Providence Metro Area
Rhode Island’s capital city and associated metro area sit at the head of Narragansett Bay where two major tributaries, the Blackstone and the Pawtuxet, and three smaller rivers, Woonasquatucket, Moshassuck, and Ten Mile, enter the estuary. The drainage from these massive watersheds disgorges in the midst of the Providence metro area, and during major storms flooding occurs. When swollen rivers meet high tide pushed by high winds, disaster occurs.
In nor’easters and intense thunder storms, when the street drains are over-capacity or clogged, local flooding makes low-lying roads unsafe or impassable for up to several hours. Hurricanes of increasing intensity cause property and infrastructure damage not only from high winds and intense rain, but from the meeting of high tide, surge, and river rampage. Flooded sewage treatment plants not only inconvenience customers but create a major public health danger.
Bay contamination from street flooding in Providence was mitigated but not totally fixed by a $1.3 billion project to build gray infrastructure — pipes leading to massive tunnels to store stormwater until it could be treated and discharged into the Bay. Previous to the project and by design from the 1800s, stormwater pipes, connected to septic sewer pipes, caused raw sewage to contaminate the Bay through Combined Sewer Overflows (CSOs). Bay water quality has benefitted from diverting the overflows to treatment. The Narragansett Bay Commission CSO Abatement Project.
Publicly funded construction of a berm and hurricane gate protects downtown Providence against storm surge coming up the Bay but prevents the release of water from flood-swollen Moshassuck and Woonasquatuket flow. On the Seekonk (Blackstone as estuary) River side of Providence, the northern end is a bluff above the river, but towards the southern, Fox Point, end, and where the water becomes the Providence River along the harbor and Fields Point shores, the land is low and subject to flooding. Land use planning that sites parks and requires raised buildings will allow the natural spread of flood waters while minimizing personal and property damage. The Pawtuxet River, draining a dense suburban metro area continues to expose critically vulnerable municipal sewage plants, interstate highways, and vast residential areas to flooding.
The increasing acres of impervious surfaces — roofs, parking lots, foundation to foundation concrete driveways, and roads — shunt rain that could soak into the earth into the system that leads to rivers and increases flooding. This ad hoc urban design by decisions of planning and zoning boards, ignores hydrologic principals and has not considered the overall consequences of single permit approvals. We need the coordination of municipal permitting to require adequate on-site infiltration of stormwater run-off and to adhere to “No net increase” in off-site run-off in new and retrofit construction.
Urban soils are compacted by use over hundreds of years and need to be loosened in residential retrofits or engineered in institutional projects. Basements need protection from water. Small-lot residences, multi-story buildings, and pavement to accommodate thousands of people challenge stormwater design. Urban Providence metro has assets in its tree canopy and CSO abatement systems, but needs a coordinated plan to solve the stormwater problem close to the source of the run-off .
See Step by Step Green Infrastructure Projects in Reservoir Triangle for an example of a small-scale project desgined to reduce imporvious surfaces in the urban environment.