To help deal with stormwater coming from downtown, Durham just put the finishing touches on buying the former Duke Diet and Fitness Center site on West Trinity Avenue, with plans to turn the site into a constructed wetlands.
This is a great idea, but we shouldn’t lose sight of the broader environmental problems that arise from our outdated urban disdain toward water. We need to turn around our attitude toward water and address our broader green infrastructure needs across downtown.
Why do we even need to care about stormwater?
In undeveloped watersheds, about 60 percent of rain water either evaporates or makes its way through plants and trees to be released through their leaves. Another third soaks into the ground in a process that’s helped by porous soils and the deep roots of shrubs and trees. It’s that infiltrated groundwater that either recharges aquifers or slowly seeps into streams and makes its way downhill.
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During heavy rains, some of the water travels across the soil’s surface and collects in shallow gullies or rills to create what are called ephemeral streams. As they join at lower elevations, enough water also seeps from the ground to create an intermittent stream, one that has flowing water during most or all of the rainy season, drying out only during the summer. The shrubs and trees that grow in and along these streams give the soil structure and strength, their roots acting like the rebar in concrete, to hold the soil against the flowing water.
It’s these small ephemeral and intermittent streams that are most important for removing nutrients from surface waters. Because of their small size, each bit of water comes into near constant contact with soil organisms, and these organisms strip out the nutrients. In waterlogged places the oxygen-poor soils also hold microbes that use nutrients to “breathe” rather than grow, releasing nitrogen back into the air, preventing nutrients from polluting downstream reservoirs.
We have a bit of a unique stormwater problem here in Durham. Instead of being nestled in a valley between hills, Durham’s Main Street runs along the top of the hill that divides the area between the Falls Lake and Jordan Lake watersheds.
As it was covered with buildings and streets, the rains that fell could only stagnate in puddles or flow downhill. In the early days the city must have been a terrible mud pit with breeding mosquitos, demanding drainage of demon water. The town’s water flushed through the remnants of ephemeral streams, and the erosive forces dug deep channels that sent the sediments further downstream. The channels drained groundwater from the soils, dried out vegetation, and weakened nutrient removal.
This all means that impermeable surfaces like pavement are the direct cause of our stormwater problems. Sadly, we often avoid dealing with direct causes in favor of treating symptoms with hopeful cures to promote economic development. Jordan Lake’s water-stirring Solarbees placed there by the North Carolina legislature are one such futile hope. The reservoir suffers from the storm water coming from Greensboro, Burlington, Chapel Hill and Durham, but instead of addressing development patterns and insufficient storm water controls in that watershed, our elected representatives spent millions on a useless elixir.
Thankfully, the pollution-removal benefits from the constructed wetlands approach intended for the nine acre fitness center site are scientifically grounded, but a one-inch rain could fill a nine-acre lake four to five feet deep. No control measure at that site could handle our occasional six-inch rainfalls, and the engineering of the site must allow excess water to bypass the wetlands.
But we’ve lost sight of water as a resource, and with our expanding population it becomes ever more valuable. As with the legislature, sites like the fitness center shift responsibility from upstream solutions to downstream Band-Aids, but in this case at the hands of the city, local property owners and developers: it’s far easier and cheaper to drain water from a site than treat it on-site.
Rather than giving stormwater a one-way ticket in a pipe, we need to think holistically about multi-faceted solutions to Durham’s environmental needs. Durham must break down any organizational silos that work against water parks, K-12 science education, green roofs, underground cisterns, urban trees, and the health and energy benefits of urban cooling. Indeed, we can address respiratory health issues through better storm water solutions, but where in Stormwater Service’s mission statement is “promote respiratory health”?
Much public and private money will be spent on storm water no matter the choices, and if we could solve broader problems with a few more dollars, we would gain many additional services for a little additional cost. A focus on green infrastructure does that.
Will Wilson teaches biology at Duke University. You can reach him at firstname.lastname@example.org