Topographical survey and hydrological analysis of the Wallis Sands and Philbrick Brook Marshes Phase II report

[From the U.S. Government Printing Office, www.gpo.gov]

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PHASE II REPORT:
LTOPOGRAPHICAL SURVEY AND
HYDROLOGICAL ANALYSIS

OF THE

WALLIS SANDS AND
PHILBRICK BROOK MARSHES

SPECIFIC RECOMMENDATIONS
FOR DRAINAGE IMPROVEMENTS

Submitted to

THE TOWN OF RYE, NEW HAMPSHIRE

Prepared by

NORMANDEAU ASSOCIATES INC.
25 Nashua Road
Bedford, New Hampshire 03102

R-4119B

August 1988

TABLE OF CONTENTS

PAGE
1.0 INTRODUCTION . . . . . . ... . . . . . . . . . . . . . . . . 1

2.0 HYDROLOGIC SUMMARY . . . . . . . . . . . . . . . . . . . . . 2

2.1 BASIN VOLUME ESTIMATES . . . . . . . . . . . . . . . . . 2
2.2 TIDAL VOLUME EXCHANGES . . . . . . . . . . . . . . . . . 4
2.3 STORM WATER RUNOFF SUMMARY . . . . . . . . . . . . . . . 4

3.0 RECOMMENDATIONS . . . . . . . . . . . . . . . . . . . . . . . 9

3.1 OVERVIEW . . . . . . . . . . . . . . . . . . . . . . . . 9
3.2 DRAINAGE IMPROVEMENTS . . . . . . . . . . . . . . . . . 13

4.0 LITERATURE CITED . . . . . . . . . . . . . . . . . . . . . . 29

1.0 INTRODUCTION

Normandeau Associates Inc. (NAI) has completed the
Topographical Survey and Hydrological Analysis of the Wallis Sands and
Philbrick Brook salt marshes in the town of Rye, New Hampshire.

The objective of the current study is to provide the physical
basis for tidal restoration in two of Rye's salt marshes located in the
Wallis Sands and Philbrick Brook watersheds. The results are presented
in three phases. Phase I is an evaluation of existing conditions in the
two study areas, including hydrology, topography and engineering
features, and general recommendations for achieving marsh restoration.
Phase II recommends specific engineering and drainage improvements to
achieve optimal tidal flushing and flood protection. Phase III assesses
the impacts of drainage alterations on surrounding development,
including properties, septic systems, structures, and roadways.

This report is a presentation of Phase II results, including
1) a summary of marsh hydrologic data; and 2) specific recommendations
for engineering and drainage improvements.

The New Hampshire Coastal Program provided a grant for the
preparation of this report, which was funded in part by the Coastal Zone
Management Act of 1972, as amended, administered by the Office of Ocean
and Coastal Resource Management, National Oceanic and Atmospheric

Administration.

2.0 HYDROLOGIC SUMMARY

Topographic and hydrologic data were integrated in Phase I to
develop general recommendations for improving stormwater drainage and
tidal exchange. The following section summarizes those data that were
used to develop specific design recommendations for Phase II. Some of
these data were included in the Phase I report, and are reiterated here
for continuity. All elevations in this report refer to the National
Geodetic Vertical Datum (NGVD).
Included in this section are: 1) volume estimates for all
basins up to 5.0 feet NGVD; and 2) volume exchange estimates for basins

with restricted flow based on tidal measurements of 16 March 1988.

2.1 BASIN VOLUME ESTIMATES

Volumes of marsh basins in the Wallis Sands and Philbrick

Brook marshes are given in Table 1. These estimates are based on
interpretation of 1" = 1000' aerial photography and field reconnais-
sance. Topographic contours were determined at 5.0-foot intervals,
relative to NGVD, up to an elevation of 10.0 feet (i.e., contours were
established at 0.0, 5.0, and 10.0 feet). The 5.0-foot contour
approximated the transition zone from salt marsh to upland throughout
the study areas, and generally corresponds to the level of spring tide
flooding. Thus, the basin volume up to the 5.0-foot contour is the
approximate capacity of the marsh during spring high tides which occur
roughly twice per month.

Basin volume estimates were used to estimate volume exchanges
(Section 2.2), and to estimate water budgets for tidally restricted
basins. Water budgeting yielded information on baseline freshwater
inflow and percent tidal exchange used in the placement and design of
drainage improvements.

TABLE 1. VOLUME ESTIMATES FOR INDIVIDUAL BASINS OF THE WALLIS SANDS
AND PHILBRICK BROOK SALT MARSHES, RYE, NEW HAMPSHIRE.

APPROXIMATE BASIN VOLUMES (CUBIC FEET)

BASIN
SERVED BY TIDAL CREEKS MOSQUITO TOTAL
BASIN DESCRIPTION CULVERT AND PONDS DITCHES MARSH UP TO 5. 01
SURFACE NGVD

WALLIS SANDS MARSH 1,043,743 45,255 3,454,609 4,543,607
South of Wallis Rd. to Concord 514,622 33,375 1,922,169 2,470,166
Washin ton Rd. and Point
east of Brackett Rd. Outlet
(Massacre marsh)
West of Brackett Rd. 5 600 - 13,360 13,960
(upper Massacre marsh)
North of Wallis Rd., 4 427,757 11,090 1,180,953 1,619,800
west of Ocean Blvd.
and south of Marsh kd.
East of Ocean Blvd *as 3A 32,673 300 72,007 104,980
south of Wallis San &
beach parking. 3B
North of Marsh Rd. 2 68,091 490 33,801 102,382
southeast of Parson's
Rd.

North of Parsons Rd., 1 - - 232,319 232,319
east of Brackett Rd.

PHILBRICK BROOK MARSH

East of Ocean Blvd. Rye 1,073,635 7,230 1,671,347 2,752,212
and south of Harbor Rd. Harbor
Outlet

West of Ocean Blvd., 7 & 8 45,379 1,100 225,417 271,896
south of Harbor Rd. to
Locke Rd.

Southwest of Locke Rd. 9 9600 3100 183,358 196,058
and west of Yushak Driveway
East of Yushak Driveway 10 26,100 430 95,629 122,159
and west of Ocean Blvd.

East of Ocean Blvd. and 11 - - 72,963 72,963
west of Old Beach Rd.

Basin volumes are given in cubic feet, and may appear immense
to those unaccustomed to these units. To put these figures in perspec-
tive, it is helpful to consider the sizes of the areas involved. The
Wallis Sands and Philbrick Brook Study areas are approximately 185 and
100 acres in area, respectively. One acre equals 43,560 square feet,
hence a foot of water covering an acre (one acre-foot) is 43,560 cubic
feet in volume. One hundred acre-feet thus contains 4,356,000 cub ic
feet of water. By comparison, the estimated volume of water leaving
Wallis Sands Marsh at Concord Point during a single ebb tide on 16
March, 1988 was 1,819,200 cubic feet.

2.2 TIDAL VOLUME EXCHANGES

Water volume exchanges were measured over a spring tidal cycle
on 16 March 1988 at suspected points of restriction throughout the

Wallis Sands and Philbrick Brook marshes. Points of restriction were

illustrated in the Phase I report using graphs of water levels measured
simultaneously on both sides of suspected pipes, culverts, sluiceways,
and bridges.

For Phase II it was necessary to determine the relative
severity of the restrictions revealed during Phase I. To accomplish
this, volume exchange measurements made on 16 March 1988 were coupled
with the basin volume estimates given in Table 1. Table 2 summarizes
these data and provides estimates of percent volume exchanges.

2.3 STORM WATER RUNOFF SUMMARY

The effectiveness of existing structures for channeling storm-
water runoff was evaluated for several scenarios of tidal height and
magnitude of storm event, using HEC-1 stormwater modeling software
(HEC-1 1985). HEC-1 evaluates stormwater runoff by estimating the peak

TABLE 2. PERCENT VOLUME EXCHANGE MEASURED IN TIDALLY RESTRICTED
BASINS ON 16 MARCH 1988 IN THE WALLIS SANDS AND PHILBRICK
BROOK SALT MARSHES, RYE, NEW HAMPSHIRE. FOR THESE
CALCULATIONS, UPSTREAM BASINS RECEIVING TIDAL INPUT DURING
SURVEY ARE ADDED TO TOTAL VOLUMES OF DOWNSTREAM BASINS.

PERCENT
BASIN SERVED BASIN VOLUME TIDAL TIDAL
BY CULVERT VOLUME (CF) OUTPUT (CF) INPUT (CF) EXCHANGE

WALLIS SANDS MARSH

Culvert #1 232,319 29,760 0 0

Culvert #2 102,382 11,331 0 0

Culverts #3A 104,980 6408 6228 6
and OB

Culvert #4
creeks only 543,827 85,184 71,179 13
creeks & surface 1,724,780 85,184 71,179 4

PHILBRICK BROOK MARSH

Culvert #11 72,963 4892 420 0.6

Culvert #10 195,122 75,337 59,170 30

Culvert #9
creeks only 207,822 152,298 41,999 20
creeks & surface 391,180 152,298 41,999 11

runoff for storms of various magnitudes. In addition to storm magni-
tude, factors must likely to affect peak runoff are the size of the
watershed, predominant soil types, and degree of development (especially
paving).

In Table 3, HEC-1 results are given for 10-year, 50-year, and
100-year storms, each of 24-hours duration. For each storm the esti-
mated peak runoff (given in cubic feet per second) that can be expected
to pass through each culvert is given for existing and hypothetical
conditions. Existing structures are further evaluated according to the
level of the tide at the time of peak runoff. Low tides mean greater
marsh volume is available to store runoff, hence flooding will be less
severe. Conversely, moon high tides (i.e., spring tides) fill the
marshes to 5.0 feet or more. If peak runoff occurs during moon high
tides, salt marsh areas are unavailable to store runoff, and local
flooding results.

Hypothetical conditions include runoff estimates with the
proposed modifications in place ("proposed structures"), and the
scenario of "no structure". The "no structure" scenario is simply a
basis for comparing existing and proposed conditions with an estimate of
runoff assuming no roads, culverts, or other structures were in place
(i.e., an unmodified, it natural" system).

Perhaps of greatest interest in evaluating flooding are the
estimates for "high elevation" listed for both the Wallis Sands and
Philbrick Brook study areas. These numbers represent flood elevations,
in feet above NGVD, for points furthest inland along each marsh's
drainage. This is the maximum flood elevation expected under each
scenario, because drainage of runoff from inland portions of the marsh
'A is restricted by downstream backup of flow.

Ila

TABLE 3. REC-1 STOP14WATER RUNOFF EVALUATIONS FOR SEVERAL SCENARIOS OF' STORM
MAGNITUDE AND TIDE LEVEL FOR THE WALLIS SANDS AND PHILBRICK BROOK
SALT MARSHES, RYE, NH.

RYE MARSH EVALUATION PEAK STORNWATER RUNOFF (cys)

14 YEAR. 24 HOUR STORM 50 TZAR, 24 HOUR STORM 100 YEAR, 24 MR STORM

No EXISTING STRUCTURES PRoposto STR UCT URES No EXISTING STRUCTURES PROPOSSO STRUCTURES No EXISTING STRUCTURES PROPOSZD STRUCTURES
STRUCTURE STRUCTURE STRUCTURE
LOU
HOOK HIGH LOW MOON HIGH LOW MOON HIGH LOW MOON HIGH LOW MOON HIGH LOW MOON HIGH
SITE TIDE ?log TIOR TIDE TIDE TIDE TIDE TIDE TIDE TIDE TIDE TIDE

WALLIS SANDS

CULVERT 1 24 37 10 36 24 36 As it 42 26 43
CULVERT 2 a a 12 12 12 12 It 13 13 is is 13
WALLIS ROAD 67 51 60 $a 52 110 82 too 93 86 131 97 121 Ila 121
CULVERT 3 32 30 29 21 is $a st so 52 58 71 70 70 60 70
CONCORD PT. 126 70 60 77 75 212 sit 106 132 133 231 148 131 159 177
HIGH ELEVATION (FT) 5.7 7.1 5.0 7.0 6.3 7.6 5.6 7.1 6.7 7.9 6.0 7.9

PHILIRICK BROO1

CULVERT It 3 2 1 3 2 4
CULVERT to 12 to 10 12 11 19 17 16 17 16 21 so to 10 19
CULVERT 9 56 44 st so 41 97 64 34 66 61 116 99 63 77 91
CULVERT 2 56 At 33 so 39 97 60 21 66 39 116
RYE HARBOR 72 36 77 74
72 44' 23 61 23 121 73 1) as 33 144 87 27 94 As
HIGH ELEVATION (FT) 5.8 8.7 4.8 714 6.7 9.8 5.9 8.4 0.5 8.9 7.2 8.4

In evaluating these data, it is important to recognize that
the numbers represent predictions of a model, not actual measurements.
Actual flood elevations may vary, especially if storm tides exceed moon
tide elevations. Actual measurements of high elevations in inland areas
for the 100-year storm of February 1978 were in the range of 7.3-9.9
feet NGVD (Gadoury 1979)

3.0 RECOMMENDATIONS

3.1 OVERVIEW

Topographic and hydrologic evaluation of the Wallis Sands and
Philbrick Brook marshes has revealed four interacting factors contrib-
uting to salt marsh degradation. These are: 1) inadequate and poorly
placed culverts under roads for channeling baseline freshwater flows out
of marsh basins, 2) inadequate and poorly placed culverts that restrict
tidal flooding, 3) clogged and inadequate tidal creeks for channeling
water between culverts, and 4) man-made features on the marsh surface
such as stone walls and dredge spoil that hinder surface drainage. In
addition, culvert and creek inadequacies contribute to poor removal of
runoff and flooding during storm events. Maps I and 2 show the Wallis
Sands and Philbrick Brook study areas, and the locations of culverts

examined in Phase I.

To develop recommendations for improvements, tidal exchange
for salt marsh restoration and stormwater management were first con-
sidered separately. Improvements to meet each objective were then
proposed, and integrated to develop a draft plan to meet both objec-
tives. Finally, consideration for impacts*due to coastal flooding were
incorporated into the final plan presented here.

Drainage improvement recommendations are targeted toward
restoring favorable conditions for the recovery and maintenance of the
salt marsh community, and improving stormwater runoff through the
marshes to reduce adverse impacts to roads and properties due to flood-
ing. These objectives are generally compatible: increased pipes and
channels that improve tidal flushing also provide improved stormwater
management under most circumstances. Salt marsh restoration and flood
protection objectives may be incompatible, however, when high tides and
storm surge flood the marshes during a storm event. In such instances
the storage capacity of marsh basins may be exceeded by tidal inputs.

East Rye Pond

VI.-

Ak
Parion's
Creek"-i
Marsh

3-A
Atlantic Ocean
3-B

Wallis Sands

ConcordPoint
Wallis Sand
s Watershed
ek
Massacre Cre
Marsh,-, - -
.00

A
5

MaPl- Wallis Sands Study Area. Points examined for tidal
resrictiOns are circled and numbered.

Rye Harbor

lp=d

Locke Fs Neck
Philbrick 10
Brook Marsh
J^%

Philbrick Brook Watershed Atlantic Ocean

CIaNe Road

Jenness Beach

Map 2. Philbrick Brook Srudy Area. Points examined for tidal
restrictions are circled and n=berrd.

Additional inputs from stormwater or snowmelt may then result in serious
flooding in low-lying areas. Based on records of the February 1978
storm (100-year frequency tidal flood), flooding due to storm surge may
reach 10.0 ft. NGVD in areas surrounding Rye's salt marshes (Gadoury
1979). This is a foot higher than the 100-year flood level estimated
for the Flood Insurance Rate Maps (FIRMs), based on 1976 data (FEMA
1986).

Absolute protection against flooding of this magnitude is not
presently compatible with existing development, or the Town's objective
of salt marsh restoration and maintenance. Existing development in
Rye's coastal zone occurs below 10.0 ft. in many areas, most of which
in-I are subject to flood hazard under present drainage and tidal conditions.
Roads built across marshes below this elevation offer little protection
to landward areas because they can be over-topped by flooding. It
follows that modifications of drainage structures passing under such
roads cannot significantly reduce the risk of tidal flooding inland.
4 Further, anticipated rates of sea level rise indicate a high likelihood
that coastal flood hazard will increase significantly over the next 50
years (Hoffman et al. 1983). Full protection of such areas may require
more sophisticated structural solutions and an active management pro-
gram. These prospects are leading some coastal areas to propose develop-
ment limitations in anticipation of sea level rise (LIRPB 1984).
Planning is currently underway in New Hampshire to provide for flood
protection and marsh preservation (Shevenell Gallen 1987, D'Agostino
1988).

Thus, a long-term plan for maintaining the Wallis Sands and
Phibrick Brook salt marshes (and other salt marshes in Rye) must be but
one component of a coastal management plan. This plan might consider
such issues as road relocation and modification, existing and future
development, and water control structures in light of the continuing
rise in sea level.

Such a management plan is obviously beyond the scope of this
study. However, coastal flooding and sea level rise must be considered
in the course of recommending drainage improvements. To meet the
objectives of this study, improvements are recommended that will:

1) improve tidal exchange to encourage marsh restoration,

2) improve stormwater removal under most circumstances, and

3) not increase, and perhaps decrease, the risk of tidal
flooding during extreme events compared to existing
conditions.

3.2 DRAINAGE IMPROVEMENTS

The following specific recommendations are made for improving
tidal exchange and stormwater removal in the Wallis Sands and Philbrick
Brook salt marshes. Place names follow Simpson (1986); and previous
reports by Normandeau Associates Inc. (NAI 1986a, NAI 1986b).

Recommended improvements are given a priority rating of "H"
(high), "M" (medium), and 'T' (low), for each stated objective. Thus,
an improvement that is critical for salt marsh restoration may have a
rating of "H" for improving tidal exchange. However, its importance to
stormwater runoff may be quite low and thus rate 'T' for that objective.
In general, improvements that will affect a large area are rated "H",
while smaller-scale improvements are rated "M" or "L". Stormwater and
flood protection improvements are all given high priority ratings.

General Specifications:

A 1) Culverts should be installed with minimal slope, not less
than .002 ft/ft, positive seaward during outflow. This
will encourage self-cleaning toward the seaward end
during outflow.

2) All elevations are given relative to NGVD-

3) Improve and extend marsh ditches as specified following
the typical section given in Figure 3. A rotary ditcher
attachment, which broadcasts spoil over the marsh sur-
face, is recommended for ditch digging.

4) Spoil material removed by means other than the rotary
ditcher should be disposed of on upland areas.

5) Low ground pressure (LGP; PSI 5 2.0) equipment is recom-
mended for any work requiring operation on the marsh
surface.

6) Work requiring operation of heavy equipment on the marsh
surface should be performed during October-April to avoid
adverse impacts to salt marsh vegetation, peat structure,
and wildlife.

7) All work in salt marsh areas should be performed in
consultation with a salt marsh specialist. A minimum of
three reviews are recommended: 1) review of final
construction drawings, 2) review of work during construc-
tion, and 3) review following construction.

8) Self-regulating tide gates of the type designed by Nekton
Associates, Inc. of Fairfield, Connecticut (Tom Steinke,
Sr., President), or similar, are recommended.

WALLIS SANDS MARSH

Site: Culvert #1

Recommendation #1: Replace existing culvert with 19" x 30"
RCP set at approximately 4.0' invert elevation. Extend new
pipe approximately one foot beyond existing culvert at both
ends. Clear rocks from channel immediately south of culvert
(Figure 1, see Map I for location).

Rationale: Improve stormwater runoff capacity (H). Maintain
East Rye Pond as brackish pond.

Site: Culvert #2

Recommendation #2: Maintain existing culvert. Extend and
improve existing ditches north and south of Culvert #2
(Figure 2) such that a continuous open channel exists between
Parsons Creek and the marsh basin served by Culvert @J2.

Optional: Install self-regulating tide gate to protect
against tidal storm surge. However, low profile of road
provides only minimal protection.

EAST RYE POND

FLOW

19' x 30' RCP

RIP RAP
00

MARSH RD.

1@0-39 1100i F-45

CLEAR ROCKS FROM
CHANNEL IMMEDIATELY
SOUTH OF CULVERT
PARSON*S CREEK MARSH

PLAN

NO SCALE

MARSH ROAD

ELEV. 7.03*
117-G, 19" 30- RCP
(TYPJ

OOL"/- MIH.

ELEV. 4.0- INV.

42-

PROFILE
WALLIS SANDS MARSH
"o

CULVERT #1

NO SCALE
FIGURE I

.01
iMPROVE
S, EXISTING
10,
DITCH
C3 Do
EYISTING1
CULVERTI
CD I
0 0 0=

10,

S1
PARKING
'/000' ALLIS SANDS
EXTEND AND STATEBEACH
IMPROVE
EXISTING
DITCH

SALT MARSH
(EL. 4.S'�:)
/hD
loo@ P07@j
R \NV@E
EXISTING
DITCHES

Q7
3A 13
@L@EAN
PARSONi
EXISTIN 10,
CREEK CULVE S
(TIDAL) ADD TIDE ATE 3B
.(SELF-REGULATING)
S,
ROCK
WALL*

DITCHES
IMPROVE
,/ENISTING-
DITCH@

Figure 2. Recommended improvements for northern part of Wallis Sands salt
marsh, Rye, NH.

Rationale: Improve tidal exchange (M). Minor protection
against tidal storm surge (optional).

Site: Culvert #3A

Recommendation #3: Clean existing culvert. Improve existing
ditches east of Ocean Blvd., especially the ditch extending
south to Culvert #3B (Figure 2). Install self-regulating tide
gate over west end of pipe.

Rationale: Improve tidal exchange (M). Protect against tidal
storm surge (H).

Site: Culvert #3B

Recommendation #4: Clean existing culvert. Improve existing
ditch between culvert and Parsons Creek to the west (Figure
2). Install self-regulating tide gate over west end of pipe.

Rationale: Improve tidal exchange (M). Protect against tidal
storm surge.

Site: Wallis Road Vicinity (Culvert #4)

Recommendation #5: Relocate creek in vicinity of Horse
Paddock and Trash Corner (Figure 5). Follow detail given in
Figure 4.

Rationale: Improve tidal exchange (H). Alleviate erosion and
encroachment problems at Trash Corner (H).

4 Recommendation #6: Deepen existing creek in the vicinity of
Wallis Road by approximately 1.0 ft., to a bottom elevation of
approximately 2.5 ft. (Figure 2).

Rationale: Improve tidal exchange (H).

Recommendation #7: Remove remnant of Old Wallis Road roadbed
from creek channel (Figure 5).' Follow detail given in Figure
6.

Rationale: Improve tidal exchange (H).

3 0-

ARSH SURFACE 4.5':t

3 30"

-SPOIL BROADCAST OVER
MARSH SURFACE USING
ROTARY DITCHER
lo..

TYPICAL DITCH SECTION
NOT TO SCALE

FIGURE 3

10,
A

4.5't
FILL FROM NEW
> E
XCAVATION
3 al@
3.5'2:

2.5't

9.3'

RELOCATED CHANNEL EXISTING CHANNEL

SECTION E E'
NOT TO SCALE
N@3

FIGURE 4

�ONS CREEK
(17DAL)

--OHO RSE
PADDOCK

10,
"TRASH,
I RELOC CORNER"
CREEK

DEEPEN
EXISTING
CREEK%,
BY 1.0- t:

00
DEEPE* \
EXISTING \51 0
CREEK Ak"w,
BY 1.0't

REMOVE
S,
10, REMAINING
ROADBED
I ZZz@@ FROM
WOODED CHANNEL
10, UPLAND
R

Figure 5. Recommended improvements for Wallis Sands salt marsh in the vicinity
of Wallis Road, Rye, NH. See Figures 6 and 7 for section details.

REMOVE ROCKS TO
3.2*t PROVI DE SMOOTH SLOPE

ROCKS
-ZPROPOSED SLOPE

OLD WALLIS ROAD ROADBED
SECTION A - A'.

NOT TO SCALE

ROAD BED
G.O,�
4.5'illLtu STONE
k-MARSH FOUNDATION
-3.2*�
ROCKS TO
BE REMOVED 0-1.0,2
LPROPOSED-
BOTTOM

OLD WALLIS ROAD ROADBED
SECTION B - B'

NOT TO SCALE
@F
L

t
RO
F
B E

FIGURE 6

Site: Culvert #5

Recommendation #8: Maintain existing culvert (Map 1). In the
course of a routine replacement program, replace with similar
capacity pipe set approximately 0.5 - 1.0 ft. below existing
invert elevation of 3.5 ft.

Rationale: Improve tidal exchange (L).

Site: Concord Point Outlet (Map 1)

Recommendation #9: Maintain channel free of sediment and
organic matter buildup. If possible, remove barge remnants
and reconfigure channel as previously specified.

Rationale: Improve tidal exchange (H).

PHILBRICK BROOK MARSH

Site: Culvert #11

Recommendation #10: Replace culvert with 24-inch RCP set at
approximately 3.5 ft. Improve and extend ditches east of the
pipe (Figures 7 and 8) to create a 6-foot radius, semicircular
basin at the pipe mouth, with drainage ditches extending north
and south from the basin at the foot of the highway
embankment.

Rationale: Improve tidal exchange (M).

Site: Culvert #10

Recommendation #11: Replace existing culvert with 29" x 45"
RCP set horizontally at approximately 2.5 ft. (existing CMP is
at approximately 3.0 ft.). Improve existing creek by removing
sediment deposits east of pipe (Figures 7 and 9).

Rationale: Improve tidal exchange (L).

Site: Culvert #9

Recommendation #12: Replace existing culvert with 29" x 45"
RCP set at approximately 2.0 ft. Improve existing creek by
removing sandbar south of pipe, and rocks and peat chunks
north of pipe (Figures 10 and 11).

Rationale: Improve.tidal exchange (H).

Lik, Jjk'1 loll

10
REPLACE
%% AS
.... % SPECIFIED
%

CLEAN
ROCKS and
SEDI
VP MENT
k-, FROM CREEK
UPLAND

01 10,

SALT
MARSH

0
EXTEND AND
50
IMPROVE
EXISTING
DITCH and BASIN

10,
REPLACE
AS
SPECIFIED

UPLAND
151 \CLEAN
1 CREEK
I TO CULVERT

Figure 7. Recommended improvements for southern part of Philbrick Brook salt
marsh, Rye, NH.

PHILBRICK BROOK
SALT MARSH
FLOW

RIP RAP

RT IA OCEAN BLVD

EXTEND AND IMPROVE
E)asnNG DITCH AND BASIN

PLAN

NO SCALE

RT. IA OCEAN BLVD.

ELEV. 9.00'

24- RCP
(TYP.)

.002% MIN.

- - - - - - - - - - - - - - - -
ELEV. 3.5' INV.

90,

PROFILE

PHILBRICK BROOK MARSH
0 voo

CULVERT #11

NO SCALE
FIGURE 8

PHILBRICK
BROOK

FLOW

PRIVATE
DRIVE

RIP RAP

CLEAN ROCKS AND
PLAN SEDIMENT FROM CREEK
NO SCALE EAST OF PIPE

PRIVAIE-DRIVE

ELEV. G.85*
(TYFJ 29' x 45" RCP SET
HORIZONTALLY

ELEV. 2.5* INV.

40'

PROFILE
PHILEIRICK BROOK MARSH

CULVERT # 10
NO SCALE

A FIGURE 9

EO
'EXTEND ANDI CEXTEND.
IMPROVE Of
AXISTING
DITCHES EXISTING
DITCHES

Lj
%TIDAL
of REE
1 NEW
ROCII I -
WALLS ITCH

SALT MARSH
(EL. 4.S'�)

EXTEND
80 /DITCHES FROM I
CREEK

EXTEND
CLEAN
ROCKS and IMPROVE CULVERTS
1 7, 8, and 9
I SEDIMENT [3 AS SPECIFIED
FROM CREEK
NEW) 10,
9 -
DI I

Figure 10. Recommended improvements for northern part of Philbrick Brook salt
marsh, Rye, NH.

REMOVE EXISTING ROCKS AND PEAT
CHUNKS NORTH OF PIPE

\--GRANITE ABUTMENT

29' x 45- RCP

LOCKE RD.

REMOVE EXISTING
SANDBAR SOUTH OF PIPE

FLOW

PLAN

NO SCALE

LOCKE RD.

ELEV.'7.68'
101-6" GRANITE ABUTMENT
po
(TYP.)

- - - - - - - - - - - - -
ELEV. Z.00* INV.

40*
-- ------- @SELF-REGULATING
TIDE GATE ON
NORTH END OF PIPE

29- 45- RCP PROFILE
PHILBRICK BROOK MARSH

CULVERT # 9
(TYP.)

NO SCALE

FIGURE I I

Site: Culvert #8 (Granite sluiceway)

Recommendation #13: Replace existing sluiceway with similar
structure approximately 48 inches wide with same invert
elevation. Install self-regulating tide gate at east end of
sluiceway.

Rationale: Improve stormwater runoff capacity (H). Improve
tidal exchange (L). Protect against tidal storm surge (H).
Replace deteriorated structure.

Recommendation J114: Dig new ditch from tidal creek near west
end of Culvert #8 southeast into panne area (Figure 10).

Rationale: Improve tidal exchange (L).

Recommendation J/15: Improve and extend existing ditch from
vicinity of west end of Culvert #8 southwest through panne
areas and existing stone walls (Figure 10).

Rationale: Improve tidal exchange (M).

Site: Culvert #7

Recommendation #16: Extend and improve existing ditches west
of Ocean Blvd to pass through existing rock walls and
intersect panne areas (Figure 10). Install self-regulating
tide gate at east end of pipe.

Rationale: Improve tidal exchange (M). Protect against tidal
storm surge (H).

Recommendation #17: Dig new ditch from vicinity of east end
of Culvert #7 south into panne area. Extend ditch through
panne area for maximum effectiveness. Locate ditch in the
marsh, as near as practicable to the base of the highway
embankment (Figure 10).

Rationale: Improve tidal exchange (M).

Site: Marsh South of Rye Harbor

Recommendation #18: Extend ditches from existing creek in
southern part of marsh through stone walls and into panne
areas (Figure 10). ,

Rationale: Improve tidal exchange (M).

Recommendation #19: Extend existing ditch east of main tidal
creek near Harbor Road bridge east into panne area (Figure
10).

Rationale: Improve tidal exchange (L).

4.0 LITERATURE CITED

COE. 1980. New England Coastline Tidal Flood Survey. U.S. Army Corps
of Engineers, Waltham, MA.

D'Agostino, S. 1988. Wetlands: Victims of sea level rise? Coastal
Planning Newsletter, New Hampshire Office of State Planning,
Concord, NH.

Federal Emergency Management Agency (FEMA). 1986. Flood Insurance Rate
Maps, Town of Rye, New Hampshire, Rockingham County. Community-
Panel Numbers 330141 0002B and 330141 0003B.

HEC-1. 1985. Flood hydrographic package (IBM XT 512K version). U.S.
Army Corps of Engineers, The Hydrologic Engineering Center, Davis,
CA.

Hoffman, J.S., D. Keyes, and J.G. Titus. 1983. Projecting future sea
level rise. Methodology, estimates to the year 2100, and research
needs. U.S. EPA Office of Policy and Resource Management.
Washington, DC. EPA 230-09-007. 121 pp.

LIRPB. 1984. Hurricane Damage Mitigation Plan. Long Island Regional
Planning Board, Hauppauge, New York. 196 pp.

Normandeau Associates Inc. 1986a. Phase 2 Report. The Coastal
Wetlands Mapping Program, New Hampshire. Prepared for the New
Hampshire Office of State Planning Coastal Program.

Normandeau Associates Inc. 1986b. Tasks 2 and 3 Final Report. Summary
of field investigations of coastal wetlands and associated road
crossings in the Town of Rye, New Hampshire. Prepared for the Town
of Rye and the New Hampshire Office of State Planning Coastal
Program.

Shevenell Gallen and Associates, Inc. 1987. Technical Report. Rise in
Sea Level and Coastal Zone Planning. Prepared for Office of State
Planning, Concord, NH 19 pp.

Simpson, M. 1986. Restoration of Parsons Creek Marsh, Rye, NH.
Antioch New England, M. Sc. Thesis.

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