Massachusetts Department of Environmental Management
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Massachusetts Department of Environmental Management Saugus River Water Budget and Instream Flow Study Prepared By: Gomez and Sullivan Engineers and Environmental Scientists 55 North Stark Highway Weare, NH 03281 Final Report, June 2002 Executive Summary Background The Executive Office of Environmental Affairs Watershed Initiative North Coastal Basin Team commissioned a study to evaluate the relationship between streamflow regulation in the Saugus River and aquatic habitat needs. The Saugus River is a small coastal stream located north of Boston, MA. The watershed is approximately 23.3 square miles. The Saugus River is located in an urban area and has been impacted by human activities for over 300 years. Several public water supply sources are located in the Saugus River Basin. Most of the water removed from the river directly, or indirectly from groundwater sources and ponds does not return to the basin, rather it is discharged out of basin to wastewater treatment facilities. In addition, development has altered wetlands, culverted the river beneath major roads, and placed barriers such as dams across the river. Surface water features in the watershed are manipulated for flood control. The magnitude and timing of river flow has been altered as a result of these human activities. Despite its location in a heavily developed urban area, large tracts of open space remain along the river corridor, including golf courses, state reservations, a national park, and vast areas of protected wetlands. Available data suggest the river water quality is suitable to maintain a warm-water fishery and an inspection shows that fish passage is available along the approximately five river miles from the fresh-water limit near the Saugus Ironworks to the Lynn Water and Sewer Commission Diversion Dam1 at the Sheraton golf course in Wakefield. Historic records indicate a once-prolific alewife run took place in the Saugus River annually. Recent surveys show a lack of a thriving fish population in the river, however. This study determined that although natural flow conditions probably did not provide optimal fish habitat, improvements to the timing and magnitude of flow could be made to increase fish populations in the river as well as improve water quality. The impacts of past human development cannot be undone; water resources must be reasonably allocated among human and environmental needs. Opportunities exist to improve aquatic habitat by managing river flow. Even modest modifications toward the natural flow regime (such as maintaining seasonal minimum flows throughout the year) may result in vast improvements in fish populations and habitation of the river. This in turn will support a healthy watershed ecosystem. Understanding Hydrology- Regulated Flow and Estimated Unregulated Flow This study examined the interrelationships between numerous water withdrawals in the basin and the resulting impact on the timing, magnitude and frequency of regulated flow in the Saugus River. Annual Water Use reports were obtained from each registered and permitted water withdrawal in the basin2 regulated by the Massachusetts Water Management Act for the period between 1994 and 1999. The monthly data for this 5-year period was displayed in various figures to understand the timing, magnitude and duration of withdrawals throughout the year. The quantified water withdrawal data, in conjunction with flow data recorded at a United States Geological Survey (USGS) gage near the Saugus Ironworks, was used to estimate virgin or 1 The Diversion Dam impounds water such that Lynn Water and Sewer Commission can divert water to Hawkes Pond, which is one LWSC’s four water supply reservoirs. 2 There are four registered withdrawals in the basin: Lynn Water and Sewer Commission, Lynnfield Center Water District, Sheraton Colonial Golf Course, Wakefield Water Department. Saugus River Study i Final Report “natural” flow conditions in the Saugus River. Comparisons between the regulated and virgin flow conditions were conducted to understand how human activities affect streamflow. The findings indicate that the Saugus River flow is affected during low flow periods in the summer and during certain periods in the fall and spring, when water suppliers are attempting to refill their storage reservoirs. The Saugus River flow is not grossly affected during extremely high runoff periods, as the quantity of water withdrawn from the watershed is minimal compared to the magnitude of runoff. LWSC’s large storage reservoirs offer operational flexibility for the timing of water withdrawals from the Saugus River; however, the slope and capacity of its diversion channel limits the rate and optimal management of its withdrawals. Instream Flow Study to Determine Minimum Flows needed for Aquatic Habitat In addition to estimating virgin flow conditions in the watershed, a habitat analysis was conducted for the purpose of developing minimum flow recommendations below the LWSC Diversion Dam3. Currently, LWSC is not required to maintain a continuous flow below the Diversion Dam and thus flow below the dam can be reduced to leakage. The lack of water below the Diversion Dam has an impact on the aquatic resources in this reach. An instream flow study (IFIM-instream flow incremental methodology) was conducted to quantify the relationship between flow and fish/macroinvertebrate habitat between the Diversion Dam and the USGS gage on the Saugus River (near the Saugus Ironworks in Saugus, MA)4. A detailed habitat map of the river was prepared from the Diversion Dam to the Saugus River USGS gage- a total of five river miles. The habitat mapping consisted of segmenting the Saugus River into habitat types of riffles, runs and pools. The breakdown of habitat types in the inventoried reach was as follows: 5.7% riffles, 93.0% runs, and 1.3% pools. The Saugus River is generally a slow moving stream comprised mostly of 1-2 foot deep runs with silt/sand substrates. There are limited riffle reaches, which are typically the most productive (in terms of food production for fish) habitat types. Using the habitat maps, an instream flow study was conducted within two reaches of the Saugus River- one just below the LWSC Diversion Dam and the other downstream of Route 1 (referred to throughout the report as the Staples Reach). The upper reach near the LWSC Diversion has a relatively steep slope and consists of riffle/run sequences. In general velocities were high, depths low and the substrate was primarily sand, gravel and cobble. In contrast, the Staples Reach consists of slower moving riffles and runs and substrates were primarily sandy. These two reaches included the majority of riffles in the inventoried river. It is believed that if suitable aquatic habitat is maintained in the riffles, the remainder of the river will contain suitable habitat conditions. Field data (flow, depth, velocity, substrate) was collected in these two reaches to develop hydraulic models. The hydraulic models were used to predict depth and velocities in each reach 3 The Diversion Dam is located in Wakefield below Reedy Meadows, a large wetland complex. The drainage area at the Diversion Dam is approximately 10.5 square miles. The Diversion Dam is the only dam on the Saugus River mainstem from the ocean to the base of Lake Quannapowitt. 4 The USGS gage is located upstream of the Saugus River’s confluence with salt water. Saugus River Study ii Final Report over a range of flow conditions observed in the Saugus River. The hydraulic data was used in conjunction with fish preference curves (fish have certain preferences for depth, velocity and substrate) to estimate the quantity of fish habitat over a range of flows. A relationship between flow and fish habitat was developed for each of four species and life stage of fish plus macroinvertebrates were examined as part of this study. The flow yielding the most habitat for a given species and life stage of fish was quantified (alewife habitat was evaluated qualitatively since preference curves are not available for this species). Flows necessary to maintain at least 80% of the optimal habitat for all life stages of each target species were identified. The instream flow study was one tool used to estimate flow needs for aquatic resources below the LWSC Diversion Dam. United States Fish and Wildlife Service- Aquatic Base Flow Policy In addition to the habitat study, the natural flow yield of the Saugus River Basin was examined to determine if the flow needs resulting from the instream flow study could be supported from the natural flow in the basin. The natural flow at the Saugus River USGS gage and at the LWSC Diversion Dam was computed and compared against the United States Fish and Wildlife Services’ (USFWS) Aquatic Base Flow Policy (ABF). Typically, the USFWS recommends that minimum flows be equivalent to the August median flow (during the summer), which is based on an unregulated river system. When no site-specific study is conducted or long-term record (25 years or greater) is available, the USFWS recommends a minimum flow equivalent to 0.50 cfs per square mile of drainage area. The estimated unregulated Saugus River flow at the gage is rather short (6 years)5, however, recognizing the limited period of record, the Saugus River has a lower August median flow per square mile of drainage area (0.20 cfs per square mile of drainage area), when compared to the ABF Policy (0.50 cfs per square mile of drainage area). Minimum Flow Recommendations at the LWSC Diversion Dam Taking into account the physical landscape of the basin above the Diversion Dam, the natural hydrology of the watershed, the results of the instream flow study and the timing of the alewife run, shown in the table below is the recommended minimum flows for the LWSC Diversion Dam. 5 It should be noted that this 6 year period was considered drier than the long-term average based on precipitation data.