Narrow River Watershed
The Narrow River (also known as the Pettaquamscutt River) is just over 9.5 kilometers long and runs parallel to the West Passage of Narragansett Bay in the southern portion of its watershed. Its watershed lies within the towns of North Kingstown, Narragansett and South Kingstown. The “river” is more appropriately described as a composite of a tidal inlet and back bay, an estuary, and two fjord-like ponds. The waterbody and the surrounding watershed are widely utilized as a wildlife habitat and recreational resource. Three perennial and seven intermittent streams discharge to Narrow River.
The principal tributaries to the river are Gilbert Stuart Stream, which discharges to Upper Pond at the northern extremity of the river, and Mumford and Crooked brooks that discharge to Pettaquamscutt Cove, near the southern extremity. The remaining regions of the river receive a majority of baseline freshwater inflow as groundwater seepage from the coastal margin. Land use within the watershed is predominantly residential with approximately 35 percent of the land area developed.
The Narrow River estuary is comprised of three distinct reaches. The relatively sparsely settled upper reach consists of two kettle-hole ponds separated from each other and the lower reaches by shallow sills less than one meter deep. The Upper Pond and the Lower Pond have maximum widths of approximately 500 meters and depths of 13.5 and 19.5 meters, respectively. The ponds are highly stratified and contain permanently anoxic bottom layers. Biogenic hydrogen sulfide accumulates to levels among the highest reported in marine waters (Gaines, 1975). The heavily developed middle reach between Lacey Bridge and Middlebridge Bridge is quite narrow (approximately 10 meters) and shallow (one to two meters) (ASA, 1989). The lower reach consists of a long narrow inlet extending 2 km. from the river mouth to Middlebridge Bridge. Depth in this reach is typically between one and two meters while width varies from approximately 10 meters in “the Narrows” near Sprague Bridge, to 100 meters in the upper portion of Pettaquamscutt Cove.
The unique geographic features and physical dimensions of the Narrow River system control much of the actual hydrodynamics. Tides at the mouth of the river follow a 12.4-hour, semi-diurnal period, with tides at the head of the river lagging by approximately 4 to 6 hours (ASA, 1989). Currents in the system can reach maximum velocities of over 1 m/s in some of the narrower sections of the river, while in the ponds, the currents are almost nonexistent. The ponds exhibit stratification with a deep stable anoxic layer that mixes only rarely with upper surface waters. The ponds and Pettaquamscutt Cove act as water storage basins because of their large surface areas relative to the surface areas of the river sections. The river’s salinity varies substantially along its length. North of Lacey Bridge, the upper and lower ponds are only slightly impacted by tidal energy from Rhode Island Sound. The intrusion of saline water into these ponds occurs only intermittently. This combination of fresh and saline water, limited tidal energy and basin depth results in substantial stratification in both Upper and Lower Ponds. The decreasing water temperatures with depth also contribute to enhanced stratification within the Ponds (ASA et al, 1995 and CRMC, 1999).
Geology and Topography
The path of the Narrow River was initially carved into bedrock millions of years ago by glaciers. During the most recent glacial period, approximately 18 thousand years ago, additional changes occurred. The glacier deepened much of the river valley by adding material to the east and west sides of the river. In addition to depositing material on the valley walls, the recent glacial action resulted in a layering of outwash material in the valley itself, some of it around massive chunks of ice. This process produced the two fjord-like ponds known as Upper Pond and Lower Pond. Further south in the watershed, glacial outwash resulted in a thinner layer of sand and gravel being deposited over the relatively flat area of the Lower River and cove (CRMC, 1999).
Finally, approximately 1,700-years ago, marine inundation of the valley occurred from Rhode Island Sound. This resulted in the formation of a permanent tidal inlet to the river with associated tidal deltas and salt marshes in the Lower River. The event completely changed the river from a closed freshwater system to a tidally influenced, saline system, or estuary (Gaines, 1975). The river bisects its watershed into two sloping, glacial till hillsides with glacial outwash and ice contact deposits at their bases immediately adjacent to and under the river.
The Soil Survey of Rhode Island (SCS, 1981) defines a number of developmental constraints for soils found in the Narrow River watershed. It should be noted that some of these limitations apply to areas of the watershed that have been densely developed. In particular, the survey indicates that, due to the highly permeable nature of the soils associated with a Merrimac-Urban Land Complex, which is found throughout a large part of the developed area of the watershed, “onsite septic systems in this complex need careful design and installation to prevent pollution of groundwater”. Other soils found in the area, such as Rainbow Silt Loam, 3 to 8 percent slopes, are limited by a seasonally high water table and slow to very slow substratum permeability. The steep slopes and surficial soils that bound the Narrow River also present a potential source of pollution to the waters resulting from erosion and subsequent sedimentation. When vegetation is removed and the land is cleared for development, the rate and volume of surface water runoff is increased dramatically and soil erosion is accelerated. Soils carried by surface water runoff enter the river causing adverse changes in the quality of the waters and the overall impacts to its ecosystem. The physical constraints mentioned have prevented development in many areas of the watershed. There is, however, concern for the future. As the easily buildable land is developed, pressure to utilize the remaining, marginal land will increase. The availability of sanitary sewers to these marginal areas will exacerbate development pressures.
The Narrow River is an area of particular archaeological importance and interest. Unlike other coastal rivers, the Narrow River was not significantly affected by sea level rise for most of the prehistoric period. This means that prehistoric sites dating back thousands of years still can be found along its banks. Surveys sponsored by the Rhode Island Historical Preservation and Heritage Commission (RIHPHC) have identified numerous archaeological sites in the Narrow River watershed. Although incomplete, these surveys have allowed archaeologists to study the land use patterns of the region as a whole, instead of having to rely only on isolated sites. They have shown that the spatial and temporal patterns of prehistoric land use along this river are different from any reported or predicted for New England.
Although many sites in the Narrow River watershed have been located, not all of the area has been systematically surveyed. Environmental models developed by the RIHPHC are based on factors including distance to salt and fresh water, degree of slope, and a high probability of archaeological resources. These include the area around Silver Spring Lake, the Mattatuxet River, and the north-western shores of Carr Pond. Little Neck and the area around the Narrows have also never been systematically surveyed. The RIHPHC considers survey of these potentially sensitive areas a high priority.
Significant historical resources within the watershed include most notably the Gilbert Stuart Birthplace, a National Historic Landmark, the Jireh Bull Blockhouse site, dating to the seventeenth century, the original Governor Sprague Bridge, the McSparran site, an eighteenth-century plantation, and the Silas Casey Farm, the oldest working farm in the U.S. These sites are all important to Rhode Island’s history and culture, as well as having aesthetic value. The protection of these sites is a priority of the RIHPHC.
Water Quality & Management
Because of coliform bacteria, the Narrow River is currently closed to shellfishing and is on the Rhode Island List of Impaired Waters. The Narrow River Preservation Association is working with the RI Department of Environmental Management (DEM) and the US Environmental Protection Agency to improve the water quality of the Narrow River.
The Narrow River Watch Program is a volunteer monitoring program that focuses on educating the public and providing information on the water quality status of the river. The program emphasizes watershed-scale monitoring because the water quality of a given river or lake reflects the activities in the lands and waters that surround and lie upstream of it.
Every two weeks volunteers measure water temperature, salinity and dissolved oxygen at their assigned location. Additionally they take water samples and process them for later analysis of algae concentration. The monitoring results are recorded and mailed to URI on pre-stamped postcards provided to the volunteers. Five times during the season the volunteers also collect water samples which they immediately bring to URI Watershed Watch Laboratory for analysis of nutrients and bacteria.
The Narrow River is listed as a Group 1 waterbody (highest priority) on the State of Rhode Island’s 1998 303(d) list of water quality impaired waterbodies (RIDEM, 1998). Gilbert Stuart Stream is listed on the State of Rhode Island’s 2000 303(d) list also as a Group 1 waterbody. Mumford Brook is not currently on the 303(d) list, however, it has been found to be impaired for bacteria based on recent sampling.
Pollutant of Concern
The pollutant of concern is fecal coliform, a parameter used by Rhode Island as an indicator of pathogen contamination.
Pollutant Sources to Narrow River
Narrow River’s three largest tributaries, Mumford Brook, Gilbert Stuart Stream and Crooked Brook act as the principal pathways by which nonpoint loadings enter the Narrow River during periods of dry and wet weather. Gilbert Stuart Stream is the primary fecal coliform source to Upper Pond while Mumford Brook and Crooked Brook are the principal sources to southern Pettaquamscutt Cove. Birds also contribute significant fecal coliform loadings to the river. They are present throughout the Narrow River watershed, however, the largest waterfowl populations are consistently seen in the heavily developed residential area between Bridgetown Bridge and Middlebridge Bridge, and within the Pettaquamscutt Cove National Wildlife Refuge located in the southern portion of Pettaquamscutt Cove. Predictably, water quality impacts that appear attributable to birds are most evident in these areas. Bird-related fecal coliform loadings to the middle section of the river are estimated through a mass balance approach explained in Chapter 5. Loadings to Pettaquamscutt Cove from wildlife and waterfowl are not estimated because accurate population counts are unavailable, other significant sources are present and tidal action increases the complexity of any calculations.
All dry weather sources continue to contribute during wet weather conditions to a larger or lesser degree. However, wet weather sources of fecal coliform to the Narrow River are dominated by storm water runoff entering the river through tributary channels, storm sewer outfalls, and overland as sheet flow. Storm sewer outfalls discharging to Segments 2, 3 and 4 have a dramatic effect on water quality during runoff events. Fecal matter from domestic animals, wildlife, waterfowl and failing septic systems is deposited on lawns, parking lots, docks, streets and along the shoreline. It accumulates during dry periods and is subsequently washed off and efficiently transported to receiving waters through storm drains during rain events.
Organizations & Links
The Narrow River Preservation Association
The Narrow River Preservation Association (NRPA), is a non profit 501(c)(3) that was founded in 1970 and recognized by the Rivers Council in 2002. NRPA is governed by a Board of Directors representing the three towns in the watershed. NRPA has a part-time administrative assistant and membership of 400 individuals, families and businesses. Their mailing list includes 5500 names. NRPA is supported by membership dues, foundations, government sources and fundraisers. NRPA has monitored water quality along the river for many years, is working with state and local government to install stormwater treatment facilities that will help clean the river. Meanwhile, federal and state agencies are developing a plan aimed at improving water quality and habitat by increasing tidal flushing at the Narrow River Inlet, just north of Narragansett Town Beach.
John H. Chafee National Wildlife Refuge
Located within the picturesque Narrow River on the Southern Coast of Rhode Island, this Refuge is comparatively small in size, but big in protecting the unique features of this area. At 317 acres, the John H. Chafee National Wildlife Refuge provides habitat for the largest black duck population in Rhode Island, and is recognized under international agreements as a critically important area for this species. The scenic vistas offered by the refuge and surrounding areas is well noted and attracts people from throughout the region.
Land acquisition is a priority for this refuge, given the rapid rate of development adjacent to the refuge, and the high demand for land in the area. While refuge lands are small, they lie adjacent to other lands set aside for conservation. Refuge lands function in concert with these adjacent areas in providing a contiguous reserve of protected habitat.3679 D Old Post Road, Box 307
Charlestown, RI 02813