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
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
Ground Elevation = 84

37. 100-year flood elevation = 89 = $20,000
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 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
Sand transport is south to north. Groins which trapped sand flow have failed leading to rapid erosion

43. Sand transport is south to north
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
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

51. Bluff location Bluff location JAN 9 2007
Consequences of failure to act:
Continued bluff erosion leading to hazardous conditions and incremental loss of the overlook parking lot.
Bluff location
Bluff location JAN

52. Photo credit:
Rod Rodgers

53. Photo credit:
Kyle Howard

54. April 17, 2007
Pre-construction photo

55. May 14, 2007
Mid-construction

56. July 10, 2007
post-construction

57. January 2008
midwinter

58. Flow of sand

60. Concern about negative effects on “downdrift” beach?

62. Thank you
Questions???