Rainwater runs downhill when it hits the ground and can’t evaporate or soak into the soil, particularly in towns like North Wilkesboro built largely on slopes rising from a floodplain.
In North Wilkesboro and most other municipalities, the strategy is to catch this runoff in storm drains and carry it in pipes to points where it can flow into streams.
Motor oil and other urban grime the storm water picks up along the way is also dumped into streams, which damages aquatic habitat and increases the cost of treating human water supplies. This method of handling runoff also increases risks of stream flooding.
In downtown North Wilkesboro on Aug. 13, streets and businesses were once again flooded when an exceptionally high volume of rainwater (about 3 inches in less than an hour and a half) fell in a short period and overwhelmed the capacity of drains and pipes.
Scientists say such weather events will continue occurring with escalating frequency and intensity, increasing the likelihood and severity of property damage and hazardous driving conditions in places like North Wilkesboro.
North Wilkesboro’s response in recent years has been to keep investing in improvements to the town’s traditional storm water infrastructure, including installing new drainage pipes behind businesses on 10th Street and raising curbing on surrounding streets to redirect runoff away from 10th Street.
These efforts weren’t enough to prevent several buildings on 10th Street from being flooded on Aug. 13 and they might have worsened street flooding elsewhere.
Town Manager Wilson Hooper said town and N.C. Department of Transportation personnel are examining drains uphill from 10th Street along D Street to make sure they’re still functioning properly after the road was resurfaced a few years ago.
A growing number of towns are taking a new approach by turning to “green storm water infrastructure” (GSI) as a cost-efficient and effective alternative to the traditional response of installing bigger storm water collection systems with drains and culverts.
GSI refers to numerous measures that cause storm water to behave more the way it would if the landscape wasn’t altered by human activity.
GSI practices include:
• rain gardens, which are shallow plant-filled basins that receive runoff from nearby surfaces and let it soak into the ground or transpire into the air;
• planter boxes, a type of rain garden with planter boxes for trees and other vegetation that catch storm water runoff;
• vegetated swales, which are more effective than ditches in slowing down storm water, letting some of it filter into the soil and letting sediment pollution settle out on the way;
• disconnected downspouts, which release roof runoff onto grass lawns to let storm water soak into the ground, rather than sending it directly onto pavement or into storm sewers;
• permeable pavement, which can keep standing water off roads and parking lots while recharging groundwater supplies;
• green roofs. With special substrates and plants adapted to exposed conditions, green roofs capture rain and evaporate it back into the air with little or no runoff;
Preserving natural features is another strategy. Parcels often have natural features, including swales, trees and highly porous soils, that slow water and let it soak into the ground. Taking care to protect these features when property is developed is important.
Likewise, as many trees as possible should be preserved when property is developed because it intercepts and absorbs significant volumes of storm water.
GSI practices often are cheaper than their conventional equivalents, so trying GSI options first will very likely also save towns like North Wilkesboro money in the long run.