Flood Avoidance and Mitigation Michael Powell Delaware Department of Natural Resources and Environmental Control Shoreli

1. Flood Avoidance and Mitigation Michael Powell Delaware Department of Natural Resources and Environmental Control Shoreline and Waterways Management

2. Shoreline and Waterways Management • What we do: • Manage public beaches (i.e. erosion control, beach nourishment • Regulate construction along the Atlantic and Delaware Bay shore • Maintain inland navigational channels • Assist in floodplain mapping • Assist in regulating development in flood prone areas • Provide technical and financial assistance for flood projects

3. What constitutes a flood disaster? • Types of flood mitigation projects • non structural - floodplain management (loss avoidance) • non structural – flood mitigation projects (acquisition / relocation) • non structural – elevation and floodproofing • structural projects • Evaluating and designing flood mitigation projects • Determining flood risk • floodplain maps and studies • flood damage history • How to select a project - alternatives analysis • project goals and constraints • environmental constraints • avoiding impacts • Benefit cost analysis • Success stories • Glenville floodplain buyout • Cape Henlopen State Park groin rehabilitation • New Castle County dry floodproofing projects

6. Is this a disaster?

7. Is this a disaster?

8. Floodplain in flood stage – no disaster here!

9. Disasters result when we occupy high risk areas New Castle County Delaware September 2003

10. Disasters result when we occupy high risk areas Gulfport, Mississippi - Hurricane Katrina

11. Hurricane Katrina was a major disaster affecting • Several states • Millions of people • Over $80 billion damage

12. The majority of flood disasters are small and localized Flooding in Sussex County Delaware, June 2006 Less than 100 properties affected

14. >$30,000 structural damage to basement wall Seaford Delaware, June, 2006

15. Types of Flood Mitigation Projects • Determining the flood risk at a given location • Floodplain management – Don’t occupy high risk areas • Best • Local land use regulations which define flood-prone areas and prohibit new development in those high risk areas. • More Common • Regulations which discourage development in high risk areas but allow development as long as buildings are designed to minimized flood risk • Types of projects to protect vulnerable development

16. FEMA issued floodplain Map Widely Available nationwide Shows 100-year floodplain

19. Base Flood Elevations (100-year) storm (1% annual chance exceedence) 89 90 91 88 Best: Local land use regulations define flood-prone areas and prohibit new development in those high risk areas.

20. Base Flood Elevation stream

21. Base Flood Elevation = 89 More Common: Regulations discourage development in flood prone areas, allow it with buildings designed tom minimize flood risk Ground Elevation = 84

22. 100-year flood elevation = 89 25-year flood elevation = 87 10-year flood elevation = 85 Ground Elevation = 84

23. Simple elevation of a flood prone house Flood Level

24. Elevation and relocation of a flood prone home on the Delaware Bay Flood Level Flood Level

25. Dry floodproofing of commercial structure in New Castle County Flood Level

26. 100 year floodplain 100 year floodplain New wetlands/flood storage

27. Evaluating and designing flood protection projects • Project goals • Site limitations • Avoiding environmental impacts • Benefit cost analysis

28. Project goals • Public safety – reducing risk to people • Property protection – public infrastructure and private property • Reduction in emergency response during storms • Avoid loss of critical services – fire, police, medical etc. • Environmental enhancement and restoration • Recreational opportunities

29. Site limitations • Property factors frequently will dictate project options • Size of property – availability of land for structural flood control • Historic properties – historic preservation issues • Environmental Protections • Wetlands • Endangered species • Hazardous materials • Local zoning and codes

30. Site limitations • Sufficient room on property • Wide open floodplain – berm does not increase flooding on adjacent properties Riverwalk Townhouses – Flood protection berm

31. Site limitations • Insufficient room on property • narrow floodplain – berm would flood adjacent vulnerable properties Dry floodproofing within existing building footprint

32. Safety Issues • Property protection vs. safety • Flood response

33. Safety Issues • Property protection vs. safety • Flood response • High risk areas

34. Benefit Cost Analysis Generally a project should provide greater benefits than the cost to construct the project

35. Benefit Cost Analysis Generally a project should provide greater benefits than the cost to construct the project • Project Benefits • (define project lifetime) • Damage prevented • Life/safety benefits • Recreational • Environmental • Reduction in response • Project costs • Planning Design • Property acquisition • Construction • Management • Maintenance

36. 100-year flood elevation = 89 25-year flood elevation = 87 10-year flood elevation = 85 Ground Elevation = 84

37. 100-year flood elevation = 89 = $20,000 25-year flood elevation = 87 = $10,000 10-year flood elevation = 85 = $5,000 Ground Elevation = 84

38. Project Benefits – Elevate house • project lifetime 25 years • Damage prevented $25,000 • Life/safety benefits ??? • Recreational No • Environmental No • Reduction in response ??? (No) • Project costs • Planning Design $2,000 • Property acquisition $0 • Construction $25,000 • Management $2,000 • Maintenance $0 100-year flood elevation = 89 = $20,000 25-year flood elevation = 87 = $10,000 10-year flood elevation = 85 = $5,000 Ground Elevation = 84

39. Success Stories

40. Examples Of Success 100 year floodplain Glenville floodplain Buyout and deed restriction • Community supported • Multi purpose project • Solves the problem “completely” • Permanent (relatively) • Environmental benefit • Roads will be removed soon 100 year floodplain New wetlands/flood storage

41. Herring Point, Cape Henlopen State Park • Failure of old rock and timber groins • Narrow beach – exposed tree stumps pose swimming risk • Deterioration of surfing • Threat to WWII Bunkers

42. Sand transport is south to north. Groins which trapped sand flow have failed leading to rapid erosion

43. Sand transport is south to north. Groins which trapped sand flow have failed leading to rapid erosion • Define problem • Swimming hazard • Loss of beach • Bluff erosion • Surf break deteriorated

44. Sand transport is south to north. Groins which trapped sand flow have failed leading to rapid erosion • Define Project Goals • Protect Historic Structures • Reduce swimming hazards • Restore beach width • Stop bluff erosion • Avoid furthing impacts to surf break

45. Herring Point, Cape Henlopen State Park Sand transport is south to north. Bunkers and parking area built in vulnerable location

46. Swimming hazard • Loss of beach

47. Damage to park facilities • Recreational impacts

48. Bluff erosion • Threat to bunkers • Safety hazard

49. Bluff erosion • WWII listening cable damaged

50. Herring Point, Cape Henlopen State Park Alternatives Evaluated Do nothing – continued erosion Breakwaters – stops erosion but swimming and surfing hazard Rebuild Groins - stops erosion while enhancing surfing and swimming quality