Flood-Inundation Maps for Cayuga Inlet, Sixmile Creek, Cascadilla Creek, and Fall Creek at Ithaca, New York Flood-Inundation
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Prepared in cooperation with the City of Ithaca, New York, and the New York State Department of State Flood-Inundation Maps for Cayuga Inlet, Sixmile Creek, Cascadilla Creek, and Fall Creek at Ithaca, New York Scientific Investigations Report 2018–5167 U.S. Department of the Interior U.S. Geological Survey Cover. Ithaca Falls on Fall Creek in Ithaca, New York. Photograph by Elizabeth Nystrom, U.S. Geological Survey. Flood-Inundation Maps for Cayuga Inlet, Sixmile Creek, Cascadilla Creek, and Fall Creek at Ithaca, New York By Elizabeth A. Nystrom, Arthur G. Lilienthal III, and William F. Coon Prepared in cooperation with the City of Ithaca, New York, and the New York State Department of State Scientific Investigations Report 2018–5167 U.S. Department of the Interior U.S. Geological Survey U.S. Department of the Interior RYAN K. ZINKE, Secretary U.S. Geological Survey James F. Reilly II, Director U.S. Geological Survey, Reston, Virginia: 2018 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 https://www.usgs.gov or call 1–888–ASK–USGS. For an overview of USGS information products, including maps, imagery, and publications, visit https://store.usgs.gov. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner. Suggested citation: Nystrom, E.A., Lilienthal, A.G., III, and Coon, W.F., 2018, Flood-inundation maps for Cayuga Inlet, Sixmile Creek, Cascadilla Creek, and Fall Creek at Ithaca, New York: U.S. Geological Survey Scientific Investigations Report 2018– 5167, 27 p., https://doi.org/10.3133/sir20185167. ISSN 2328-0328 (online) iii Acknowledgments The authors wish to thank the City of Ithaca Department of Public Works, Cornell University, the New York State Department of Environmental Conservation, and the New York State Canal Corporation for funding the operation and maintenance of gages whose discharge or stage records were used as part of this study. iv v Contents Acknowledgments ........................................................................................................................................iii Abstract ...........................................................................................................................................................1 Introduction.....................................................................................................................................................1 Purpose and Scope ..............................................................................................................................3 Study Area Description ........................................................................................................................4 Previous Studies ...................................................................................................................................7 Creation of Flood-Inundation-Map Library ................................................................................................9 Computation of Water-Surface Profiles ............................................................................................9 Hydrologic Data............................................................................................................................9 Topographic and Bathymetric Data ........................................................................................10 Hydraulic Structures .................................................................................................................11 Energy-Loss Factors ..................................................................................................................11 Hydraulic Model .........................................................................................................................11 Development of Flood-Inundation Maps ........................................................................................19 Disclaimer For Flood-Inundation Maps ..................................................................................25 Uncertainties and Limitations Regarding Use of Flood-Inundation Maps .......................25 Summary........................................................................................................................................................25 References Cited..........................................................................................................................................26 Figures 1. Map showing study area in Ithaca, New York .........................................................................2 2. Map showing topography in and around the study area in Ithaca, New York, and locations of nearby U.S. Geological Survey gages .................................................................5 3. Map showing land cover of the study area in Ithaca, New York ..........................................6 4. Graphs showing unsteady-flow time series used in the hydraulic model for Ithaca, New York .........................................................................................................................10 5. Map showing topography and hydraulic model geometry for the study area in Ithaca, New York .........................................................................................................................12 6. Graph showing observed water-surface elevations and simulated water-surface profiles for the flood of June 14, 2015, for Cayuga Inlet at Ithaca, New York ...................16 7. Graph showing observed water-surface elevations and simulated water-surface profiles for the floods of February 25, 2016, April 7, 2017, April 21, 2017, and October 30, 2017, for Sixmile Creek at Ithaca, New York .....................................................17 8. Graph showing observed water-surface elevations and simulated water-surface profiles for the floods of February 25, 2016, April 21, 2017, and October 30, 2017, for Cascadilla Creek at Ithaca, New York ...............................................................................18 9. Graph showing observed water-surface elevations and simulated water-surface profiles for the floods of February 25, 2016, April 7, 2017, April 21, 2017, and October 30, 2017, for Fall Creek at Ithaca, New York ............................................................19 10. Flood-inundation map for Ithaca, New York, corresponding to an annual exceedance probability of 50 percent (or a 2-year recurrence interval) and to Cayuga Lake water-surface elevations of 380.38 feet (ft), 382.88 ft, and 385.68 ft ...........20 vi 11. Flood-inundation map for Ithaca, New York, corresponding to an annual exceedance probability of 10 percent (or a 10-year recurrence interval) and to Cayuga Lake water-surface elevations of 380.38 feet (ft), 382.88 ft, and 385.68 ft ...........21 12. Flood-inundation map for Ithaca, New York, corresponding to an annual exceedance probability of 2 percent (or a 50-year recurrence interval) and to Cayuga Lake water-surface elevations of 380.38 feet (ft), 382.88 ft, and 385.68 ft ...........22 13. Flood-inundation map for the Ithaca, New York, corresponding to an annual exceedance probability of 1 percent (or a 100-year recurrence interval) and to Cayuga Lake water-surface elevations of 380.38 feet (ft), 382.88 ft, and 385.68 ft ...........23 14. Flood-inundation map for the Ithaca, New York, corresponding to an annual exceedance probability of 0.2 percent (or a 500-year recurrence interval) and to Cayuga Lake water-surface elevations of 380.38 feet (ft), 382.88 ft, and 385.68 ft ...........24 Tables 1. Estimated peak flows for corresponding annual exceedance probabilities (or recurrence intervals) at upstream end of study reaches used in the hydraulic model of Ithaca, New York ..........................................................................................................3 2. Cayuga Lake water-surface elevations used in the hydraulic model of Ithaca, New York ........................................................................................................................................3 3. Drainage areas of modeled reaches in Ithaca, New York .....................................................4 4. U.S. Geological Survey stations near Ithaca, New York ........................................................8 5. Bridges and other structures crossing streams in the study area, Ithaca, New York ......9 6. Calibration of model to water-surface elevations at selected locations in Ithaca, New York, along Cayuga Inlet, Sixmile Creek, Cascadilla Creek, and Fall Creek for the high flows of June 14, 2015, February 25, 2016, April 7, 2017, April 21, 2017, and October 30, 2017 ..................................................................................................................14 vii Conversion Factors U.S. customary units to International System of Units Multiply By To obtain foot (ft) 0.3048 meter (m) mile (mi) 1.609 kilometer (km) square mile (mi2) 2.590 square kilometer (km2) cubic foot per second (ft3/s) 0.02832 cubic meter per second (m3/s) Datum Vertical coordinate information is referenced to (1) stage, the height above an arbitrary datum established