DES MOINES CITY OF TWO RIVERS. Flooding Risk & Impact to Development

Transcription

1 DES MOINES CITY OF TWO RIVERS Flooding Risk & Impact to Development

2 River System

3 Des Moines Flood Protection

4 Des Moines Flood Protection cont. Infrastructure Over 24 miles of levees 21stormwater pump stations along levees Over $116 million in improvements since 1993 Operation Personnel Equipment Materials Organization Flood fighting plan

5 How high will the water get? Rainfall Land use/runoff characteristics Operations of reservoir Historical data Future conditions are variable

6 Des Moines River Regulated Flow Frequency Study January 19, 2011 Corps releases study results Period of Record analysis, including data through 2008 Analysis forecast 100 year flow increased 24% at SE 6 th Street Current levee heights exceed all historical flood elevations Study did not analyze flood elevations

7 Levee Accreditation FEMA determines accreditation requirements not the Corps FEMA generates flood maps which show base flood elevations (BFE) BFE are based upon flood flow frequency and river modeling FEMA will initiate study of Corps results and other data to determine new BFE and create new Flood Insurance Rate Maps (FIRM) no earlier than 2014

8 Improvements to DSM System Levees, Channel improvements, Operation changes Multiple sources of funding required (Fed, State, City, etc) Immediate action for ongoing projects Pump station modifications (Jackson-3/28) Corps agreement & Birdland / Central Place (3/28) Consultant analysis (3/28) Iowa DOT US65 bridge modification

9 DEVELOPMENT ISSUES

10 History Pre - FIRM Development State regulations 1965 Stream studies with flood elevations High water field observations in ponding areas Zoning districts since 1965 Implementation of Regulations FIRM implementation 1981 Federal regulation protect to base flood elevation (BFE) Match State regulations protect to base flood elevation (100-year) + 1 foot

11 General Regulation of Flood Plain A Zones X Zones AE BFEs established; protect to BFE + 1 foot A approximate; no flood elevation established; requires engineered study; protect to study elevation + 1 foot AO(depth) protect to depth above highest adjoining grade Protection Residential lowest habitable floor elevation Commercial lowest floor or floodproof Shaded X no restrictions; 500-year flood areas, areas protected from 100-year by levees, and areas of 100-year with average depth of flooding less than 1 foot or with drainage areas less than 1 square mile X no restrictions; areas outside 500-year Proposed State legislation to regulate to 500-year has stalled Current legislative actions may alter these definitions further

12 FIRM Map

13 Requirements Based on Use Residential Commercial Elevate habitable areas +1 foot above regulatory elevation Elevate HVAC, electrical & other building systems No basements Flow through foundations Flood protect Elevate development Flood proof building Ring levee Flood wall

14 REGULATIONS BASED ON SPECIFIC AREAS

15 Birdland / Central Place Timing and Requirements Map Current Interim FIRM zone shaded X - protected by levee; unrestricted development allowed through December 2011 FIRM zone AE; new levee under construction. New and substantial improvement construction projects subject to protection requirements. Completion of reconstruction estimated in 2012, with subsequent certification allowing unrestricted development. Future (post 2014) Accredited levee; FIRM zone shaded X; unrestricted development allowed

16 SE Des Moines Timing and Requirements Map Current FIRM zone shaded X - protected by levee; unrestricted development allowed through December 2011 Interim Future FIRM zone A; new and substantial improvement construction projects subject to development restrictions. No current flood protection project; USACE owner Dependent on CORPS & FEMA Map revisions Future FIRM Zone uncertain

17 Downtown Timing and Requirements Map Current FIRM zone shaded X - protected by levee; unrestricted development allowed through December 2011 Interim Future FIRM zone shaded X - protected by levee; unrestricted development allowed through 2014 Anticipate flood protection project needed to maintain shaded X; City owner Date dependent on FEMA Map revisions

18 Future Zoning Map Implications Amend zoning map to align with regulatory flood plain post 2014 Map revisions will create new legal non-conforming land uses & structures Match U-1 & Floodway to the new regulatory floodplains following anticipated 2014 FIRM Maps Reassess disparity between the zoning ordinance & floodplain development regulations for substantial damage threshold

19 Impacts Immediate and Future Message to Property Owners Insurance Rates Current rates Preferred risk rates available for 2 yrs Future rates will increase Physical Improvements required to maintain shaded X Levees Channel improvements Operation changes Multiple sources of funding required (Fed, State, City, etc) City is carefully considering improvements to protect Development allowed subject to Zoning & Floodplain Development regulations Buy Flood Insurance Now (Available to all)

20 Questions