THIS PAGE INTENTIONALLY LEFT BLANK Prepared in cooperation with the Massachusetts Department of Environmental Protection Refinement and Evaluation of the Massachusetts Firm-Yield Estimator Model Version 2.0 Scientific Investigations Report 2011–5125 U.S. Department of the Interior U.S. Geological Survey Cover. Top: Gatehouse at Flints (Sandy) Pond in Lincoln, Massachusetts. Bottom: Water entering Holden Pond #1 from Kendall Reservoir, Holden, Massachusetts. Refinement and Evaluation of the Massachusetts Firm-Yield Estimator Model Version 2.0 By Sara B. Levin, Stacey A. Archfield, and Andrew J. Massey Prepared in cooperation with the Massachusetts Department of Environmental Protection Scientific Investigations Report 2011–5125 U.S. Department of the Interior U.S. Geological Survey U.S. Department of the Interior KEN SALAZAR, Secretary U.S. Geological Survey Marcia K. McNutt, Director U.S. Geological Survey, Reston, Virginia: 2011 Revised: October 2011 For more information on the USGS—the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment, visit http://www.usgs.gov or call 1–888–ASK–USGS. For an overview of USGS information products, including maps, imagery, and publications, visit http://www.usgs.gov/pubprod To order this and other USGS information products, visit http://store.usgs.gov Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Although this report is in the public domain, permission must be secured from the individual copyright owners to reproduce any copyrighted materials contained within this report. Suggested citation: Levin, S.B., Archfield, S.A., and Massey, A.J., 2011, Refinement and evaluation of the Massachusetts firm-yield estimator model version 2.0: U.S. Geological Survey Scientific Investigations Report 2011–5125, 49 p., plus CD–ROM (Also available at http://pubs.usgs.gov/sir/2011/5125.) iii Acknowledgments The authors thank Thomas Lamonte and Kari Winfield of the Massachusetts Department of Environmental Protection and Linda Hutchins of the Massachusetts Department of Conservation and Recreation for their technical reviews of this report. The authors thank U.S. Geological Survey colleagues Marcus C. Waldron and Robert Dudley for their reviews and Lance Ostiguy for his help in the processing of bathymetric measurement data. THIS PAGE INTENTIONALLY LEFT BLANK v Contents Abstract ...........................................................................................................................................................1 Introduction.....................................................................................................................................................1 Purpose and Scope ..............................................................................................................................2 Refinements to the Existing Firm-Yield Estimator Model ........................................................................2 Bathymetry and Stage-Storage Relations ........................................................................................3 Surface-Water Inflows ........................................................................................................................7 Precipitation and Evaporation ............................................................................................................7 Groundwater Contributions ...............................................................................................................13 Applications of the Firm-Yield Estimator Model .....................................................................................14 Application of the Firm-Yield Estimator Model to a Single-Reservoir System .........................14 Application of the Firm-Yield Estimator Model to a Multiple-Reservoir System ......................14 Firm-Yield Estimate Uncertainty and Sensitivity to Model Inputs........................................................16 Sensitivity of Firm-Yield Estimates to Errors in Daily Streamflow...............................................16 Sensitivity of the Firm-Yield Model to Bathymetric-Map Accuracy...........................................20 Validation of Groundwater Parameters ..........................................................................................25 Effect of Drought Severity on Firm-Yield Estimates ...............................................................................26 Effect of Controlled Releases and Demand Management on Firm Yield ............................................33 Controlled-Release Scenarios ..........................................................................................................33 Summer Water-Demand Management ...........................................................................................36 Reducing Reservoir Reliability Requirements ................................................................................37 Tradeoffs Between Demand Management, Controlled Releases, and Reliability ...................37 Summary and Conclusions .........................................................................................................................39 References Cited..........................................................................................................................................40 Appendix 1. Hypsographic Data ............................................................................................................43 Appendix 2. Bathymetric Maps ..............................................................................................................45 Appendix 3. Reservoir-System Diagrams .............................................................................................47 Appendix 4. Monthly Percentile Streamflows .....................................................................................49 vi Figures 1. Map showing locations of drainage areas for 71 drinking-water reservoirs in Massachusetts ..............................................................................................................................4 2. Maps showing location of reservoirs and record length at A, precipitation stations and validations sites, and B, meteorological stations in Massachusetts and vicinity ...12 3. Diagrams showing water balances for a system of reservoirs in which A, water is transported by gravity and B, water is pumped from Reservoir 1 to Reservoir 2 ............17 4. Scatterplots showing A, mean percent difference and B, standard deviation of the percent difference of daily streamflows generated by the Sustainable Yield Estimator at 18 U.S. Geological Survey gaged sites in Massachusetts ..............................................19 5. Boxplot showing percent change in firm yield of selected reservoirs in Massachusetts after accounting for potential errors in daily streamflow in 500 Monte Carlo simulations ............................................................................................................21 6. Diagrams showing original and hypothetical 30-meter transect spacing for Upper Sackett Reservoir in Pittsfield, Massachusetts .....................................................................23 7. Graphs showing A–C, percent change in reservoir storage capacity and D–F, firm yield, resulting from transect spacings and patterns for three study reservoirs in Massachusetts ............................................................................................................................24 8. Graph showing daily simulated and observed reservoir stage for Atkins Reservoir in Amherst, Massachusetts ..........................................................................................................26 9. Graph showing daily simulated and observed reservoir stage for Nagog Pond in Concord, Massachusetts ..........................................................................................................27 10. Boxplots showing A, percent below average streamflow and B, duration of droughts of the 1960s, 1980s, and 2002. C, Percent change in firm yield and D, reliability of firm yields when calculated with the droughts of the 1980s or 2002 .........................................32 11. Graph showing maximum monthly releases as a percentile of long-term monthly flows that is possible at various demand ratios for four reservoirs of increasing storage ratio ................................................................................................................................36 12. Boxplot showing percent changes of firm yield for Massachusetts reservoirs under various management scenarios ...............................................................................................38 13. Graph showing tradeoff curves depicting the estimated yield in relation to controlled releases under various management scenarios for Upper Leahy Reservoir, in Lee, Massachusetts ............................................................................................................................39 vii Tables 1. Massachusetts drinking-water-supply systems and associated reservoirs included in this study ....................................................................................................................................5 2. Reservoir basin characteristics and index streamgages in Massachusetts used in the Sustainable Yield Estimator ..................................................................................................8