Preliminary Alternatives Flood Mitigation Planning

Burdette, Jennifer a
From: Henry, Sabrina <[e-mail]>
Sent: Friday, March 24, 2017 3:27 PM
To: John Hammond; May, David; Scarbraugh, Anthony; Sipe, Randy; Tankard, Robert;
Govoni, Daniel; Jennings, Frank; John Ellis; Josh R SAW Pelletier; Kathryn Matthews;
Dunn, Maria T.; Staples, Shane; Spears, Courtney; Huggett, Doug; Potts, J; Higgins,
Karen; ken. riley; Henry, Nathan; [e-mail]; Dumpor, Samir;
Mark Ford; Johnson, Jimmy; Burdette, Jennifer a
Cc: Hardison, Lyn; Hallac, Dave; William Thompson; Shelly Rollinson; John Kowlok
Subject: PLEASE REVIEW: Preliminary Alternatives Flood Mitigation Planning
Attachments: InteragencyReview_Preliminary Alternatives_FloodMitigationPlan_2017_0317.docx
All,
I apologize for my last email which probably confused you all. This was the email that I had wanted you to see
and respond to:
We have worked through several preliminary alternatives for the mitigation of flooding at the Cape Point area
in Cape Hatteras National Seashore. We have now identified four alternatives we would like to share with you
all for review and discussion in order to determine which alternatives you could support as we move forward
through the NEPA process.
I would like to coordinate a meeting for the week of April 17 in which we all can discuss these alternatives in
further detail either by phone or face to face. I will work with Lyn to determine availability and to send out an
invite for the meeting.
Thanks for your continued review of this project as we move through our environmental analysis.
Sabrina
Sabrina S. lienry
(Aic
1 Sabrina henryknps.gov

Cape Hatteras National Seashore
Flood Mitigation Plan
Interagency Review of Preliminary Alternatives
Purpose of Plan: Identify actions to mitigate the flooding which occurs within the Cape
Point areas after storm events that would not adversely impact the wetland values nor
violate federal and state wetland policies.
Need for Plan: The flooding affects access and the opening of parking areas for
pedestrians at Ramp 43 and Old 45, two of the Seashore's most popular off road vehicle
(ORV) ramps, the Cape Point Campground, Lighthouse Road, the Park's Ranger
Station, and a septic drain field that services 16 park -owned housing units. Flooding of
the septic drain field and campground can preclude the Seashore's ability to house staff
and complicates maintenance activities. Flooded areas, such as the vehicle ramps and
parking lots may have 1-3 feet of standing water for weeks following rainfall events. It is
noteworthy that this area, and possibly the hydrology, has been dramatically altered by
past human activities through the construction of a large dune line, a 40 -acre dredge
pond, roads, ditches, and canals. Sea level rise may also be exacerbating flooding.
Many stakeholder groups, local citizens, employees, and local, State, and Federal
elected officials have expressed significant concern about the flooding.
From around the 1960s until 2004, the Seashore used an existing drainage system to
manage flooding by draining water through the dune line and into the ocean. The
Seashore received a Notice of Violation (NOV) from the State of N.C. for unregulated
wetland draining in 2004 and halted all drainage activities. Following receipt of the NOV,
Seashore staff intended to develop a long-term water management plan, as
recommended by the State. However, other high priorities, including the development of
an ORV management plan, did not allow the water management plan to be developed
during the last decade. A flood mitigation plan is needed to identify actions which could
be implemented in order to achieve desired conditions of the area.
Desired Conditions: Wetland values within the project area would not be diminished by
management actions. Campground and roads within the area would be accessible to
visitors for the majority of the year. Significant flooding would be minimal and facilities
would not be affected by significant flooding events.
Page 1 of 4

Figure 1 Project Area
Preliminary Alternatives for further analysis:
1. Elevate and Restore
Remove the man-made secondary dune system between South Beach Road (old
Ramp 45) and Ramp 44 and restore the inside road between these ramps.
Elevate half of the campground 3-4 feet by using the sand from the removal of
the man-made dunes. Restore the other half of campground by removing
campground facilities (pavement, comfort stations).
Redesign the campground and provide access from Lighthouse Road through
the campground to South Beach Road (old Ramp 45) and inside road to Ramp
49.
Roads will need to be elevated and culverts installed
2. Weir: Construct a weir in the location of the old drainage site
• Installation of a 2 -feet wide weir (concrete or sandbags) set at an elevation of 5.2
feet, approximately 45 feet long and keyed into existing dunes up to a minimum
dune height of 7 feet.
• Potential conveyance of up to 88 cubic feet per second in flood events.
• Requires grading or construction of a ditch to the beach front.
o Grading: approximately 3 acres of beach seaward of weir such that
overtopping events can drain to the ocean. At least 2 feet of sand needs
Page 2 of 4

to be scraped off within the 3 acres. Requires routine inspection and
maintenance of weir, keeping the top and seaward side of the weir in
operational condition (occasional clearing of sand as the structure has the
potential of operating as a dune fence.)
r"igure 2 Graded Weir Option
• Ditch: Dig a line from the weir to the beach front at an elevation where water
could naturally flow to the ocean. Ditch only constructed when flooding is
overtopping weir and closed up when flooding has subsided. Ditch would not be
maintained. Requires routine inspection and maintenance of weir, keeping the
top and seaward side of the weir in operational condition (occasional clearing of
sand as the structure has the potential of operating as a dune fence.)
Page 3 of 4

Figure 3 Ditch Weir Option
-J_Existing3o-inch '11:1 1: :11D
ion
Dig ditch toward ocean -
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3. Dune infiltration system -
Create a drain system in which the excess flood waters infiltrate into the drain
system and flows back toward the ocean under the ground through a set of
drainage pipes. Ex. Kure Beach and Wrightsville Beach in North Carolina
4. Pre -2004 drainage system
• If allowed by the state, the NPS would cut a ditch from the current drainage area
to the ocean as was done for each flood event prior to 2004.
• Once the flood levels are reduced, the NPS would fill the ditch back up again.
Page 4 of 4