Watershed Geology

The First Herring Brook Watershed is largely a product of New England's glacial history. Overlying much of the bedrock in Scituate are sediments laid down during the last glaciation, which ended about 15,000 years ago. Glacial till and outwash plain sediments are the most common glacial deposits in Scituate. Till, an unsorted mixture of clay, sand and boulders, covers many of the higher uplands in the watershed. Outwash sediments, on the other hand, are well-sorted sands and gravels that typically accumulated in stream valleys and other lowlands. Unlike till, permeable outwash deposits often serve as aquifers (i.e., geologic formations that supply water for wells), particularly where the sediments are thickest. More recent geologic deposits, namely salt marsh and intertidal sediments, underlie and confine First Herring Brook just upstream of its confluence with the North River.

The First Herring Brook Watershed Initiative (FHBWI) and Maxwell Conservation Trust's Watershed Neighbor Project has divided the watershed into four sections (see diagram). The West Watershed Neighborhood includes most of the upper half of the First Herring Brook watershed. Groundwater seeps along the upper watershed boundary feed intermittent streams and wetlands that drain into large forested wetlands such as South Swamp. Field investigations by FHBWI's Stream Team have expanded the West Watershed boundary to include even a larger share of South Swamp, several previously unmapped tributaries, as well as a portion of Black Pond Swamp in Norwell. Although the most sparsely developed section of the watershed, several new development projects threaten watershed resources within this area. These "at risk" areas include some of the best remaining pieces of open space in Scituate including the extensive forests surrounding Bates Lane (located off Clapp Road) and the diverse upland and wetland habitats near scenic Galen Damon Pond.

The Tack Factory Pond Watershed Neighborhood contains watershed resources from Satsuit Meadow to the Cushing Elementary School and from Pincin Hill to Tack Factory Pond. Route 3A, Scituate's main transportation corridor, falls mostly within this section of the watershed. Stormwater runoff, along with groundwater discharge, helps maintain stream levels within First Herring Brook during the summer to support plants and wildlife. Its importance notwithstanding, stormwater in developed watersheds such as First Herring Brook's may carry an insidious cargo of pollutants and sediments that pose significant risks to organisms dependent on clean water, not to mention our drinking water supply. One need only study stormwater pathways within the watershed to appreciate this serious threat. In an effort to counter the potential negative impacts of development in the watershed, the Town purchased the 22-acres south of Tack Factory Pond in 1999 for water supply protection.

The section of the First Herring Brook watershed draining into the Reservoir along Route 3A is identified as the Reservoir Watershed Neighborhood. This water body, along with the water treatment plant on Old Oaken Bucket Pond, was constructed in 1969 to improve the quality and capacity of Scituate's water supply. At less than 10 feet deep, the Reservoir, like Tack Factory Pond and Old Oaken Bucket Pond, replaced a formerly cold-water stream that once supported brook trout with warm water habitat that is populated today by pumpkinseed, bluegill, and yellow perch. First Herring Brook, as its name indicates, once supported anadromous fish (salt water fish that migrate to freshwater to spawn) such as shad, alewife and, of course, herring. Archeological investigations conducted prior to the impoundment of First Herring Brook found evidence that Native Americans once indulged in this abundant resource. Repair of the fish ladder at the reservoir's outlet may someday restore this valuable fishery resource.

The Old Oaken Bucket Pond Watershed Neighborhood, located at the downstream end of the watershed, encompasses extensive wetlands between Brushy Hill and Stockbridge Road, the Greenbush rail bed, as well as Old Oaken Bucket Pond next to the water treatment plant. Identifying the location of tributary streams is critical in watershed planning since they readily convey the byproducts of adjacent land-use activities into the water supply. The FHBWI Stream Team recently identified two, previously unmapped tributaries of First Herring Brook (Clapp Brook and Tan Brook) within this section of the watershed. Vernal pools and the state-listed Mystic Valley amphipod are among the rich, biological resources found in this area. The urgency of the Stream Team's work is heightened by the imminent restoration of the Greenbush rail line, which may significantly impact some of these resources.

The First Herring Brook Watershed is among Scituate's most critically important natural resources. This complex web of surface water and groundwater features is a sensitive barometer of our actions on the surrounding landscape. As Scituate plans its future, its citizens must respect the integrity of this natural system, not only for the biological resources it protects but for the drinking water that sustains this seaside community.

J. Andrew Walsh, Ecologist, FHBWI Steering Committee