My work is, a lot of the time, focused on reducing the negative environmental impacts of engineering projects, usually highways. Generally, we focus on the stormwater impacts, as they are something that is directly generated by the project, and are treatable. Up until about 30 years ago, the point of stormwater management was to get it away from the road and into the stream as quickly as possible. Water on the road was bad for cars and bad for the pavement. That’s all well and good, but what that did was to take a lot of water that would go slowly into the streams and dump it all in at once. It also made a lot of area that used to let rainwater infiltrate into the groundwater supply so that it couldn’t do that (the definition of impervious area). All that water that would seep into the ground, and eventually make its way downhill to the stream, slowly, providing a baseflow between storms, was suddenly channeled quickly to the stream, leading to an increased peak discharge and a reduced baseflow. The net effect on streams in urban and suburban areas has been close to devastating. The entire stream response to a rainfall event changed. Now, with much higher peak flows, much more frequently, the stream banks are eroded much faster, leading to severe channel incision. Streams became disconnected from their floodplains, further increasing the rate of erosion as higher flows stay within the banks. And with the lower baseflows, the stream level goes up and down and up and down and up and down, making it much less hospitable to wildlife. Further, the sun beats down on that pavement all day, then it rains, and the water picks up a LOT of additional heat, and discharges directly into the stream, creating bad thermal impacts.
As a result of the damage being done, stormwater management controls were enacted into law, at first requiring the management of peak discharges. This meant that the 2-year storm peak after the project was built couldn’t exceed the peak before the project from that area. Or the 10-year storm. This worked somewhat, but was only applicable to new projects, and did little to repair damage from previous development. Additionally, this peak management kept the maximum flow down, but held the flow at that maximum for longer periods of time. At the same time, water quality controls were enacted, to reduce the amounts of pollutants that were released into the streams: nutrients, metals, suspended solids. This was frequently done with a pond or an infiltration area.
As it was recognized that this was still allowing, even contributing, to the degradation of streams, tougher regulations were brought online. Maryland’s Department of the Environment published new ways of providing stormwater management. Peak control was brought down to more frequent storms, as it was determined that the more frequent the storm, the more overall damage it does to the receiving stream. New water quality measures were recommended, using Bioretention filters, sand filters, even some wet ponds. Water Quality and Quantity treatment computation was separated. And other factors started to be looked at, like temperature impacts, and cumulative effects. And these were applied in such a way that new projects had to make up some for the lack of treatment in the past. All new impervious area must be treated, and portions of existing untreated impervious area have to be treated. Credit is given for impervious area removed permanently.
And the main thing it comes down to is that there will still be problems with the degradation of streams, because there’s just been so much already done that we can’t make up for. We’ll slowly improve them, through redevelopment and through stream restoration, but we need to reduce more impervious areas. And one way I think to do that is to seriously consider *removing* sidewalks, and not putting more in. Look how much use a normal roadway lane gets. Then look over on your typical suburban or urban sidewalk. In residential areas, you’ll sometimes see people on them, but along arterials? Hah. Why not return that area to at least grass, and save that impervious area? Why build new roadways with 8 or 10 foot wide ‘hiker-biker trails’? That’s almost a whole lane of impervious area that gets little use. Or worse, have the trail outside the road and then make the roadway ‘bicycle compatible’ with a 14 or 15 foot wide lane.
I applaud people who try to bike in urban and suburban areas. It’s rough, I wouldn’t want to do it, and I’ve tried it. But think about this: there is not enough traffic on that pavement to justify the environmental damage they do just by existing. And if we can save money, and save our environment, by not putting them in, why should we, for the extraordinarly few pedestrians that are along these roads?
Roadside Riprap 