LOCAL FLOOD ANALYSIS TOWN OF LEXINGTON ALONG SCHOHARIE CREEK AND THE WEST KILL IN THE HAMLETS OF LEXINGTON AND WEST KILL GREENE COUNTY, NEW YORK MAY 2016 MMI #2884‐03 Photo Source: Milone & MacBroom, Inc. (2014) This document was prepared for the Lexington Flood Commission with funding provided by the Greene County Soil and Water Conservation District's Stream Management Program through contract with the New York City Department of Environmental Protection. Prepared by: MILONE & MACBROOM, INC. 231 Main Street, Suite 102 New Paltz, NY 12561 (845) 633‐8153 www.miloneandmacbroom.com Copyright 2016 Milone & MacBroom, Inc. TABLE OF CONTENTS Page EXECUTIVE SUMMARY ............................................................................................................................. ES‐1 1.0 INTRODUCTION ................................................................................................................................... 1 1.1 Project Background .............................................................................................................................. 1 1.2 Study Areas .......................................................................................................................................... 2 1.3 Nomenclature ...................................................................................................................................... 2 1.4 Community Involvement ...................................................................................................................... 5 2.0 EXISTING CONDITIONS ........................................................................................................................ 6 2.1 Initial Data Collection ......................................................................................................................... 6 2.2 Field Assessment ................................................................................................................................. 9 2.3 Watershed Land Use ......................................................................................................................... 10 2.4 Watershed and Stream Characteristics ............................................................................................ 10 2.5 Infrastructure .................................................................................................................................... 13 2.6 Hydrology .......................................................................................................................................... 14 3.0 FLOODING HAZARDS AND MITIGATION ALTERNATIVES .................................................................. 18 3.1 Flood History Along Schoharie Creek and the West Kill.................................................................... 18 3.2 FEMA Mapping .................................................................................................................................. 18 3.3 Tropical Storm Irene ......................................................................................................................... 21 4.0 FLOOD MITIGATION ANALYSIS AND ALTERNATIVES ........................................................................ 23 4.1 Analysis Approach ............................................................................................................................. 23 4.2 Mitigation Approaches ...................................................................................................................... 24 4.3 Analysis of Flood Mitigation Approaches .......................................................................................... 26 4.4 Evaluation Results ............................................................................................................................. 33 4.5 Property‐Specific Mitigations and Relocations ................................................................................. 36 4.6 Other Flood Concerns ....................................................................................................................... 39 4.7 Limited Stream Stabilization ............................................................................................................. 40 5.0 BENEFIT‐COST ANALYSIS ................................................................................................................... 41 5.1 Overview of Benefit‐Cost Analysis ..................................................................................................... 41 5.2 BCA Results ......................................................................................................................................... 42 6.0 FINDINGS, RECOMMENDATIONS, AND IMPLEMENTATION ............................................................ 47 6.1 Summary of Findings .......................................................................................................................... 47 6.2 Recommendations ............................................................................................................................. 47 6.3 Implementation Plan .......................................................................................................................... 49 6.4 Descriptions of Funding Sources ........................................................................................................ 51 6.5 Potential Funding Sources for Mitigation Projects ............................................................................ 54 7.0 REFERENCES ........................................................................................................................................ 57 LOCAL FLOOD ANALYSIS TOWN OF LEXINGTON, GREENE COUNTY, NEW YORK MAY 2016 TC ‐ i TABLE OF CONTENTS (continued) Page LIST OF TABLES Table ES‐1 Lexington Flood Mitigation Alternatives ........................................................................ ES‐2 Table ES‐2 Potential Funding Sources for Components of Mitigation Projects in Lexington Hamlet ............................................................................................................................ ES‐4 Table ES‐3 Potential Funding Sources for Mitigation Projects in West Hill Hamlet ......................... ES‐5 Table 2‐1 Bridge Crossings ................................................................................................................. 13 Table 2‐2 USGS Gauging Stations ...................................................................................................... 15 Table 2‐3 FEMA Peak Discharges ....................................................................................................... 15 Table 2‐4 StreamStats Peak Discharges ............................................................................................ 16 Table 2‐5 Estimated Bankfull Discharge, Width, and Depth ............................................................. 17 Table 4‐1 Flood Mitigation Alternatives – Study Area A – West Kill Hamlet .................................... 28 Table 4‐2 Flood Mitigation Alternatives – Study Area B Lexington Hamlet ..................................... 30 Table 4‐3 Alternative B‐1 Water Surface Elevation Reductions ........................................................ 33 Table 4‐4 Alternative B‐5a Water Surface Elevation Reductions ...................................................... 34 Table 4‐5 Combination of Alternatives B‐1 and B‐5a Water Surface Elevation Reductions ............. 35 Table 4‐6 Alternative B‐6b Water Surface Elevation Reductions ...................................................... 35 Table 4‐7 Combination of Alternatives B‐1 and B‐6b Water Surface Elevation Reductions ............. 36 Table 5‐1 Alternative B‐1 Benefit‐Cost Analysis ................................................................................ 42 Table 5‐2 Alternative B‐5a Benefit‐Cost Analysis .............................................................................. 43 Table 5‐3 Combination of Alternatives B‐1 and B‐5a Benefit‐Cost Analysis ..................................... 43 Table 5‐4 Alternative B‐6b Benefit‐Cost Analysis .............................................................................. 44 Table 5‐5 Combination of Alternatives B‐1 and B‐6b Benefit‐Cost Analysis ..................................... 45 Table 5‐6 Comparison of Benefits ‐ Bridge Replacement and Right Floodplain .............................. 45 Table 5‐7 Comparison of Benefits ‐ Bridge Replacement and Left Floodplain .................................. 46 Table 6‐1 Potential Funding Sources for Components of Mitigation Projects in Lexington Hamlet 54 Table 6‐2 Potential Funding Sources for Mitigation Projects in West Kill Hamlet ............................ 55 LIST OF FIGURES Figure 1‐1 Study Area A ........................................................................................................................ 3 Figure 1‐2 Study Area B ........................................................................................................................ 4 Figure 2‐1 Watershed Map ................................................................................................................ 11 Figure 2‐2 Schoharie Creek Channel Profile ....................................................................................... 12 Figure 2‐3 West Kill Channel Profile .................................................................................................. 13 Figure 3‐1 Floodplain