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Stormwater Management
Article by: Jessica Warren, ANR Agent

One of the challenges of coastal life is dealing with coastal storms and their aftermath. Whether it’s an afternoon thunderstorm or a tropical storm, the water left behind can leave homeowners and municipalities with management challenges – especially when that water load is coupled with a high water table, impervious surfaces, and poorly drained soils. I know this has been an unusually dry year here in Camden, but stormwater is a chronic challenge that will never cease in coastal areas.

Today we’ll address stormwater management as it relates to residential properties – as I don’t think Scott wants to give me a multi-page space to address stormwater as a whole. Stormwater, put simply, is rainfall or melting snow on the landscape due to a recent weather event. It can infiltrate into the ground, be stored in surface waters, evaporate, or run off the land. Typically, the term stormwater is used to refer to runoff. Runoff is precipitation that hits saturated or impervious ground and flows overland downhill. Interception is rainfall that is caught and held, or slowed, by vegetation. Infiltration is precipitation that soaks into soil and recharges aquifers.

There are two causes if stormwater runoff – infiltration excess overland flow, and saturation excess overland flow. Infiltration excess overland flow occurs when rain falls at a faster rate than the ground can infiltrate it. Saturation excess overland flow occurs when soils are soaked and cannot hold any more water. Stormwater flow increases with high rainfall rates and the presence of more impervious surfaces (think roads, buildings, houses, driveways, sidewalks, etc. – anything that doesn’t absorb water) on the landscape. Stormwater contributes to non-point source water pollution. Contaminated runoff from landscapes enters local surface waters across broad sections of their boundaries, and water that washes into our storm drains flows directly into our creeks and rivers without any type of treatment.

Green infrastructure is landscaping and building techniques with plants, soils, and materials intended to mimic natural hydrologic processes. The main goal of green infrastructure is to treat, slow, and reduce stormwater flow from landscapes. Green infrastructure reduces and treats stormwater at its source, while delivering environmental, social, and economic benefits. Green infrastructure promotes stormwater infiltration to soils and surface aquifers, prevents stormwater flooding and damage, protects surface waters and aquifers from contamination, prevents soil erosion, is designed to drain or move water without stagnation, creates wildlife habitat, creates a cooling effect on urban surroundings, conserves water for landscape irrigation, can be installed where space is limited, and is aesthetically pleasing. Green infrastructure techniques include green roofs, rainwater harvesting, permeable pavement, stormwater wetlands, bioretention cells and planters, tree trenches, vegetated curb extensions, bioswales, and rain gardens. You can see many of these techniques in practice in Downtown St. Marys along St. Marys Street. For today’s purposes we’ll focus on practices that are accessible for the majority of homeowners – rainwater harvesting and rain gardens.

Rainwater harvesting is typically accomplished with rain barrels or cisterns. Rainwater harvesting may be practiced to conserve water, to retain or treat stormwater, or to save on municipal water bills by re-use in the landscape. Rainwater harvesting reduces the volume and rate of stormwater flow from impervious surfaces – most often roof tops. Rain barrels can be made from reclaimed food grade barrels (most often from housing soft drink syrup) or purchased premade. Workshops to make a rain barrel are offered locally through the Coastal Resources Division of the Department of Natural Resources, and we will be offering one at our office on August 16th (see our website for details). When installing a rain barrel, raise it off the ground to allow room to fill a watering can and maintain pressure for a drip hose. Multiple rain barrels can be installed and connected in succession.

Raingardens and bioretention cells are vegetated depressions that receive stormwater for slowing, storing and treatment. Stormwater infiltrates soil and plant roots, where it is treated by physical, chemical, and biological processes. Rain gardens are low maintenance, low water use, beautiful landscape features that increase the infiltration of stormwater, reducing stormwater runoff and pollution. Rain gardens reduce flooding risks and flood damage and can provide a different kind of habitat in the landscape. A 100 square foot rain garden can often receive water from an area 5 to 10 times larger than its size. Rain gardens can receive water from downspouts or funneled across a surface of lawn or pavement. Typical rain garden depth is 6 to 8 inches, and ponding should last no more than 48 hours after rain stops. A properly constructed rain garden will not increase mosquito numbers, but keep in mind that it will attract a diversity of wildlife including frogs, lizards, salamanders, birds, and snakes. If you’d like to see rain barrels and a raingarden/bioretention cell in practice, please visit our office at 1409 Georgia Avenue in Woodbine where we have incorporated both of these practices into our native plant gardens and landscape. A good list of plants (and construction advice) can be found in the UGA Extension Bulletin: Rain Gardens in Home Landscapes.