Riverdale's greenbelt is great, and really should be emulated


(re: “Is decision near on SNAD’s fate?” Aug. 22)

Right here in the Northwest Bronx, we have an amazing piece of nature — 900 acres in the big city — where people have discovered a way to live and protect their watershed by limiting landscape development to only 30 percent cover.

This is quite a feat!

Congratulations to the Special Natural Area District protectors in creating the urban rain forest. There are probably only a few other areas of the city that would fill this prescriptions — Jamaica Bay comes to mind. So does our own 1,100 acres of Van Cortlandt Park with even less than a 30 percent cover.

Savor these areas — the lungs and kidneys of the city — as they are just as important as our highways, subways and stock market in keeping the heart of the city beating.

In the city of 9 million people, the development cover is at 72 percent. The Harlem River Watershed Plan in the Bronx — which covers community boards 4, 5, 7 and most of 8 — is 66 percent impervious. In understanding how unique and significant this is, we turn to science.

Tom Schueler of The Center for Watershed Protection, classifies stream quality levels by percent impervious: Up to 10 percent are “stressed,” 11 to 25 percent are “impacted,” and 26 to 100 percent are “degraded.”

In fact, research indicates that watersheds are demonstrably and irreversibly degraded when as little as 10 percent of their surface area is covered by imperviousness. This impacts runoff volume quite dramatically.

For example, one inch of rain over an acre of open space will typically generate 218 cubic feet of runoff. One inch of rain over an acre of a paved parking lot will produce 3,450 cubic feet of runoff — nearly 16 times more than the natural setting.

The SNAD of Riverdale, Spuyten Duyvil and Fieldston is already delineated and protected. While over the last 40 years, the city built out 72 percent, the SNAD managed to survive with only 30 percent impervious cover.

Let’s look at the area as an urban natural area watershed — an oasis, if you will — and begin a stakeholder-managed watershed group with subgroups reflecting the land ownership distinctions. Separate working groups of homeowners, multifamily residential, community facility institutions, and municipal agencies.

Instead of complicated zoning amendments, choose indicators of living creatures. Easily found in this fragile ecosystem is a large array of bugs, caterpillars, birds, trees, native plantings and rain gardens, natural integrated pest management processes, large rain gardens strategically placed to promote infiltration. All these indicators will be evident and can be demonstrated by examining the flow levels in local catch basins.

A good plan will show lower flow levels as the land becomes more sponge-like and runoff is absorbed, temperatures are lowered, storms are not as severe than other parts of the city. It will also cost less to provide these ordinary city services because of the protections voluntarily accepted in this area.

Of course, there will be a goal to this big experiment. Let’s lower the 30 percent impervious cover by 1 percent each year for a five-year study period.

This is an opportunity of a lifetime, cutting edge for an urban environment. Time to take a stand and pull the environmental impact statement. Allocate interagency expending funding, or apply for a grant to create a watershed plan for our SNAD.

Tell your city leaders now!

The author is a member of the Bronx Council for Environmental Quality board of directors.


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Karen Argenti,