Local Flood Hazard Mitigation Program. A framework for hazard mitigation in the NYC West of Hudson Water Supply Watersheds

Transcription

1 Local Flood Hazard Mitigation Program A framework for hazard mitigation in the NYC West of Hudson Water Supply Watersheds

2 Flood Hazard Mitigation Defined 2 2

3 Presentation Overview Why and how is the NYC DEP involved in flood hazard mitigation in Catskill region of upstate New York? o History of NYC DEP in flood related activities in the Catskill and Delaware watersheds o Tropical Storm Irene and its impact on mitigation programs o Local Flood Hazard Mitigation Program a City funded effort to reduce flood impacts and improve resiliency in watershed population centers 3

4 NYC s Water Supply Catskill/Delaware Watershed Constructed Rural land use patterns Currently unfiltered Traditional working landscape 1 million acres, 3000 stream miles Croton Watershed Constructed Suburban land use patterns Intense development pressure Scheduled to be filtered 4

5 NYC Watershed Programs Established under a MOA related to a filtration waiver from the USEPA in DEP manages a wide variety of source water protection programs including: Land acquisition and conservation Agricultural programs for extension of best management practices Septic system replacement and maintenance Community Waste Water Treatment Plant construction Forest Management and Wetland Protection And Stream Management 5

6 NYC DEP Stream Management Program Pursues a multi-objective approach to improving stream stability through an expanded understanding of fluvial geomorphic principles and close stakeholder involvement since 1995 Sponsors multi-year, consecutive contracts with upstate partnering agencies including Soil and Water Conservation Districts and Cooperative Extension Led by a skilled cadre of approx. 30 stream management professionals (engineers, technicians, educators, scientists, and administrators) who have worked together for years Knowledge based on assessment of river conditions and understanding of stream processes Supported by a network of community leaders and involved agencies Provides grants to communities and not-for-profits for a wide range of stream protection related projects and programs 6

7 From Stream Restoration to Flood Recovery 7

8 Tropical Storm Irene Impacts 8

9 Following Tropical Storm Irene DEP Stream Management and its Partnering Agencies o Dispatched consulting engineers to assess damages to infrastructure o Assessed and documented damages and prioritized sites for stream work o Supervised stream work including channel realignment and reestablishment o Assessed debris jams, prioritized and supervised removals o Funded local cost share on Emergency Watershed Protection projects at 35 sites and a total cost of approximately $15 million. o Designed and will supervise construction on EWP projects (on-going) 9

10 Directing Contractors Post Flood 10

11 DEP and County SMP Irene Response 11

12 Local Flood Hazard Mitigation Program Genesis Working group USEPA, NYS DOH, NYS DOS, NYS DEC, NYC DEP, Environmental Groups and watershed counties met monthly following Tropical Storms Irene and Lee. They resolved that there should be: o Short term action flood buyout program of substantially damaged structures o Long term action a locally organized and funded Hazard Mitigation Program for improving community resilience o One of the goals of the program was for it be ongoing, able to respond quickly in the wake of a flood to make changes when people were ready to change 12

13 Why NYC DEP supports Flood Hazard Mitigation? 13 13

14 Hazard Mitigation is Source Water Protection 14

15 Timing and a good foundation is everything Conditions making it a good time to undertake this effort o Heightened community awareness of long term climate change post Irene o Stream Management Planning and river restoration established dialog with communities and a common language o New DFIRMs o New FEMA Hazard Mitigation Plans o Existing funding programs o Trained CEOs, leaders and highway superintendents o An appreciation by NYC DEP that this effort can protect water quality 15

16 DFIRM Mapping WOH watersheds Map of DFIRM restudies 16

17 Local Flood Hazard Mitigation Program How will it work o Analysis and Planning Review and analyze river systems and river infrastructure using flood study models find source of exacerbated flooding problems Consider options for reducing problems using modeling Review options with community and with those favorable options perform Benefit Cost Analysis o Implementation Seek funding City watershed, state and federal Design, permit and construct / implement 17

18 Local Flood Hazard Mitigation Projects Potential Projects o Relocations, buyouts and elevations of critical community facilities coupled with community plans for safe development o Floodplain restoration and channel modification o Infrastructure modification o Community Programs for flood proofing Securing sources of pollution, tanks, chemicals, vehicles Evacuation planning and disaster preparation 18

19 LFHMA Program Organization Organization o Watershed Programs provide technical advice and base FHM funding Stream Management - Grant Program Catskill Watershed Corporation - Grant Program o County and Local Government Organization Planning, Public Works and County government advise communities Flood Commissions or Committees lead consultants Soil and Water Conservation Districts contract with consultants and issue task orders for each community 19

20 Program Progress to date Flood Commissions formed in three communities Funds have been dedicated to analysis in these communities One community engaged in analysis RFPs under development to secure consulting support for engineering and planning assistance New contracts registering for 5 years worth of funding with a value of $ 2.5 Million for LFHMA and $20 million for a broad range of projects including FHM 20

21 Timeline LFHMA over the next 4-5 years, likely to occur in most communities with a history of flood impacts Several LFHMP projects will be approved in the next 2 years Education and community organization on-going As part of Filtration Avoidance Determination renewal the program will be reviewed in five years 21

22 Example of the Prattsville Pilot LFHMA Irene Catalyzed a New Dialog: Communities Outreach for a new Partnership in FHM based on Flooding as a Water Quality Threat for NYC 22 22

23 Example of the Prattsville Pilot LFHMA DEP tasks Malone and MacBroom Inc to conduct Local Flood Hazard Mitigation Analysis with Prattsville 23 23

24 Prattsville Flood History New Dialog - Moving Aggressively with Monthly Meetings Shift in focus to 24

25 FEMA FIRM The FEMA Flood Insurance Study published in 2008, included developing a new hydraulic computer model of Schoharie Creek and its major tributaries to predict floodwater elevations. The preliminary hydraulic analysis prepared used this computer model as the foundation for the assessment. Rte 23 Bridge Hamlet of Prattsville 100-yr Floodplain (blue) Schoharie Creek Batavia Kill Direction of Flow 25

26 HYDRAULIC MODELING SCENARIOS Determine channel size required to convey the 100-yr event. Assess the Route 23 Bridge Evaluate potential impacts of the fish migration barrier Evaluate potential effect of the Schoharie Reservoir Evaluate potential for floodplain improvements (remove encroachments & berms, enhance floodplain areas, Huntersfield Creek) 26

27 CHANNEL SIZE Determine the required channel size for a basic cross section adequate to convey the 100-yr peak flow, plus sediment, without the use of the (developed) floodplain. Required Depth = 27 ft. This channel would be roughly twice as deep as the existing channel. However, the depth makes it impossible to construct due to the need for continuity with the downstream channel. Alternate approach is to maintain the existing channel depth of 16 ft. and determine the required channel width adequate to convey the 100-yr peak flow, plus sediment. Required Channel Bottom Width = 496 ft. Required Channel Top Width = 560 ft. Increases channel width by +200 ft. This channel has the correct depth and slope, but is three times wider than the existing channel approaching the bridge. 27

28 CHANNEL SIZE 500 WIDE FLOODWAY Requires much of the space between Main Street and the Schoharie Creek, as well as several existing including existing infrastructure and private properties. 28

29 ROUTE 23 BRIDGE 29 29

30 ROUTE 23 BRIDGE Schoharie Creek Prattsville Plan: Ex Short MMI Bankfull 12/2/2011 Geom: Ex Short FEMA MMI Channel Geometry Flow : FEMA Bankfull (short) Discharges Milone & MacBroom Inc for NYDEP R1 R1 Legend ~3.75 ft. WS 500 yr WS 100 yr WS 50 yr WS 10 yr Ground 1150 Elevation (ft) FEMA C Prattsville Cen FEMA E Fish Block Weir Main Channel Distance (ft) 30

31 Floodplain Encroachments

32 FLOODPLAIN ENCROACHMENTS Schoharie Creek Prattsville Plan: Ex Short MMI 11/30/2011 Geom: Ex Short FEMA MMI Channel Geometry Flow : FEMA (Short Geo) Discharges Milone & MacBroom Inc for NYDEP R1 R FLOW Area (sq ft) PRATTSVILLE Main Channel Distance ( ft) Cross-sectional area of the total flood flow. 32

33 REMOVE BRIDGE, DREDGE, & WIDEN Existing 100 Yr Flood Potential 100 Yr Flood 33

34 CONCEPTUAL BYPASS PLAN Compound Channel with Floodplain Overflow BYPASS CHANNEL RELOCATE HIGHWAY COMPOUND CHANNEL 34

35 PRELIMINARY CONCLUSIONS The active river corridor (channel and floodplain) need to average 500 feet wide to convey major floods. Schoharie Creek floodplain is too narrow from Washington Street to the Rt. 23 bridge. Channel widening and dredging alone are not a feasible alternatives, but in combination with floodplain widening and improvements may help reduce flood elevation in the upper portion of the Hamlet. Modification of the Route 23 bridge crossing (and approach) could result in measurable flood reductions through the lower portion of the Hamlet. The outlet from Huntersfield Creek should be re-aligned The best probable scenario is a combination of the above. 35

36 Information For More Information Contact: Elizabeth Reichheld, NYC DEP Stream Management Program Phillip Eskeli, NYC DEP Stream Management Program - peskeli@dep.nyc.gov Visit Catskillstreams.org web site 36