Technical Report Series
Number 82-1
STRUCTURAL CONTROL
OF DRAINAGE MORPHOLOGY
OF SALT MARSHES ON
ST. CATHERINE'S ISLAND, GA.
Joe R. Wadsworth, Jr.
Georgia Marine Science Center
University System of Georgia
Skidaway Island, Georgia
STRUCTURAL CONTROL OF DRAINAGE MORPHOLOGY
OF SALT MARSHES ON
ST. CATHERINE•s ISLAND, GEORGIA
Technical Report 82-1
by
Joe R. Wadsworth, Jr.
November 1981
(written June 1978)
Department of Geology
University of South Florida
Tampa, FL 33620
The Technical Report Series of the Georgia Marine Science Center is
issued by the Georgia Sea Grant Program and the Marine Extension Service
of the University of Georgia on Skidaway Island (P.O. Box 13687,
Savannah, Georgia 31406). It was established to provide dissemination
of technical information and progress reports resulting from marine
studies and investigations mainly by staff and faculty of the University
System of Georgia. In addition, it is intended for the presentation
of techniques and methods, reduced data and general information of
interest to industry, local, regional, and state governments and the
public. Information contained in these reports is in the public domain.
If this publication is cited, it should be cited as an unpublished manuscript.
ACKNOWLEDGEMENTS
The author gratefully acknowledges the help of many organizations
and individuals in this study. The Edward John Noble Foundation provided
financial aid~ accommodations~ and the opportunity to study a unique and
undisturbed marsh environment. Dr. Roy Welch and the University of Georgia
Department of Geography provided use of photogrammetric equipment. Dr. Paul
Pinet reviewed the manuscript and offered helpful suggestions. Dr. J.D.
Howard gave permission to use several diagrams.
TABLE OF CONTENTS
Page
ACKNOWLEDGEMENTS
ii
LIST OF ILLUSTRATIONS
v
ABSTRACT
vi
INTRODUCTION
PREVIOUS STUDIES
2
REGIONAL SETTING
3
LOCAL SETTING
3
GENERAL APPROACH
5
IMAGERY SELECTION AND ANALYSIS
9
RESULTS - TOPOGRAPHIC INVESTIGATION
10
RESULTS - FIELD INVESTIGATION
10
RESULTS - PHOTOGRAMMETRIC ANALYSES
General Observations
Fore- vs. Back-Island Marsh Drainage
Evidence of Structural Control
13
13
18
19
CONCLUSIONS
25
REFERENCES CITED
27
APPENDIX I - Drainage Network Maps
29
APPENDIX II - Juncture Angles (Raw Data)
34
APPENDIX III - Juncture Angles (Deviation from 90°)
36
APPENDIX IV - Tabulation of Juncture Angle Sign
38
APPENDIX V - Channel Segment Orientations (Raw Data)
39 ·
APPENDIX VI - Tabulation of Channel Segment Orientations
42
iii
Page
APPENDIX VII - Numerical Breakdown of Juncture Angle
Distribution
43
APPENDIX VIII - Percentage Breakdown of Juncture Angle
Distribution
43
iV
LIST OF ILLUSTRATIONS
Page
Figure
1
Regional and local map of St. Catherine ' s Island,
Georgia
4
2
Generalized salt marsh crosssection
6
3
Generalized crosssection of washover fan
12
4
Location of drainage networks included in photogrammetric analysis
14
5
Distributions of juncture angles for all drainage
networks
17
6
Ebb versus flood domination for fore- and backisland marshes
20
7
Comparative distributions of juncture angles for
large and small channels
23
8
Rose diagrams showing distributions of channel
orientations
24
LIST OF TABLES
Page
Table
1
Summary of data from photogrammetric analysis
v
15
ABSTRACT
A combination of photogrammetric, topographic, and field analyses
showed that significant structural control by relict beach ridges is
exerted on development of drainage morphology of salt marshes on
St. Catherine's Island, Ga. Structural control was indicated by bifurcation ratio, juncture angle, and most clearly, in preferred orientation
of channels, which was strongest in second order channels. Factors
affecting structural control included stream order, basin size, and
type of juncture. The principal mechanism of control was lateral confinement of channels by ridge remnants eroded below the marsh surface;
extent of control appeared related to depth of channel incision below
marsh surface.
vi
l
INTRODUCTION
The purpose of this study was to identify the effects of structural
control exerted by relict Holocene beach ridges on morphology of tidal
drainage networks on St. Catherine's Island, Georgia. Like many barrier
islands on the Georgia coast, St. Catherine's consists of a core of
Pleistocene material, surrounded by an extensive series of Holocene
salt marshes and relict beach ridges. These marshes are very dynamic
sedimentary systems, and have extensive and intricate drainage networks
that are constantly changing through processes of lateral migration,
stream capture, and channel blockage and fill.
The extent and manner in which these processes operate depend upon
such regional variables as tidal range, climate, and sediment type, as
well as upon many local influences. Among the most significant local
influences affecting the development of tidal-drainage morphology is
structural control. Only when the effects of this control have been
evaluated is it possible to interpret the true response of drainage
morphology to regional variables and to make legitimate comparisons
between the tidal drainage morphologies of widely separated localities.
Ideally, one would like to know the following:
1.
Which tidal-drainage networks exhibit strong structural control?
2.
Which morphologic parameters describing these drainages are
most strongly affected? Which are best for evaluating the
effects of control?
3.
How great is the effect of control?
depend?
4.
At what level in the stream order heirarchy do the effects of
structural control become most evident? Why is this the case?
5.
By what mechanisms is this control exerted?
Upon which factors does it
Effects of local structural control on salt marsh drainage networks
on St. Catherine's Island were studied using photogrammetric methods
along with field investigation and topographic analysis. Initial topographic analysis was used to check the validity of the photogrammetric
approach, and to help select morphologic variables for subsequent
measurement. Aerial photography of the study area was examined, and
measurements describing the morphology of several tidal drainage networks
were made. A field investigation was used to check photoidentification
of drainage features and provided close-up observation of some specific
control mechanisms.
2
PREVIOUS STUDIES
Few studies have been conducted on the development of salt marsh geomorphology, although many previous studies have addressed their ecology
(Chapman, 1960; Hinde, 1952), landforms (Johnson, 1925; Stevenson, 1954),
and sedimentological significance (Straaten and Kuenen, 1957; Straaten,
1963). Three papers are of particular relevance to the present study.
Pestrong (1965) studied San Francisco Bay marshes, which are similar in
many respects to those on the Georgia coast. He noted several important
mechanisms that influence surface development of the marshes, and measured
their physiography and sediment properties. Ragotskie (1958) summarized
the important controls that affect the development of Georgia salt marshes
and concluded that little evidence from the morphology of the tidal drainages exists to suggest that structural control was an important factor
in their development. Wadsworth (1980) characterized the network morphology of tidal drainage in the Duplin River system, Georgia, and compared
it to that of typical fluvial systems. He described an annular drainage
pattern that was a reflector of structural control by underlying beach
ridge remnants.
Studies of fluvial drainage systems are more numerous, and are useful
in drawing inferences concerning salt marsh drainage geomorphology. Strahler (1964) gives an excellent review of frequently used fluvial geomorphic
parameters, including specific techniques for measurement and some generalized lines of interpretation. Technical reports by Howard and Jaffe (1977)
and Deery (1976) describe the sedimentary environments of St. Catherine's
Island and its surroundings. Howard and Jaffe evaluate the various sedimentary environments on the island, including salt marshes, active beaches,
and relict beach ridges. Deery examines washover fans as an important
sedimentary process on St. Catherine's Island. · (As explained later in this
paper, these fans may play a role in one structural control mechanism.)
Many general papers have been written on the salt marsh environment of
the Georgia coast, including those by Basan and Frey (1976), and Howard,
Frey, and Reineck (1973). Papers concerning the use of various types of
remote-sensing imagery in studying salt marshes of this region include
those by Reimold, Gallagher, and Thompson (1972), Gallagher and Reimold
(1972), and McEwen, Kosco, and Carter (1976).
3
REGIONAL SETTING
St. Catherine's Island lies midway down the Sea Island Section, a
barrier island chain along the Georgia-South Carolina coast (Figure 1).
Approximately 18 km long and 2 to 6 km wide and oriented NNE by SSW,
St. Catherine's Island is separated from the mainland by an expanse
of intertidal salt marsh 6 to 10 km wide. St. Catherine's Island and
the adjacent marsh belt to the west are bounded by two major tidal inlets; St. Catherine's Sound in the north separates the island from
Ossabaw Island, and Sapelo Sound in the south separates it from Blackbeard and Sapelo Islands. These sounds are the lower reaches of "salt
water estuaries" (i.e., marine embayments lacking true river input).
Barrier islands along the Georgia coast consist of Holocene or adjacent Holocene and Pleistocene sediments deposited during successive
stands of sea level. St. Catherine's Island consists of a Pleistocene core (a remnant of the Silver Bluff shoreline formed 20,000 to
40,000 years B.P.), from which extends a series of Holocene tidal
marshes, relict beach ridges, and modern beaches. The Pleistocene core
and relict beach ridges represent relative topographic highs, between
which the low-lying tidal marshes have developed.
LOCAL SETTING
Salt marshes on St. Catherine's Island are typical of those along
the Georgia-South Carolina coast, and consist of "well-vegetated intertidal flats" (Basan and Frey, 1972) dominated by the salt grass Spartina
alterniflora. These marshes have extensive and intricate drainage
networks connecting with the open sea through large tidal inlets that
separate the individual barrier islands.
Except in those marshes
lying along the "true estuaries" (_e.g., the Savannah and Altamaha
Rivers), marsh salinities generally range from 20 to 30 ppt (0/00),
but can vary from about 4 (after a heavy rain) to 70 (in isolated
low areas). Marsh sediments consist mainly of homogeneous silty clays,
with muddy to fairly clean sands and oyster pavements present locally
(Frey, 1973; Edwards and Frey, 1972; Wiedemann, 1972). Thicknesses of
marsh sediment vary from a few centimeters bordering terrestrial environments to more than two meters in midmarsh areas (Hoyt et al., 1964},
depending upon the topography of the underlying Pleistocene surface.
Tidal flushing and rapid decomposition of plant debris retard the accumulation of peat.
4
S 0 U T H
CAROLINA
N~TH
&EACH
MIDOLE lEACH
SOUTH 8EACH
0~_ __.__~,. ....
Figure 1. Regional and local map of St. Catherine's Island, Georgia.
St. Catherine's lies in the middle part of the Sea Island Section of
Georgia and South Carolina (from Howard and Jaffe, 1977).
5
Georgia tidal marshes are subdivided into the general categories
of "high marsh" and "low marsh" on the basis of vegetative zonation
and/or sedimentological characteristics; these two areas are further
divided into subenvironments determined by vegetative zonation and
slight differences in topography (Frey & Howard, 1969) (Figure 2). The
breakdown of subenvironments within a marsh generally is independent of
the distance across the marsh, although relative proportions of the
various subenvironments are variable, depending on factors such as the
age of the marsh.
The Holocene relict beach ridge series on St. Catherine's Island
presents a ridge and swale topography recognizable in aerial photography
by relief of three to four meters between the ridge tops and the surface
of the marsh, expressed by an obvious change in vegetative assemblage.
Ridges are made of sand and generally show dune cross-stratification.
Ridge vegetation on the southern end of the island is dominated by live
oak (Quercus vir iniana) and cabbage palm (Sabal palmetto) with an understory of saw palmetto Serenoa repens), and in the north by live oak,
slash pine (Pinus elliotti), and longleaf pine(~. palustris). These
ridges represent former positions of accreting shorelines along
St. Catherine's Island, presumably formed in the same manner as the
modern actively depositing recurved spits and shoals of McQueens and
Seaside Inlets and the northeastern tip of the island.
Except for the tidal-delta deposits immediately south of McQueens
and Seaside Inlets, all beaches bordering the salt marsh in the areas
studied are erosional. Consequently, beaches on the eastern side of the
island are continually moving inland over the marsA surface; active
beaches are absent from the western side. Beach sand is transported
inland chiefly by dune chain migration and emplacement of washover fans.
The most intense washover activity in the Sea Island Section occurs on
St. Catherine's Island, and may represent a link in one mechanism of
structural control, as discussed later in this report.
GENERAL APPROACH
Photogrammetric analytical methods were used to study tidal-drainage
networks for the following reasons:
1.
accessibility: The intertidal environment is difficult to study
on the ground, as it is inaccessible by terrestrial vehicles and
only periodically accessible by boat. Travel on foot is slow
and difficult, particularly in the wetter areas of the marsh.
Aerial photographs provide ready access to any part of the marsh
for purposes of simple visual inspection.
2.
synchroneity: Considerable time may elapse between ground observations of widely separated areas of marsh, during which conditions
may change significantly. For example, tidal marshes can completely
change their circulation patterns in the space of an hour. Aerial
6
- - - - L O W MARSH---=-----
- - - - - H I G H MARSH--'-----
Figure 2. Generalized marsh cross-section, showing zonation of salt
marsh environments. This basic sequence of subenvironments tends to
be repeated along any transect, regardless of marsh width, although the
relative extent of the various subenvironments may vary considerably
(from Howard and Jaffe, 1977).
7
photographs minimize this problem by capturing an instant in
time.
3.
scale: The tidal marshes on St . Catherine S Island are
extensive, and only a small part of the marsh can be seen in
the field at one time. Aerial photographs provide an overview
of an entire drainage networ k and offer a more complete perspective of the whole tidal system.
4.
ease of measurement: f':leasurement of the location and distribution of tidal drainage channels may be obtained easily through
analysis of aerial photographs, requiring only a minimum of
equipment and training.
5.
parallax error: Positional errors introduced by elevation
differences within a study area are minimal for the salt marsh
environment because of its extreme flatness and relative
horizontality. Consequently, no adjustments for height differences
are necessary for this type of study, which greatly simplifies
the analytical procedure.
6.
time of analysis: Compared to other methods, a photogrammetric
approach to the study of tidal drainage networks greatly reduces
the time needed to collect basic data.
7.
cost of analysis: A photoanalytical approach to studying the
intertidal environment is economical because it provides ease
of data collection, minimum training and equipment requirements,
and reduced overall project time.
8.
permanent record: Photographs used in the study are permanently
available for later reexamination or use in subsequent studies,
and m1n1m1ze the possibility of personal bias being inherent in
the data.
1
St. Catherine S Island is an excellent location for a photogrammetric
study of the development of tidal drainage networks for the following
reasons:
1
1.
Photographic coverage at varying scales is available for the
island, including color and panchromatic imagery.
2.
Because of its designation as a protected area for scientific
investigation, St. Catherine 1 S Island salt marshes remain
essentially undisturbed, simplifying problems of cultural overprint and misidentification of artificial features.
3.
Previous studies of the island provide supporting data in many
fields that bear on the present study.
4.
The island has both fore- and back-island tidal marshes (the
former being a less common environment along the Georgia coast),
which invite comparison of drainage development of the two.
8
5.
Distribution of salt marshes on the island relative to locations
of relict Holocene beach ridges includes both areas where the
marshes are thin strips between closely-spaced ridges and broad
areas of marsh in which no ridges are visible. This range
permits determination of the relationship between structural
control by relict beach ridges and drainage morphology of the
tidal marshes by comparision of the two types of areas.
6.
Ground access to the marshes is simplified by the presence of
Holocene beach ridges and the network of sand roads on the island.
7.
The broad strip of open marsh separating St. Catherine's Island
from the mainland contains drainage networks essentially free of
structural control, and useful for comparison to more controlled
drainage networks on the island.
Based upon the conclusions drawn in the preliminary topographic
investigation and from previous related studies, the following parameters
were chosen for the photogrammetric phase of the study as being most
likely to show the degree of structural control inherent in the tidal
drainage networks:
1.
Stream order was used to indicate relative channel size for
comparison of data from different networks, and in calculating
bifurcation and stream length ratios (Appendix I). Stream orders
were determined by the standard procedure used for fluvial systems
(Strahler, 1964).
2.
Drainage basin areas were measured for all drainage networks
studied and were used in ranking all data obtained for those
drainages (Table 1). Drainage basin area limits the maximum
potential size of the corresponding drainage network, and therefore influences other descriptive parameters.
3.
Drainage density has been a good indicator of structural control
in related studies (Strahler, 1964; Manual of Remote Sensing,
1975), with high drainage densitiescorresponding to greater control. Measures were obtained by dividing total stream length of
the drainage network by its drainage basin area (Table I).
4.
Preferred orientation: In the prelim·inary topographic study, a
direct relationship was indicated between the degree of preferred
orientation of channel segments and proximity to elevated land.
Orientation was measured for each stream segment in the photogrammetric study (Appendices V and VI) and plotted for different
stream orders and for the entire network.
5.
Juncture angles are related to the relative velocities of merging
tidal channels (Pestrong, 1965), and therefore indicate tidal
circulation patterns. Juncture angles were measured for each
channel intersection (Appendices II, III, and IV) and plotted for
different levels of stream order and for the entire drainage
network.
9
6.
Stream length ratios may indicate structural control, with low
ratios corresponding to low control (Strahler, 1964). The ratio
used in this study was derived by dividing total length of the
stream segments of each stream order by the total length of
segments of the next higher order, and was calculated for each
pair of successive stream orders (Table I).
7.
Bifurcation ratios also indicate structural control, with low
ratios corresponding to greater structural control. This ratio
equals the total number of stream segments of a particular order
divided by the total number of the next higher order, and was
calculated for each pair of successive stream orders (Table I).
IMAGERY SELECTION AND ANALYSIS
Tnree types of photography were used in the study: medium altitude
(15,000 feet) vertical color transparencies, low altitude vertical
panchromatic prints, and low altitude oblique color slides. Whenever
possible, transparencies were used rather than prints because of their
greater resolution (Welch, 1968). Color transparencies were obtained
from the National Ocean Survey, and were taken at low tide on 11/4/71
for purposes of general delineation of the intertidal zone. The scale
of 1:30,000 permitted viewing of an entire individual drainage network
on a single image, and this imagery was used to assess the regional extent
of relationships observed in larger scale imagery.
Low-altitude oblique-color slides were taken by the author on
April 15, 1976, during the year's lowest tide, from a light plane at an
average altitude of 500 feet and using a Kodak 35mm camera. This imagery
was used in conjunction with the field investigation to identify specific
control mechanisms affecting the development of tidal drainage networks.
Panchromatic photographs used in the study were taken during low
tide on April 13, 1976. The scale of 1:24,000 allowed recognition of
first order drainage channels, and the photos were used for final preparation of drainage network maps.
Vertical photography was examined with a Bausch and Lomb Zoom Transfer
Scope at magnifications ranging from lX to 7X. Drainage networks were
transferred from the photographs to a set of base maps at a scale of
1:17,550. Ground control for transfer of imagery detail was obtained
from U. S. Geological Survey 1:24,000 scale topographic sheets, which
were sufficiently accurate for this study. Measurements of the
drainage networks were than taken from the base maps, shown in Appendix I.
10
RESULTS - TOPOGRAPHIC INVESTIGATION
A general examination of tidal drainage networks along the
Georgia-South Carolina coast was made, using 1:24 , 000 scale U.S.G.S.
topographic maps, to determine if detection of structural control
through the study of marsh drainage networks was a practical approach,
and to select morphologic parameters to assess this control. The
following points were noted:
1.
Although the total relief of the marsh environment spanned
only a ten-foot contour interval, direction of the local slope
could be determined from the orientation of stream junctures.
This relationship was also useful in recognizing local structural
control.
2.
Drainage typically was dendritic, but stream segments close to
the mainland or the barrier islands displayed preferred orientation normal to the shoreline, while drainage networks located
centrally between the mainland and the barrier chain displayed
no preferred orientation of their stream segments.
3.
Deflected drainage networks appeared in some areas of the marsh
with no visible physical barriers, possibly due to the presence
of partially eroded relict beach ridges hidden below the marsh
surface.
4.
Drainage networks in marsh areas confined by adjacent beach
ridges had lower drainage densities and stream orders than
adjacent unconfined networks, and showed a decrease in overall
drainage development.
It was concluded that structural control exerted by relict beach
ridges on the development of tidal marsh drainage was evident in the
morphology of some of the tidal drainage networks, and was expressed
by differences in the degree of preferred orientation, stream order, and
juncture angle.
RESULTS - FIELD INVESTIGATION
The field investigation conducted August 1976 fulfilled two objectives:
It verified features identified as tidal channel s on the image ry, and
it examined in situ some specific processes by which relict beach ridges
exert structurar-oDntrol upon the morphology of tidal drainage networks.
Field verification of imagery was comparatively simple, because of the
relatively undisturbed state of St. Catherine•s Island and the lack of
car tracks, drainage control ditches, and other artificial lineaments.
11
Channels identified on the imagery correlated perfectly with the
actual drainage networks.
Several structural control mechanisms and their effects on
drainage network morphology were identified during the field investigation, as follows:
1.
2.
3.
Examples were seen of large tidal channels that had meandered
against the side of relict beach ridges, beyond which point
they apparently were unable to progress. Associated aspects
include the following:
a.
The stream segment involved apparently became "fixed" in
position until it naturally meandered in the opposite
direction.
b.
This stream segment consequently developed an "artificial"
orientation, which it would not have assumed had the ridge
not been present.
c.
The stream segment had no tributaries on the ridgeward side.
Both fore- and back-island drainage networks showed evidence of
restricted tributary development, as indicated by higher-order
channels extending to the limits of the drainage area, rather
than bifurcating into successively lower-order channels near
the perimeter of the drainage basin. Associated features include
the following:
a.
Drainage density of higher-order channels appeared to be
greater than in other areas which were not so confined.
b.
Conversely, drainage density of lower-order channels
appeared lower than in less confined areas.
c.
Bifurcation was low.
d.
A greater percentage of the drainage area appeared to be
low marsh than in comparable, less restricted areas.
Numerous washover fans blocked off segments of tidal channels
near the seaward marg i n of the island (Figure 3). Washover fans
seemtohavedeposited sand preferentially in tidal channels,
extending tongues beyond the main body of the fan. This was
expected, because tidal channels are local depressions, and
will channel sediment flow during washover deposition. Some
associated features follow:
a.
Channel blockage Dccurred principally in those segments
lying perpendicular to the direction of washover sediment
movement. Blockage of channels which lay parallel to the
direction of sediment movement proceeded more slowly. The
net result was a preferential blockage and elimination of
channels lying parallel and close to the eastern shoreline
of the island.
12
durt~l
lligh
t id~
low tide-
Figure 3. General cross-section of a washover fan, showing associated
facies. As the beach erodes, washover fans are built across the seaward edge of the marsh, ultimately coalescing into a broad apron which
is then overtaken by the dunes as they migrate inland (from Howard
and Jaffe, 1977).
13
4.
b.
Location of the washovers was controlled by the spacing and
orientation of relict ridges relative to the eastern shoreline
of the island. This determined the shore areas where washover blockage of tidal channels was an effective process.
c.
The channel blocking process operates only on drainage
networks located on the seaward side, because washover fans
occur only on this side .
Higher-order stream segments tended to align parallel to the
general orientation of the relict Holocene beach ridges, even
where channel segments did not closely approach visible ridges.
Some associated features are listed below .
.
a.
Alignment of the higher-order stream segments parallel to
the beach ridges theoretically would reinforce blockage of
smaller laterally branching channels by washover deposition.
b.
Alignment of the higher-order stream segments extended to
the orientations of lower-order streams within the same
network, resulting in a degree of preferred orientation at
several stream orders.
c.
Alignment of higher-order stream segments in areas where no
beach ridges are visible suggests that structural control in
these areas is exerted by ridges that have been eroded below
the marsh surface.
RESULTS - PHOTOGRAMMETRIC ANALYSIS
Four drainage networks were analyzed in the photogrammetric phase of
the study--two from the fore-island marshes and two from the back-island
marshes (Figure 4). These networks occupied the four largest tidal
drainage basins (and have the highest stream orders) on the island.
Results of this analysis fall into three categories: (1) general observation on drainage morphology and comparisons with previous work, (2) comparison of the drainage morphology of fore- versus back-island marshes, and
(3) evidence of structural control shown by various morphologic parameters
describing drainage.
1.
General observations were made, based on measurements of channel
segment lengths, drainage basin areas, and ratios derived from
both (Table I):
a.
In each of the four drainage networks, maximum stream order
was directly related to the area of the respective drainage
basin (Appendix I), as is the case for fluvial systems .
(Strahler, 1964).
b.
Drainage density was uniform for the three largest drainage
basins, with the smallest having a slightly higher value.
14
c
Figure 4. Locations of the four tidal drainage networks included in
the photogrammetric analysis.
Table I - Summary of geomorphic data from photogrammetric analysis.
# of
Network
segments
Order
- - - B
(backisland)
-
-
2
3
9
- - - -
1
19
6
1
2
3
- -
c
(backisland)
64
17
3
1
2
3
4
- - - -
-
0
(foreisland)
Stream
length
3.56
9.00
4. 72 km
2.88 km
2.88 km
32
A
(foreisland)
Bifurcation
ratio
2
3
4
5
-
- 148
32
11
3
1
- - - - - - - - - 4.54 km
4. 72 km
3.15 km
3.17
6.00
- -
-
Stream
length
ratio
-
- - - -
1.64
1.00
-
- -
.963
1.50
- - - - -
Cumulative
stream
length
4. 72
7.60
10.49
- - 4.54
9.26
12.41
km
km
km
- km
km
km
10.75 km
10.75 km
3. 77
6.82 km
1.58
17.56 km
5.67
2.48 km
2.79
20.01 km
3.00
5.33 km
.459
25.34 km
------ - - 29.80 km
29.80 km
4.62
12.06 km
2.47
41.86 km
2.91
6.20 km
1. 94
48.06 km
3.15 km
51.21 km
3.67
1.97
3.00
4.81 km b .655
56.01 km
Drainage
density
Basin
area
1.23 km
2
------2.05 km
3.84 km
2
8.53 km/km
- - - - - - -
2
-
2
6.05 km/km
2
------
6.60 km/km
2
------- -------
8.35 km 2
6. 71 km/km 2
16
c.
Cumulative stream length in each basin was directly related
to drainage area, again similar to fluvial systems. However,
the total number of stream segments in a given drainage
basin showed no consistent relationship to basin area.
d.
In all cases, bifurcation ratios were not consistent within
a given drainage netv'lork from one level or order to the next.
This is in sharp contrast to the morphology of fluvial systems,
where bifurcation ratios are fairly constant on all levels of
any given drainage network (Strahler, lg64). This implies
that an additional control or controls operates in the tidal
system that is absent in the typical fluvial system.
e.
In all cases, stream length ratios were inconsistent within
a given drainage network from one level or order to the next.
The variation in stream length ratio was similar to variation
in bifurcation ratio of the same network, with the exception
of the smallest drainage basin (where high drainage density
of small channels was probably an overriding factor).
Extensive measurements of juncture angle were also made
{Appendices II, III, IV) and examined for evidence of ebb flow
dominance (see Pestrong, lg65) and for evidence of control by
relative channel velocities. According to Pestrong, as the
difference in velocities between two intersecting channels
increases, the angle of their juncture tends to approach goo.
This hypothesis was examined relative to the St. Catherine's
marsh data by plotting a family of histograms showing the
deviation from goo of all types of junctures encountered in
the study, treating the data from all four of the drainage
networks collectively (Figure 5). Based upon these graphs,
the following observations were made:
a.
Juncture angles of first-order channels with channels of all
orders commonly approached 90°, suggesting that currents in
first-order channels are weak in comparison to higher order
channels in the network.
b.
Kurtosis and skewness toward goo increased markedly for
junctures of first-order channels with channels of increasingly
higher order; this supports Pestrong's previously cited
hypothesis.
c.
Junctures between channels of order two or greater showed
much lower skewness and kurtosis than did first-order channel
junctures, and did not tend toward goo . While this may simply
be a function of the larger channels being fewer than the
first-order channels (and hence less clearly indicative of
the relationships mentioned in (a) and (b) above), other
possibilities which may enter into this variation include
the fo 11 owing:
17
ORDER
first
- oF
SECOND
second
CHANNEL
third
40
70
40
70
40
70
8
Cll
a::
H
r..
15
15
10
Notes Horizontal axis shows j uncture
angle in degrees. Vertical axis
shows number of observations for
each ten degree interval of
juncture angle, All combinations
of stream order are shown.
40
70
15
10
40
15
15
10
10
..c::
+>
~
....0
10
40
70
10
Figure 5. Distributions of all types of juncture angles. Data from
all four drainage networks have been treated collectively. Juncture
angles are given as degrees of inclination from a right angle (0° =
right angle).
18
i.
ii.
2.
The relative differences in the velocities are smaller,
and consequently junctures tend less strongly toward
goo.
The absolut~ range of the velocities is greater, resulting
in a lower kurtosis.
iii.
The effects of bidirectional flow are more important,
obscuring the effects of cont~by relative velocities.
iv.
Some additional factor (e.g., structural control), which
was relatively unimportant for the smaller channels,
might be more influential in determining the juncture
angles of the larger channels, obscuring the effects
of control by relative velocities.
Fore- versus Back-Island Marsh Drainage: Data for all geomorphic
parameters routinely were grouped throughout the study into a
subset for fore-island marshes and a subset for back-island marshes,
to determine if marsh location on the island influenced the development of its drainage morphology. The rationale for making this
comparison was threefold.
a.
Location on the seaward side of the island exposes the marsh
to much more direct action by the sea, through such processes
as formation, migration, and erosion of active beaches, and
emplacement of washover fans. As explained previously,
these processes may play a role in the development of foreisland drainage morphology.
b.
Aerial photo analyses indicate that the main beach ridge
series which interfingers with the fore-island marshes has
a somewhat different origin from that bordering the backisland marshes. Fore-island relict beach ridges appear to
have formed throu9h the successive development of beaches
and dune ridges that parallel the present shoreline. These
may have developed by accretion of offshore bars, chenierlike ridges, or similar mechanisms, during the gradual progradation of the island seaward.
In contrast, the back-island ridge series seems to have
developed as a series of recurved spits deposited around the
end of the island by longshore drift. This contrast could
have played a role in differentiating the development of
the respective drainage networks.
c.
The dissimilar locations of the fore- and back-island
marshes affect their tidal circulation patterns and hence
drainage morphologies.
With one exception, the results of this study do not offer much
support for any of these possibilities. At the scale of this
study, none of the measures showed any significant differences
19
between the morphology of fore- and back-island marshes. However, this simply may be a function of the small number of networks available on the island for consideration.
The one exception to this lack of contrast was seen in a second
analysis of juncture angle data (Appendix IV) in which the
deviation of juncture angle from 90° was denoted as positive
(+) if the angle was obtuse relative to its seaward limb, and
as negative (-) if the angle was acute. The percentage of (+)
versus (-) inclinations then was plotted for each order (taken
as the lowest order of the two stream segments making up the
angle) for each drainage network. The author felt that this
might indicate the relative importance of ebb versus flood flow
as related to channel order. Pestrong (1965) observed that
l ower-order channels appeared to be strongly dominated by ebbing
flow in the San Francisco bay marshes. Despite the scarcity of
available measurements in the present study, significantly
different trends were evident in the lumped data for the foreand back-island marshes (Figure 6). For each order, fore-island
marshes showed positive values, while each order of back-island
marshes showed negative values.
Using the limited data available, it is impossible to determine
the cause of this difference. As suggested previously, it may
indicate that channels in the fore-island marshes are ebbdominated, while those in the back-island marshes are flooddominated. Even if this is the case, however, the reason for
thi s contrast in dominance is unknown, and offers an opportunity
f or future research.
3.
Evidence for Structural Control: The discussion of structural
control will proceed by evaluating in succession the evidence
offered
a.
drainage density: Drainage densities of all networks were
very low (Table I) in comparison to other Georgia coastal
marshes (see Wadsworth, 1980), in keeping with their lack
of relief, high permeability and dense vegetative cover;
these properties were described by Strahler (1964) as related
to low drainage densities in fluvia l systems. The similarity
of these values among the networks suggests that the aforementioned factors are also uniform for the four networks
considered in this study, but offers no evidence for the
presence or absence of structural control.
b.
bifurcation and stream-length ratios: Strahler (1964)
states that fluvial watersheds free of structural control
have bifurcation ratios between 3.0 and 5.0, and that
abnormally high ratios are to be expected where structural
control results in confinement of the stream valleys. On
this basis, all four of the drainage networks considered in
this study show evidence of structural control (Table 1) .
Furthermore, two important trends should be noted:
20
+10
---order
•
: fore-island marshes
~ '
back-island marshes
Figure 6. Ebb versus flood domination in fore- and back-island
marshes. Order on the horizontal axis i s taken as that of the
lowest order limb of the juncture. Position of the vertical bars
relative to the zero line indicates the relative proportion of
juncture angles which are inclined positively (upstream) or
negatively (downstream) from a right angle. Positive deviation
indicates ebb domination; negative deviation indicates flood
domination.
21
i.
The highest bifurcation ratios occur beb1een secondand third-order channels in the three smallest networks,
and between first- and second-order channels in the
largest network. This suggests that the effects of
structural control are most strongly imposed on channels
of this size (i.e., larger channels). This is in agreement with the model advanced earlier in the section on
field results, in which it was hypothesized that structural
control by relict beach ridges which have been eroded
below the marsh surface is most strongly imposed on the
larger channels, as these channels are more capable of
eroding down to the depth necessary for contact with the
ridges.
Why the channels of order four and greater do not show
the effects of structural control as clearly as somewhat
smaller channels is not known, but may be the result of
another factor (e.g., discharge, peak velocity) overriding
the effects of structural control on these larger channels.
ii.
The "extremism of maximum values for bifurcation ratio
within a given drainage network decreases steadily with
increasing size of the respective drainage basin (Table
I). The reason for this is unclear, but it may relate
to the size of the channels, since there is a general
increase in the cross-sectional area of channels with
·
increasing drainage basin area.
11
Perhaps as the drainage basin gets larger in size there
are more orders of channels capable of responding to
structural control, and so bifurcation ratio value
extremes are lessened.
The pattern of stream length ratios (Table I) for a given
drainage network is consistent with that of its bifurcation ratios, but when taken by themselves the ratios offer
little indication of structural control, as they display
neither the uniformity of pattern nor the trend of decreasing
extremism shown by the bifurcation ratios.
c.
juncture angle: As explained in the section on general observations, the decreasing kurtosis and shift of modality to
more acute angles of juncture (Figure 5) which occur with
increasing channel order are in agreement with one mechanism
of structural control. In this mechanism, larger channels
incise the marsh surface to a depth at which they interact
with relict beach ridge remnants that have been eroded to a
level below the marsh surface. An expected consequence of
this model would be a tendency toward parallelism of the
larger channels induced by structural control, which would
be expressed by these channels having more acute juncture
angles with one another. A graph comparing the distribution
of all juncture angles for first-order channels with the
22
distribution of all juncture angles between channels of
order two or greater (Figure 7) shows a general displacement
of juncture angles of the larger channels toward the more
acute angles, agreeing with the hypothesis concerning
parallelism given above. However, it is not possible with
the limited data available to say if this displacement
toward the more acute angles is a reflection of parallelism
due to structural control or a product of control by the
relative velocities of the pairs of stream segments as
explained earlier, or perhaps a combination of the two.
Juncture angle may also play an important role in the
expression of structural control through preferred orientation, as explained below.
d.
preferred orientation: The analysis of drainage networks
for evidence of preferred orientation is based on the fact
that the presumed controlling features {relict beach ridges)
occur in "sets," each of which has it own preferred orientation which is reflected in the orientation of the channel
segments it influences. Since very few or no ridge remnants
are visible within the expanse of the marshes themselves,
it was assumed that the orientations of the ridge sets adjacent to the particular drainage networks in question would
approximate those of the ridge remnants lying below the
marsh surface. The bordering ridge sets were measured and
plotted as dashed lines and fields on Figure 8. Network A,
however, had no relict ridges left in the immediate vicinity,
and so the orientations of ridges bounding Network D (which
borders A) were used as an approximation. Also plotted in
Figure 8 are the distributions of first-order channel segments, of segments second-order and larger, and of all
segments for each of the four drainage networks (see
Appendices V and VI). Note that since all of these lineations are bidirectional, the resulting diagrams have twofold rotational symmetry. The following relationships were
noted:
i.
All major relict beach r idge sets were represented by
at least one major channel orientation mode.
ii.
This ridge/orientation relationship was weakest for
Network A, presumably because of the lack of accurate
ridge set orientations as explained above .
iii.
iv.
The ridge/orientation relationship was much clearer for
channels of order two or higher than it was for firstorder channels, supporting the mechanism for structural
control explained previously.
For all networks, there was at least one major channel
orientation mode not explained by coincidence with ridge
set orientations, suggesting that at least one other major
control is inducing preferred orientation in the channel
networks.
23
30
~:
small channels (1st order)
~~
large channels (greater
than 1st order)
5
90
Figure 7. Comparative di stributions of juncture angles for small
(1st order) and larger (greater than 1st order) channels. Juncture
angles are given as degrees of inclination from a right angle (0° =
right angle).
24
x=s
A ( c=1)
x=4
B(c=1)
x=7
C(c:::1)
n=64
x=4
x=16
D(c-1 )
n=148
x:::;:6
n=10
x=6
A( all)
n=7
x=7
Btall)
n=26
C(C>1)
n=21
x=a
Ctall)
n=85
D(c> 1 )
n=47
x=9
Dtall)
n=95
A( C>1)
n=19
B(C>1)
Figure 8. Rose diagrams showing the distributions of channel orientations for all drainage networks; n is the total number of data in the
rose, x is the value of the largest mode, c is the channel order, and
r•s are ridge modes.
25
Although it is not possible to definitely identify the
second control just mentioned from the limited data presently
available, examination of the angular relationships between
the various channel-orientation modes suggests an interesting
possibility. In plots of first order channels, channel
orientation modes which do not coincide with ridge set
orientations are generall y inclined at about goo to modes
which do coincide. This suggests that direct structural
control imposed on the latter modes is being extended to
the former through the influence of juncture angle, which
for first-order channels tends toward goo. Further supporting
this possibility is the fact that first-order junctures tend
most strongly toward 90° when they include higher order
channels, which in turn have orientations most reflective
of direct structural control by the relict beach ridge sets.
In plots of channels of order two or greater, channel orientation modes whic h do not coincide with ridge set orientations generally differ by angles of less than 90° from
modes which do coincide with ridge set orientations. This
finding agrees with the distribution of juncture angles
for these larger channels, which tend to be more acute than
those of first-order channels.
CONCLUSIONS
In summary , a review of the res ults of the topographic, field, and
photogrammetric studies shows evidence of structural control in all three
approaches. With reference to the questions asked at the very beginning
of this paper, the following statements can be made:
1. Evidence of structural control was seen in all four networks
· analyzed in the photogrammetric phase of the study. Even network A,
which had no bordering ridge sets, showed some evidence of structural
control. No difference in control was seen between fore-island and
back-island marshes.
2. Evidence of structural control was seen in bifurcation and
stream-length ratios, juncture angles, and preferred orientation of
stream segments, and was clearest for preferred orientations; this was
also considered to be the measure yielding the most information about
control.
3. The degree of structural control varied both within and between
the various drainage networks, and appeared to be modified by stream
order, drainage basin size, nature of stream juncture, and perhaps
drainage density.
4. Structural contr ol was expressed most clearly by second-order
streams in most networks , and by first-order streams in the largest
network. This difference was presumably related to the depth of incision
26
into the marsh surface (due to different channel sizes), as well as to
other unnamed factors.
5. Structural control appears to be imposed upon the drainage
networks through laterial confinement of the channels by relict beach
ridges which have eroded below the marsh surface. This control may be
extended to smaller channels through the influence of juncture angles
determined by relative flow velocities. A less important mechanism of
structural control may be the preferential elimination of channel segments by washover fans near the seaward edge of the island.
27
REFERENCES CITED
Basan, Paul B. and Frey, R.A., 1976, Actual Paleontology and Neoichnology
of Salt Marshes near Sapelo Island, Georgia: Geol. Jour., Spec. is.
No.9 Seel House Press, Liverpool, pp.41-70.
Chapman, V.J., 1960, Salt Marshes and Salt Deserts of the World:
Interscience Publishers, 392p.
London,
Deery, J.R., 1976, Washover Fans of St. Catherine's Island, Georgia:
Report to the Edward John Noble Foundation, 22p and 25 figs.
Edwards, J.M. and Frey, R.W., 1976, Sedimentological Characteristics of
a Holocene Salt Marsh, Sapelo Island, Georgia: Senckenberg. Marit.,
9/5-6, p.215-259.
Frey, R.W. and Howard J.D., 1969, A Profile of Biogenic Sedimentary
Structures in a Holocene Barrier Island-Salt Marsh Complex, Georgia:
Trans. Gulf Coast Assn. Geol. Soc., Vol.l9, p.427.
Gallagher, J.L. and Reimold, R.J., 1972, A Comparison of Four Remote
Sensing Media for Assessing Salt Marsh Productivity: Proceed. of
8th Int. Symp. of Remote Sensing of Environment, Ann Arbor, tH,
p.l287-1295, illus.
Hinde, J.P., 1952, Vertical Distribution of Salt Marsh Phanerograms in
Relation to Tide Levels: Unpublished Doctoral Dissertation, Dept. of
Biological Sciences, Stanford University, 93p.
Howard, J.D., Frey, R.W. and Reineck, H.-E., 1973, Holocene Sediments of
the Georgia Coastal Area: IN The Neogene of the Georgia Coast,
Frey, R.W. (ed.), p.l-58. Howard, James D. and Jaffe, Louise C., 1976, Holocene Sedimentary Facies
of St. Catherine's Island, Georgia: Report to the Edward John Noble
Foundation, 58p.
Hoyt, J.H., Weimer, and Henry, V.J., Jr., 1964, Late Pleistocene and
Recent Sedimentation Central Georgia Coast, U.S.A.: in Deltaic and
Shallow Marine Deposits (L.M.J.U. Von Straaten, ed.)-,Elsevier Publ.
Co., Amsterdam, p.l70-176.
Johnson, D.W., 1925, New England Acadian Shoreline:
New York, New York, 608p.
John Wiley Co.,
McEwen, Robert B., Kosco, William J., and Carter, Virginia, 1976,
Coastal Wetland Mapping: Photogrammetric Engineering and Remote
Sensing, Vol.42, No.2, p.221-232.
Pestrong, Raymond, 1965, The Development of Drainage Patte~ns on Tidal
Marshes: Stanford Univ. Publ., Vol. 10, No.2, 87p., 1llus.
28
Ragotskie, Robert A., 1959, Drainage Patterns in Salt Marshes: Proc.
Salt Marsh Conf. at Marine Inst . of Univ . of Ga., Sapelo Island,
Ga., March 25-28, 1958, p.22-28.
Reeves, Robert G. (ed.), 1975, Manual of Remote Sensing: Amer. Soc. of
Photogrammetry, Falls Church, Va., 2 vols., 2144p.
Reimold, Robert J., Gallagher, John L., and Thompson, Donald E., 1972,
Coastal Mapping with Remote Sensors: Proc . of the Coastal Mapping
Symp., Amer. Soc. of Photogrammetry, Washington, D.C., 1972,
p.99-ll2.
Stevenson, R.E., 1954, Marshlands at Newport Bay: Unpublished Doctoral
Dissertation, Dept. of Geology, Univ. So. Calif., 199p.
Straaten, L.M.J.U. van, 1963, Aspects of Holocene Sedimentation in the
Netherlands: Verhand. Kon. Nederl . Geol. Mijnb. Genootsch, Vol.2l,
p. 161-172.
, and Kuenen, Ph. H., 1957, Accumulation of Fine-Grained
Sediments in the Dutch Wadden Sea: Geol. en Mijnb., 19e Jrg.,
p.329-354.
--~~~~-
Strahler, Authur N., 1964, Quantitative Geomorphology of Drainage
Basins and Channel Networks: In Handbook of Applied Hydrology,
McGraw-Hill Book Co., New York--,N.Y.
Wadsworth, Joe R., Jr., 1980, Geomorphic Characteristics of Tidal
Drainage Networks in the Duplin River System, Sapelo Island,
Georgia: Ph.D. dissertation, The University of Georgia, Athens,
GA, 247p.
Wiedemann, H.U., 1972, Shell Deposits and Shell Preservation in
Quaternary and Tertiary Estuarine Sediments in Georgia, U.S.A.:
Sediment. Geol., Vol.7, p.l03.
29
Appendix I - Drainage network maps prepared in the photogrammetric
phase of the study
w
0
/
I
I'
/
/
N
I
~
I
I
I
1000.
0.
1000.
2000.
Map of drainage network A, Seaside Inlet, St. Catherine's Island, Georgia. Boundary of the
drainage basin is shown by a dashed line. All stream orders are indicated.
N
/
1000 °
0
I
1000 I
2000
°
of drainage network B, south end of St. Catherine's Island, Georgia. Boundary of the
drainage basin is shown by a dashed line. All stream orders are indicated.
f~ap
w
Map of drainage network C, south end of St. Catherine•s Island, Georgia. Boundary of the
drainage basin is shown by a dashed line. All stream orders are indicated.
M~p
of drainage network D, McQueen's Inlet, St.
Catherine's Island, Georgia. Boundary of the
by a dashed line, All
stream orders are
indicated,
'
1000'
0'
1000'
w
w
34
Appendix II.
Juncture angles, measured in degrees from downstream
1i mb (raw data)
Network~ (fore~sland)
Level 1-1 :
081
128 055
123 123
1-2:
056
061
138 122 090
1-3:
135
112 104 067 068 087
Level 2-2:
126
2-3:
077
057
100
127 090
1-3:
062
Level 2-2:
073
2-3:
057
121
117
080
047 037
106
167 085
128
118 087
061
039
041
090
Network I (back~sland)
Level 1-1: 089 050 028 064
142 071
023
047
128 090 028 123 087
117
102 090
1-2:
144 076
129 090
102
146 091
1-3:
120 090
1-4:
069
064 060
047
090
090
090
148
128 090
095
103
Level 2-2:
053
049 090
2-3:
117
2-4:
159
031
092 037
Level 3-3:
021
3-4:
090
086
128
050 092 068 103
Network ~ (back~sland)
Level 1-1 : 036 090 045
1-2:
129
075
022
033 090
071
062 084
131
038
097 027
105
144
053
35
Network Q (fore4sland)
Level 1-1: 160 102 033
087
053
034
086
100
093
102 084
080
091
135
123 073
126
116
048 037
103 095
083
021
065
067
100
080
035
101
119
076
051
090
043
127
093
068
116
108 085
065
102
097
074 056
098 073
084
133
126 084 090
090
091
094
113 093
116
126
078
077
112
078
154 092
105
062
051
161
090
110
052
109
110
093
101
113 089
092
051
144
118 109 092
135
064 092
083
078
088
129
108
101
079
109
104 091
109 090
092
090
091
090
090
148 106 064
084 046
119
101
090
102 109
Level 2-2:
125
095
106
147
133
2-3:
090
034 090
120
090
2-4:
117
089
2-5:
151
055
Level 3-3:
095
110 078
3-4:
093
161
3-5:
072
Level 4-4:
156
4-5:
090
1-2:
1- 3:
1- 4:
1-5:
133
121
074
102
102 044
097
125
104
36
Appendix III.
Juncture angles, given as degrees of deviation from
a right angle (90°)
Network~
(fore4sland)
Level 1-1 : -09 +38 -35
+33
+33
+39
+31
+27
-53
1-2:
-34
-29
+10
+48
+32
0
-43
l-3:
+45 +22
+14
-23
-22
-03
+16
-40
+02
-22
+13
Network!!_ (back-island)
Level 1-1 : -54 0 -45
-10
+77 -05
Level 2-2:
+36
2-3:
-13
-33
1-2:
+37
1-3:
-28 +28
Level 2-2:
-17
2-3:
-23
0
-51
+38
-03
-29
0
-49
Network f (back-island)
Level 1-1 : -01 -40 -62
+38
-26
+52
-19
-67
-43
.. 62
+33
-03
+27
+12
0
-14 -15
+39
0
+12 +56
-43
0
0
1-2:
+54
l-3:
+30
0
1-4:
-21
-26
Level 2-2:
0
-37 -41
0
+27
2-4:
+69
Level 3-3:
-69
3-4:
-30
+58 +38
2-3:
0
-04
+38
-68
-28
-06
+01
+41
-52
-63
0
0
-19
+07
-59
+02
-53
+15
+05 +13
-57
0
+54
-37
37
Network Q (fore4s1and)
Level 1-1 : +70 +12 -57
1-2:
1-3:
1-4:
1-5:
Level 2-2:
-56
-04
+10
+03
+12
-06
-03
-10 +01
+45 +33
-17 +36 +26
-42
-53
+13
+05
-07
-69
-25
-23
+10
-10
-55
+11
+29
-14
-39
-47 +37 +03
-22
+26 +18
-05
-25 +12
-17
0
+07
-16
-34 +08
-06
+43
+36
-06
0
+01
+04 +23 +03 +26
+36
-12
-13
+22
-12
+64 +02 +15
-28 -39
+71
0
+20
-38 +19
+20 +03
+11
+23
-01
+02
-26 +02
-07
-12
+54 +28 +19
+02
+45
-11
+19
+19
0
-26
-06
-44
+07
+35 +14
+39
+02
0
+01
0
0
+29
+11
0
+12
+19
+35
+05 +16
+57
+43 +12
+30
+18 +ll
0
-56
0
2-4:
+27
-01
+43
2-5:
+61
-35
Level 3-3:
+05
+20
-12
3-4:
+03 +71
+31
3-5:
-18
Level 4-4:
+66
0
-16
0
-39
-02
2-3:
4-5:
-27
0
+14 +01
+58 +16
+12
-46
38
Appendix IV - Tabulation of juncture angles by sign of deviation from
90°. (0) signifies a right angle
Drainage
Network
A
B
1-1
1-2
(+)
7
3
4
(-)
1
4
3
(0)
2
0
all
9
8
0
7
(+)
1
4
2
1
0
3
1
6
1
3
0
4
(-)
(0)
all
c
1-3
Juncture Level
1-4 1-5 2-2 2-3 2-4
-
1
2
0
4
-
0
1
0
6
-
0
1
0
3
-
0
1
-
1
4
-
0
1
-
2
0
1
3
16
9
0
1
1
1
-
9
1
0
5
5
1
0
1
3
1
1
14
26
-
5
3
3
-
10
10
-
-
-
1
5
0
3
-
11
11
0
3
1
-
-
-
(+}
6
6
1
(-)
11
3
0
5
7
(0)
2
19
15
18
1
2
4
16
9
4
1
9
5
0
1
10
15
11
3
all
A&D (+)
33
22
29
18
(-)
20
12
(0)
0
7
all
B&C (+)
42
37
7
2
(-)
15
3
25
8
3
3
-
2
13
1
6
-
26
15
11
14
12
16
5
4
30
5
1
26
15
D
all
(+)
(-)
(0)
(0)
All
all
(+}
(-)
29
35
15
14
13
8
1
21
(0)
3
9
2
all
67
50
28
-
-
-
2-5
3-3
3-4
3-5
4-4
-
-
-
-
-
4-5
-
-
-
-
- -
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
3
-
0
0
5
-
1
0
-
-
-
-
-
0
1
1
-
-
-
-
-
-
1
1
0
0
0
1
0
1
0
0
2
1
0
1
3
0
1
2
3
4
1
1
1
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
1
-
-
0
-
-
10
1
5
4
-
4
1
2
3
0
1
0
4
8
6
1
2
1
1
0
4
2
0
0
1
0
0
0
1
16
12
2
4
5
1
1
1
1
4
3
-
39
Appendix V.
Bidirectional orientations in degrees for all channel
segments* (raw data). Due north is (000).
Network~ (for~island)
Level 1:
097(277) 093(273)
174(354) 244(064)
141(321) 203(023)
254(074) 294(114)
009(189) 246(066)
086(266) 069(249)
337( 157) 063(243)
193(013) 204(024)
336(156) 076(256)
190(010)/273(093)
196(016)
246(066)
100(280)
221(041)
124(304)
044(224)
217(037)
220(040)
181(001)
038(218)
104(284)
092(272)
227(047)
185(005)
009(189)
030(210)
104(284)
090(270)
209(029)
224(044)
173(353)
278(098)
196(016)
132(312)
303(123)
044(224)
065(245)
017(197)
342(162)
314(134)
097(277)
077(257)
341(161)
344(164)
350(170)
048(228)
Network f (back~s1and)
Level 1: 032(212) 323(143) 329(149)
285 ( 105) 047 ( 227) 045(225)
039(219) 235(055) 119(299)
102(282) 073(253) 073(253)
060(240) 065(245) 109(289)
212(032) 310(130) 211(031)
047(227) 063(243) 172(352)
092(272) 101(281) 355(175)
304(124) 270{090) 159(339)
257(077) 101(281) 037 (217)
286( 106)
250(070)
223(043)
018(198)
282(102)
006(186)
079(259)
052(232)
132(312)
017(197)
294(114)
090(270)
350(170)
074(254)
303(123)
037(217)
091(271)
176(356)
252(072)
034(214)
Level 2:
Level 3:
Network ~ (back~sland)
Level 1: 050(230) 081(261)
025(205) 065(245)
034(214) 021(201)
058(238) 062(242)
Level 2: 057 ( 237) 020(200)
187(007) 084(264)
Level 3: 058(238)
059(239)
40
Network f (back-island)
Level 1 (continued):
045(225) 170(350) 068(248)
156(336) 165(345) 126(306)
128(308) 137(317) 090(270)
Level 2: 331(151) 329(149) 327(147)
019(199) 055(235) 087(267)
064(244) 140{320) /023(203)
084(264) 156 ( 336) 116 ( 296)
Level 3: 338(158) 075(255) I 319(139)
Level 4: 067 ( 247)
Network Q (fore-island)
Level l: 117( 297) 143(323)
324(144) 061 (241)
071(251) 057 ( 237)
000(180) 284(104)
011(191) 325(145)
210(030) 305(125)
092(272) 019(199)
061(241) 009( 189)
008{ 188) 074(254)
157(337) 215(035)
165(345) 348(168)
192(012) 120(300)
179(359) 167{347)
350(170) 348(168)
020(200) 207 ( 027)
158(338) I 262(082)
324 ( 144) 351{171)
339(159) 006( 186)
150(330) 165(345)
125(305) 047(227)
199(019) 191(011)
251(071) /301(121)
135(315) 122{302)
140(320)
186(006)
059(239)
354(174)
239{059)
078(258)
074(254)
026(206)
253(073)
174(354)
343 ( 163)
214(034)
325(145)
346(166)
127(307)
178(358)
354(174)
012(192)
170(350)
068(248)
192(012)
224(044)
174(354)
100(280)
107{287)
106(286)
087(267)
150(330)
033{213)
104(284)
090(270)
046(226)
078(258)
097(277)
063(243)
057 ( 237)
196(016)
054(234)
068(248)
355{175)
090(270)
154(334)
355(175)
007( 187)
198(018)
288(108)
190(010)
335(155)
336(156)
180(000)
188(008)
000(180)
079(259)
153(333)
062(242)
076{256)
221 (041)
158(338)
047(227)
202(022)
029(209)
037{217)
214(034)
091 ( 271)
039(219)
058(238)
261 (081)
165(345)
193(013)
180(000)
002(182)
330(150)
295(115)
250(070)
336(156)
275(095)
127( 307)
173(353)
302(122)
219(039)
004(184)
41
Network Q (fore~sland)
Level 1 (continued):
134(314) 312(132) 304(124)
291 (111) 304(124) 315(135)
191(011) 144(324) 154(334)
190(010) 163(343) 180(000)
216(036) 180(000) 130 ( 310)
152(332) 029(209) 044(224)
336(156) 352(172) 049(229)
Level 2: 131(311) 341 (161) 163(343)
038(218) 283{103) 014(194)
335{155) 144(324) 177{357)
193(013) 324(144) 030(210)
048(228) 199(019) 219(039)
212(032) 163(343) 237 (057)
064(244) 329(149)
Level 3: 142(322) 085 ( 265) I 058( 238)
014(194) I 105(285) I 355(175)
163(343) 277(097) 195{015)
Level 4: 326(146) 1034(214) 219(039)
Level 5: 264(084) I 153(333)
*Note:
315(135) 036(216)
229(049) 270(090)
047 ( 127) 049(129)
090(270) I 149(329)
122(302) 326(146)
061(241) 271(091)
070{250) 169(349)
103(283) 326{146)
333(153) 031 (211)
186(006) 120(300)
051(231) 276(096)
346(166) 309(129)
211(031) 193(013)
348(168)
051(231)
323(143)
040(220)
269(089)
248(068)
Slashes (I) indicate stream segments which displayed two or
more distinct orientations.
Appendix VI - Tabulation of all channel segment orientations by network and order
Dr ainage
c
B
A
network
stream
order
8
2
0
11
9
11
2
2
1
0
1
4
8
8
5
7
1
0
3
6
7
4
0
1
0
2
4
4
5
10
7
2
2
3
11
12
9
5
12
16
6
3
1
2
4
.o
1
2
4
2
4
0
0
0
0
3
0
076 -085
OR6-095
096-105
0
4
1
1
5
2
4
1
1
0
1
1
0
0
106- 115
116-125
1
0
1
0
1
0
0
0
0
0
1
0
0
2
0
0
0
0
2
1
0
0
1
126-135
136-145
146-155
156-165
0
1
166- 175
176-185
186-195
1
2
2
1
0
2
196-205
206-215
2
1
2
1
216-225
5
226-235
236- 2~5
246- 2!;5
256- 265
266-275
1
2
4
1
0
0
0
4
0
1
1
276-285
286-295
4
1
1
0
296-305
306-3 15
316-325
326-335
336-345
1
0
1
0
1
0
0
0
0
1
346-355
1
1
1
5
1
1
0
1
0
2
2
2
4
4
2
6
1
2
1
0
0
4
1
5
5
1
1
0
1
0
2
2
0
6
2
6
7
5
0
1
2
3
4
2
1
0
0
3
4
1
1
2
4
6
3
1
0
1
4
2
0
0
0
2
1
2
1
1
2
0
2
4
0
3
4
1
1
2
7
0
2
0
0
1
0
0
3
0
6
2
6
1
0
0
0
1
0
7
5
i
2
0
0
0
1
2
0
3
4
2
0
1
0
0
3
1
3
2
4
0
0
0
2
1
0
1
4
3
I
0
2
2
2
2
2
1
0
1
0
2
4
10
6
13
7
7
12
9
9
9
046-055
4
13
12
1
2
1
4
2
5
8
1
1
5
7
6
6
2
2
0
0
15
18
13
2
3
1
1
11
2
0
4
7
0
3
0
1
2
1
2
6
5
2
2
1
1
19
7
an
0
9
d
1
5
056-065
066- 075
1
5
6
026-035
036-045
6
6
8
8
7
1
4
>1
13
23
5
6
1
2
ll
1
1
4
1
6
3
1
0
2
1
4
•1
>1
4
4
4
all
13
13.
5
11
5
All
B&C
0
•1
12
17
8
1
1
4
2
2
006-0 15
016-025
all
all
0
0
2
all
0
>1
>1
>1
0
•1
2
=1
10
15
•1
1
1
2
2
•1
0
>1
0
2
2
356-005
A~
D
all
1
4
8
6
7
26
22
3
2
7
8
9
9
17
13
6
4
5
15
21
5
5
9
15
0
2
0
2
4
6
4
16
10
10
2
6
10
9
17
18
16
20
3
8
5
18
22
13
18
8
4
26
26
14
27
3
8
6
5
18
7
9
2
2
9
11
8
11
2
2
10
13
8
4
8
9
5
7
0
1
.o
13
7
12
6
4
6
3
2
1
3
0
13
5
11
5
4
0
2
1
8
5
9
6
7
4
3
4
0
9
4
8
5
1
0
4
11
12
11
10
1
0
2
5
5
4
9
12
16
8
9
13
17
12
12
10
15
17
19
5
9
1
2
2
6
4
2
4
4
4
10
10
7
1
5
4
5
0
5
8
5
3
1
2
2
6
3
1
13
17
2
11
19
12
17
6
15
15
17
1
15
17
19
13
23
11
15
6
2
21
25
8
3
9
13
4
17
15
12
12"
10
7
5
5
18
19
8
2
2
6
9
4
14
27
19
8
7
6
8
15
0
1
9
7
all
12
8
13
12
4
5
6
6
5
10
15
1
1
4
9
4
11
10
8
9
1
5
2
1
5
4
4
1
1
1
3
10
>1
20
14
0
2
.4
6
8
5
4
6
2
1
5
5
1
1
4
5
7
6
7
5
4
I
•1
13
18
12
14
1
0
1
0
0
1
4
1
0
2
5
2
3
5
1
2
19
18
8
6
7
12
14
1
9
7
7
20
5
25
8
12
8
7
8
9
5
14
18
19
5
8
3
6
4
19
26
6
4
9
17
13
19
21
22
15
21
5
0
18
10
18
2
2
6
10
8
17
18
16
20
26
22
4
26
9
15
16
10
9
43
Appendix VII (supplemental)*.
Numerical breakdown of juncture angle
distribution b~' order and angle
~
0-9°
10-19°
20-29°
30-39°
40-49°
50-59°
l (all)
58
44
32
29
14
14
6
3
2 (all)
12
7
4
7
6
6
3
0
3 (all)
3
3
l
1
0
0
1
1
4 (a 11)
1
0
0
0
0
0
1
0
2-4 (a 11)
16
10
5
8
6
6
5
1
order
tota 1 # of
junctures
e
1
200
2
45
3
10
4
2
2-4
57
Appendix VIII (supplemental)*.
50-59°
orde~
29
22
16
2-4 (all)
28
18
9
*Note:
70-79°
Percentage breakdown of juncture angle
distribution by order and angle
~g1e
1 (all)
60-69°
14.5
14
7
ll
60-69°
70-79°
1.5
2
Supplemental appendices are those containing data which is
neither included nor referred to in the original report to the
Edward John Noble Foundation, but may be of interest to other
readers.