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Simulated effects of the 2003 permitted withdrawals and water-management alternatives on reservoir storage and firm yields of three surface-water supplies, Ipswich River Basin, Massachusetts

The Hydrologic Simulation ProgramFORTRAN (HSPF) model of the Ipswich River Basin previously developed by the U.S. Geological Survey was modified to evaluate the effects of the 2003 withdrawal permits and water-management alternatives on reservoir storage and yields of the Lynn, Peabody, and SalemBeverly water-supply systems. These systems obtain all or part of their water from the Ipswich River Basin. The HSPF model simulated the complex water budgets to the three supply systems, including effects of regulations that restrict withdrawals by the time of year, minimum streamflow thresholds, and the capacity of each system to pump water from the river. The 2003 permits restrict withdrawals from the Ipswich River between November 1 and May 31 to streamflows above a 1.0 cubic foot per second per square mile (ft3/s/mi2) threshold, to high flows between June 1 and October 31, and to a maximum annual volume. Yields and changes in reservoir storage over the 35-year simulation period (196195) were also evaluated for each system with a hypothetical low-capacity pump, alternative seasonal streamflow thresholds, and withdrawals that result in successive failures (depleted storage). The firm yields, the maximum yields that can be met during a severe drought, calculated for each water-supply system, under the 2003 permitted withdrawals, were 7.31 million gallons per day (Mgal/d) for the Lynn, 3.01 Mgal/d for the Peabody, and 7.98 Mgal/d for the SalemBeverly systems; these yields are 31, 49, and 21 percent less than their average 19982000 demands, respectively. The simulations with the same permit restrictions and a hypothetical low-capacity pump for each system resulted in slightly increased yields for the Lynn and SalemBeverly systems, but a slightly decreased yield for the Peabody system. Simulations to evaluate the effects of alternative streamflow thresholds on water supply indicated that firm yields were generally about twice as sensitive to decreases in the NovemberFebruary or MarchMay thresholds than to increases in these thresholds. Firm yields were also generally slightly less sensitive to changes in the NovemberFebruary than to changes in the MarchMay thresholds in the Peabody and SalemBeverly water-supply systems. Decreases in the JuneOctober streamflow threshold did not affect any of the system's firm yield. Simulations of withdrawal rates that resulted in successive near failures during the 196195 period indicated the tradeoff between increased yield and risks. The Lynn and Peabody systems were allowed to near failure up to six times. At the sixth near failure, yields of these systems increased to 10.18 and 4.43 Mgal/d, respectively; these rates increased the amount of water obtained from the Ipswich River Basin (relative to the firm-yield rate), as a percentage of average 19982000 demands, from 68 to 96 percent and from 51 to 75 percent, respectively. The SalemBeverly system was able to meet demands after the third near failure. Reservoir storage was depleted about 6 percent of the time at the withdrawal rate that caused the sixth near failure in the Lynn and Peabody system and about 3 percent of the time at the withdrawal rate that caused the third near failure in the SalemBeverly system. Supply systems are at greatest risk of failure from persistent droughts (lasting more than 1 year), but short-term droughts also present risks during the fall and winter when the supply systems are most vulnerable. Uncertainties in model performance, simplification of reservoir systems and their management, and the possibility of droughts of severity greater than simulated in this investigation underscore the fact that the firm yield calculated for each system cannot be considered a withdrawal rate that is absolutely fail-safe. Thus, the consequences of failure are an important consideration in the planning and management of these systems.

Scientific Investigations Report

Evaluation of alternative groundwater-withdrawal scenarios on water levels in Kingsbury Pond, upper Charles River Basin, eastern Massachusetts

Kingsbury Pond is a glacial kettle pond in the town of Norfolk, Massachusetts, in the Mill River Basin, which is part of the Upper Charles River Basin in eastern Massachusetts. The pond is hydraulically connected to the surrounding groundwater-flow system, and water levels in the pond fluctuate in response to recharge to the aquifer from precipitation and wastewater return flows through septic systems, to withdrawals from the aquifer at nearby wells, and to precipitation directly on the pond surface. Concerns about the effects of withdrawals on water levels in the pond prompted an investigation to better understand the hydrology of Kingsbury Pond and its response to groundwater withdrawals and to determine if withdrawals from wells in Franklin, Mass., can be modified to simultaneously reduce the effect on water levels in the pond and yet meet the water-supply demands of the Town of Franklin. An existing, transient groundwater-flow model of the Upper Charles River Basin was modified for this study in the area near Kingsbury Pond to improve representation of the hydrologic system near the pond. The mean annual water-level altitude simulated for the pond for nonpumping conditions using the modified model is 136 feet (ft), which falls within the range of likely annual pond-altitude fluctuations of 135 to 140 ft estimated for average hydrologic conditions before the beginning of withdrawals at two nearby wells operated by the Town of Franklin (wells FR–04 and FR–05). The mean annual water-level altitude at the pond decreased by 3.8 ft to 132.2 ft for simulated mean monthly withdrawal rates at all wells within the Upper Charles River Basin from 2010 to 2019 (referred to as the baseline withdrawal condition). A groundwater management model that links the groundwater-flow model with a mathematical optimization method was developed to evaluate the effects of three alternative groundwater-withdrawal scenarios for the Franklin public-water system on water levels in Kingsbury Pond. In the first scenario, monthly withdrawal rates at wells FR–04 and FR–05 were increased from the baseline withdrawal rates to their maximum authorized rates for all months of the year; all other Franklin wells were specified at their baseline withdrawal rates. This scenario resulted in a mean annual water-level altitude at the pond of 129.3 ft, or a mean annual decline of 6.7 ft compared with nonpumping conditions and a decline of 2.9 ft compared with baseline conditions. The results of the second scenario showed that water levels in the pond can be increased relative to 2010–19 conditions while meeting Franklin’s 2010–19 monthly water-supply demands if withdrawals at wells FR–04 and FR–05 were shifted to other Franklin wells. In this scenario, monthly withdrawal rates at wells FR–04 and FR–05 were decreased from their baseline rates to one-third their maximum practical rates for all months of the year; increased withdrawal rates at other Franklin wells were determined by the management model. The decrease in withdrawal rates at wells FR–04 and FR–05 resulted in a mean water-level altitude at the pond of 134.1 ft, which was equivalent to a 51 percent increase (improvement) in the mean annual water level of the pond relative to the baseline condition. A third scenario was done to determine if Franklin’s existing water-supply system has the capacity to meet the mean annual maximum permitted withdrawal rate of the system of 3.45 million gallons per day while maintaining monthly withdrawal rates at wells FR–04 and FR–05 at their 2010–19 rates and water levels in Kingsbury Pond at baseline conditions. The analysis indicated that the capacity of the system cannot meet the increased demand during some months of the year with withdrawal rates at the two wells fixed at their monthly 2010–19 rates; however, the existing system is capable of meeting about 90 percent of the maximum permitted rate (3.10 million gallons per day) by increasing withdrawal rates at other Franklin wells above their 2010–19 rates.

Massachusetts

Use of Numerical Models to Simulate Transport of Sewage-Derived Nitrate in a Coastal Aquifer, Central and Western Cape Cod, Massachusetts

The unconsolidated glacial sediments underlying Cape Cod, Massachusetts compose a regional aquifer system that is used both as a source of drinking water and as a disposal site for wastewater; in addition, the discharge of clean ground water from the aquifer system is needed for the maintenance of freshwater and marine ecosystems throughout the region. Because these uses of the aquifer conflict with one another in many areas of the Cape, local and regional planners have begun to develop sustainable wastewater plans that will facilitate the disposal of wastewater while protecting water supplies and improving the health of aquatic ecosystems. To assist local and regional planners in these efforts, the U.S. Geological Survey conducted a 2-year investigation to (1) assist local and regional planners in the evaluation of potential wastewater scenarios, (2) use results and interpretation from these analyses to develop hydrologic concepts transferable throughout the region, and (3) establish and test methods that would be of use in future evaluations. Wastewater-disposal scenarios need to be evaluated in the context of the regional ground-water-flow system. For a given rate of disposal, wastewater from sites at or near a regional ground-water divide is transported in a wider arc of flow directions, flows deeper in the system, and contaminates a larger part of the aquifer than does wastewater discharged from sites farther from the divide. Also, traveltimes of wastewater from sites near a ground-water divide to receptors are longer (as much as several hundred years) than traveltimes from sites farther from the divide. Thus, wastewater disposal at or near a divide will affect a larger part of the aquifer and likely contribute wastewater to more receptors than wastewater disposal farther from a divide; however, longer traveltimes could allow for more attenuation of wastewater-derived nitrate from those sites. Ground-water-flow models and particle tracking can be used to identify advective-transport patterns downgradient from wastewater-disposal sites and estimate traveltimes; however, these tools cannot predict the distribution of mass or concentrations of wastewater constituents, such as nitrate, in the aquifer. Flow-based particle-tracking analyses can be used to estimate mass-loading rates and time-varying concentrations at wells and ecological receptors by the accounting of mass-weighted particles discharging into the receptor of interest. This method requires no additional development beyond the flow model; however, post-modeling analyses are required. In addition, the method is based on the assumption that no mass is lost during transport, an assumption that likely is not valid in many systems. Solute-transport models simulate the subsurface transport of nitrate through the aquifer and predict the distribution of the mass of a solute in the aquifer at different transport times. This method does require additional model development beyond the flow model, but can predict timevarying concentrations at receptors. Estimates of mass-loading rates require minimal post-modeling analyses. Time-varying concentrations and mass-loading rates calculated for wells in eastern Barnstable by the two methods generally were in reasonable agreement. Inherent in the flow-based particle-tracking method is the assumption that mass is conserved along a given flow line and that there is no spreading of mass in the aquifer. Although the solute-transport models also incorporate a system-wide conservation of mass, these models allow for a spreading of mass in the aquifer, and mass is not conserved along a given flow line. As a result, estimates of concentrations and mass loading rates generally were higher in particle-tracking analyses than in solute-transport simulations. Results from the two types of simulations agreed best for wells that receive large amounts of wastewater with short traveltimes (less than 10 years) because insufficient transport

Scientific Investigations Report

A brief history and summary of the effects of river engineering and dams on the Mississippi River system and delta

The U.S. Geological Survey Forecast Mekong project is providing technical assistance and information to aid management decisions and build science capacity of institutions in the Mekong River Basin. A component of this effort is to produce a synthesis of the effects of dams and other engineering structures on large-river hydrology, sediment transport, geomorphology, ecology, water quality, and deltaic systems. The Mississippi River Basin (MRB) of the United States was used as the backdrop and context for this synthesis because it is a continental scale river system with a total annual water discharge proportional to the Mekong River, has been highly engineered over the past two centuries, and the effects of engineering have been widely studied and documented by scientists and engineers. The MRB is controlled and regulated by dams and river-engineering structures. These modifications have resulted in multiple benefits including navigation, flood control, hydropower, bank stabilization, and recreation. Dams and other river-engineering structures in the MRB have afforded the United States substantial socioeconomic benefits; however, these benefits also have transformed the hydrologic, sediment transport, geomorphic, water-quality, and ecologic characteristics of the river and its delta. Large dams on the middle Missouri River have substantially reduced the magnitude of peak floods, increased base discharges, and reduced the overall variability of intraannual discharges. The extensive system of levees and wing dikes throughout the MRB, although providing protection from intermediate magnitude floods, have reduced overall channel capacity and increased flood stage by up to 4 meters for higher magnitude floods. Prior to major river engineering, the estimated average annual sediment yield of the Mississippi River Basin was approximately 400 million metric tons. The construction of large main-channel reservoirs on the Missouri and Arkansas Rivers, sedimentation in dike fields, and protection of channel banks by revetments throughout the basin, have reduced the overall sediment yield of the MRB by more than 60 percent. The primary alterations to channel morphology by dams and other engineering projects have been (1) channel simplification and reduced dynamism; (2) lowering of channel-bed elevation; and (3) disconnection of the river channel from the flood plain, except during extreme flood events. Freshwater discharge from the Mississippi River and its associated sediment and nutrient loads strongly influence the physical and biological components in the northern Gulf of Mexico. Ninety percent of the nitrogen load reaching the Gulf of Mexico is from nonpoint sources with about 60 percent coming from fertilizer and mineralized soil nitrogen. Much of the phosphorus is from animal manure from pasture and rangelands followed by fertilizer applied to corn and soybeans. Increased nutrient enrichment in the northern Gulf of Mexico has resulted in the degradation of water quality as more phytoplankton grow, which increases turbidity and depletes oxygen in the lower depths creating what is known as the "dead zone." In 2002, the dead zone was 22,000 square kilometers (km2), an area similar to the size of the State of Massachusetts. Changes in the flow regime from engineered structures have had direct and indirect effects on the fish communities. The navigation pools in the upper Mississippi River have aged, and these overwintering habitats, which were created when the pools filled, have declined as sedimentation reduces water depth. Reproduction of paddlefish may have been adversely affected by dams, which impede access to suitable spawning habitats. Fishes that inhabit swift-current habitats in the unimpounded lower Mississippi River have not declined as much as in the upper Mississippi River. The decline of the pallid sturgeon may be attributable to channelization of the Missouri River above St. Louis, Missouri. The Missouri River supports a rich fish community and remains relatively intact. Nevertheless, the widespread and long history of human intervention in river discharge has contributed to the declines of about 25 percent of the species. The Mississippi River Delta Plain is built from six delta complexes composed of a massive area of coastal wetlands that support the largest commercial fishery in the conterminous United States. Since the early 20th century, approximately 4,900 km2 of coastal lands have been lost in Louisiana. One of the primary mechanisms of wetland loss on the Plaquemines-Balize complex is believed to be the disconnection of the river distributary network from the delta plain by the massive system of levees on the delta top, which prevent overbank flooding and replenishment of the delta top by sediment and nutrient deliveries. Efforts by Federal and State agencies to conserve and restore the Mississippi River Delta Plain began over three decades ago and have accelerated over the past decade. Regardless of these efforts, however, land losses are expected to continue because the reduced upstream sediment supplies are not sufficient to keep up with the projected depositional space being created by the combined forces of delta plain subsidence and global sea-level rise.

Alabama;Alberta;Arkansas;Colorado;Georgia;Illinois

Nutrient, suspended sediment, and trace element loads in the Blackstone River Basin in Massachusetts and Rhode Island, 2007 to 2009

Nutrients, suspended sediment, and trace element loads in the Blackstone River and selected tributaries were estimated from composite water-quality samples in order to better understand the distribution and sources of these constituents in the river basin. The flow-proportional composite water-quality samples were collected during sequential 2-week periods at six stations along the river’s main stem, at three stations on tributaries, and at four wastewater treatment plants in the Massachusetts segment of the basin from June 2007 to September 2009. Samples were collected at an additional station on the Blackstone River near the mouth in Pawtucket, Rhode Island, from September 2008 to September 2009. The flow-proportional composite samples were used to estimate average daily loads during the sampling periods; annual loads for water years 2008 and 2009 also were estimated for the monitoring station on the Blackstone River near the Massachusetts-Rhode Island border. The effects of hydrologic conditions and net attenuation of nitrogen were investigated for loads in the Massachusetts segment of the basin. Sediment resuspension and contaminant loading dynamics were evaluated in two Blackstone River impoundments, the former Rockdale Pond (a breached impoundment) and Rice City Pond. Total nitrogen and phosphorus loads along the Blackstone River in Massachusetts showed similar general patterns during the sampling periods monitored in this study. Total nitrogen loads were relatively low at the farthest upstream monitoring station in Millbury, Massachusetts (typically less than 430 kilograms per day (kg/d) for total nitrogen and 37 kg/d for total phosphorus). Loads typically increased (5- to 10-fold for nitrogen and 6- to 15-fold for phosphorus) downstream from the first, large wastewater treatment plant along the river, the Upper Blackstone Water Pollution Control Abatement District in Millbury. Further downstream, total nitrogen and phosphorus loads remained elevated but variable (typically about 1,000 to 3,000 kg/d for nitrogen and about 100 to 370 kg/d for phosphorus) from Millbury to the Massachusetts-Rhode Island border near Millville, Mass. Monitored tributaries of the Blackstone River and wastewater treatment plants other than the Upper Blackstone Water Pollution Control Abatement District rarely contributed more than a small fraction of the total nitrogen and phosphorus loads observed at the main stem monitoring stations. Loads of suspended sediment also were substantially larger along the river’s main stem than in tributaries during most sampling periods. Very large loads of suspended sediment from the West River tributary during several sampling periods may have been associated with flood-control operations. The estimated annual load of total nitrogen in the Blackstone River at Millville, about 1.3 miles upstream from the Massachusetts-Rhode Island border, was 936,000 kilograms (kg) (2,600 kg/d) in water year 2008 and 878,000 kg (2,400 kg/d) in water year 2009. The estimated annual load of total phosphorus at Millville was 81,400 kg in water year 2008 (223 kg/d) and 80,900 kg (222 kg/d) in water year 2009. The estimated annual load of suspended sediment in was 4,940,000 kg (13,600 kg/d) in water year 2008 and 7,040,000 kg (19,300 kg/d) in water year 2009. The higher load in water year 2009 likely reflects several large storms in summer 2009, which resulted in streamflows in the Blackstone River that were 10 times the typical July flows. Loads of total nitrogen, total phosphorus, and trace elements were almost always lower in the Blackstone River at Millville than in the river near its mouth at the Pawtucket monitoring station, when loads were monitored at both stations in the latter part of water year 2008 and in water year 2009. Loads of suspended sediment at Millville and Pawtucket varied by about the same range, but were usually lower at Pawtucket than at Millville. Total nitrogen loads were higher during sampling periods when the base-flow contribution to streamflow was substantially less than the runoff contribution than in sampling periods when the base-flow dominated. During these sampling periods when the runoff component of streamflow was relatively large, loads of total nitrogen in wastewater discharge from Upper Blackstone Water Pollution Control Abatement District also were high but also constituted smaller fractions of the total nitrogen loads in the river. Nitrogen attenuation may have occurred during some sampling periods, based on net changes in total nitrogen load between consecutive monitoring stations, especially in the Blackstone River reach between the South Grafton and Uxbridge monitoring stations. Analysis of the representative constituents (total phosphorus, total chromium, and suspended sediment) upstream and downstream of impoundments indicated that the existing impoundments, such as Rice City Pond, can be sources of particulate contaminant loads in the Blackstone River. Loads of particulate phosphorus, particulate chromium, and suspended sediment were consistently higher downstream from Rice City Pond than upstream during high-flow events, and there was a positive, linear relation between streamflow and changes in these constituents from upstream to downstream of the impoundment. Thus, particulate contaminants were mobilized from Rice City Pond during high-flow events and transported downstream. In contrast, downstream loads of particulate phosphorus, particulate chromium, and suspended sediment were generally lower than or equal to upstream loads for the former Rockdale Pond impoundment. Sediments associated with the former impoundment at Rockdale Pond, breached in the late 1960s, did not appear to be mobilized during the high-flow events monitored during this study.

Massachusetts, Rhode Island

Simulated water sources and effects of pumping on surface and ground water, Sagamore and Monomoy flow lenses, Cape Cod, Massachusetts

The sandy sediments underlying Cape Cod, Massachusetts, compose an important aquifer that is the sole source of water for a region undergoing rapid development. Population increases and urbanization on Cape Cod lead to two primary environmental effects that relate directly to water supply: (1) adverse effects of land use on the quality of water in the aquifer and (2) increases in pumping that can adversely affect environmentally sensitive surface waters, such as ponds and streams. These considerations are particularly important on the Sagamore and Monomoy flow lenses, which underlie the largest and most populous areas on Cape Cod. Numerical models of the two flow lenses were developed to simulate ground-water-flow conditions in the aquifer and to (1) delineate areas at the water table contributing water to wells and (2) estimate the effects of pumping and natural changes in recharge on surface waters. About 350 million gallons per day (Mgal/d) of water recharges the aquifer at the water table in this area; most water (about 65 percent) discharges at the coast and most of the remaining water (about 28 percent) discharges into streams. A total of about 24.9 Mgal/d, or about 7 percent, of water in the aquifer is withdrawn for water supply; most pumped water is returned to the hydrologic system as return flow creating a state of near mass balance in the aquifer. Areas at the water table that contribute water directly to production wells total about 17 square miles; some water (about 10 percent) pumped from the wells flows through ponds prior to reaching the wells. Current (2003) steady-state pumping reduces simulated ground-water levels in some areas by more than 4 feet; projected (2020) pumping may reduce water levels by an additional 3 feet or more in these same areas. Current (2003) and future (2020) pumping reduces total streamflow by about 4 and 9 cubic feet per second (ft3/s), corresponding to about 5 percent and 9 percent, respectively, of total streamflow. Natural recharge varies with time, over both monthly and multiyear time scales. Monthly changes in recharge cause pond levels to vary between 1 and 2 feet in an average year; annual changes in recharge, which can be much larger than monthly variations, can cause pond levels to vary by more than 10 feet in some areas over a period of years. Streamflow, which also changes in response to changes in recharge, varies by a factor of two over an average year and can vary more over multiyear periods. On average, monthly pumping ranges from 15.8 Mgal/d in March to 45.3 Mgal/d in August. Pumping and the distribution of return flow can seasonally affect the hydrologic system by lowering ground-water and pond levels and by depleting streamflows, particularly in the summer months. Maximum drawdowns in March and August exceed 3 feet and 6 feet, respectively, for current (2003) pumping. Simulated drawdowns from projected (2020) pumping, relative to water levels representing 2003 pumping conditions, exceed 2 feet in March and 5 feet in August. Current (2003) and future (2020) pumping can decrease pond levels in some areas by more than 3 feet; drawdown generally is largest during the month of August of an average year. Over multiyear periods, seasonal pumping can lower pond levels in some areas by more than 4 feet; the effects of seasonal pumping are largest during periods of reduced recharge. Monthly streamflow depletion varies in individual streams but can exceed 2 ft3/s in some streams. The combined effects of seasonal pumping and drought can reduce pond levels by more than 10 feet below average levels. Water levels in Mary Dunn Pond, which is in an area of large current and projected pumping, are predicted (2020) to decline during drought conditions by about 10.6 feet: about 6.9 feet from lower recharge, about 2.3 feet from current (2003) pumping, and about 1.4 feet from additional future (2020) pumping. The results indicate that pumping generally does not cause substantial streamflow depletion and that the primary effect of pumping is on water levels in ponds. Natural changes in recharge account for most of the variation in pond levels; however, pumping can cause substantial declines in the levels of ponds near pumping wells. Also, the effects of pumping and recharge can combine to cause drawdowns of more than 10 feet in some areas.

Massachusetts

Evaluation of Streamflow Requirements for Habitat Protection by Comparison to Streamflow Characteristics at Index Streamflow-Gaging Stations in Southern New England

Streamflow characteristics and methods for determining streamflow requirements for habitat protection were investigated at 23 active index streamflow-gaging stations in southern New England. Fish communities sampled near index streamflow-gaging stations in Massachusetts have a high percentage of fish that require flowing-water habitats for some or all of their life cycle. The relatively unaltered flow condition at these sites was assumed to be one factor that has contributed to this condition. Monthly flow durations and low flow statistics were determined for the index streamflow-gaging stations for a 25- year period from 1976 to 2000. Annual hydrographs were prepared for each index station from median streamflows at the 50-percent monthly flow duration, normalized by drainage area. A median monthly flow of 1 ft 3 /s/mi 2 was used to split hydrographs into a high-flow period (November–May), and a low-flow period (June–October). The hydrographs were used to classify index stations into groups with similar median monthly flow durations. Index stations were divided into four regional groups, roughly paralleling the coast, to characterize streamflows for November to May; and into two groups, on the basis of base-flow index and percentage of sand and gravel in the contributing area, for June to October. For the June to October period, for index stations with a high base-flow index and contributing areas greater than 20 percent sand and gravel, median streamflows at the 50-percent monthly flow duration, normalized by drainage area, were 0.57, 0.49, and 0.46 ft 3 /s/mi 2 for July, August, and September, respectively. For index stations with a low base-flow index and contributing areas less than 20 percent sand and gravel, median streamflows at the 50-percent monthly flow duration, normalized by drainage area, were 0.34, 0.28, and 0.27 ft 3 /s/mi 2 for July, August, and September, respectively. Streamflow variability between wet and dry years can be characterized by use of the interquartile range of median streamflows at selected monthly flow durations. For example, the median Q50 discharge for August had an interquartile range of 0.30 to 0.87 ft 3 /s/mi 2 for the high-flow group and 0.16 to 0.47 ft 3 /s/mi 2 for the low-flow group. Streamflow requirements for habitat protection were determined for 23 index stations by use of three methods based on hydrologic records, the Range of Variability Approach, the Tennant method, and the New England Aquatic-Base-Flow method. Normalized flow management targets determined by the Range of Variability Approach for July, August, and September ranged between 0.21 and 0.84 ft 3 /s/mi 2 for the low monthly flow duration group, and 0.37 and 1.27 ft 3 /s/mi 2 for the high monthly flow duration group. Median streamflow requirements for habitat protection during summer for the 23 index streamflow-gaging stations determined by the Tennant method, normalized by drainage area, were 0.81, 0.61, and 0.21 ft 3 /s/mi 2 for the Tennant 40-, 30-, and 10-percent of the mean annual flow methods, representing good, fair, and poor stream habitat conditions in summer, according to Tennant. New England Aquatic-Base-Flow streamflow requirements for habitat protection during summer were determined from median of monthly mean flows for August for index streamflow-gaging stations having drainage areas greater than 50 mi 2 . For five index streamflow-gaging stations in the low median monthly flow group, the average median monthly mean streamflow for August, normalized by drainage area, was 0.48 ft 3 /s/mi 2 . Streamflow requirements for habitat protection were determined for riffle habitats near 10 index stations by use of two methods based on hydraulic ratings, the Wetted-Perimeter and R2Cross methods. Hydraulic parameters required by these methods were simulated by calibrated HEC-RAS models. Wetted-Perimeter streamflow requirements for habitat protection, normalized by drainage area, ranged between 0.13 and 0.58 ft 3 /s/mi 2 , and had a median value of 0.37 ft 3 /s/mi 2 . Streamflow requirements determined by the R2Cross 3-of-3 criteria method ranged between 0.39 and 2.1 ft 3 /s/mi 2 , and had a median of 0.84 ft 3 /s/mi 2 . Streamflow requirements determined by the R2Cross 2-of-3 criteria method, normalized by drainage area, ranged between 0.16 and 0.85 ft 3 /s/mi 2 and had a median of 0.36 ft 3 /s/mi 2 , respectively. Streamflow requirements determined by the different methods were evaluated by comparison to streamflow statistics from the index streamflow-gaging stations.

Water-Resources Investigations Report

Effects of low-impact-development (LID) practices on streamflow, runoff quantity, and runoff quality in the Ipswich River Basin, Massachusetts: A summary of field and modeling studies

Low-impact-development (LID) approaches are intended to create, retain, or restore natural hydrologic and water-quality conditions that may be affected by human alterations. Wide-scale implementation of LID techniques may offer the possibility of improving conditions in river basins, such as the Ipswich River Basin in Massachusetts, that have run dry during the summer because of groundwater withdrawals and drought. From 2005 to 2008, the U.S. Geological Survey, in a cooperative funding agreement with the Massachusetts Department of Conservation and Recreation, monitored small-scale installations of LID enhancements designed to diminish the effects of storm runoff on the quantity and quality of surface water and groundwater. Funding for the studies also was contributed by the U.S. Environmental Protection Agency’s Targeted Watersheds Grant Program through a financial assistance agreement with Massachusetts Department of Conservation and Recreation. The monitoring studies examined the effects of replacing an impervious parking-lot surface with a porous surface on groundwater quality, installing rain gardens and porous pavement in a neighborhood of 3 acres on the quantity and quality of stormwater runoff, and installing a 3,000-ft2 (square-foot) green roof on the quantity and quality of rainfall-generated roof runoff. In addition to these small-scale installations, the U.S. Geological Survey’s Ipswich River Basin model was used to simulate the basin-wide effects on streamflow of several changes: broad-scale implementation of LID techniques, reduced water-supply withdrawals, and water-conservation measures. Water-supply and conservation scenarios for application in model simulations were developed with the assistance of two technical advisory committees that included representatives of State agencies responsible for water resources, the U.S. Environmental Protection Agency, the U.S. Geological Survey, water suppliers, and non-governmental organizations. From June 2005 to June 2007, groundwater quality was monitored at the Silver Lake town beach parking lot in Wilmington, Massachusetts, prior to and following the replacement of the conventional, impervious-asphalt surface with a porous surface consisting primarily of porous asphalt and porous pavers designed to enhance rainfall infiltration into the groundwater and to minimize runoff to Silver Lake. Concentrations of phosphorus, nitrogen, cadmium, chromium, copper, lead, nickel, zinc, and total petroleum hydrocarbons in groundwater were monitored. Enhancing infiltration of precipitation did not result in discernible increases in concentrations of these potential groundwater contaminants. Concentrations of dissolved oxygen increased slightly in groundwater profiles following the removal of the impervious asphalt parking-lot surface. In Wilmington, Massachusetts, in a 3-acre neighborhood, stormwater runoff volume and quality were monitored to determine the ability of selected LID enhancements (rain gardens and porous paving stones) to reduce flows and loads of the selected constituents to Silver Lake. Water-quality samples were analyzed for nutrients, metals, total petroleum hydrocarbons, and total-coliform and E. coli bacteria. A decrease in runoff quantity was observed for storms of 0.25 inch or less of precipitation. Water-quality-monitoring results were inconclusive; there were no statistically significant differences in concentrations or loads when the pre- and post-installation-period samples were compared. In a third field study, the characteristics of runoff from a vegetated "green" roof and a conventional, rubber-membrane roof were compared. The two primary factors affecting the green roof’s water-storage capacity were the amount of precipitation and antecedent dry period. Although concentrations of many of the chemicals in roof runoff were higher from the green roof than from the conventional roof, the ability of the green roof to retain water generally resulted in decreased differences between the total amounts (loads) of the chemicals that ran off the roofs. Land-use and water-management changes associated with LID implementation were investigated at multiple spatial scales, using the U.S. Geological Survey’s Ipswich River Basin model, to evaluate the effects of updated water-supply withdrawals for the towns of Reading and Wilmington (representing new baseline conditions for all simulations), potential land-use changes at buildout (potential future development), widespread implementation of retrofitting LID techniques, basin-scale water withdrawal reductions based on water-conservation pilot programs conducted by the Massachusetts Department of Conservation and Recreation, and land-use change and LID applications at a local scale. The new baseline simulation indicated that reduced water-supply withdrawals for the towns of Reading and Wilmington led to substantially higher medium and low flows in most of the reaches upstream from the South Middleton streamgage in the upper Ipswich River basin. Overall, simulations pointed to the importance of spatial scale in determining the effects of land-use change and LID practices on streamflow. Potential land-use changes at buildout had modest effects on streamflow in most subbasins (percent differences of less than 20 percent) because relatively little land in the basin was available for development. Results of the simulations conducted to evaluate widespread effective-impervious-area reductions upstream from the South Middleton streamgage indicated that the percentages of urban land use and associated effective impervious area were too small for even a 50-percent reduction of effective impervious area to appreciably affect streamflow in most subbasins. In contrast, the results of the hypothetical local-scale simulations indicated that for smaller streams, with high percentages of urban land use and associated effective impervious area, land-use change, development patterns, and LID practices may have substantial effects on streamflow. Modeling studies concurred with the results of fieldwork in the assessment that LID enhancements would likely have the greatest effect on decreasing stormwater runoff when broadly applied to highly impervious urban areas.

Massachusetts

Simulation of the effects of water withdrawals, wastewater-return flows, and land-use change on streamflow in the Blackstone River basin, Massachusetts and Rhode Island

Streamflow in many parts of the Blackstone River Basin in south-central Massachusetts and northern Rhode Island is altered by water-supply withdrawals, wastewater-return flows, and land-use change associated with a growing population. Simulations from a previously developed and calibrated Hydrological Simulation Program—FORTRAN (HSPF) precipitation-runoff model for the basin were used to evaluate the effects of water withdrawals, wastewater-return flows, and land-use change on streamflow. Most of the simulations were done for recent (1996–2001) conditions and potential buildout conditions in the future when all available land is developed to provide a long-range assessment of the effects of possible future human activities on water resources in the basin. The effects of land-use change were evaluated by comparing the results of long-term (1960–2004) simulations with (1) undeveloped land use, (2) 1995–1999 land use, and (3) potential buildout land use at selected sites across the basin. Flow-duration curves for these land-use scenarios were similar, indicating that land-use change, as represented in the HSPF model, had little effect on flow in the major tributary streams and rivers in the basin. However, land-use change—particularly increased effective impervious area—could potentially have greater effects on the hydrology, water quality, and aquatic habitat of the smaller streams in the basin. The effects of water withdrawals and wastewater-return flows were evaluated by comparing the results of long-term simulations with (1) no withdrawals and return flows, (2) actual (measured) 1996–2001 withdrawals and wastewater-return flows, and (3) potential withdrawals and wastewater-return flows at buildout. Overall, the results indicated that water use had a much larger effect on streamflow than did land use, and that the location and magnitude of wastewater-return flows were important for lessening the effects of withdrawals on streamflow in the Blackstone River Basin. Ratios of long-term (1960–2004) simulated flows with 1996–2001 water use (representing the net effect of withdrawals and wastewater-return flows) to long-term simulated flows with no water use indicated that, for many reaches, 1996–2001 water use did not deplete flows at the 90-percent flow duration substantially compared to flows unaffected by water use. Flows generally were more severely depleted in the reaches that include surface-water supplies for the larger cities in the basin (Kettle and Tatnuck Brooks, Worcester, Mass. water supply; Quinsigamond River, Shrewsbury, Mass. water supply; Crookfall Brook, Woonsocket, R.I. water supply; and Abbott Run, Pawtucket, R.I. water supply). These reaches did not have substantial wastewater-return flows that could offset the effects of the withdrawals. In contrast, wastewater-return flows from the Upper Blackstone Wastewater Treatment Facility in Millbury, Mass. increased flows at the 90-percent flow duration in the main stem of the Blackstone River compared to no-water-use conditions. Under the assumptions used to develop the buildout scenario, nearly all of the new water withdrawals were returned to the Blackstone River Basin at municipal wastewater-treatment plants or on-site septic systems. Consequently, buildout generally had small effects on simulated low flows in the Blackstone River and most of the major tributary streams compared to flows with 1996–2001 water use. To evaluate the effects of water use on flows in the rivers and major tributary streams in the Rhode Island part of the basin in greater detail, the magnitudes of water withdrawals and wastewater-return flows in relation to simulated streamflow were calculated as unique ratios for individual HSPF subbasins, total contributing areas to HSPF subbasins, and total contributing areas to the major tributary streams. For recent conditions (1996–2001 withdrawals and 1995–1999 land use), ratios of average summer (June through September) withdrawals to the long-term (1960–2004) medians of average summer streamflow simulated in the absence of water use ranged from 0.039 to 2.5 with a median value of 0.11 for total contributing areas to HSPF subbasins. The largest ratios of withdrawal rates to streamflow were for Crookfall Brook and Abbott Run, the subbasins with major withdrawals for municipal water supply. The smallest ratios were for the rural subbasins in the Branch River drainage area in the southwestern part of the basin. For recent conditions, ratios of average summer wastewater-return flows to average summer streamflows ranged from 0.0 to 0.20 with a median value of 0.029 for total contributing areas to HSPF subbasins. The largest ratios of wastewater-return flows to streamflows were for the subbasins that contained return flows from municipal wastewater-treatment plants and the subbasins along the Blackstone River because of high wastewater-return-flow rates from upstream facilities. Under the assumptions used to develop the buildout analysis, withdrawal and return-flow ratios were estimated to increase for most of the HSPF subbasins in the Rhode Island part of the basin. Ratios more than doubled for some subbasins, but the large increases mainly were for subbasins that had low ratios in 1996–2001. The HSPF model also was used to estimate the effects of water-conservation measures on low flows in rivers and major tributary streams in the Rhode Island part of the basin, the contribution of wastewater-return flows to streamflow in the Blackstone River, and the effects of changes to two local water supplies in Rhode Island. Water-conservation measures were evaluated by reducing 1996–2001 withdrawals by 20 percent. Simulations with 20-percent reductions in withdrawal rates indicated that conservation measures would result in appreciable increases in low flows in the subbasins with the highest withdrawal rates in the Rhode Island part of the Blackstone River Basin, whereas the effects on streamflow would be much less pronounced in subbasins with lower withdrawal rates. The contribution of wastewater-return flows to streamflow in the Blackstone River was evaluated by comparing simulated flows with and without municipal wastewater-return flows. Under typical summer low-flow conditions, treated wastewater was a major component of streamflow (35 to 50 percent) in the Blackstone River, and the percentage of treated wastewater was larger during the driest periods. The simulations conducted to evaluate changes to local water supplies (effects of potential withdrawals from an inactive well adjacent to Slatersville Reservoir in North Smithfield on flows in the Branch River, and the effects of connecting the town of North Smithfield to the water-supply system for the city of Woonsocket, Rhode Island) indicated that each of these activities would alter low flows only slightly in the associated stream reaches.

Massachusetts, Rhode Island