Carring Capacity Analysis-1984

coastal resources collaborative, ltd. l9gf
Y
DCM COPY DCM COPY
lease do not removet ff
Division of Coastal Management
CARRYING
CAPACITY ANALYSIS
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TOWN OF
NORTH CAROLINA
NAGS
HEAD,
-
612 Shady Lawn Road
919-942-8937
Chapel Hill, North Caroline 275 14.

CARRYING CAPACITY ANALYSIS
TOWN OF NAGS HEAD
1984
Coastal Resources Collaborative, Inc.
David J. Brower
Lee D. Einsweiler
Luther Propst

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The preparation of this document was financed in part through a grant
provided by the North Carolina Coastal Management Program, through funds
provided by the Coastal Zone Management Act of 1972, as amended, which is
administered by the Office of Ocean and Coastal Resources Management,
National Oceanic and Atmospheric Administration.

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TABLE OF CONTENTS Page
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
I. Land Availability and Wastewater Treatment . . . . . . . . . . . . . . 3
1. Summary Description of Available Wastewater
Treatment and Disposal Methods . . . . . . . . . . . . . . . .3
A. On -Site Disposal Using Conventional Septic Systems. .4
B. On -Site Disposal Using Non -Conventional Systems . . .5
C. Package Wastewater Treatment Facilities . . . . . ...6
2. Description of the Current Wastewater Treatment
Systems in Nags Head . . . . . . . . . . . . . . . . . . . . .7
3. Limitations to Septic Tank Use . . . . . . . . . . . . . . .8
4. State Regulations for the Use of Septic Systems . . . . . . . 11
5. Land Availability and Wastewater Treatment
Carrying Capacity Analysis . . . . . . . . . . . . . . . . . .11
6. Building Activity Trends . . . . . . . . . . . . . . . . . . .19
II. Water Supply and Capacity . . . . . . . . . . . . . . . . . . . . . . .21
1. Aquifer Capacity . . . . . . . . . . . . . . . . . . . . . . .21
2. Water Distribution System Capacity . . . . . . . . . . . . . .25
III. Hurricane Evacuation Capacity . . . . . . . . . . . . . . . . . . . . .27
1. Bridge Capacity . . . . . . . . . . . . . . . . . . . . . . . 28
2. Evacuation Demand . . . . . . . . . . . . . . . . . . . . . . 29
3. Travel Time . . . . . . . . . . . . . . . . . . . . . . . . 29
4. Evacuation Capacity . . . . . . . . . . . . . . . . . . . . . 30
References
0

' TABLE OF FIGURES
Chart
1:
Nags Head Carrying Capacity Analysis
Chart
2:
Nags Head Carrying Capacity Analysis - Water Availability
'
Table
1:
Existing (and Proposed) Package Wastewater Treatment
Facilities Serving Multi -Unit Housing Projects
Table
2:
Nags Head Septic Suitability of Soils
Figure
1:
Characteristic Soil Types and Dominant Vegetation
for
Table
3:
Buildout Factors Unimproved Platted Lots
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Table
4:
Buildout Factors for Unimproved Unplatted Parcels
Table
5:
Nags Head Building Activity Trends
Table
6:
Nags Head Water System
Table
1:
Nags Head Water Distirbution
Table
8:
Nags Head Evacuation Analysis
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' INTRODUCTION
' The purpose of a carrying capacity analysis is to determine the
amount of development a given geographic area can absorb without significantly
' damaging the environment or the public health, safety and welfare of the
residents. Carrying capacity analysis is based on the assumption that the
ability of the physical environment and the public infrastructure to absorb
development is limited. Development which exceeds that ability will require
the expenditure of public funds to avoid significant damage to the environment
' and/or harm to the public health, safety and welfare.
Carrying capacity analysis permits municipal officials to manage
' development to avoid exceeding carrying capacity thresholds or to budget
for capaital improvements to make it possible to exceed these carrying
capacity thresholds without endangering the public health, safety and welfare.
Several elements determine the ability of a municipality to absorb
development (i.e. the carrying capacity of a municipality). The relevance
of each in municipal decision -making varies according to existing development
and infrastructure, the institutional framework of the jurisdiction, and
the characteristics of the natural systems,,for example soil conditions,
flood prone areas, etc.
This report analyzes four primary factors that are important to the
capacity of Nags Head to absorb development (i.e. four carrying capacity
thresholds): the availability of land for development, wastewater treatment
and disposal, water supply and distribution, and hurricane evacuation.

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Land availability in Nags Head is determined by the amount of
developable acreage which has not yet been developed and the permissible
development densities within the Town. Densities are limited both by
septic tank regulations and by the zoning ordinance.
Wastewater treatment and disposal is a pressing concern in Nags Head
and throughout coastal North Carolina. It is A -concern of both local and
state government. This carrying capacity threshold plays the most important
role in determining the capacity of Nags Head to absorb development.
The Dare County Water System is the source of water for Nags Head
and is beyond the direct control of the town. The developed aquifer on
Roanoke Island has the capacity to meet the needs of the system for the
near future. The aquifer however does have a capacity that growth in Dare
County could exceed, requiring development of an expensive new source of
raw water.
Hurricane evacuation is a regional concern. One cannot responsibly
plan for evacuation by considering only local factors. It is important,
however, for municipal officials to be aware of the parameters imposed by
the need to evacuate a barrier island in the face of a hurricane.
The report indicates the approximate number of dwelling units and
other development that the Town can absorb before the reasonable capacity
of these thresholds is exceeded.
The capacity of the municipality to absorb development is a function
of,capital expenditures. For example, a regional wastewater collection
and treatment system, several new bridges to the mainland and increased
road capacity for hurricane evacuation and traffic circulation, and develop-
ment of new aquifers or desalinization technology could support virtually
unlimited growth in Nags Head. Afterall, Hong Kong, Manhattan, and
Singapore are each located on small islands.

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Nags Head Carrying Capacity Analysis
15,000
10,000
5000
tiG"g~0
e
4b
� ��
4� 4�w 0 ti90
4

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50,001
39,28
25,33
13,09,
10,1&
654!
3921
Water Availability
Nags Head Carrying Capacity Analysis
',QUIFER CAPACITY
RANGE OF COUNTY USE
AT FULL BUILDOUT
RANGE OF NAGS HEAD USE
AT FULL BUILDOUT
'LIMPING CAPACITY
:URRENT DWELLING UNITS
(Gallons/day converted to dwelling units)

LAND AVAILABILITY AND WASTEWATER TREATMENT`
It is known with a great degree of confidence that untreated or
inadequately treated effluent can contaminate both groundwater supplies and
surface waters, endangering public health and environmental quality. The
primary factors that govern the overall acceptability of wastewater treatment
and disposal with respect to protecting the public health and environmental
quality include the following: 1) the method of wastewater treatment and
disposal, 2) soil suitability for on -site wastewater disposal, 3) depth to
the groundwater table, 4) proximity to surface waters, and 5) density of
development.
It is possible to establish a relationship between development densities
and practices in Nags Head and the ability of the soils to absorb and
treat wastewater effluent using different wastewater treatment methods. It
is, however, not possible to simplify the wastewater treatment and disposal
problem enough to indicate precisely the density of development served by
septic tanks or other wastewater treatment methods per given land area that
will cause unacceptable contamination of the surficial or underlying aquifers
and the adjacent surface waters.
The methods of treating wastewater that are considered feasible in Nags
Head in the near future include the following: 1) on -site disposal using
conventional septic systems, 2) on -site disposal using non -conventional
septic systems, 3) package treatment plants with disposal by land application
or by subsurface drainfields. A centralized sewage system is not considered
economically feasible.

Before discussing development capacity limitations due to wastewater
treatment constraints, four subjects require elaboration as background
information: 1) a description of the three alternative methods of waste-
water treatment and disposal that are feasible in Nags Head, 2) a description
of the current wastewater treatment and disposal situation in Nags Head,
3) a discussion of the limitations to septic tank use based upon soil con-
ditions, and 4) a discussion of the state regulations governing density
limitations for development using septic tanks. Following these background
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sections, the report discusses actual carrying capacity thresholds.
1. Summary Description of Available Wastewater Treatment
and Disposal Methods
A. On -Site Disposal Using Conventional Septic Systems
Currently the predominant method of wastewater disposal in Nags Head
is by septic tank. A septic tank is basically a detention tank in which
some of the solids settle out of the wastewater and undergo anaerobic
digestion in the tank. The liquid effluent moves by gravity out of the
tank to a system of subsurface trenches, the drainfield, where treatment
by bacteria in the soil is followed by absorption of the wastewater by the
soil. This is a form of on -site land application.
A properly functioning system relies upon the soil to absorb and
adequately treat all wastewater generated from a site. All soils are not
suitable for septic tanks as they may not allow wastewater to drain through
the soil or they may allow wastewater to pass to the groundwater without
adequate treatment.

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The advantages af-sept'ic.systems'are the�use.of natural -aeration -and
filtration to treat wastewater close to the source of the wastewater, and
the cost-effectiveness of the alternative. The disadvantages of and the
limitations to
the use of septic
systems are discussed later in this section.
Overdependence
on septic systems
for
wastewater disposal on the Dare Beaches
has been associated with degradation
of water quality in Roanoke Sound,
the closing of
shellfish beds in
the
Sound, contamination of the surface
aquifer on the
Dare Beaches, and
the
possible contamination of the underlying
' water supply aquifer for the region.
' B. On -Site Disposal Using Non -Conventional Systems
There are several on -site alternatives to conventional septic systems,
including mound systems, low-pressure pipe systems, evapotranspiration beds,
duplex drain fields, aerobic systems, land application, holding tanks, and
no -flush toilets. These alternative systems may permit on -site disposal in
areas where state regulations do not permit conventional systems and may
improve treatment of effluent in areas where septic tanks are permitted but
soil conditions or proximity to surface waters insure that treatment by a
conventional system will be inadequate. Development using alternative
wastewater treatment systems is, however, likely to require larger minimum
lot sizes than required for the use of a conventional system, due to the
need to provide a large portion of the site to the wastewater disposal system.
For information on alternative wastewater treatment and disposal systems,
contact EPA National Wastewater Flows Clearinghouse, West Virginia University,
Morgantown, WV 26506, 800-624-8301. Two of the more promising technologies
are low-pressure pipe systems and mound systems. Information on these

systems is available in C. Cogger, B. Carlile, D. Osborne and E. Holland,
May 1982, Design and Installation of Low -Pressure Pipe Waste Treatment Systems.
UNC Sea Grant College Publication UNC-SG-82-03, and C. Cogger, B. Carlile,
D. Osborne and E. Holland, August 1982, Design and Installation of Mound
Systems for Waste Treatment. UNC Sea Grant College Publication UNC-SG-82-04.
Alternative wastewater treatment systems are also discussed in the North '
Carolina Barrier Island Wastewater Management Environmental Impact Statement,
June 1983.
IC. Package Wastewater Treatment Facilities
Package wastewater treatment facilities are prefabricated units, which
are smaller versions of conventional central wastewater treatment facilities.
Package plants are commonly used to treat and dispose of wastewater from
multi -unit condominium, motel, or townhouse projects. There are three
primary methods of effluent disposal used with package plants: land applica-
tion by spray irrigation, subsurface disposal by drain fields, and land
application by rotary distributors. Discharge into surface waters is no
longer permitted for new facilities under state regulations. Disposal by
spray irrigation is not often used in coastal areas because the method requires
large amounts of land. Subsurface disposal uses nitrification lines similar
to septic systems for the distribution of effluent beneath the gound surface.
This method of disposal requires a smaller land area for a drainfield than is
required for spray irrigation. Land application by rotary distributors is
particularly advantageous on barrier islands where high perculation rates are
common. It uses rotary distributors similar to those employed on conventional

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trickling filters to disperse effluent into a prepared circular bermed pit
of sandy soil. This method of effluent discharge requires less land than
rother methods and is more easily operated and maintained.
There are many advantages to the use of package plants: relatively
small acreage required for the actual plant, ease of installation, capability
of modular expansion to increase capacity to a certain maximum, and the
potential for a private developer to lease or purchase capacity at a privately -
owned facility. The disadvantages include: relatively high cost per unit
especially for facilities with less than 10,000 gallons per day capacity
(capacity for approximately 20 to 30 dwelling units), difficulty in assuring
that the facility meets design specifications, sensitivity to seasonal fluc-
uations in wastewater flows, and the need for careful supervision of the
facility.
2. Description of the Current Wastewater Treatment
System in Nags Head
Two methods of wastewater treatment and disposal are commonly used in
Nags Head: on -site disposal by septic systems and package treatment facilities.
There are five package plants, all providing tertiary treatment, serving
multi -family residential projects and a nursing home. The capacity, mode
1 of effluent disposal, and the status of these treatment facilities are provided
in Table 1. In addition to the 135 rooms at Elder Lodge Nursing Home, there
are 295 dwelling units either completed or approved that are served by package
wastewater treatment facilities.
All of the package plants except the facility at the Villas Condominiums
utilize land application as the method of effluent disposal. Spray irrigation

PROJECT/DEVELOPMENT
TOTAL
UNITS
Armada Inn
105
Elder Lodge Nursing
135
rooms
Dune Lantern
16
Nags Head Village
36
Villas Condominiums 120
Table 1
EXISTING (AND PROPOSED) PACKAGE WASTEWATER TREATMENT
FACILITIES SERVING MULTI -UNIT HOUSING PROJECTS(1)
SIZIJNG OF TREATMENT DEGREE OF
LOCATION FACILITY (GPD)(2) TREATMENT
Old Lighthouse Road 31,700 GPD Tertiary
Health Center Drive 20,000 GPD Tertiary
Virginia Dare Trail 6,400 GPD Tertiary
Ocean to Sound Approved: 60,000 built Tertiary
14 mile post 120,000 GPD
Permit (b) to construct (pending)
Permit (a) to discharge
additional 60,000 approved
Villa Dunes Drive 60,000 GPD Tertiary
MODE OF
PROJECT
EFFLUENT DISPOSAL
STATUS
Subsurface disposal
All units
complete
Subsurface disposal
All rooms
complete
Tertiary subsurface
All units
disposal
complete
Rotary distributors
18 units
complete
1S additional
units local
have rec. all
permits
Discharges into
All units
Roanoke Sound
complete
(1) Source: Based on data on file with Washington Regional Office, N. C. Division of Environmental Management, Washington, N. C.
(2) Some facilities are to be built in stages and, therefore, are sized to accommodate only a portion of ultimate flow.
M Mon in it M no M m m M M� M M M$ar W

is not used, and -is not.likely to be used, because of the large amount of
land required by the method. The two methods of disposal most commonly used
on barrier islands are in use in Nags Head: subsurface application by drain -
field and land application by rotary distributor.
The package plant at the Villas Condominiums discharges into Roanoke
Sound. All future units will use some form of land application or alternative
method of disposal because discharge into surface waters is no longer permitted
by state regulations. The Villas package plant discharges into waters
classified as SC waters, which could be classified as SA or SB if not for
thiswastewater discharge. The discharge existed prior to classification
of the state's surface waters.
The remainder of the wastewater generated in Nags Head is disposed of by
septic tanks. Currently (through May 1984) there are 3928 dwelling units
completed or approved.in Nags Head. 3633 of these are served by septic tanks.
3. Limitations to Septic Tank Use
There are three primary limitations to the on -site disposal of waste-
water in a barrier island setting such as Nags Head: soil suitability and
type, depth to the seasonal high water table, and proximity to surface waters.
The first of these is soil suitability, or the ability of the soil to absorb
tand treat wastewater. The ability of the soil to absorb wastewater is largely
a function of the texture of the soil material. The soil types found in Nags
■ Head are described in Table 2. A cross-section of a typical portion of Nags
Head is shown in Figure 1, which indicates the location of soil groupings and
associated vegetation.

Table Z
n
Naas Head Septic Suitability of Soils
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Suitability
Limitations to
Depth
to
Sail
under State
on -site Disposal,
Flooding
Seasonal
High
Permeability
Sail MRme
Symbol
Regulations
SCS criteria
Water
Table
(in/hr)
----------------------------------------------------------
beach For-edune Assn.
3
Suitable
-------------------------------------------
Very Severe - flooding
frequent to rare
o.0'
- 6.0'
Rapid, 6.3
Dunelarid
14
Suitable
Severe - blowing sand
none
6.0
Very Rapid,
20.0
Fr±pp Firre Sand
15
Suitable
Slight
rare, storm tides
6.0,
Rapid, 6.3
Nowhan Fine Sz.nd
-1
Suitable
Slignt
none
6.0
Very Rapid,
_20.0
tJer;ran :ompler.es
2-2 4
Suitable
Depends on soil mi.,
-
1.5'
-
3.0'
-
Very Rapid,
20.0
Corolla Fine Land.
7
Marginal
Very Severe
rare to common
-
2_0.0 i
Car-clla Fine Sand, Forested
a
Marginal
Very Severe
rare, storm tides
1.5
- 3.0'
Very Rapid,
Corolla - Duck:ston Complex
9
Unsuitable
Depends on soil mix
-
-
-
Habonny Soils
11
Unsuitable
Severe - flooding
surface ponding
0.'>'
- 0.5'
Very Rapid,
�U.C'
Duckz;'ton Fine Cands
12
Unsuitable
Severe - wet
rare to common
C1.0'
- 2.rY
Very Rapid,
ZO.C>
Duckston Fine Sands, Forested
13
Unsuitable
Severe - wet
rare to common
ri.0'
- 2.0'
Rapid, 6.3
Carteret Soils, High
18
Unsuitable
Very Severe
monthly
1.0'
- _.O'
Rapid, 6.3
Carteret Soils
19
Unsuitable
Very Severe
monthly
0.0'
- 3.0'
Rapid, 6.3
Cont.by Soils
26
Unsuitable
Very Severe
surface ponding
!%.0'
- 1.0
Rapid, 6.3
Dredge Spoils
10
Questionable
rare
7.C1'
Rapid, 6.v
Maaeland
17
Questionable
Severe
rare
3.0'
Rapid, 6.7,

harsh Zone
Figure 1
CHARACTERISTIC SOIL TYFES AND DOMINANT VEGETATION
1'AC-S PEAD VCCCS & NOFTN SECTION OF OUTER BANKS,'
PiORTF CAECLINA
Forest Zone
Shrub Zone
wa.xmyrtle
American. beactgrass
American
blarl: rri:clervsh
loblolly
pine
sweetgum
saltrreadow cordgr•ass
beachgrass
giant cordgrass
kmericar-
beech
redbay
eastern baccharis
cattails
live oar:
red maple
bitter panicgrass
sea —oats
easterr baccharis
water cak
dogwood
= hickcry
b eb rrryy
loblolly pine sea —oats
waxen rtle bayberry
bitter
/`
;
1 �
�'� •, f
I broom sedge live oak
panicgrass
scud�
,� a ocear.
'
�
1
Hobonny or
( Fripp,
Corolla
or Duckston Soils
Newhan, Corolla or
Beach and
Currituck Soils
�
Duckston Soils
Foredune
I
401"M IMM IMW M M .M WON M M M Now= r

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Table 2 lists the depth to the groundwater table of the soil types
found in Nags Head. This is considered the most important factor affecting
the suitability of a site for wastewater treatment and disposal. Unsaturated
soil is necessary below the drainfield piping of an on -site wastewater
disposal system in order to allow adequate treatment of the effluent before
it reaches the groundwater. If the level of the groundwater table rises
above the drainfield of the on -site disposal system, septic tank effluent
can reach the surface of the gound, resulting in both public health concerns
and aesthetic problems. The amount of unsaturated soil required for adequate
treatment is between 1 foot and 4 feet, depending upon the permeability of
the soil, in order to prevent contamination of the groundwater and nearby
surface waters. The closer the system is to surface waters, the more likely
ris contamination of such waters.
State regulations require 12 inches of unsaturated soil for the issuance
of a septic tank permit, without taking into account the permeability of the
soil. The Soil Conservation Service ratings are based upon the assumption
that when wastewater percolates rapidly through the soil, adequate time
may not be allowed for proper biological treatment of the effluent. A 1980
study by the Water Resources Research Institute, Wastewater Management in
Coastal North Carolina, states that in places where the water table rises to
within four feet of the gound surface that there*is inadequate filter depth
for septic tank usage.
It should be noted that there is a large difference between the amount
of land considered severely limited or very severely limited for on -site
wastewater disposal systems according to the Soil Conservation Service
criteria and the amount of land considered suitable for on -site wastewater
disposal under existing state regulations. According to the SCS criteria,

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Newhan Fine Sand is the only soil type in Nags Head with slight limitations
for septic tank use. The other soils are severely or very severely limited
according to the SCS rating. Slight limitations indicate that soil properties
are generally favorable or that minor limitations to the use of on -site septic
systems can be easily overcome. The SCS criteria for rating soil suitability
involves examination of properties that limit the absorption or treatment of
effluent. Slope, susceptibility to flooding, depth to seasonal water table,
and soil permeability are all considered.
The Soil Conservation Service criteria classifies the remainder of the
soil types in Nags Head as having severe or very severe limitations for on -
site wastewater treatment and disposal. A severe rating indicates that soil
properties are unfavorable for septic system use and will require major and
often expensive reclamation, usually including the addition of fill mateiral,
for proper system performance. A very severe rating is reserved for soil
types so unfavorable for wastewater disposal that extreme alteration will be
required for septic tank use.
The discrepancy between the SCS criteria and the state regulations
exists because the state regulations -- unlike the Soil Conservation Service
criteria -- do not address soil permeability as a factor in soil suitability
for septic system use. State regulations allow on -site wastewater disposal
in extremely porous soil where depth to water table is greater than 12 inches.
The soils on the Outer Banks are generally unsuitable for septic systems,
with the state regulations for septic tank use distinguishing between the
varying degrees of unacceptability. An overlay of a map of the soil types
in Nags Head and a map of current residential development indicates that the
more suitable soils are currently developed and that future development is
likely to take place on more severely limited soils.

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4'. State Regulations for the Use of Septic Tanks
State regulations govern the installation, location and use of septic
tanks. (15 N.C.A.C. 2H, section .0300 et sue. and section .0400 et sue. and
10 N.C.A.C. 10A, section .1900 et seq.) The regulations which govern the
density of development permitted with the use of septic tank systems are
as follows: lots platted prior to July 1, 1977 may use on -site systems on
parcels as small as 5000 square feet, which produces a density equivalent
to approximately 8.7 units per acre; lots platted between July 1, 1977 and
July 1, 1982 must be a minimum of 7500 square feet, a density equivalent of
5.8 units per acre; lots platted after July 1, 1982 must be a minimum of
15,000 square feet, or a density equivalent of 2.9 units per acre. These
new regulations require a repair and replacement aiea:.of equal size to the
septic system utilized, and a 50 percent increase in the absorption area
requirements if beds instead of trenches are used. The new regulations also
make it more difficult for property owners to obtain an exception to the
minimum horizontal distance requirements for previously platted lots.
5. Nags Head Land Availability and Wastewater Treatment Carrying Capacity
This section of the report provides information on the capacity of Nags
Head to absorb development and applies several scenarios concerning the
density of future development in Nags Head. All of the build -out scenarios
are based upon the assumption that future development will contain a mix of
septic systems and package plants for wastewater treatment and disposal.
The development scenarios are explained later.
t
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First it is important to discuss the implications of widespread reliance
on individual septic systems for wastewater disposal. Development in Nags
1 Head will continue to use septic systems when permitted by state health
regulations. The state regulations define extremely sandy soils as suitable
for on -site wastewater treatment systems. The questionable effluent -filtering
capabilities of these soils may lead to contamination of groundwater supplies
and surface waters.
Several studies of wastewater management on the Outer Banks have
indicated the inadequacies of wastewater
disposal by septic tanks.
According
to the 1980 Land Use Plan Update for Nags
Head, the major cause of
pollution
in the Sound west of Nags Head is septic
tank failure. In January
1979,
45 of 459 private sewage disposal systems
examined were in need of
repair.
This failure rate corresponds with similar
rates documented in other surveys.
(See 1980 Land Use Plan, p.65.).
In addition, a 1980 report by the Water Resources Research Institute,
Wastewater Management in Coastal North Carolina, concluded that "septic tanks
cannot be assumed to be an adequate solution for wastewater disposal through-
out the [Dare Beaches]." (p.2-10) The report concludes that "wastewater
treatment and disposal facilities are inadequate in the Dare County area.
The high water table and poor soils limit the effectiveness of septic tanks
and overdevelopment of the area is beginning to show its effects on water
1� quality. Direct contamination of the water supply aquifers is likely as the
■ unconfined aquifer receives the effluents of the septic tank systems. . ..
Stringent protection of the water resources is needed." The unconfined
aquifer in Nags Head is connected to Freshwater Pond, which has been identified
as a potential supplementary or reserve water supply source. The unconfined
aquifer is also connected to the surface waters of the Roanoke Sound.

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Both the Water Resources Research Institute study (1980) and the Dare
Beaches Complex 201 Facility Plan (1977, von Oesen and Associates) recommend
a community wastewater treatment and disposal system. They conclude that a
community system with ocean disposal is the most environmentally sound method
of wastewater management, as ocean disposal would end discharges to the
fragile inland coastal waters and would offer the prospect of reclaiming
and preserving shellfish growing areas.
Finally, a study done in New Hanover County by the North Carolina
Department of Environmental Management has shown that septic tank systems
can pollute the groundwater and adjacent estuarine waters. (The Impact of
Septic Tanks on Shellfish Waters) This study indicates that as more septic
tanks are installed in coastal areas with a high amount of soil with severe
j limitations for septic tank use, greater levels of fecal and total coliform
bacteria are recorded in nearby estuarine areas. Higher bacteria counts
are recorded in both wet and dry periods, indicating that the contamination
is due to septic tank systems rather than surface runoff. In the study,
a watershed with an estimated density of one septic tank drainfield per
every seven acres had acceptable water quality. Two watersheds with
estimated densities greater than one drainfield per every four acres were
contaminated to the point of having to be closed to shellfishing. The
conclusion of the study is that contamination of'estuarine waters is to be
expected when dense development with conventional septic tank systems occurs
on unacceptable soils.
These studies are referred to as a preface to the discussion of the
Nags Head wastewater carrying capacity to point out that development in Nags
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Head served by on -site septic tank systems already exceeds the capacity
of the soils in the area to treat and absorb wastewater effluent. The
data concerning the maximum permissible densities of development served
by septic systems should not therefore be considered as the carrying capacity
of the Town of Nags Head for septic tank disposal of wastewater without
significant environmental deterioration and risk to public health.
There are approximately 3928 dwelling units in Nags Head, of which
approximately 3633 are served by.septic systems. The study done by the
Department of Environmental Management, The Impact of Septic Tanks on
Shellfish Waters, indicates that the maximum density for septic tank use
without contamination of surface waters may be one septic tank for between
every four to seven acres. Septic tank densities of one tank every four
acres, in soils commonly found in coastal North Carolina, were found to
lead to contamination of nearby surface waters.
Nags Head contains approximately 4600 acres. There are currently
about 3600 septic systems in the Town. The average septic system density
over the acreage of the entire Town is therefore 1.1 systems per acre.
Approximately 850 acres in Nags Head are currently developed. There
are approximately 3600 septic systems on these 850 acres. This produces
an average density on developed acreage in Nags Head of 4.2 systems per acre.
According to the data derived by the Department of Environmental
Management in the septic tank study done in New Hanover county, the maximum
density of septic tanks that does not result in water quality degradation
is one tank for every four to seven acres. Based upon this.data, the maximum
number of septic tanks that Nags Head can sustain within the entire Town is

1
15
1
1
between.661 and 1157 septic systems. The total number of systems that
can be sustained in Nags Head on the 850 developed acres within the Town
without the likelihood of water quality degradation is between 122 and 213
units. Instead the Town currently has 3600 units on the 850 acres.
The information concerning the possible densities of septic tanks
without water quality degradation around Nags Head is not definitive, so
these numbers should be treated as conditional. These figures do provide
an accurate representation of the wastewater management problem facing
future development in Nags Head with the continued reliance on septic tanks.
In summary, this report discusses buildout scenarios that include
development served by septic systems. The use of septic systems at the density
of development already existing in Nags Head on the type of soils found in
Nags Head and the depth of water table commonly -found on the Outer Banks,
with the proximity of the Roanoke Sound and freshwater lakes in Nags Head,
leads to the contamination of the groundwater and the adjacent surface waters.
Given this caveat on the continued use of septic systems for waste-
water disposal, this report analyzes the wastewater treatment carrying capacity
of the Town of Nags Head. This entails a projection of buildout at maximum
permissible density for the currently undeveloped land. This projection
assumes that no redevelopment of currently developed acreage at higher
densities than currently exist will take place. 'In other words, existing
development is left at existing densities and all growth is assumed to
take place on currently undeveloped acreage. Maximum development and
wastewater flows will be higher if tracts in Nags Head undergo redevelop-
ment at higher than existing densities.

A 16
1
The report also compares development densities under market trends
derived from building activity over the past four years to determine
differences in densities under current development patterns and maximum
permissible densities.
Development projections assume undeveloped platted lots in existing
subdivisions to represent the potential for one dwelling unit with a
conventional septic system, in areas where conventional septic systems
and residential development are allowed. Platted lots that cannot support
residential development or a septic tank under state regulations are also
computed. This figure includes lots that are entirely within a CAMA Area
Mof Environmental Concern, that are entirely situated on unsuitable soils,
and that are within the purview of federal or state wetlands regulations.
Unplatted parcels are computed at maximum regulatory density according
to the zoning ordinance, and alternatively at maximum density that may be
served by septic tanks for newly platted parcels, i.e. at 15,000 square
foot lots.
The maximum density of development served by septic tanks is determined
by density limitations imposed by state regulations governing the use of
septic tanks. The maximum density of development served by a community
wastewater treatment system -- either a developer provided package facility
or a regional wastewater collection and treatment system -- is not determined
by limitations due to wastewater disposal. The density of such development
is determined instead by local regulatory density limits and the amount of
land available for development or redevelopment.
r

17
i Finally, this section of the report accounts for development that
is possible on platted lots with unsuitable soils for the use of conventional
septic systems, that may be developed at lower densities with the use of
alternative on -site waste treatment and disposal systems.
There are 2621 unimproved platted lots in the Town of Nags Head. Of
these, 1883 are acceptable for development and connection to a conventional
on -site septic system. The remaining 709 unimproved platted lots cannot
be developed with a conventional system due to location in a CAMA ocean
,., erodible AEC, in a regulated wetland, or in an area with unsuitable soils.
127 of these lots are completely unbuildable due to CAMA and the federal
wetlands protection program. The remaining 582 lots are unbuildable with
conventional septic systems due to unsuitable soils. These 582 lots may
be built upon using alternative methods of wastewater treatment and disposal.
The total number of improved and unimproved platted lots in Nags Head
is 6520. Of these, the total potential buildout on lots not subject to state
or federal wetland or ocean erodible constraints of dwelling units with
septic systems is 5811 dwelling units. An additional 582 dwelling units
can be built, but are located on soils considered unsuitable for the use
of conventional septic systems. See Table 3.
The buildout potential of unplatted parcels is measured under two
scenarios: assuming the use of septic systems at a density of 15,000
square feet per dwelling unit; and assuming package wastewater treatment
at maximum density permitted by the Town zoning ordinance.
1
I

0 18
As shown in Table 4, there are 1526 acres in the Town of Nags Head
that are unplatted, unimproved, privately -owned and subject to development.
i This acreage does not include Jockey's Ridge State Park or property in Nags
Head Woods owned by the Town or by The Nature Conservancy. Approximately
106 acres of this total consist of parcels which are entirely unsuitable
for development with the use of on -site septic systems. This results in
1111 acres which are suitable for development with conventional septic
systems, at a density of 15,000 square foot lots. In addition, 411 acres
in the Epstein tract will be developed without septic tanks. The capacity
of the 1486 acres at a density of 2;9:units per acre (15,000 square foot
lots) is 1848 dwelling units served by septic systems on unimproved and
unplatted parcels. An additional 1798 dwelling units and 900 motel rooms
have been approved for development on the Epstein tract.
If development on the unplatted and unimproved parcels is served by
package wastewater treatment facilities, the density of this development
is determined by the Nags Head zoning ordinance. 1526 acres, including the
Epstein tract, are available for development with the use of package facilities.
At the permitted levels of density in the various zoning districts, 6576
dwelling units could be built, plus 900 motel rooms approved on the Epstein
tract.
There are 582 unimproved platted lots in Nags Head which cannot be
developed with the use of a septic system due to unsuitable soils. These lots
may however be developed with the use of alternative on -site wastewater
treatment technology. The two most widely -used methods of on -site wastewater
treatment on unsuitable soils are low-pressure pipe systems and mound systems.
These systems require approximately one acre per dwelling unit for use.

l�
W
In summary, the total amount of,buildout in Nags Head on currently
platted lots, assuming no redevelopment at higher than existing densities,
is 6520 dwelling units, not including development on the approved Master
Plan for the Epstein tract. 3928 of these already exist and 2592 are
unimproved lots. Approximately 709 of these lots face severe constraints
to development, leaving a likely buildout between 5811 dwelling units and
6520 dwelling units.
Total buildout of the Epstein tract is 1798 dwelling units and 900
motel rooms. The total buildout on unimproved and unplatted parcels other
than the Epstein tract is between 1848 and 4778 dwelling units. The total
amount of buildout, including the Epstein tract, on unimproved and unplatted
parcels is between a low figure of 3646 dwelling units and a high figure of
6576 dwelling units, plus 900 motel rooms.
The total buildout in Nags Head is therefore between 10,166 dwelling
units and 13,096 dwelling units, plus the 900 motel rooms in the Epstein tract.
6. Building Activity Trends
The density of actual construction that has occurred in Nags Head
since April 1980 has been higher than the density permitted by the zoning
ordinance. This is due to development on lots which were platted earlier
when the zoning regulations permitted smaller lots than currently permitted.
The actual "market" buildout trend over the past five years indicates
that buildout is occurring at maximum permissible densities or greater.
In none of the zoning districts in Nags Head is development proceeding
at a density appreciably less than the density permitted by the zoning

1
1
1
1
1
1
1
1
ordinance... See Table 5. .The only significant differences between maximum
permissible buildout under the zoning ordinance and market trends over the
past five years are due to the development of giandfathered lots in
previously platted parcels.
During the period between 1975 and 1979, there were 479 building
starts in Nags Head according to the Land Use Plan Update. From April
1980 through May 1984, there were approximately 530 building starts
according to data from the county Tax Office. The development over the
past five years has consumed approximately 50 acres per year. See Table
5. With approximately 1500 acres of undeveloped privately -owned land
subject to development, and assuming a continuation of recent development
rates (50 acres per year.), Nags Head will reach full buildout in approx-
imately 30 years.

Table •3
buildout Factors for Unimproved Flatted Lots
Total 'Acceptable'
District
Pl. Lots F1.
Lots *
------------------------------------------
R 1
27
•J
23
R2
1229
909
R3
70
63
CR
We
73
C2
959
625
SFD-20
199
190
------------------------------------------
Total
2592
1883
?� Acceptable
based on marginal or suitable
soils and location not in CAMA
AEC.
Existing Dwelling Units
(from 1980 Land Use Flan +
bldg. permits to 1984)
Unimproved Flatted Lots
------------------------------------
Total potential buildout on pl. lots
(on septic systems)
Unacceptable platted lots
wetland.AEC lots
ocean erodible AEC lots
unsuitable soil lots
-----------------------------------
Estimated Carrying Capacity
(using septic systems on lots
permitted by state regulations.)
3928 DU ' s
2592
------------------
652 0 DU ' s
-709
SO
47
582
------------------
5811 DU's

L (7
Table 4
Buildout Factors for Unimproved Unplatted Parcels
Total
Unimproved
'Unsuitable'
District
Acreage
Acreage *
------------------------------------------
R1
95.3
31.5
R2
237.6
25.6
RL
25.2
CR
7.0
C2
90.8
17.1
SPD-4! �
658.7
31.5
SPD-C
411.2
-
------------------------------------------
Total Acres
1525.8
103.7
Note: This total does not include publicly owned land.
* Unsuitable soil on entire parcel.
Densities�Permitted by
Nags Head Zoning Ordinance
District
Acreage
Density Permitted
-----------------------------------------------------------
R1
95.3
2.9 DU's/acre
R2
237.6
3.9 DU's/acre
R3
25.2
(8.0 DU's on first acre,
CR
7.0
12.0 DU's on all
C2
90.8
subsequent acres)
SPD-40
653.7
4.0 DU/acre
SPD-C
* as in master plan
---------------------
Total
--411_y---
1525.8
--------------------------
Acres
Table continued on nest page
1

Table 4 (cont.)
Buildout at Maximum Permissible Densities
(as found in the Zoning Ordinance)
District
Acreage
Buildout
-----------------------
F�1
7 --------------------------------
95.3
249
DU's
R2
237.6
834
DU's
R3
25.2
272
DU's
CR
7.0
72
DU's
C2
90.8
980
DU's
SPD-40
658.7
2371
DU's
SPD-C
411.2
1798
DU's
SPD-C
-
900
Motel Rooms
--------------------------------------------------------
Total
1525.8
6576
DU's
900
Motel Rooms
Note: Acreage here
not constrained
by septic regulations.
Buildout at Densities from State Health Regulations
(based on 15,000 sq. ft. lots for septic use)
District
R1
R2
R3
CR
C2
SPD-40
SPD-C
SPD-C
Total
Acreage Buildout
____________________________________________
95.3
249
DU's
237.6
620
DU's
25.2
66
DU's
7.0
18
DU's
90.8
237
DU's
658.7
658
DU's
411.2
. 1798
DU's
-
900
Motel Rooms
_________________________________________
1525.8
3646
DU's
900
Motel Rooms

-Jab le S
..._ .
Nags Head Building
Activity Tr.ends
(April 1,1980
- May 23,
1984)
'
Zone
4/1/80 to
Calendar
1/1/84 to
Period
Acres
Implied
12/31/So
81-82-83
5/23/84
Total
Used
Density
SF
SF
----5----------SF-
-DU-s---r----
R2
58
200
44
302
104.1
* 2. 9
'
SF
SF
SF
SF
DU's/acre
2
17
2
21
10.8
* 3. 9
Dup 1 ex:
Dup 1 ex;
Dup 1 ex;
Dup 1 ex<
DU ' s /acre
'
----------------------------------------------------------------•------------
R3
5
8
-
1=
4.5
* 2.9
SF
---------------5-
SF
---
SF
----------------DU_-r_F_-
sac
'
CR
-
6
SF
2
SF
8
SF
4.0
2.0
DU's/acre
1
13
1
15
1 1. 1
2. 7
Duplex
Dup l ex:
Dup l ex
Dup l e:;
DU ' s / acr e
'
-
41
45
86
6.5
1:3.2
MF
MF
MF
DU' s/acre
-
69
17
36
5.1
16.9
'
---------------------
Motel-- -------------------------------------r--.----
Motel
Motel
Rooms/acre
'
C2
25
SF
61
SF
9
SF
95
SF
16.3
5.3
DU's/acre
1
1
-
2
0. 7
`_= .7
Duplex:
Duplex
DUplex,
DU's/acre
-
-----------------------------------------------------------------------
Other:
Motel, retail, etc.
61.7
'
SPD
1
1=
1
24
11.4
2.1
20&4(:) SF
SF
SF
SF
DU ' s/acre
'
1
1
NUrsina home
17,
-----Church
Acres used
according
to zoning
density
Table continued
on next
page

Table 5 (cont.)
N�
Total New Construction, 4/1/80 through 5/23/84
453
Single Family DU's on
144.1
acres, or
N�
76
Duplex DU's on
22.6
acres, or
86
Multi -family DU's on
6.5
acres, or
N�
N�
Other
83.8
acres
----------------------------------------------------
Total
257.0
acres
Total Residential Acreage
Overall Residential Density
3.1 DU's/acre
3.4 DU's/acre
13.2 DU's/acre
173.2 acres
3.6 DU's/acre
Note: All MF development occurred in CR zoning district
Building Starts, Single Family, 1975 - 1979 (1980 LUP)
Building Starts, Single Family, 4/80 - 5/84
479
529

it
1
IWATER SUPPLY AND DISTRIBUTION SYSTEM CAPACITY
The central issue with respect to water supply carrying capacity is at
what level of development are capital improvements in the water supply,
transmission, and distribution system required. Each component in the
water supply system represents a fixed and limited capacity which must be
' increased when demand exceeds that supply capacity. Increased capacity is
' a matter of increased capital expenditure.
1. Aquifer Capacity
The most important supply threshold is the capacity of the Roanoke
Island aquifer. A recent Engineering Report by Moore, Gardner and Associates
' for the County of Dare concluded that "it is evident that sufficient water
supplies are available from the Roanoke Island Aquifer System to supply 15 mgd
to the county water system." (p.5-14). The report concludes that once the
capacity of the Roanoke Island aquifer is exceeded, the most feasible source
of supply is development of the aquifer on the mainland. Development of
' this water supply source would be costly, requiring the construction of
a transmission main across Croatan Sound. The 15 mgd capacity of the Roanoke
' Island aquifer seems to represent the most important water supply threshold.
This threshold applies to water demand for the entire county population
' served by the regional water system. This includes Nags Head, Kill Devil
Hills, Kitty Hawk, Manteo and unincorporated portions of the county.
The Moore Gardner Water System Improvement Study also projects water
' demand for the Dare County Water Authority Service Area. They project
the water demand for Nags Head in 2005 to be 6.1 mgd, and the water demand
r

22
' for,the county-system'to be 15-.4.9 mgd.. (Moore Gardner, Table 4.2-1)
In 1983 Nags Head accounted for a demand of 1.5 mgd out of a total
demand for 4.5 mgd for the entire system. This constitutes 33 percent of
' the total demand. In 2005 Nags Head is projected to account for a demand
of 6.1 mgd out of a total demand for 15.49 mgd for the entire system. This
' will constitute approximately 40 percent of the total system demand.
These projections in the Moore Gardner Study are based upon continuation
' of the population and water demand trends that occurred between 1980 and
' 1984. Average annual growth between 1980 and 1984 was approximately 15
percent.. (Moore Gardner, p.4-1)
Based upon projected water demand at full buildout in Nags Head, the
ultimate water demand created within the Town of Nags Head will be substantially
less than the 6.1 mgd projected by Moore Gardner. Total water demand in
' Nags Head at full buildout -- under the conditions as explained in the land
availability and wastewater section of this report =- will be between 4.39 mgd
and 4.68 mgd See Table 6.
Under existing development patterns, therefore, the portion of the
' total county water system demand created by Nags Head will allow the Roanoke
' Island aquifer to provide adequate quantities of water for the county without
the need for development of a new aquifer on the mainland. If the share of
' the entire county supply devoted to Nags Head remains at 33 to 40 percent
of the total county demand, then the total county demand will be between
10.9 mgd and 14..0 mgd. This level of demand is within the sustainable
capacity of the Roanoke Island aquifer.
Table 6 indicates the computations performed to derive these projections.
' Total potential buildout on platted lots in Nags Head is 6520 dwelling units.
Total potential buildout on unimproved parcels with the use of package

23
wastewater treatment facilities-is:65.76 dwelling units plus 900 motel rooms.
The total potential buildout in Nags Head is therefore 13,096 dwelling units
and 900 motel rooms. These figures are explained in earlier sections of the
' report.
In order to establish the relationship between the number of total
dwelling units and the total potential water demand in Nags Head, the
demand for water generated by each additional dwelling unit must be
determined. The 1980 Nags Head Land Use Plan Update and the 1984 Moore
' Gardner Water System Improvement Study provide data that establish the
relationship between the total number of dwelling units and the demand for
water. According to the Land Use Plan Update, average daily water use for
residential users is 303.8 gallons per unit during the peak season, with that
' of motel rooms at 75 gallons per day. (p.31)
' Average non -housing water sales to restaurants, retail businesses,
and so forth in 1980 was approximately 10 percent of the total water sales
for the Town. In 1980, 94,900 gallons out of total sales of 949,000 gallons
in a representative month were to non -housing commercial users.
The Land Use Plan Update provides a second method of projecting water
'
demand.
According to the Update, dwelling units along the beach area
consume
110 gallons per day
per bedroom. Dwelling units along the Bypass
'
and toward the Sound consume
85 gallons per day per bedroom. 100 gallons
per day
per bedroom seems a
reasonable estimate of the total per day per
bedroom
water consumption.
The Land Use Plan Update also contains data
that indicates that the average number of bedrooms per dwelling unit in
Nags Head is 3.2. (p.27) As shown in Table 6, Projection 1 -- which assumes

24
water demand of 300 gallons per day for dwelling units and 75 gallons per
day for motel rooms -- indicates that projected water demand at full build -
out is 4.39 mgd.
Projection 2, which assumes 100 gallons water demand per day per
bedroom and assumes a continuation of the average number of bedrooms per
dwelling unit as 3.2, indicates that projected water demand at full build -
out is 4.68 mgd.
Both of these projections assume that water demand by commercial
users remains at 10 percent of total demand. These projections also
assume that the Nags Head zoning districts C-2 and C-R will continue the
recent trend of developing with multi -family housing rather than hotel/
motel development. Therefore the assumed densities within these zoning
districts is approximately 12 units per acre, rather than approximately
50 units per acre which would be permitted with the construction of hotel
or motel units.
If total potential water demand in Nags Head is limited to between
4.39 mgd and 4.68 mgd and the other areas within the Dare County Water
' Service Area limit their water demand to similar ratios of the total county
' water demand, the total demand on the Roanoke Island aquifer will peak at
between 10.9 mgd and 14.0 mgd. This is based upon the demand created in
' Nags Head remaining between 33 percent and 40 percent of the total county
demand.

25
2. Water Distribution System.
There are three factors affecting the capacity of the Town of Nags
Head to transport and distribute water to its residents following delivery
' to the Town by the Dare County Water System. These portions of the water
delivery under the town's control include the following: local pumping
capacity, storage tank capacity, and capacity of the local water mains used
for distribution.
' The current capacity of the pumps which provide water for Nags Head
' is 2500 gallons per minute. During peak periods in the summer months, Nags
Head consumes 1500 gallons per minute of this capacity. This results in
1000 gallons per minute excess capacity for use by future development. At
current average use per dwelling unit, an additional 2600 dwelling units
can be added to the system before additional pumping capacity is necessary.
' See Table 7. The units approved for the Epstein tract alone will consume
this excess capacity.
An additional concern with pumping capacity is the speed with which
storage tanks serving the town can be refilled. As the town approaches
' its pumping capacity, less excess capacity is available to refill these
' tanks and the rate of refill therefore is slower.
Storage tank capacity in Nags Head is currently 300,000 gallons. An
additional 500,000 gallon tank is expected to be completed this summer.
This 800,000 gallon storage capacity could serve Nags Head water consumption
' from storage alone for approximately 9 hours at peak consumption. If the
tanks were empty, over 13 hours would be required to refill them while
serving regular demand, using the excess 1000 gallons per minute of pumping

1
26
' capacitycurrently available.. As;more water users are added to the system,
this excess capacity diminishes, and the refill period becomes longer.
The capacity of the water distribution mains which serve individual
neighborhoods in Nags Head is a critical threshold to the growth in these
neighborhoods. When the size of a water main is inadequate for the volume
of water demanded by its users, pressure loss results. This leads to user
dissatisfaction and potential safety concerns. Relating the size of such
mains in newly developed areas to the potential total demand on the main
is crucial to the future capacity of the main to provide water to all
potential users.
Currently, 12 inch trunk lines carry water to the town along the beach
road and the bypass. These 12 inch lines feed a distirbution network of
10 inch, 8 inch and 6 inch water lines, with much of the town served by
the 6 inch line. The number of dwelling units which can be connected to
the 6 inch line is limited. As more units tap onto this system, velocity
of the water in the mains must increase to provide the same level of service.
This in turn increases the head loss, or loss of pressure due to friction
in the pipes.
The Nags Head system currently operates at 58 to 62 p.s.i.. The losses
of pressure due to friction over distance can be severe. If pressure falls
low enough, the ability to fight fires using hydrants along the water line
becomes inadequate.
11

Jab -I e b
'
d WANSystem
Total Potential Buildout on Flatted Lots (DU's)
6520
Total Potential Buildout on Unimproved
Parcels
6576
Additional Motel Rooms
900
------------------------------------------------------------
Total Potential Dwelling Units at Full
Buildout
130?6
Additional Motel Rooms
900
Projection 1
- Assume 300 gal /DU/day
'
- Assume 10% of water used by commercial
sector
- Assume 75 gal/unit/day in motels
Expected Residential Water Use
3928800
gal /day
Expected Motel Water Use
67500
gal/dry
Expected Commercial Water Use
392880
gal/day
-----------------------------------------------------------
Total Water Use at Full Buildout
4389180a
7 al/day
or
4..?9
MGD
Projection 2
- Assume 100 gal/bedroom/day
- Assume 3.2 bedrooms/DU
- Assume 10% of water used by commercial
sector.
- Assume 75 gal/unit/day in motels
Expected Residential Water Use
4190720
gal/day
Expected Motel Water Use
67500
Expected Commercial Water Use
-419072
gal/day----
Total Water- Use at Full Buildout
4677292
gal /day
or
'
4.68
MGD
LI

`
Pumping Capacity
Capacity
°= Current Pumping Capacity of Dare County System 2500 gal/min
(supply available to Nags Head)
N� Current Nags Head Peak Use 1500 gal/min
________________________________________________________________________
Excess Capacity for Future Use 1000 gal/min
T
-
N� T
Current
Dwelling Units
3928
DU's
Current
Peak Use
1500
gal/min
______________________________________________
Current
Avg. Use
0.382
gal/DU/min
�otal Capacity Currently Available 2500 gal/min
Current Average Use per Dwelling Unit 0.382 gal/DU/min
___________________________ __________________________________
�
otal Dwelling Units Served at Capacity 6545 DU's
(capacity divided by average use)
�
-- Note that this is pumping capacity only...
=======================================================================
Total Additional Units Possible 2617 DU's
(without adding pumping capacity) -
Storage Tank Capacity
Current Capacity of Tanks
Current Consumption per Hour
Hours Available on Tank Service Alone
Hours Required to Fill Tanks from Empty
(while still servingat peak use)
_ 800000
gallons
90000
gallons
8.9
hours
13.3
hours

HURRICANE .EVACUAT.ION.CAPACITY':
Hurricanes are a major threat in any coastal community. They are
even more dangerous on a barrier island because of thetuhstable nature of
the island's natural systems, the limited elevation of the island, and the
limited number of transportation links to the mainland. In addition,
there are usually not enough adequate shelters in beach communities to
' safely allow people to remain, therefore the majority of residents and
visitors must evacuate.
The capacity of the bridges and causeways which connect the islands
to the mainland present a threshold beyond which development results:in
safety concerns, since evacuation beyond this capacity cannot be assured.
It is difficult to create an effective model of hurricane evacuation for
Nags Head because the community is only one of many which rely on the same
evacuation routes. Nags Head is one portion of a far larger -.area -- covering
from the Currituck Banks to Ocracoke -- which responsible evacuation
planning_must treat as a single system.
The methodology used here is adapted
from John R. Stone's
manuscript,
Hurricane Emergency Planning: Estimating
Evacuation Times for
Non -Metro-
politan Coastal Communities (UNC Sea Grant
Publication, 1982).
His process
isolates the bottleneck in the evacuation
system, and then calculates the
time necessary to get -all the evacuating vehicles
through this
bottleneck.
For Nags Head, this bottleneck is the bridge and causeway to Roanoke Island.
Four elements must be considered to determine the total evacuation time:
bridge capacity, evacuation demand, travel time, and evacuation capacity.

F
P*]
'I
_j
Each of these elements.is described below, with the -calculations which
lead to total evacuation time.
1. Bridge Capacity
g P Y
Capacity of the bridge and causeway system is based upon the maximum
normal flow of traffic over the bridge. Five factors are then subtracted
from this normal maximum to allow for the specific conditions during
1 hurricane evacuation. These factors assume that the capacity will be
reduced by blocked lanes, inclement weather, shoulder width and sight
distance, oversize vehicles, and emergency vehicles. Each factor is
discussed below:
Normal Flow - The Highway Capacity Manual describes normal flow for
this type of road (the bridge and causeway) as 2000 vehicles per hour total
in both lanes. Blockage Factor - Fifteen percent of normal flow is lost due to stalled
cars, fallen road signs, loose electric or phone lines, and so forth.
Weather Reduction Factor - Another 35 percent of the normal capacity
is lost due to slippery roads, gale force winds, and heavy rains.
Lane/Clearance Factor - A further 23 percent reduction in capacity
is due to limitations of the road itself such as lack of shoulder and
limited sight distances.
Oversize Vehicle -.Factor.- One lane is closed for emergency vehicle use
ten percent of the time.
After these five factors are subtracted from the normal flow capacity,
the remaining total bridge capacity for hurricane evacuation is found to be
768 vehicles per hour.

1 29
2. Evacuation Demand
The number of vehicles which will be used to evacuate prior to a
hurricane is calculated by using the number of dwelling units in Nags Head.
rOther vehicles which can be expected to arrive from Hatteras Island are also
included. This does not include day tourists who are not staying either
in Nags Head or on Hatteras Island.
' Evacuation demand is computed as follows:
Permanent and Tourist Residential Units - Data determining the number
of dwelling units was taken from the 1980 Nags Head Land Use Plan and
updated to the present using building permit information. There are 2238
tourist residential dwelling units (cottage courts and motels) and 1690
permanent residential dwelling units.
Vehicles Per Duelling Unit - Estimates from current trends are: 1.6
ivehicles per permanent dwelling unit, and 1.1 vehicles per tourist dwelling
unit.
Early Evacuators - Fifteen percent of the population leaves before the
order to evacuate is given.
Other Vehicles - Approximately 5000 vehicles can be expected to arrive
ifrom Hatteras Island according to the Hatteras Island Carrying Capacity
Analysis (May 1984).
Total evacuation Demand at peak occupancy is 9391 vehicles.
3. Travel Time
Travel time is the amount of time it would ordinarily take to drive from
the furthest point'in Nags Head to the bridge. The calculation is a simple
division of maximum distance (15 miles) by average speed (35 MPH).
li

1 30
Travel time'for Nags Head is under one-half hour.
1 4. Evacuation Capacity
The bottleneck for Nags Head evacuees is
clearly
the bridge and causeway
which link the island to the mainland. This
section
calculates the amount of
time required to move the evacuating vehicles
through
this bottleneck.
First, the period during which evacuation takes
place
is calculated, then
the demand for evacuation during that period
is examined to evaluate the
bottleneck:
Warning Time - The National Weather Service can be counted on to
provide no more than a 12-hour warning which is accurate to within
approximately 50 miles of the landfall of the eye.
Hazard Cutoff Time - Roads are inundated or high winds prevent
s evacuation four hours before the landfall of the hurricane eye.
Evacuation Period - The amount of time during which evacuation may
take place, i.e 12 hour warning minus 4 hour hazard cutoff results in an
8 hour evacuation period.
Moving the total evacuation demand over the bridge and causeway takes
Iover 12 hours; 9391 divided by 768. If fifteen percent of the vehicles
leave before the order is given, this leaves over 1800 vehicles stranded on
the island, after the 8 hour evacuation period. 'An additional 2.4 hours are
needed to evacuate these remaining vehicles. The total time necessary for
full evacuation is almost 15 hours, even if 15 percent of the population
leaves prior to the warning. If no significant number of vehicles leaves
prior to the warning, over 16 hours are necessary for full evacuation
1

31
F'i
LJ
An example given in Stone's'manuscript asserts that only 400 to 500
vehicles per hour can pass over a two-lane bridge during hurricane evacuation
conditions. This results in a scenario far worse than that resulting from
the 768 vehicles per hour estimated in this analysis.
In addition, this evacuation model merely evacuates vehicles from
Nags Head and Hatteras Island to Roanoke Island. On Roanoke Island, the
Mwl vehicles from the barrier islands will be joined by vehicles from Manteo
and Wanchese, further aggravating evacuation to the mainland.
1
1
U,
1
11

Table.8
Fags Head. Evacuation Analysis
BRIDGE CAPACITY
Formal Flow
1000
veh/lane/hr
Blockage Factor
0.85
(stalled cars,etc.)
Weather Reduction Factor
0.65
(slick: roads, etc.)
Lane/Clearance Factor
Oversize Vehicle Factor
0.77
0.95
(shoulder,sight distance)
(tr-uck:,trailer,RV)
Emergency Vehicle Factor
0.90
(1 lane,10 use)
Total Bridge Capacity using two lanes
(veh/hr)
768
EVACUATION DEMAND
Permanent Residential
1690
D.U. 's
Tourist Residential
2238
D.U.'s
Vehicles per Permanent D.U.
1.60
Vehicles per Tourist D.U.
1.10
Early Evacuators Q)
0.15
Nags Head Vehicles
4391
Other Vehicles (areas outside Nags
Head)`
5000
Evacuation Demand at Peak Occupancy
(total vehicles)
- 391
I -RAVEL TIME
Average Speed
35.00
MPH
Maxi mum Distance
15.00 i
Miles
Travel Time
0.43
Hours
EVACUATION CAPACITY
NWS Warning Time
12.00
Hours
--zard---- Cutoff -Time------------4--
-----_
Hours
Evacuation Period
8.00
Hours
Vehicles Remaining Until Evacuation
Order- is Given
7982
Vehicles
Vehicles Which Can Be Evacuated in
8Hours Over the Bridge
614.3
Vehicles
--- --------------------------------------------------
Vehicles Stranded on the
18=9
Vehicles
Island
Additional Hours Needed to
Evacuate These Vehicles
2.40
Hours
continued on next page

Table S (cont.)
TOTAL EVACUATION TIME
(time necessary before landfall of the eye,
assuming that 15% leave early)
Hazard Cut-off Time
Evacuation Period
4.00
3.00
Hours
Hours
Travel Time
0.43
Hours
Add'1 Hours Needed
2.40
Hours
Hour-
Total
14.82
Time Necessary for Complete Evacuation
(no vehicles leave before the order)
16.66
Hours
u
1
1

1
F1
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REFERENCES
Coastal Consultants, Limited, Nags Head Land Use Plan Update, 1980.
Moore, Gardner and Associates, Comprehensive Engineering Report on Water
System Improvements for County of Dare, March 1984.
North Carolina Division of Environmental Management, The Impacts of Septic
Tanks on Shellfish Waters, 1982.
Rogers, Golden and Halpern, Hurricane Evacuation and Hazard Mitigation Study
for. the City of Sanibel, 1981.
Stone, Hurricane Emergency Planning: Estimating Evacuation Times for
Non -Metropolitan Coastal Communities. UNC Sea Grant College
Publication, 1982.
United States Department of Agriculture, Soil Survey: Outer Banks, North
Carolina. Soil Conservation Service, 1977.
von Oesen and Associates, Dare County Complex 201 Facility Plan, 1977.
von Oesen and Associates, Relationship of Wastewater Disposal Practices on
Development Density of Emerald Isle, North Carolina, 1983.
Water Resources Research Institute, Wastewater Management in Coastal North
Carolina., Report Number 165,.1980.
Zoning Ordinance, Town of Nags Head. Amended Through February 1983.