Impacts of Urbanization on the Natural Water Cycle (expand image)
In Part 6 of this series, I suggested that taking treated effluent from our distributed wastewater treatment plants and putting it into the ground or into restored urban streams offered a tremendous environmental opportunity.
Urbanization impacts natural hydrology in a number of ways. Over time, to accommodate new development, tributaries and wetlands surrounding urban rivers have been channelized, put into pipes, and in many cases, simply filled. Pavement, buildings, and compacted soils (collectively referred to as impervious surfaces) prevent rainwater from infiltrating into the ground, and increase both the volume and speed with which stormwater flows into storm drains. Fast moving runoff carries the nutrients phosphorus and nitrogen, and pollutants like oil and grease, ethanol, grit and whatever else ends up on pavement, into urban rivers. Stormwater runoff remains the largest source of pollution to surface waters in the United States.1 Further, the loss of natural hydrologic systems such as streams and wetlands in cities makes them more vulnerable to flooding by dramatically reducing both the storage and natural conveyance of large volumes of water.
Green infrastructure at the Waltham Watch Factory
|Daylighted Providence River, Providence, RI
The question is whether we can restore urban water features and replicate the flood storage and conveyance they once provided using green infrastructure to slow down, capture, and infiltrate stormwater runoff, restoring the natural water cycle. The answer, of course, is yes. There have been a number of “daylighting” projects (i.e., taking streams out of channels and pipes and more closely replicating their historic meanderings) all over the country.
CRWA is currently designing restored urban streams as part of distributed waste recovery plants. Restored streams would carry treated effluent and stormwater while creating attractive neighborhood amenities and providing urban aquatic habitats. There are a number of benefits with our approach. We Keep Water Local by discharging the treated effluent into a restored stream, providing the stream with permanent base flow. In the subwatershed surrounding the stream, green infrastructure designed to infiltrate stormwater runoff increases groundwater flow, which also enhances streamflow. The stream can be designed to have an expansive wetland area that acts as a floodplain and increases the storage area for flood water as well as giving it a way to move through and out of the city. By restoring or redesigning city streams, we increase city capacity to handle floods by hundreds of times over existing conditions. Finally, restored streams also offer very attractive economic development opportunities nearby.
In effect, we are replicating natural hydrology to enlist nature as an ally in our efforts to anticipate and control both the flooding and drought consequences of climate change. The restored stream systems would also provide evaporative cooling, and aesthetics and open space benefits.
There is a tendency for some to dismiss all this good stuff as far too costly. I will be getting more into the particulars of CRWA’s work on financing in later posts to this series. I hope it suffices at this juncture to suggest that CRWA has not ignored costs as some other organization’s responsibility. On the contrary, we are conscious of the financial and political climates in which we operate and have dedicated nearly eight years of work to developing solutions to overcome these barriers.
1: U.S. Environmental Protection Agency - http://water.epa.gov/polwaste/nps/outreach/point1.cfm
Image source: U.S. EPA