|Daylighted Saw Mill River, Yonkers, NY
Photo by Zach Youngerman
In my last post, I introduced the concept of distributed wastewater treatment as an important tool for getting distributed energy generation and water reclamation, and increased resilience, while Restoring Nature. Building on the concept, we at Charles River Watershed Association (CRWA) have been looking at collecting wastewater, treating it, and infiltrating it into the ground near each of the treatment plants. Most distributed wastewater treatment plant conceptualizations I’ve seen would send reclaimed water once reused back to the piped sewage system it was originally collected from. If we were to do that, though we would capture the energy and reclaimed water, we would miss a significant environmental opportunity.
Climate change brings much larger rainstorms and extended periods of drought. The American Southwest is not only suffering an extended drought, but as we have seen in both Arizona and California, occasional pounding rainstorms causing flash flooding. CRWA’s work in Boston has revealed tributaries and first order streams to the Charles River which we have simply made go away over the last two centuries through culverting and fill. Historic hydrology. The problem with burying streams is that rainwater, land, groundwater, and surface water continue to behave as if the streams were still there. Streams routed into a pipe have a fixed capacity, whereas natural systems can expand. Loss of stream capacity causes areas immediately surrounding those old streams to be more susceptible to flooding.
"The question is not how we exploit nature to sustain ourselves. The question is how we understand nature and configure our systems to respect and restore her abundance, thereby creating a real sustainable future for ourselves, and all species."
|The Natural Valley Storage Area; over 8,000 acres of protected
wetlands that provide flood storage for Charles River communities.
As CRWA has been conceptually designing pilot distributed wastewater treatment plants for urban Boston, we have also been working to link effluent discharge from those plants to “daylighted” (i.e., restored) urban streams. By replicating historic hydrology, we gain flood storage and conveyance capacity, create new open space in the City, and encourage new economic development zones surrounding the restored streams and open space. The treatment plant effluent discharge would provide a constant minimum baseflow to the stream.
Further, stormwater green infrastructure (rain gardens, swales, etc.) introduced to attenuate and infiltrate stormwater runoff can be designed to connect to restored streams in each municipal district, or subwatershed, again replicating historic hydrology and increasing both flood and drought resilience. In Boston, such an approach would have the added benefit of alleviating depleted groundwater problems leading to foundation piles rotting on exposure to air. Overflows from the green infrastructure installations might use existing stormdrains for conveyance of excess water to restored streams.
We believe it is paramount to engineer all elements of city water collection and disposal together as a linked system. Wastewater capture, use, and discharge; stormwater runoff capture and discharge; surface water infiltration with recharge to groundwater; water quality, and water quantity. With our approach, Flexibility, Adaptability, and Interconnectedness are significantly enhanced. Economically, we benefit from Resource to Waste to Resource (energy, thermal energy, reclaimed water) and Keeping Water Local (sustained baseflow, significant flood storage and conveyance, resilience to drought, reclaimed water, reduced demand, economic development zones around restored streams, evaporative city cooling). Additionally, we benefit from the aesthetics of green infrastructure and daylighted streams, while we Restore Nature.
In other words, our concept is to replicate natural hydrology to the extent technology currently allows, building significant flexibility into our water systems, preparing for the vagaries of climate change, and enhancing our urban communities. By building systems that by their nature are more flexible and adaptable, we also allow for adoption of technological advances with time. As we pursue the goal to Restore Nature, we are certain to become better at enhancing existing technologies and inventing new ones.
“Sustainability” as currently used often means providing enough water for us now while ensuring the needs of future generations are also met, but CRWA’s work has shown over periods longer than meeting immediate demand, there is no such thing as sustainability for us without Restoring Nature. I’m reminded of a childhood fable about a goose and golden eggs.
Our approach, then, centers on these elements: distributed wastewater treatment, reclaimed water, and energy generation; treatment plant discharge to restored urban natural hydrology and streams; and the creation of economic development zones and tools to help incentivize the transformation.
For CRWA, metropolitan Boston and its Charles River is our laboratory. We study land scoured by glaciers and a river about 12,000 years old. The natural principles guiding us, however, apply to every region of the country, and for that matter the world. The question is not how we exploit nature to sustain ourselves. The question is how we understand nature and configure our systems to respect and restore her abundance, thereby creating a real sustainable future for ourselves, and all species.
Over the coming 20 years, we could achieve full transformation.