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Flooding in Sag Harbor after Superstorm Sandy. JOE LOUCHHEIM
Ninety percent of all natural disasters in the United States involve flooding. Flood damage frequently strikes in low- or moderate-risk areas, according to the Insurance Information Institute. As the atmosphere heats up, flooding is on the rise throughout the world.
Flash floods are when a lot of stormwater fills normally dry areas in a short amount of time, typically less than six hours with little or no warning. This is the fastest moving type of flood and is often a surprise. It occurs from very heavy rainfall during brief, intense storms.
Forecasters can usually tell in advance when conditions are right for flash floods to occur, but there is often little lead-time for an actual warning. They are difficult to predict because they are frequently a part of a larger storm system, making pinpoint detection a challenge. A flash flood threat can be overshadowed by other severe weather events. Flooding is a separate, long-term event that may last days or weeks, such as when a river overflows its banks. Floods affect a large geographic area. Flood zones are usually well known. Flash floods can happen virtually anywhere.
There are, however, relatively simple steps homeowners can take to help protect property from flood damage. The first line of defense is being sure the ground around your home and other buildings slopes away from the structures in all directions. Locate the low and high points of the property. Add soil to slope the yard away from the home and other important elements. Depending on the amount of land and the desired grade it may be worthwhile to consult a professional. Consider an efficient stormwater drainage system supplemented with hardscaping — the use of materials such as wood, stone or concrete to shape, support and build landscaping that can direct surplus water to a drainage system. Selecting plants that bear high water volumes and managing your lawn can also help.
“Flash floods can be hard to control,” said Michael Maskiell of Mahoney Associates Inc., a landscaping firm in Southampton. “The design of the home, proper gutters and the property pitch each play a role in slowing down water flow and controlling erosion.”
Geotextiles are natural materials that when used in soil applications, can separate, filter, reinforce, drain and otherwise protect a landscape. “We typically use a coconut fiber log, an organic barrier to help deter water movement,” said Dave Rivkind of Rivkind Landscaping in Montauk. “The town [of East Hampton] has drainage and revegetative requirements for new construction to control runoff into wetlands and neighboring property.”
Walks or driveways that lead to or run close by wetlands, ponds or beaches, should use an S-curve design and be lined with gravel instead of a paved, straight path paved with asphalt. Water will flow into the earth through the spaces between the gravel. This also eliminates any petroleum runoff from asphalt. For reinforcement, shrubs should be planted in adjoining spaces.
Lawns should be graded (or leveled) to ensure proper drainage. Run-off should be directed in a down movement toward the street, alleyway or storm sewer. If the landscaping does not incorporate proper drainage angles water may collect faster than it can drain. Insufficient drainage can also cause natural low spots in a yard to accumulate more water with each rainfall.
Proper drainage also depends on the lawn’s permeability. A permeable lawn allows water to seep into the earth instead of collecting on the surface. When grass clippings or leaf litter clog a lawn, they can prevent the soil from absorbing water as well as it could under normal conditions. Similarly, soil density will impact drainage capability. Hard, compact soils and heavy, sticky clay soils are less absorbent and prevent surface water from seeping into the ground as it would in a more sandy mixture.
Grasses have various root structures. The root structure of some grasses can help absorb water from heavy rainfall and prevent it from reaching a home’s foundation better than others. Consider planting such strains as seashore paspalum and St. Augustine. These grasses are noted for their ability to tolerate wet conditions. Conversely, fine fescue is a reliable shade grass but does not do well in submerged conditions. Tall fescue would be a better choice.
How you cut matters. When grass is too short roots will not properly spread, limiting their moisture-absorption ability. Cut grass to around 2.5 to 3 inches high — any shorter and the grass and soil will suffer. Working organic matter into the soil can increase a lawn’s water absorption capacity as well. Garden compost, leaf mold and manure will “open” the soil, creating smaller channels through which water can escape. A heavy mulch of bark and/or wood can help stabilize soil. Lighter materials like pine needle mulch will not do as good a job and can be haphazardly transported across a landscape by runoff.
According to the Woody Shrubs for Stormwater Retention report from Cornell University’s School of Integrative Plant Science (hort.cornell.edu), woody plants, especially shrubs, provide good flood control while also requiring the least amount of maintenance. Additionally tree canopies temporarily catch and slow or stop water from reaching the ground while absorbing some of the water through roots. Be sure chosen plants are appropriate to the USDA hardiness zone of the site. Hardiness zone is a measure of the average minimum winter temperature an area is likely to receive.
“Look for plants that like wet feet,” added Maskiell, who often recommends willows. “East End soil generally has good drainage but there are problem areas.”
Ponding is the accumulation of water at or near the point where the rain fell. Stagnant water can destroy grass, damage ornamental plants, encourage root rot and compromise a home’s foundation while serving as a breeding ground for mosquitoes. A rain garden can help eliminate standing water by collecting run-off, which can then be used to irrigate shallow-rooted plants capable of surviving moist conditions.
Still have ponding? Consider a French drain. Also known as a curtain drain, it is a comprehensive system made from relatively simple materials. Based on a graded trench, it directs water flow away from the home. The trench is filled with gravel, allowing gravity to channel the water into a perforated pipe that sits at the trench’s base emitting excess water.
Landscaping for Flood Reduction/Prevention
