Much of the opposition to the town’s proposed Ephesus-Fordham plan has centered on stormwater. But how much do most of us really know about stormwater? Here’s what I’ve learned from talking with Alan Rimer, an engineer and member of the town’s Stormwater Advisory Board.
One basic principle underlies most of what you need to know about stormwater: Water flows downhill.
As it flows downhill, it picks up speed and non-point source pollution, such as lawn-care chemicals or dirt that is disturbed during construction. In undeveloped areas, stream flow is slowed down by floodplains, or low, flat areas around rivers, creeks and lakes where surface water slowly seeps into the ground, filtering out the pollution and replenishing groundwater.
When the natural soils of a floodplain are replaced with impervious surfaces, such as pavements or compacted soils like lawns and playing fields, the area loses its ability to absorb the runoff and filter the pollutants. Instead of stopping or slowing the stormwater, impervious surfaces in the floodplain cause the waters to continue flowing downstream, creating the potential for flooding in lower-lying areas.
To assess the impact of such conditions, the town has developed a comprehensive stormwater management plan that will be applied to all watersheds and subwatersheds in Chapel Hill. The plan includes strategies and tools for managing volume and rate of flow as well as quality of the storm water as it runs off into surface waters and infiltrates down into the water table or passes on into Jordan Lake.
To understand the problems and potential solutions for the frequent flooding in the Ephesus Fordham area, you need to understand the local topography.
Eastgate Shopping Center which is in the Lower Booker Creek subwatershed is at the bottom of the path of stormwater flow from two other subwatersheds: Cedar Fork (Weaver Dairy Road area) and Eastwood Lake (Lakeshore Drive area). A large portion of the relatively dense development in all three of those watersheds occurred before stormwater controls were required. So in major storms, like the ones we experienced in 2013, the stormwater that wasn’t absorbed by the floodplains in those two northerly watersheds merge at Eastgate. That collected volume then goes on to flood the golf course at the Chapel Hill Country Club and the soccer fields on Mason Farm Road where Booker and Bolin Creeks merge (Little Creek subwatershed). The Stormwater Master Plan prioritizes the evaluation of those three subwatersheds to determine what strategies might be employed to reduce flooding at Eastgate.
In organizational theory, there is a concept called double-loop learning. Single-loop learning is when solutions are operationalized based on long-held beliefs and historical practices. Basically, it means applying the same solutions over and over again, even when there is evidence that they aren’t working. That’s the way stormwater has been treated in Chapel Hill for years now.
By contrast, double-loop learning occurs when well-established practices, such as viewing stormwater as a problem that exists within isolated areas, gives way to new and creative planning solutions, like treating stormwater as an integrated system that needs to be managed as a whole rather than separate parts. The draft Stormwater Master Plan has set the town on the path for double-loop learning (for stormwater only). Let’s hope that progress continues and that this new double-loop approach to problem solving will eventually extend to traffic planning.
In the meantime, citizens can help, especially when it comes to controlling non-point source pollutants. Rain gardens and green roofs are beautiful landscape amenities that help filter out pollutants from stormwater. Rain barrels can collect drainage from your roofs and lessen the flow of stormwater while also helping conserve potable water.
Alan Rimer, chairman of the Orange County Water and Sewer Authority Board of Directors, assisted in the writing of today’s column. Terri Buckner is a member of the OWASA board.