Teaching Introductory Hydrology using the Hobbs Brook Reservoir Wateshed in Eastern Massachusetts as a Case Study

An introductory hydrology course at Bentley College uses field trips and lab exercises to complement theories and concepts pertaining to surface and groundwater flow. Two field trips visit the Stony Brook watershed in Weston and the City of Cambridge's water filtration plant. In 1887, the City of Cambridge acquired 22 sq miles of watershed and in 1892 constructed Hobbs Brook reservoir (~558 acres, 2700 million gallon capacity) to collect water from the smaller Hobbs Brook sub-basin to augment the diminished summer flow from the larger Stony Brook sub-basin, which remains primarily residential. The Hobbs Brook sub-basin is situated precariously along Rt. 128 (I-95), a major transportation conduit and center for intense light-industrial and commercial development, thus is continuously at risk for contamination.

At a site ~2 km south of Hobbs Brook reservoir, Hobbs Brook converges with Stony Brook, which flows into Stony Brook reservoir, and then via an 18 km aqueduct feeds Fresh Pond in Cambridge, location of the water treatment plant. The convergence site, similar to an example provided for a stream flow measurement exercise described in Marie Morisawa's Geomorphology Laboratory Manual (John Wiley, NY, 1982), allows students to measure width, depth, and velocity to calculate discharge for the three streams. Given that precipitation in New England is fairly evenly distributed throughout the year, students must explain the flip-flop in summer and winter seasonal discharge data between Hobbs and Stony Brooks, along with the peak flows in early spring. Students can also compare their discharge data for Hobbs Brook with two remotely operated hydrographs by the City of Cambridge. Finally, students invariably find that the sum discharge of the two streams does not equal the discharge below the convergence, which also must be explained.