Floodplain Considerations in the Permitting Process

Transcription

1 Floodplain Considerations in the Permitting Process OFMA Fall Conference September 2007 Harold Tohlen, P.E., CFM Infrastructure Development Manager 1

2 Flooding 2

3 FEMA FLOODWAY FEMA FLOODWAY FEMA A ZONE BOUNDARY FEMA FLOODPLAIN Horizontal view Criteria: FEMA FLOODPLAIN Vertical view 100-year storm event from 640-acres of drainage area and existing development conditions 3

4 FEMA FLOODWAY TULSA REGULATORY FLOODPLAIN FEMA FLOODWAY COT REG FLOODPLAIN STREAM FEMA A ZONE BOUNDARY FEMA FLOODPLAIN Horizontal Vertical CITY OF TULSA REGULATORY FLOODPLAIN Criteria: 100-year storm event from 40 acres of drainage area and fully-urbanized watershed conditions. 4

5 Tulsa Floodplains 5

6 TULSA WATERSHED MAP 6

7 Tulsa Master Drainage Plans Coal Cr Swan Cr. Audubon Cr. Elm Cr. Little Joe Cr. Upper Joe Cr. Dirty Butter Cr. Lower Middle Mingo Cr. Sugar Cr. Center Cr. Nickel Cr. Harlow Cr. Upper Mingo Cr. Parkview Cr. Adams Cr. Mooser Cr. Fry Ditch No. 1&2 Flat Rock Cr. Crow Cr. Fred Cr. Vensel Cr. Haikey Cr. Bell Cr. Bird Cr. Cherry/Red Fork Cr. Rolling Hills Cr. Cooley Cr. Lower Basin Oak Cr. Garden City Bigheart Cr. South Fork Joe Cr. Perryman Ditch Hager Cr. Fulton Cr. Downtown Quarry Cr. Eagle Cr. Douglass Cr. Ark R. Mainstem Reservoir Cr. Spunky Cr. Brookhollow Cr. South Park Cr. Ford Cr. Catfish Cr. Tupelo Cr. Alsuma Crl Jones Cr. Pond Cr. 7

8 OBJECTIVES OF STORMWATER MANAGEMENT Ensure that the development doesn t harm its neighbors. Ensure that the development doesn t harm itself. Provides conveyance for every flood. Mitigates impact of increase in impervious surfaces. No loss in floodplain storage. 8

9 UNDEVELOPED FLOW CONDITIONS O FF-S ITE W A TER A A 100 C FS U N D E V E LO P E D R U N O FF B A 50 C FS C TO TA L O U TFLO W 150 C FS 9

10 DEVELOPED FLOW CONDITIONS OFF-SITE W ATER 100 CFS DEVELOPED RUNOFF 100 CFS TOTAL UNCONTROLLED OUTFLOW 200 CFS 10

11 DEVELOPED FLOW CONDITIONS WITH DETENTION O F F -S IT E W A T E R C F S D E V E L O P E D R U N O F F 7 5 C F S 2 5 C F S D E T E N T IO N P O N D 2 5 C F S T O T A L O U T F L O W C F S 11

12 STORMWATER EVALUATION CRITERIA NO increase in peak discharge ALL discharges calculated for full development conditions including off-site development Conduct detention vs. fees-in-lieu determination - downstream storm drainage system capacity - magnitude of drainage from site - possible detention sites available Check hydrology/hydraulic design calculations - drainage area/runoff calculations - storm inlet and drain size/capacities - detention basin capacity Increase in impervious area 12

13 FLOODPLAIN DEVELOPMENT STANDARDS PROPERTY STATUS IN Floodplain OUT of Floodplain* Elevation Certificate Required Lowest floor elevated BFE+1ft(residential) Flood vents required for crawl space/garage (res) Elevated or Floodproofing required BFE+1ft(commercial) No loss of floodplain storage (Compensatory Storage) N/A N/A N/A N/A N/A *Areas located in a low area that are not in a floodplain may still be required to obtain an elevation certificate and elevated slab for other reasons. 13

14 Processing Permits Customer Submits Application City Reviews Application City Issues Permit Customer Constructs Project 14

15 Processing Permits City Reviews Application City Checks for floodplain 15

16 Processing Permits City Checks for floodplain Site B Site A 16

17 Processing Permits City Checks for floodplain Yes Check MDP and FIRMS 17

18 Processing Permits Check MDP 18

19 Processing Permits Scale: Site Plan B 19

20 Processing Permits City Checks for floodplain Yes Check MDP and FIRMS Check Site Plan 20

21 Processing Permits Site Plan A 21

22 Processing Permits City Checks for floodplain Site A FP on Property Work not in FP Issue Permit Yes Site B Work in Floodway Work in FP (Next Slide) Require CLOMR 22

23 Processing Permits Work in FP Special Requirements (Elevate, Floodproof, Flood vents, ECs, CLOMR, etc.) Issue Permit Customer Constructs Project 2 ECs Required Certificate of Occupancy 23

24 Questions? 24