow traffic, and can be an Riverine flooding stems in part from rivers attractive landscape feature. and streams that no longer look like they did pre-human settlement. Over time, people have straightened the course of the waterway, put dams on it, built structures in the floodplain, filled in wetlands, and did other actions that remove the river’s ability to absorb and slow down flood waters. Green infrastructure, such as floodplain restoration and planting riparian buffers, can help regain some of the lost function. For localized flooding, green infrastructure technologies like porous pavement allow rainwater to trickle through the pores in the concrete/asphalt, rather than flow over it. The water can then be stored in underground tanks or flow through a filter to slowly re-enter groundwater, rather than rush into a stream or river, thereby overwhelming it. Flooding leads to streambank Rain gardens act in a similar fashion, where rainwater is slowly absorbed into the erosion and water pollution. ground and into plant roots, rather than flow quickly across traditional pavement into an overwhelmed storm drain. Green infrastructure slows the flow and enhances absorption, thus reducing the intensity of potential floods. Now that you know how green infrastructure can reduce the frequency and intensity of riverine and localized flooding, let’s explore these ten best management practices list to reduce the impacts and intensity of floods. • Rain gardens: These shallow depressions in the ground are planted with various native plants to treat and capture stormwater runoff. They can be placed in areas visible to park visitors and can be enhanced with educational signage. West Liberty Rain Garden • Vegetated swales: These shallow channels are planted with various native plants and used instead of underground pipes and concrete channels to move stormwater from one location to another. They have the bonus of allowing for infiltration and cleaning of the runoff. • Naturalized infiltration basins: These are depressions in the ground that provide temporary storage and infiltration of runoff. They are planted with myriad natives to provide wildlife habitat and to look Vegetated swale at Landis Homes in Lititz aesthetically pleasing. • Green roofs: These are flat or gently sloping and covered with a planting medium and plants on top of the roof material. Usually, a green roof has a filter membrane, drainage layer, waterproof membrane, support panel, thermal insulation, and vapor control layer. The plants on the roof absorb precipitation and then it returns to the atmosphere via evapotranspiration, rather than entering the gutters and storm drain. Green roofs have the added benefit of helping to regulate a building’s temperature. • Stormwater runoff capture and/or reuse: This may consist of a simple rain barrel attached to the gutter downspout on a visitor center building to more complex underground storage tanks or cisterns. The water collected in these devices can be used to irrigate gardens, wash vehicles, among other tasks. Riparian buffer planting at Landis • Riparian buffers: These are vegetated areas near a stream or river that Homes in Lititz, PA typically contain trees, which helps shade and partially protect a waterway from the impacts of adjacent land uses. The roots of trees and other vegetation can absorb pollutants and water, protecting water quality and slowing the flow of both stormwater runoff and water that has overflowed the stream bank. • Tree box filters: Nearly every municipality has trees near their curbs and in parking lots. By using a tree box filter in the planting area, not only can pollutants in stormwater be filtered out so it doesn’t end up in nearby streams, but the water is absorbed into the ground more Trees help absorb stormwater and slowly, helping to reduce flood intensity. filter out pollutants, as they are doing here in Lancaster, PA • Porous pavement (also known as pervious or permeable): Unlike regular paving that allows water to quickly run off, porous pavement allows precipitation to soak into the ground. Storage cells or other structures may be placed under the pavement to add additional filtration benefits. • Wetland restoration: Many natural wetlands have been drained or filled in. This is unfortunate because wetlands act as sponges, absorbing excess water that could lead to flooding. Restoring wetlands or constructing new ones can bring back some of those water quantity benefits while also cleaning pollutants from the water and providing wildlife habitat. • Floodplain restoration: While true floodplain restoration can be the most expensive of these BMPs it can also be the most effective at reducing the frequency and intensity of both riverine and localized flooding. The BMP best mimics the interaction of groundwater, stream flow, and plant roots to reduce flooding, filter out pollution, recharge groundwater, prevent erosion, and lessen stream flows. The restoration may include grading stream banks to make them less steep, planting trees and other native vegetation, creating pools and meandering channels in the stream, and restoring wetlands. Any municipal land (or privately-owned land for that matter) with a stream, river, Floodplain restoration project on pond, or lake may benefit from these restoration practices. Rife Run, Logan Park, Lititz, PA Where Has This Worked Well in Pennsylvania? Lancaster City uses green infrastructure to manage stormwater in its municipal parking lots. The city has installed a variety of rain gardens and biobasins that allow rain to slowly absorb into the ground, rather than flow across the parking lots into storm drains. By using green infrastructure, the city is able to better meet the requirements of its Municipal Separate Storm Sewer System (MS4) permit and reduce localized flooding problems. More at https://www.epa.gov/green-infrastructure/economic-benefits-green-infrastructure-lancaster-pa. INSERT PHOTO OF BIOBASIN HERE Biobasins in Lancaster City Manheim Borough in Lancaster County had a problem with flooding in two parks adjacent to Rife Run, a tributary to Chiques Creek. The flooding made the parks difficult to maintain and keep open for people to use. It also caused a significant amount of soil and nutrients like nitrogen and phosphorus to wash downstream to the Chesapeake Bay. In two separate projects completed nearly 10 years apart, floodplain restoration projects were constructed at the two parks to help reduce non-point source pollution and improve water quality in the Chiques Creek Watershed, helping to meet the borough’s MS4 permit requirements. Read more about the restoration work at https://landstudies.com/rife-run- a-restoration-story. Logan Park Master Plan for Restoration Work on Chiques Creek The Rock Lititz industrial campus in Warwick Township, PA is designed to hold as much as 1 million square feet of offices, music studios, and warehouses, centered around the music industry. A floodplain runs through the 93-acre site, which experienced periodic flooding prior to site development. LandStudies, Inc, restored over 3,100 square feet of the Santo Domingo Creek that runs through the property, bringing the floodplain back to pre-human settlement conditions. Officials with Lititz Borough have offered anecdotes that the project has reduced flooding in the creek’s watershed. For Additional Information To learn more about the benefits of using green infrastructure to reduce flood risks and help meet your MS4 permit requirements, check out the Floodplain restoration post following sites: construction at Rock Lititz https://coast.noaa.gov/data/docs/digitalcoast/gi-econ.pdf https://www.epa.gov/green-infrastructure/manage-flood-risk http://www.dcnr.state.pa.us/cs/groups/public/documents/document/d_000620.pdf https://www.epa.gov/sites/production/files/2016-06/documents/city_green_0.pdf https://landstudies.com/floodplain-restoration i Environmental Protection Agency. “Green Infrastructure: Manage Flood Risk”. https://www.epa.gov/green-infrastructure/manage- flood-risk.
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