Hydrologic investigation of surface water for water supply and hydropower, Tutuila Island, American Samoa/for U.S. Army Corps of Engineers ; prepared by Dames & Moore.United States.Army.Corps of Engineers.Dames & Moore.Honolulu, Hawaii:Dames & Moore,1978.Water-supplyAmerican SamoaTutuila Island.Water-powerAmerican SamoaTutuila Island.Tutuila Island (American Samoa)
Coastal Zone
Information
Center AMERICAN SAMOA WATER RESOURCES STUDY.
HYDROLOGIC INVESTIGATION
OF SURFACE WATER
FOR WATER SUPPLY & HYDROPOWER
TUTUILA ISLAND,
AMERICAN SAMOA
C)
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a s Tta'l one
Z
lon for at ion
U-S-ARMY ENGINEER DISTRICT, HONOLULU
HYDROLOGIC INVESTIGATION OF SURFACE WATER
FOR WATER SUPPLY AND HYDROPOWER
TUTUILA ISLAND, AMERICAN SAMOA
FOR
U.S. ARMY CORPS OF ENGINEERS
SEPTEMBER, 1978
Prepared by
DAMES & MOORE
Consultants in the Environmental and
Applied Earth Sciences
Suite 200
1144 10th Avenue
Honolulu, Hawaii 96816
SUITE 200 1144 10th AVENUE - HONOLULU, HAWAII S8816 - (808) 735-3585
CABLE: DAMEMORE TELEX: 63-4100
September 18, 1978
U.S. Army Corps of Engineers
Pacific Ocean Division
Building 230, Fort Shafter
Honolulu, Hawaii 96858
Attention: Mr. Kisuk Cheung
Chief, Engineering Division
Gentlemen:
Hydrologic Investigation of Surface
Water for Water Supply and Hydropower
Tutuila Island, American Samoa
We are pleased to present our final report on the.
water supply and hydropower potential of Tutuila Island,
American Samoa, prepared for you under the terms of
Contract No. DACW 84-78-C-0013.
The study describes available water resources,
and impoundment area characteristics, and assesses the
possible use of an impoundment at five separate locations
for the dual purposes of water supply and hydropower.
The analysis provided in this report should prove
valuable to the Corps of Engineers and others, in any
future consideration to meeting electrical power or water
supply requirements through surface water impoundment in
American Samoa.
U.S. Army Corps of Engineers
September 18, 1978
Page 2
It has been a pleasure to prepare this report for
you, and we hope that it meets you needs. Please feel
free to contact us if you have any questions, or require
further information.
Sincerely,
DAMES & MOORE
6L ZI.-IIZ41
Eric Will
Chief Planning Engineer
Water Resources Engineering Services
S.K. D30U
Principal-in-Charge
EW:SKD:jo
TABLE OF CONTENTS
PAGE
SUMMARY ..................................................1
INTRODUCTION .............................................4
Authority ............................................4
Purpose ..............................................5
STUDY AREA ...............................................6
PREVIOUS INVESTIGATIONS ..................................7
CLIMATE AND HYDROLOGY ....................................8
METHODOLOGY ..............................................9
Drainage Basin Selection .............................9
Flow-Duration Curve Development ..................... 11
Mass Curve Analysis and Storage-Yield Probability ... 14
Plot of Annual Values .......................... 16
Plot of Monthly Values ......................... 17
Gaging Station Data ............................ 18
Required Storage ............................... 20
STORAGE SITES SELECTION ................................. 21
CONCLUSIONS ............................................. 23
Hydropower Potential ................................ 23
Water Supply Potential .............................. 25
BIBLIOGRAPHY ............................................ 54
LIST OF TABLES
NO. TITLE PAGE
DRAINAGE BASIN CHARACTERISTICS ................. 27
2 GAGING STATION DATA ............................ 28
3 REQUIRED STORAGE VS. REGULATED FLOW ............ 29
4 POWER AND ENERGY POTENTIAL ..................... 30
5 WATER SUPPLY POTENTIAL ......................... 31
LIST OF PLATES
NO,- TITLE PAGE
Location Map ................................... 32
2 Drainage Basins ................................ 33
3 Flow Duration Curve - Atauloma ................. 34
4 Flow Duration Curve - Basin 7, Aasu ............ 35
5 Flow Duration Curve - Basin 11, Leele .......... 36
6 Flow Duration Curve - Basin 14, Afuelo ......... 37
7 Flow Duration Curve - Basin 16, Pago ........... 38
8 Flow Duration Curve - Basin 19, Alega .......... 39
9 Flow Duration Curves - Composite ............... 40
10 Parametric Duration Curves ..................... 41
11 Flow Duration Curve - Basin 2, Maloata ......... 42
12 Flow Duration Curve - Basin 6, Leafu ........... 43
13 Flow Duration Curve - Basin 10, Papa ........... 44
14 Flow Duration Curve - Basin 15, Maga ........... 45
15 Mass Curves for Six Basins ..................... 46
16 Required Storage vs. Regulated Flow ............ 47
17 Storage Site - Basin 2, Maloata ................ 48
18 Storage Site - Basin 6, Leafu .................. 49
19 Storage Site - Basin 10, Papa .................. 50
20 Storage Site - Basin 15, Maga .................. 51
21 Storage Site - Basin 16, Pago .................. 52
22 Storage Volumes for Five Basins ................ 53
SUMMARY
* The small, steep drainage basins of Tutuila yield
an average annual runoff of about 6 cubic feet
per second (cfs) per square mile. This amount is
equivalent to about 80 inches of annual runoff,
which appears reasonable, considering average
rainfall and evapotranspiration.
* All 23 basins delineated are quite similar in
topography and shape, with steep, narrow uplands
draining to the sea. Of these 23 basins, the six
basins with gaged streamflows of up to 18 years
of good records, exhibit similar flow patterns.
Although unofficial rainfall data collected by
the American Samoa government and others indicate
that higher elevations receive more rainfall, the
existing official data base of two long-term
raingaging stations does not warrant dividing the
basins into higher and lower sub-areas to
estimate yields in more detail.
0 The flow patterns of the five basins studied in
detail, Nos. 2-Maloata, 6-Leafu, 10-Papa,
15-Maga, and 16-Pago, are such that regulated
flows of about 4 cfs per square mile can be
obtained with reservoir storage. Based on
mass-curve analysis of the gaged basins, storages
of about 300 acre-feet per cfs of regulated flow
are required (see Table 3 for further detail).
0 Storage sites are small, of low capacity, and
need a relatively high embankment to achieve
required storage. To achieve maximum storage, a
site was selected in the lower reaches of each
basin. Because of the limited storage volume
available, embankments of more than 100 feet high
are required in each case.
0 Run of the river hydropower development is
generally not feasible due to extremely low or
intermittent stream flows.
2
0 Even with the maximization of storage, hydropower
potential is very small and unattractive when
compared to the power and energy demands of the
island. The best of the five basins studied, No.
6-Leafu, would only yield about 30 KW of continu-
ous power, and about 260,000 KWh of annual
energy. This is less than one-half of 1 percent
of the island's 1977 energy generation.
0 The potential for surface water development is
more attractive. Basin 6-Leafu, with a regulated
flow of about 3.3 mgd, could supply about 28
percent of the estimated average water demand in
the Year 2000. The other basins could also
supply reasonable portions of future water
needs. Although no evaluation of reservoir
construction, pumping, treatment, or distribution
costs for water supply was made in this report;
from a purely supply standpoint, it would seem
that surface storage for future water supply
development is worthy of more detailed investi-
gation.
3
0 Development of the selected basins, as described
herein, may not be appropriate at this time. For
this reason, curves of storage, elevation, and
regulated flow, are shown in Plates 16 and 22.
With these curves, it is possible to select lower
rates of flow and find the required storage that
may be in keeping with more immediate needs.
Conversely, it is possi ble to determine the rate
of flow that will result from construction of
reservoirs of a less than the selected sizes.
INTRODUCTION
AUTHORITY
This study has been undertaken as a part of the
American Samoa Water Resources Study (ASWRS), as author-
ized by Section 143 of the Water Resources Development Act
of 1976, Public Law 94-587. The goal of ASWRS is to
develop a comprehensive water resources plan for the
waters for American Samoa, including flood plain
management, hydroelectric power generation, regional water
and wastewater management facilities, water quality,
water-related land recreation, fish and wildlife propaga-
tion, navigation, and flood control.
4
In response to expressed concern on the part of
the U.S. Congress, certain federal agencies, and local
officials, the U.S. Army Engineer District Honolulu,
contracted with Dames & Moore, consultants in the environ-
mental and applied earth sciences, to conduct this inves-
tigation under the terms of Contract No. DACW
84-78-C-0013, executed 19 May 1978.
PURPOSE The basic purpose of this study is to identify
the drainage basins on Tutuila Island, American Samoa,
with the highest potential for water supply and hydropower
development and to estimate these potentials for at least
five selected basins. This report will then serve as a
source of information for interested federal and local
agencies. The study is a reconnaissance-level investiga-
tion, utilizing existing data, records, and previous
reports. No field survey was undertaken as a part of this
study; however, extensive knowledge of American Samoa from
on-island experience of the Dames & Moore staff was
utilized in selecting the likely candidate basins.
5
STUDY AREA
The island of Tutuila is the largest and most
populous of the seven principal islands of American Samoa;.
its location is shown on Plate 1. The island is about 18
miles long, and varies in width from 1 to 6 miles; total
land area is about 53 square miles. Topography is rugged,
as in most Pacific volcanic islands; about 70 percent of
0
Tutuila's land area has slopes greater than 30 .
While rainfall appears abundant, continued water
shortages have been experienced in the territory since
1960. Subsequently, tens of millions of dollars have been
spent in capital improvements to the water systems, on
both ground water and surface water. The current American
Samoa Government (ASG) water systems improvement program
is directed toward further development of ground water
supplies as the primary source of water for the central
government system (URS, 1978). While ground water does
appear to be the more desirable source, possible limita-
tions to its development and the attractive advantages of
a surface water reservoir with a gravity-fed distribution
system have led some engineers and laymen alike to favor
the development of more surface water sources.
6
Similarly, chronic operational problems with the
island's diesel-powered electric generators, the likely
prospect of increasing fuel and operational costs, and the
steep topography of the island have led many to believe
that hydropower would be a more reliable source of the
island's electrical energy, if sufficient potential
exists.
PREVIOUS INVESTIGATIONS
Several previous studies and reports on water
supply and surface water availability in American Samoa
were used as data sources in this study. They are listed
in the bibliography.
In addition, unpublished United States Geological
Survey (U.S.G.S.) information was reviewed. Several
excellent published papers on hydropower evaluation were
also used for guidance, and are referenced in the biblio-
graphy.
7
CLIMATE AND HYDROLOGY
The climate of Tutuila is tropical, with wet and
dry seasons. During the wet or summer period, from
November through April, the island lies in the inter-
tropical convergence zone, with weak and variable winds,
high temperatures, rainfall, and high humidity. In the
dry winter seasons, from May through October, the climate
is influenced by the southeasterly tradewinds, with
slightly lower temperatures and less rain.
Precipitation results from the upward deflection
of the trades as they pass over the island, as well as
from.major storms and isolated thunderstorms. The annual
precipitation varies with location and elevation; the Pago
Pago airport at sea level, receives an average of 125
inches per year, while nearby Mount Alava, at Elevation
1,600 feet, receives more than 250 inches. Seasonal
variation is considerable, and extended dry periods of 2
or 3 months are common. Generally, the driest months are
June through September, and the wettest are December
through March.
8
In view of the small catchment areas, steep
terrain, and limited storage sites, these wet and dry
periods pose problems for water supply and hydropower
development.
METHODOLOGY
DRAINAGE BASIN SELECTION
Twenty-three drainage basins on Tutuila were
selected to be examined for the dual purpose of water
supply and hydropower potential. They are shown on Plate
Preliminary basin evaluation was accomplished by
tabulating drainage area, years of record for gaged
basins, and the lowest 7-day flow over a 10-year interval
(7-day Q10), from unpublished U.S.G.S. data. Seven-day
Q10 was chosen as an initial indication of flow reliabili-
ty. On the basis of drainage area and 7-day Q10 rankings,
Basins 2-Maloata, 6-Leafu, 7-Aasu, 8-Leaveave, and
13-Fagaalu, were selected. However, in order to provide a
better east-west distribution of the final basins to be
selected, and to provide more basins where gravity water
supply could supply the population centers on the southern
9
shore of Tutuila, the northern drainage Basins 7-Aasu, and
8-Leaveave, and the already developed Basin 13-Fagaalu,
were discarded. The final basins selected were 2-Maloata,
6 Leafu, and 10-Papa, in the Western District, and
15-Maga, and 16-Pago, in the Eastern District.
The basin number, name, and characteristics of
all 23 basins are given on Table 1. The drainage areas
of the delineated basins were computed by planimetry from
the U.S.G.S. topographic map of Tutuila. Identification
numbers for U.S.G.S. partial-record and discontinued
streamgaging stations are shown, as well as the period of
record for currently active stations. U.S.G.S.-recorded
average yield and unit yield, in cfs per square mile, are
shown for the gaged basins. Values for 7-day Q10, from
unpublished U.S.G.S. data, are also shown.
Estimated average annual yields, in cfs and
acre-feet, are shown for each basin. These values were
computed by multiplying the planimetered drainage area by
an average value of 6 cfs per square mile. This value is
the approximate average of the 83 station-years of data
available from the gaged basins.
10 -
If an island-wide network of rain gages is
established in the future, and if more basins are gaged
for streamflow so that isohyetal maps and better runoff
data can be obtained, this approximate estimate of average
annual yield can be revised to accommodate differences in
estimated runoff between drainage basins, and by different
elevations within the same basin. For now, however, the
data available does not warrant further manipulation,
especially at this level of investigation.
The estimated average yields range from over
5,000 acre-feet for the largest basin (8-Leaveave) to 900
for the smallest one (21-Lepa). The last two columns in
the table show the initial basins selected and the final
basins selected, following the procedure previously
discussed.
FLOW DURATION CURVE DEVELOPMENT
To develop flow duration curves for the final
five basins selected, curves were developed for a total of
ten drainage basins. Six of these basins, Atauloma,
Basins 7-Aasu, 11-Leele, 14-Afuelo, 16-Pago, and 19-Alega,
have stream gages with 10 to 19 years of records,
monitored by U.S.G.S. One basin, 10-Papa, has only 8
years of fair to poor records. The other three,
2-Maloata, 6-Leafu, and 15-Maga, are ungaged. The curves
were developed as follows:
First, flow-duration curves for the six gaged
streams of Atauloma, 7-Aasu, 11-Leele, 14-Afuelo, 16-Pago,
and 19-Alega, were constructed. The data were taken from
a U.S.G.S. computer printout, which included a duration
table of daily values for all years of record. This table
shows values of discharge in cubic feet per second (cfs)
with corresponding exceedance percentages. These values
were plotted directly on a flow-duration curve of flow
versus exceedance percentage. The six curves for the
gaged basins are shown on Plates 3 through 8.
Next, the six curves were plotted together for
comparison. The plots are shown on Plate 9. As shown,
the curve shapes are quite similar. From this composite,
and the annual average flow (AAF) for the gaged basins
also given in the U.S.G.S. data, parametric duration
curves were plotted. These curves show average daily flow
versus AAF values as shown on Plate 10 (see Heitz 1978 for
a detailed description of procedure). This graph has
12 -
daily flow plotted against AAF. Values of seven different
exceedance percentages were plotted for each of the six
streams, and the best-f,it curve was developed for each of
the exceedance values. With this graph and a value of
AAF, flow duration curves of ungaged streams can be
constructed.
Finally, curves for the remaining basins were
prepared from the parametric curves and estimates of AAF.
The values of AAF are most readily determined
from streamflow data or from an isophyetal map. However,
no such map has been developed for American Samoa, as
there are only two official long-term rain gages on the
island. The estimated AAP values from Table 1 were used
for this portion and are listed below.
BASIN NO. AAF, CFS
2, Maloata 6.2
6, Leafu 6.9
10, Papa 5.1
15, Maga 3.7
13 -
These AAF values were then used to enter the
parametric duration curves on Plate 10. Values of the
seven exceedance percentages were read from the curves for
each of the three ungaged basins. The resultant flow
duration curves for Basins 2-Maloata, 6-Leafu, 10-Papa,
and 15-Maga, are shown on Plates 11, 12, 13, and 14.
Examination of the composite flow-duration curve
on Plate 9 shows a marked similarity of flow pattern in
all the gaged basins. This similarity inspires confidence
in employing the parametric duration curve and annual flow
to prepare flow-duration curves for the ungaged basins.
It would appear from the curves that there is little
variation in flow pattern from basin to basin, throughout
the island, at least as far as can be deduced from the
data available.
MASS CURVE ANALYSIS AND STORAGE-YIELD PROBABILITY
A flow-duration curve will give a good idea of
the persistence of streamflow, and of the low-flow values
that may be expected during dry periods. Low-flow fre-
quency tables or graphs are also helpful, especially when
considering direct diversion, or "run of the river"
development without storage.
14
In the small drainage basins on Tutuila, however,
low-flow values approach zero in most cases, and storage
would be required for any reasonable development for water
supply or hydropower. For storage evaluation, then, a
mass curve analysis is required.
There are several ways of analyzing storage
requirements with mass-curve techniques. The first
method, sometimes called a Rippl diagram, is a cumulative
plot of flow values for the period of record. Its
advantage is that it shows the effect of carryover
storage, and portrays more realistically how the reservoir
would actually operate. Its principal weakness is that
little can be said about the probability of yield because
of the lack of certainty that the historical record will
occur again in the same way.
The second method (Riggs and others, 1971),
involves a way to estimate the probability of the storage
reservoir being able to yield a selected draft rate, but
does so by calculating the storage required to refill the
reservoir.each year, thereby sacrificing evaluation of the
carryover storage.
15
A third method, probability routing, is based on
a distribution of annual inflows and involves calculating
the probability of the reservoir being empty at year-end
under a given draft rate. This method combines the advan-
tages of the first and second methods, but only uses
annual values, and is expensive and cumbersome to use.
The first method was used to evaluate the
probable flow persistence with storage in this study
because it gives a better idea of how the reservoir would
actually operate. Another consideration was that it is
not very meaningful to compute the 50 and 100-year proba-
bilities, required in the second method, with only 18
years of record. In addition to being cumbersome, the
third method was not used because of the limited years of
record available.
Plot of Annual Values - Annual values for each of
the six stations with significant years of record were
taken from U.S.G.S. records, accumulated, and plotted
against time. The plot of these curves for the six
stations are shown on Plate 15. From this plot, it was
apparent that all six streams exhibit similar annual flow
16 -
patterns, which would be expected from the similarity in
shape of their flow-duration curves. Also, a relatively
dry period from 1971 through 1974 can be noted. The rest
of the years recorded exhibited more normal flows, so the
period of 1971 through 1975 was utilized, to ensure that
the selected draft rates would permit recovery after each
dry period.
The selected draft rates appear as the regulated
flows of 1 through 5 cfs in Plate 16.
Plot of Monthly Values - Monthly values for each
stream-gaging station, taken from the U.S.G.S. records,
were accumulated and plotted for each of the six
stations. The plotted data indicated that 1974 was the
more severe dry period.
Because of the five basins to be analyzed, only
Basin 16-Pago, has records of suitable length for
analysis, the next step was to select one or more sets of
monthly values as representative of the ungaged basins.
After examining the monthly plots of the six stations with
long-term records, Atauloma and Basin 7-Aasu, both with
good records, were considered further. Basin 14-Afuelo,
17
was discarded because of only fair records. Data from
Basin 11-Leele, was discarded because of the relatively
short period of record of 10 years. Basin 19-Alega, was
also used for guidance. Comparison of Basin 7-Aasu, one
of the largest basins, and Atauloma, a small one, showed
little difference in flow pattern, and when adjusted for
basin size, were virtually identical. The six basins with
long record flow showed an estimated average yield of 6
cfs per square mile. Therefore, these basins, and the
estimated average yield of 6 cfs per square mile of basin
area, were used to develop monthly flow data for Basins
2-Maloata, 6-Leafu, 10-Papa, and 15-Maga.
Gaging Station Data - The first step in the
analysis is to examine available stream-flow records. A
summary of gaging station data is given in Table 2. As
shown, seven U.S.G.S. stream-gaging stations are listed,
with their name, U.S.G.S. number, drainage area, average
discharge, and period of record. Also, the basin number,
corresponding to the basin map on Plate 2, is given for
all stations except Atauloma, which was not delineated as
one of the 23 basins to be considered in this study.
As noted in Table 2, two of the stream gages,
10-Papa, and 11-Leele, have been discontinued, and have
shorter periods of record than the rest. Also, it is
noted that 10-Papa, has records of fair to poor quality.
For these reasons, the records from Basins 10-Papa, and
11-Leele, were discarded, and the analysis was based on
the remaining five sets of records. These five sets of
flow data, plus the flow data from Basin 16-Pago, were
then accumulated and plotted in mass-curve format.
It is of interest to note that the flow rates for
Basins 15-Maga, and 16-Pago, were almost exactly the same,
exhibiting but little difference in pattern and magni-
tude. These two basins are virtually the same size, but
on opposite sides of Pioa Mountain. Basin 16-Pago had its
own streamflow records, while the ungaged Basin 15-Maga
values were obtained by correlation from gaged basins to
the west.
Based on three preliminary findings, it appears
that the basins on Tutuila are very similar in flow
pattern, irrespective of location or orientation, and
until more data is gathered, flows and yields can be based
on drainage basin size. Thus, basin size, and the esti-
19 -
mated average yield of 6 cfs per square mile can be used,
with caution, as a crude method of estimating yield from
any of the other drainage basins on Tutuila.
ReAuired Storage - Values of required storage to
sustain different rates of regulated flow through the 1974
dry period were determined graphically from the mass curve
plot for each basin. The maximum draft rate in each case
was a rate that would permit refilling in 1975. With only
19 years of record and two dry periods for analysis, it
must be noted that these maximum values should be used
with caution, as considerably more storage may be required
to sustain these draft rates through drier periods in the
future. The draft, or regulated flow, and required
storages are listed in Table 3.
As shown in Table 3 and Plate 16, Basin 6-Leafu,
the largest, will yield a regulated flow of 5 cfs, about
70 percent of it long-term average flow, with about 1,650
acre-feet of storage. Basins 2-Maloata, 10-Papa, and
15-Maga, are smaller in size, and hence have propor-
tionately lower sustainable regulated flows.
20
Basin 16-Pago, however, is somewhat different.
Although its flow pattern is very similar to the other
basins, as previously noted, it did not receive as much
rainfall in mid-1975, and therefore, by the criteria of
permitting refilling in the relatively dry year of 1975,
cannot sustain as high a draft rate, in proportion to its
size, as the other basins do. It is for this reason that
the Basin 16 curve, shown on Plate 16, is shaped differ-
ently than the others.
STORAGE SITES SELECTION
In 1971, large-scale topographic maps for the
entire island, 1 inch to 200 feet, were prepared by the
American Samoa Government Public Works Department. These
maps were used to select the most suitable storage site in
each basin.
As noted previously, the basins on Tutuila are
characteristically small and steep; few storage sites are
available. Nevertheless, a site was selected for each
basin, as far downstream as possible, to provide maximum
reservoir storage capacity. Upstream reaches of each
basin were examined as well, to see whether any sites
21 -
might exist in the valleys at higher elevations, so that
water supply by gravity could be more easily accom-
plished. Unfortunately, no upstream sites of storage size
sufficient to sustain the selected draft rate were found,
and the lower downstream site was used in each case.
At the location which appeared most suitable in
each of the five basins, an earth embankment was sketched
in. These preliminary layouts are shown on Plates 16, 17,
18, 19, and 20. The embankments are shown with 20-foot
wide crests and slopes of 3 horizontal to 1 vertical, both
upstream and downstream.
As can be seen from the plates, the embankment
itself occupies a considerable portion of the storage
volume in each reservoir. This fact was taken into
account by planimetering around the embankment at each
site in the measuring and computing of the
elevation-storage relationships, shown for each site on
Plate 22, Storage Volumes.
As shown on Plate 22, Basins 6-Leafu, and
10-Papa, have the best storage characteristics; more than
2,500 acre-feet of storage could be obtained at either
site with an embankment 150 feet high (200 feet above mean
22 -
sea level). Basins 2-Maloata, 15-Maga, and 16-Pago, are
less desirable for storage since only about 1,500
acre-feet could be obtained with an embankment of the same
height.
This very preliminary storage evaluation was
conducted on the basis of topography only, as shown on the
large-scale maps. Foundation conditions, availability of
construction materials, land acquisition, sediment
problems, and all the other factors involved in damsite
selection were not considered at this time.
CONCLUSIONS
HYDROPOWER POTENTIAL
Examination of the storage-regulated flow curves
and the storage-elevation curves given on Plates 16 and 22
permits computing a rough estimate of the hydropower
potential in each basin. As shown in Table 3, Basin
6-Leafu is the most efficient storage site and will yield
about 5 cfs of regulated flow with about 1,650 acre-feet
of storage.
23 -
If an embankment were to be built in Basin
6-Leafu, to Elevation 180, about 1,650 acre-feet of live
storage could be provided between Elevations 100 and 180.
Assuming an average pool of Elevation 150, and a tailwater
at Elevation 50, 100 feet of gross head would be avail-
able. At 70 percent overall efficiency, and using the
formula: KW = QH (e)
11.8
where KW kilowatts generated
Q flow in cfs
H available head
e efficiency,
11.8 engineering constant,
about 30 KW of continuous power would be generated.
This procedure was used to estimate corresponding
estimates of hydropower potential for each of the other
four basins. Table 4 lists the comparable results for all
five basins. Comparing the values from Table 4 with the
amount of power and energy generated on Tutuila, we find
that even by assuming a 25 percent plant factor in Basin
6-Leafu, and installing 120 KW of capacity, only about 1
percent would be added to the system capacity.
24
From a brief review of the drainage basin charac-
teristics presented in Table 1, it is unlikely that any of
the -other basins could contribute significantly more
hydropower than the five basins studied. The combined
annual energy-contribution of the five basins studied
would likewise be small. The total contribution of all
five basins, about 972,000 KWh, is only about 2 percent of
last year's gross generation of 61,963,700 KWh (OSI,
1977).
WATER SUPPLY POTENTIAL
A recent study prepared in August 1978 (URS,
1978), provides estimates of water supply demand on
Tutuila. Table 11-6 of that report estimates the average
day water demand in the Year 2000 to be about 11.9 mgd.
These average system flow rates are further subdivided
into service area values ranging from about 0.1 mgd to
over 1.7 mgd. Even without detailed examination of the
service areas and distribution systems, it would appear
that the quantities of water from the five basins could
provide for a substantial portion of this demand. Table 5
25
shows the same storage and regulated flow values for each
basin, from Table 4, but expressed in water-supply units
of million gallon (mg) and million gallons per day (mgd).
As shown in Table 5, each basin would yield more
than 1 mgd, with the largest, Basin 6-Leafu, yielding 3.3
mgd if the required storage were provided. The total of
12.1 mgd shows that all five basins together could provide
all of Tutuila's estimated water demand in the Year 2000.
There is much more to evaluating Tutuila's water
supply situation than the preliminary sizing of a few
catchments (see URS, 1978 for a complete discussion).
Based on the findings of this preliminary investigation
however, estimates show that surface water supplies are
available in reasonable quantities for future develop-
ment.
26
mom= m m m m m m
T A B L E I D R A I N A G E B A S I N C 1-1 A R A C T E R 1 5 T I C S
RECORDED EST614ATEo AvuRA6E
DRA INA GE U.S. G. t;. PERIOD of AvERAGE RECORDED ANNUAL YIELD (9)
BASIN BASIN NAME SQ. AREA ST AT I ON RLCORD, YIELD CFS CF"/SQ.mI J-DAY Q10
NUMBER Mi. 0) NumucH YHS. (61 (8) CFS ACRE-fT
UNNAMED o.36 NONE Notic 2.2 1,500
2 MALOATA 1.03 925o 4) o.48 6.2 11,500
3 MAYAVAI 0.28 92,10 ()1) 0.o6 1.7 1,200
11 VAILOLO 1.13 9220 0.10 6.8 )1,900
2')
5 AsILI o.64 9 j4 -
3? 0.40 3.8 2,800
6 LEAFU 1.1
93
0.40 6.9 ow
AASU 1.00 9205 (2) 18 6.03 5.85 0.33 6.o 11,300
8 LEAVEAVE 1.17 gigo (4) 0.23 7.0 @'100
9 VIAPUNA 0.37 9330 (5) 0.02 2.2 i,6oo
10 PAPA o.85 9442 (3) 0.29 5.1
31100
11 LEELE 0.32 9175 (4) 10 1.50 6.52 o.oli 1.9 1,400
12 ___VAIMA 0.92 ____ -9505 ('1) 0.03 5.5 4, ow
CIT00- I'.
N) 91 4-1
13 FAGAALU 049 14) NONE 11.7 3,400
AFUCLO 0.31 948o (2) 19 1.42 5.68 0.07 1.9 1,300
15 MAGA o.61
9565 '1) 0.22 3.7 ?,6oo
16 PAGO o.69 9120 (2) 18 3.20 5.33 0.29 11.1 3,000
17 TAGAU 0.70 9100 (4) NONE 11.2 3, CK)()
18 -MULOOLEVAI 0.38 ___961o (4) oA 2.3 N
- 9 ALLGA 0. 2 6 9600 (4) 18 1.21 6.37 0.25 1.6 1,100--.
20 VAITOLU 0.25 9060 (5) 0.01 1.5 1,100
21- LcPA 0.21 905 0 02 1 .3- 900
22 VAILOA 0.31 9000 (5) 0.00 1.9 1,300
23 MuLiVAITELL 96,jo OIL 0-03 2.1-
-, -) - L' 800
UNNUMBEHLU ATAULOMA 1 0.27 9@1 0 (?). -T 18 1.42 1 5.92 0.10 1.6 1,200
NOTES: (1). By PLANIMETRY FROM USGS 72" TOPo, 1963, 014 BASINS
DESIGNATED uy U.S. ARMY.
(2j. CONT:NUOUS RECORD: ACTIVE;'..@U.
CONT'.UOUl ECORU 015 ON
1) Low- LOW, PARTIAL RECORD, ACFIVE.
OW FLOW, PARTIAL RECORD, DISCONTINUED.
Foom.USGS RECORDS.
BASED ON USGS GAGED CATCHMENT AREA.
lJNPUbL 1. S'if 0USGSTDATA -
BASED U PLANIMF ERED DRAINAGE A14EA A140 RECORDED AVERAVE YIELDS FROM GAGED BASINS.
TABLE 2
GAGING STATION DATA
PERIOD
GAGED AVG. CFS OF
USGS BASIN AREA DISCH. PER RECORD
NAME NO. NO. (SQ-MI.) (CFS) SQ.Mi. (YRS) REMARK
Aasu 9205 7 1.03 6.03 5.85 18 Record
Papa 9442 10 0.78 4.18 5.36 8 Record
to Poo
discon
Leele 9175 11 0.23 1.50 6.52 10 Discon
Afuelo 9480 14 0.25 1.42 6.58 19 Record
Pago 9120 16 0.60 3.20 5.33 18 Record
Alega 9600 19 0.19 1.21 6.32 18 Record
discon
Atauloma 9310 None 0.24 1.42 5.92 18 Record
" m m wo am so rm
TABLE 3
REQUIRED STORAGE VS REGULATED FLOW
REGULATED FLOW
AVERAGE PERCENT
ACRE- DISCHG. OF AVG.
BASIN CFS GPM FT/YR MGD (CFS) DISCHG.
2-Maloata 4.5 2020 3258 2.9 6.2 73
6-Leafu 5.0 2245 3620 3.3 6.9 72
10-Papa 3.8 1706 2751 2.5 5.1 75
15-Maga 2.7 1212 1955 1.8 3.1 73
16-Pago 2.5 1122 1810 1.6. 4.1 61
mmm womwww M"m onto""
TABLE 4
POWER AND ENERGY POTENTIAL
REQUIRED CREST GROSS CONTINUOUS
REGULATED STORAGE -ELEV. HEAD POWER
BASIN FLOW, CFS (ACRE-FT) (FT) (FT) (KW)
2-Maloata 4.5 1,600 200 110 29.4
6-Leafu 5.0 1,650 180 100 29.7
10-Papa 3.8 1,200 170 100 22.5
15-Maga 2.7 1,000 185 110 17.6
16-Pago 2.5 600 185 80 11.9
TOTALS 111.1
SM. an as sm so No
TABLE 5
WATER SUPPLY POTENTIAL
BASIN STORAGE, MG REGULATED FLO
2-Maloata 521 2.9
6-Leafu 544 3.3
10-Papa 396 2.5
15-Maga 330 1.8
16-Pago 198 1.6
TOTALS 1,989 12.1
som
HYDROLOGIC INVESTIGATION OF SURFACE WATER
TUTUILA, AMERICAN SAMOA
U.S. ARMY ENGINEER DISTRICT
HONOLULU, OAHU, HAWAII
SAN FRANCISCO
TOKYO
P A CIFI C OCEAN
19 HONOLULU
MANILA
GUAM
LOCATION MA
WATER SUPPLY AND HYDRO
TUTUILA, AMERICAN
FIJI TAHITI SAMOA ISLANDS - SOUT
(NOT TO SCALE)
WESTERN SAMOA
S@AVAUI. --'IUPOLU IS.
is
TUTUILA
STUDY AREA-/ `AUNU!U
GOT TO SCALE) '&-RICAN
N
Pago If Lepa
-Vagou vailolu
Vaimo
19
Vailolo Aosu Leele 12 - %-- Muliolevoi
Motavoi 13 Alega
Mago
Malouto /f Fagoolu
Papa Aluelo
(Unnamed)
Leoveave
a 9 6
Leofu
lauloma
Asib
Viapuno
DRAINAGE BASINS
TUTUILA ISLAND
AMERICAN SAMOA
SAMI&EI-11. 1.11 rl.., HYDROLOGIC IN
... ... ... TUTUI
U.S. AR
FROM US. ENGREER OtSIRHIT. HAWAII "ON(
DISCHARGE IN CUBIC FEET PER SECOND (CFS)
IQ 4%
@4 W
/000@
x0
0
fn
00
-LL
F
HYDROLOGIC INVESTIGATION OF
FLOW. DURATION CURVE TUTUILA, AMERICAN
m ATAULOMA STREAM AT AFAO) TUTUILA., AMERICAN SAMOA
WEST OF BASIN NUMBER 5 (YEARS OF RECORD: 196o - 1977) U.S. ARMY ENGINEER D
HONOLULU, OAHU, 1-
DISCHARGE IN CUBIC FEET PER SECOND (CFS)
N .4 4A
0 0 0
to m -4 wwo
0
0
-0
rn
;u
0
m
z
in
rn
X
C-)0
rn
rn
FLOW DURATION CURVE HYDROLOGIC INVESTIGATION 0
AASU STREAM AT AASU., TUTUILA., AMERICAN SAMOA TUTUILA, AMERICA
BASIN NUMBER 7 (YEARS OF RECORD: 196o - 1977) U.S. ARMY ENGINEER
HONOLULU, OAHU,
904MI" ads* in m"mmoom "ll" "'m
DISCHARGE IN CUBIC FEET PER SECOND (CFS)
N fQ
io 8 0 0 0 0
_0
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rn
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FLOW DURATION CURVE HYDROLOGIC INVESTIGATION 0
LEELE STREAM AT MOUTH, AT FAGASA, TUTUILA, AMERICAN SAMOA TUTUILA, AMERICA
BASIN NUMBER 11 (YEARS OF RECORD: 1961 - 1976) U.S. ARMY ENGINEER
HONOLULU, OAHU,
"""WOO m
DISCHARGE IN CUBIC FEET PER SECOND (CFS)
L%
0 0 0
-0
;u
r)
rq
z
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0
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X
rl
xob
0
rq
pi
V
FLOW DURATION CURVE HYDROLOGIC INVESTIGATION 0
AFUELO STREAM AT MATUU., TUTUILA, AMERICAN SAMOA TUTUILA, AMERICA
BASIN NUMBER 14 (YEARS OF RECORD: 1959 - 1977) U.S. ARMY ENGINEER
HONOLULU, OAHU,
Men"
DISCHARGE IN CUBIC FEET PER SECOND (CFS)
a)
0 0 0 0
rri
0
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fn
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00
m
rri
0
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FLOW DURATION CURVE HYDROLOGIC INVESTIGATION 0
PAGO STREAM AT AFONO, TUTUILA., AMERICAN SAMOA TUTUILA, AMERICA
BASIN NUMBER 16 (YEARS OF RECORD: I 96o - I gly) U.S. ARMY ENGINEER
HONOLULU, OAHU,
Mae "so" ",No
DISCHARGE IN CUBIC FEET PER SECOND WFS)
to La LA
0 0 0
TT I
CA
0
Q0 m
FTI
>4
0ch
fn0
rn
HYDROLOGIC INVESTIGATION OF
FLOW DURATION CURVE
ALEGA STREAM AT ALEGA, TUTUILA, AMERICAN SAMOA TUTUILA, AMERICAN
00 BASIN NUMBER 19 (YEARS OF RECORD: 1959 - 1976) U.S. ARMY ENGINEER D
HONOLULU, OAHU, 1-
men'" ""mm"'Wwaw "so m
DISCHARGE IN CUBIC FEET PER SECOND (CFS)
ro 4% Lp
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x cn cn -1
cf) > -i -i X TUTUILA, AMERICAN
;a x fri
co m m >
-i > > :K X
;u :K X U.S. ARMY ENGINEER D
HONOLULU, OAHU, H
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0
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1.0
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0.1 1.0 10 co
ANNUAL AvERAGE FLOW, CFS
PARAMETRIC DURATION CURVES
VALUES FROM 'GAGED STATIONS ON AME71CAN SAMOA
HYDROLOGIC INVESTIGATION OF SURFACE WATERI
TUTUILA, AMERICAN SAMOA
U.S. ARMY ENGINEER DISTRICT
HONOLULU, OAHU, HAWAII
41 PLATE 10
"MOM"
DISCHARGE IN CUBIC FEET PER SECOND (CFS)
0
0 0 0 0
X
rq
0
M
or
M
HYDROLOGIC INVESTIGATION 0
FLOW DURATION CURVE
BASIN #2 MALOATA TUTUILA, AMERICA
U.S. ARMY ENGINEER
HONOLULU, OAHU,
Men"
DISCHARGE IN CUBIC FEET PER SECOND (CFS)
rv
W 0 0 0
0
OF
-0
m
X
0
z
-4
0
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00
V
FLOW DURATION CURVE HYDROLOGIC INVESTIGATION OF
BASIN # 6 - LEAFU TUTUILA, AMERICAN
U.S. ARMY ENGINEER D
HONOLULU, OAHU, H
DISCHARGE IN CUBIC FEET PER SECOND (CFS)
Lo tx
IA
0
r9
x
0
rn
0
rn
OD
V
FLOW DURATION CURVE HYDROLOGIC INVESTIGATION 0
BASIN #10 - PAPA TUTUILA, AMERICA
U.S. ARMY ENGINEER
HONOLULU, OAHU,
mIIWIWaw"m"m ""SNOW
DISCHARGE IN CUBIC FEET PER SECOND (CFS)
0
rn
z
0
9
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-0
t_n
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m
F9
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C)
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FLW DURATION CURVE HYDROLOGIC INVESTIGATION 0
BASIN #15 - MAGA TUTUILA, AMERICA
U.S. ARMY ENGINEER
HONOLULU, OAHU,
HYDROLOGIC INVESTIGATION OF SURFACE WATER
TUTUILA, AMERICAN SAMOA
U.S. ARMY ENGINEER DISTRICT
HONOLULU, OAHU, HAWAII
100,000
8o'Ooo
6o,ooo
4o,ooo
sip'.
20,000 P,7rAULOMA
NoJELO LEELE
S-fR.
ACEGA
0
", @@S'3
'61 '62 19' '64 1 '66 19'67 19'68 1169 1 1 1
1 -9 0 19 19 63 19 1 '65 9 970 1971 1972
91r,:9 19 9 9 1973
T I M E Y E A R S
MASS CURVES FOR SIX BASINS
sm so m m m m " m SOON m 4w m
HYDROLOGIC INVESTIGATION OF SURFACE WATER
TUTUILA, AMERICAN SAMOA
U.S. ARMY ENGINEER DISTRICT
HONOLULU, OAHU, HAWAII
5
0-
4
0
(n
3
"oooool
00'e
c2l
I-le _'0000
2
.00
00 200 )too 6oo 800 1000 1200 1 4oo
REQUIRED STORAULP ACRE-FEET
REQUIRED STORAGE vs. REGULATED FLOW
MALOATA BAY
EL. 200
iT5
i3o
75
el
@, 16 itk
'lip
SAMOA HYDROPOWER STUDY
STORAGE SITE - BASIN NO. 2
MALOATA
$CALL IN FEET
FROM PWO TOPOGRAPHIC MAP, SHEETS 25 & 36
HYDROLOGIC INVESTIGATION OF SURFACE WATER'
TUTUILA, AMERICAN SAMOA
U.S. ARMY ENGINEER DISTRICT
HONOLULU, OAHU, HAWAII
48 - PLATE 17
A \
@P//
op J I
lp ()"
It
i0a
150
till I EL 200-
ISO
if
100
SAMOA HYDROPOWER STUDY
BASIN NO. 6
LEAFU
200-%@@- m@*'Zo
SCALE IN FEET
FROM PWO TOPOGRAPHIC MAP, SHEETS 45
HYDROLOGIC INVESTIGATION OF SURFACE WATER
It
TUTUILA, AMERICAN SAMOA
U.S. ARMY ENGINEER DISTRICT
HONOLULU, OAHU, HAWAII
49 - PLATE 18
1011
so
12
ISO
0 '\
.pal 175
200
12
-125
-100 --200
-173
-.Z-,
QAcIo
76" 75 75
50 so
t 25
r-'L/ In
so
SAMOA HYDROPOWER STbDY
BASIN NO. 10
wo PAPA
SCALE 114 fEET
FROM MAID 70@0135RAPHM MAP, SHEET NO. 3-5
HYDROLOGIC INVESTIGATION OF SURFACE WATER
TUTUILA, AMERICAN SAMOA
U.S. ARMY ENGINEER DISTRICT
HONOLULU, OAHU, HAWAII
PLATE IQ
so -
Iit
\0
v.
too
150
14
-ago
75 /so
za
25
N
SAMOA HYDROPOWER STUDY
BASIN NO. 15
MAGA
SCALE iN FEET
FROM PWO MPOGRAPHIC MAP. SHEET NO. 23
HYDROLOGIC INVESTIGATION OF SURFACE WATER
TUTUILA, AMERICAN SAMOA
U.S. ARMY ENGINEER DISTRICT
HONOLULU, OAHU, HAWAII
51 - PLATE 20
J.
i25
tlA
N 100
N-1
tl
oo'-_
SAMOA HYDROPOWER STUDY
BASIN NO. 16
PAGO
FMM PW'l TOPOGRAPHC MP, SHEET NO. 12
HYDROLOGIC INVES71GATION OF SURFACE INATER!
TUTUILA, AMERICAN SAMOA
U.S. ARMY ENGINEER DISTRICT
HONOLULU, OAHU, HAWAII
52 PLATF_ 21
300
2@0
>7
xro -
200
LA
Ln
w
de"
0 150
2
r
0
c -40 Ld
c: 0 _j
-1 W
z c:
0 x i=
r- K > M 100
c
rn
z
C)
z m
rn x 0
ril F)-Z
> 0 50
x 0 Z 0 jOO 1000 1500 2000 2@00 3000
*> U)
(n
c: STORAGE VOLUME ACRE-FEET
0 0
>
rn STORAGE VOLUMES FOR FIVE BASINS.
1>
HYDROLOGIC INVESTIGATION OF SURFACE WATER
FOR WATER SUPPLY AND HYDROPOWER
TUTUILA, AMERICAN SAMOA
BIBLIOGRAPHY
1. Austin, Smith & Associates, Inc., Report Covering a
Master Planned Water Supply and istribution Syste
foF__thePago Pago and Tafuna Areas, prepared for the
Government of American Samoa, February 1963.
2. Austin, Smith & Associates, Inc., Report Updating the
1963 Master Planned Water Supply and Distribution
System for the Pago Pago and Tafuna Areas and
Including the Leone Plain, prepared for the Department
of Public Works, Government of American Samoa, April
1972.
3. Austin, Smith & Associates, Inc. Water Supply and
Distribution Systems Pago Pago anU-Tafuna Areas, April
1966.
4. CH2M Hill, Water System Study: Western Portion of
Tutuila Island, November 1975.
5. Government of American Samoa, Office of Samoan
Information, Annual Report, 1977.
6. Heitz, L.F. Maximum Stream Potential for Hydroelectric
Power Production, Universi y of Idaho, Moscow, Idaho,
June 7, 1978.
7. Linsley, R.K., M.A. Kohler and J.L.H. Paulhus,
Hydrology for Engineers, McGraw-Hill Book Company,
1958.
8. Riggs & Hardison, Techniques of Water Resources
Investigations, 1971.
9. Stearns, H.T., "Geology of the Samoan Islands,"
Geological Society of America, Bulletin, 1944, volume
55, pp. 1279-1332.
54 -
10. URS, Draft Report, Assessment of Water Systems,
prepared for the Department of the Army, 197F
11. U.S. Army Engineer District, Honolulu, American Samoa
Water Resources Study Plan of Study, December 1977.
12. U.S. Geological Survey, Flow Characteristics of
Streams in Tutuila, AmerTc-ansamoa, prepared in'
cooperation with the Government of American Samoa,
Draft Report, (unpublished) March 1978.
13. U.S. Geological Survey, Water Resources Data for
Hawaii and other Pacific Areas, 1960 through 1978.
55
INIOAA COASTAL SERVICES CTR LIBRARY I
"I
r
3 6668 1411OD94 3 1
L@-
This XML file does not appear to have any style information associated with it. The document tree is shown below.
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<metadata>
<titleStmt>
<mainTitlenfc="0">
<title>Hydrologic investigation of surface water for water supply and hydropower, Tutuila Island, American Samoa</title>
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<respStmt>for U.S. Army Corps of Engineers ; prepared by Dames & Moore.</respStmt>
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</titleStmt>
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<locClass>
<subjectcat="top">Water-power</subject>
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Coastal Zone
Information
Center AMERICAN SAMOA WATER RESOURCES STUDY.
HYDROLOGIC INVESTIGATION
OF SURFACE WATER
FOR WATER SUPPLY & HYDROPOWER
TUTUILA ISLAND,
AMERICAN SAMOA
C)
F
a s Tta'l one
Z
lon for at ion
U-S-ARMY ENGINEER DISTRICT, HONOLULU
<pbn="2"/>
HYDROLOGIC INVESTIGATION OF SURFACE WATER
FOR WATER SUPPLY AND HYDROPOWER
TUTUILA ISLAND, AMERICAN SAMOA
FOR
U.S. ARMY CORPS OF ENGINEERS
SEPTEMBER, 1978
Prepared by
DAMES & MOORE
Consultants in the Environmental and
Applied Earth Sciences
Suite 200
1144 10th Avenue
Honolulu, Hawaii 96816
<pbn="3"/>
SUITE 200 1144 10th AVENUE - HONOLULU, HAWAII S8816 - (808) 735-3585
CABLE: DAMEMORE TELEX: 63-4100
September 18, 1978
U.S. Army Corps of Engineers
Pacific Ocean Division
Building 230, Fort Shafter
Honolulu, Hawaii 96858
Attention: Mr. Kisuk Cheung
Chief, Engineering Division
Gentlemen:
Hydrologic Investigation of Surface
Water for Water Supply and Hydropower
Tutuila Island, American Samoa
We are pleased to present our final report on the.
water supply and hydropower potential of Tutuila Island,
American Samoa, prepared for you under the terms of
Contract No. DACW 84-78-C-0013.
The study describes available water resources,
and impoundment area characteristics, and assesses the
possible use of an impoundment at five separate locations
for the dual purposes of water supply and hydropower.
The analysis provided in this report should prove
valuable to the Corps of Engineers and others, in any
future consideration to meeting electrical power or water
supply requirements through surface water impoundment in
American Samoa.
<pbn="4"/>
U.S. Army Corps of Engineers
September 18, 1978
Page 2
It has been a pleasure to prepare this report for
you, and we hope that it meets you needs. Please feel
free to contact us if you have any questions, or require
further information.
Sincerely,
DAMES & MOORE
6L ZI.-IIZ41
Eric Will
Chief Planning Engineer
Water Resources Engineering Services
S.K. D30U
Principal-in-Charge
EW:SKD:jo
<pbn="5"/>
TABLE OF CONTENTS
PAGE
SUMMARY ..................................................1
INTRODUCTION .............................................4
Authority ............................................4
Purpose ..............................................5
STUDY AREA ...............................................6
PREVIOUS INVESTIGATIONS ..................................7
CLIMATE AND HYDROLOGY ....................................8
METHODOLOGY ..............................................9
Drainage Basin Selection .............................9
Flow-Duration Curve Development ..................... 11
Mass Curve Analysis and Storage-Yield Probability ... 14
Plot of Annual Values .......................... 16
Plot of Monthly Values ......................... 17
Gaging Station Data ............................ 18
Required Storage ............................... 20
STORAGE SITES SELECTION ................................. 21
CONCLUSIONS ............................................. 23
Hydropower Potential ................................ 23
Water Supply Potential .............................. 25
BIBLIOGRAPHY ............................................ 54
<pbn="6"/>
LIST OF TABLES
NO. TITLE PAGE
DRAINAGE BASIN CHARACTERISTICS ................. 27
2 GAGING STATION DATA ............................ 28
3 REQUIRED STORAGE VS. REGULATED FLOW ............ 29
4 POWER AND ENERGY POTENTIAL ..................... 30
5 WATER SUPPLY POTENTIAL ......................... 31
<pbn="7"/>
LIST OF PLATES
NO,- TITLE PAGE
Location Map ................................... 32
2 Drainage Basins ................................ 33
3 Flow Duration Curve - Atauloma ................. 34
4 Flow Duration Curve - Basin 7, Aasu ............ 35
5 Flow Duration Curve - Basin 11, Leele .......... 36
6 Flow Duration Curve - Basin 14, Afuelo ......... 37
7 Flow Duration Curve - Basin 16, Pago ........... 38
8 Flow Duration Curve - Basin 19, Alega .......... 39
9 Flow Duration Curves - Composite ............... 40
10 Parametric Duration Curves ..................... 41
11 Flow Duration Curve - Basin 2, Maloata ......... 42
12 Flow Duration Curve - Basin 6, Leafu ........... 43
13 Flow Duration Curve - Basin 10, Papa ........... 44
14 Flow Duration Curve - Basin 15, Maga ........... 45
15 Mass Curves for Six Basins ..................... 46
16 Required Storage vs. Regulated Flow ............ 47
17 Storage Site - Basin 2, Maloata ................ 48
18 Storage Site - Basin 6, Leafu .................. 49
19 Storage Site - Basin 10, Papa .................. 50
20 Storage Site - Basin 15, Maga .................. 51
21 Storage Site - Basin 16, Pago .................. 52
22 Storage Volumes for Five Basins ................ 53
<pbn="8"/>
SUMMARY
* The small, steep drainage basins of Tutuila yield
an average annual runoff of about 6 cubic feet
per second (cfs) per square mile. This amount is
equivalent to about 80 inches of annual runoff,
which appears reasonable, considering average
rainfall and evapotranspiration.
* All 23 basins delineated are quite similar in
topography and shape, with steep, narrow uplands
draining to the sea. Of these 23 basins, the six
basins with gaged streamflows of up to 18 years
of good records, exhibit similar flow patterns.
Although unofficial rainfall data collected by
the American Samoa government and others indicate
that higher elevations receive more rainfall, the
existing official data base of two long-term
raingaging stations does not warrant dividing the
basins into higher and lower sub-areas to
estimate yields in more detail.
<pbn="9"/>
0 The flow patterns of the five basins studied in
detail, Nos. 2-Maloata, 6-Leafu, 10-Papa,
15-Maga, and 16-Pago, are such that regulated
flows of about 4 cfs per square mile can be
obtained with reservoir storage. Based on
mass-curve analysis of the gaged basins, storages
of about 300 acre-feet per cfs of regulated flow
are required (see Table 3 for further detail).
0 Storage sites are small, of low capacity, and
need a relatively high embankment to achieve
required storage. To achieve maximum storage, a
site was selected in the lower reaches of each
basin. Because of the limited storage volume
available, embankments of more than 100 feet high
are required in each case.
0 Run of the river hydropower development is
generally not feasible due to extremely low or
intermittent stream flows.
2
<pbn="10"/>
0 Even with the maximization of storage, hydropower
potential is very small and unattractive when
compared to the power and energy demands of the
island. The best of the five basins studied, No.
6-Leafu, would only yield about 30 KW of continu-
ous power, and about 260,000 KWh of annual
energy. This is less than one-half of 1 percent
of the island's 1977 energy generation.
0 The potential for surface water development is
more attractive. Basin 6-Leafu, with a regulated
flow of about 3.3 mgd, could supply about 28
percent of the estimated average water demand in
the Year 2000. The other basins could also
supply reasonable portions of future water
needs. Although no evaluation of reservoir
construction, pumping, treatment, or distribution
costs for water supply was made in this report;
from a purely supply standpoint, it would seem
that surface storage for future water supply
development is worthy of more detailed investi-
gation.
3
<pbn="11"/>
0 Development of the selected basins, as described
herein, may not be appropriate at this time. For
this reason, curves of storage, elevation, and
regulated flow, are shown in Plates 16 and 22.
With these curves, it is possible to select lower
rates of flow and find the required storage that
may be in keeping with more immediate needs.
Conversely, it is possi ble to determine the rate
of flow that will result from construction of
reservoirs of a less than the selected sizes.
INTRODUCTION
AUTHORITY
This study has been undertaken as a part of the
American Samoa Water Resources Study (ASWRS), as author-
ized by Section 143 of the Water Resources Development Act
of 1976, Public Law 94-587. The goal of ASWRS is to
develop a comprehensive water resources plan for the
waters for American Samoa, including flood plain
management, hydroelectric power generation, regional water
and wastewater management facilities, water quality,
water-related land recreation, fish and wildlife propaga-
tion, navigation, and flood control.
4
<pbn="12"/>
In response to expressed concern on the part of
the U.S. Congress, certain federal agencies, and local
officials, the U.S. Army Engineer District Honolulu,
contracted with Dames & Moore, consultants in the environ-
mental and applied earth sciences, to conduct this inves-
tigation under the terms of Contract No. DACW
84-78-C-0013, executed 19 May 1978.
PURPOSE The basic purpose of this study is to identify
the drainage basins on Tutuila Island, American Samoa,
with the highest potential for water supply and hydropower
development and to estimate these potentials for at least
five selected basins. This report will then serve as a
source of information for interested federal and local
agencies. The study is a reconnaissance-level investiga-
tion, utilizing existing data, records, and previous
reports. No field survey was undertaken as a part of this
study; however, extensive knowledge of American Samoa from
on-island experience of the Dames & Moore staff was
utilized in selecting the likely candidate basins.
5
<pbn="13"/>
STUDY AREA
The island of Tutuila is the largest and most
populous of the seven principal islands of American Samoa;.
its location is shown on Plate 1. The island is about 18
miles long, and varies in width from 1 to 6 miles; total
land area is about 53 square miles. Topography is rugged,
as in most Pacific volcanic islands; about 70 percent of
0
Tutuila's land area has slopes greater than 30 .
While rainfall appears abundant, continued water
shortages have been experienced in the territory since
1960. Subsequently, tens of millions of dollars have been
spent in capital improvements to the water systems, on
both ground water and surface water. The current American
Samoa Government (ASG) water systems improvement program
is directed toward further development of ground water
supplies as the primary source of water for the central
government system (URS, 1978). While ground water does
appear to be the more desirable source, possible limita-
tions to its development and the attractive advantages of
a surface water reservoir with a gravity-fed distribution
system have led some engineers and laymen alike to favor
the development of more surface water sources.
6
<pbn="14"/>
Similarly, chronic operational problems with the
island's diesel-powered electric generators, the likely
prospect of increasing fuel and operational costs, and the
steep topography of the island have led many to believe
that hydropower would be a more reliable source of the
island's electrical energy, if sufficient potential
exists.
PREVIOUS INVESTIGATIONS
Several previous studies and reports on water
supply and surface water availability in American Samoa
were used as data sources in this study. They are listed
in the bibliography.
In addition, unpublished United States Geological
Survey (U.S.G.S.) information was reviewed. Several
excellent published papers on hydropower evaluation were
also used for guidance, and are referenced in the biblio-
graphy.
7
<pbn="15"/>
CLIMATE AND HYDROLOGY
The climate of Tutuila is tropical, with wet and
dry seasons. During the wet or summer period, from
November through April, the island lies in the inter-
tropical convergence zone, with weak and variable winds,
high temperatures, rainfall, and high humidity. In the
dry winter seasons, from May through October, the climate
is influenced by the southeasterly tradewinds, with
slightly lower temperatures and less rain.
Precipitation results from the upward deflection
of the trades as they pass over the island, as well as
from.major storms and isolated thunderstorms. The annual
precipitation varies with location and elevation; the Pago
Pago airport at sea level, receives an average of 125
inches per year, while nearby Mount Alava, at Elevation
1,600 feet, receives more than 250 inches. Seasonal
variation is considerable, and extended dry periods of 2
or 3 months are common. Generally, the driest months are
June through September, and the wettest are December
through March.
8
<pbn="16"/>
In view of the small catchment areas, steep
terrain, and limited storage sites, these wet and dry
periods pose problems for water supply and hydropower
development.
METHODOLOGY
DRAINAGE BASIN SELECTION
Twenty-three drainage basins on Tutuila were
selected to be examined for the dual purpose of water
supply and hydropower potential. They are shown on Plate
Preliminary basin evaluation was accomplished by
tabulating drainage area, years of record for gaged
basins, and the lowest 7-day flow over a 10-year interval
(7-day Q10), from unpublished U.S.G.S. data. Seven-day
Q10 was chosen as an initial indication of flow reliabili-
ty. On the basis of drainage area and 7-day Q10 rankings,
Basins 2-Maloata, 6-Leafu, 7-Aasu, 8-Leaveave, and
13-Fagaalu, were selected. However, in order to provide a
better east-west distribution of the final basins to be
selected, and to provide more basins where gravity water
supply could supply the population centers on the southern
9
<pbn="17"/>
shore of Tutuila, the northern drainage Basins 7-Aasu, and
8-Leaveave, and the already developed Basin 13-Fagaalu,
were discarded. The final basins selected were 2-Maloata,
6 Leafu, and 10-Papa, in the Western District, and
15-Maga, and 16-Pago, in the Eastern District.
The basin number, name, and characteristics of
all 23 basins are given on Table 1. The drainage areas
of the delineated basins were computed by planimetry from
the U.S.G.S. topographic map of Tutuila. Identification
numbers for U.S.G.S. partial-record and discontinued
streamgaging stations are shown, as well as the period of
record for currently active stations. U.S.G.S.-recorded
average yield and unit yield, in cfs per square mile, are
shown for the gaged basins. Values for 7-day Q10, from
unpublished U.S.G.S. data, are also shown.
Estimated average annual yields, in cfs and
acre-feet, are shown for each basin. These values were
computed by multiplying the planimetered drainage area by
an average value of 6 cfs per square mile. This value is
the approximate average of the 83 station-years of data
available from the gaged basins.
10 -
<pbn="18"/>
If an island-wide network of rain gages is
established in the future, and if more basins are gaged
for streamflow so that isohyetal maps and better runoff
data can be obtained, this approximate estimate of average
annual yield can be revised to accommodate differences in
estimated runoff between drainage basins, and by different
elevations within the same basin. For now, however, the
data available does not warrant further manipulation,
especially at this level of investigation.
The estimated average yields range from over
5,000 acre-feet for the largest basin (8-Leaveave) to 900
for the smallest one (21-Lepa). The last two columns in
the table show the initial basins selected and the final
basins selected, following the procedure previously
discussed.
FLOW DURATION CURVE DEVELOPMENT
To develop flow duration curves for the final
five basins selected, curves were developed for a total of
ten drainage basins. Six of these basins, Atauloma,
Basins 7-Aasu, 11-Leele, 14-Afuelo, 16-Pago, and 19-Alega,
have stream gages with 10 to 19 years of records,
<pbn="19"/>
monitored by U.S.G.S. One basin, 10-Papa, has only 8
years of fair to poor records. The other three,
2-Maloata, 6-Leafu, and 15-Maga, are ungaged. The curves
were developed as follows:
First, flow-duration curves for the six gaged
streams of Atauloma, 7-Aasu, 11-Leele, 14-Afuelo, 16-Pago,
and 19-Alega, were constructed. The data were taken from
a U.S.G.S. computer printout, which included a duration
table of daily values for all years of record. This table
shows values of discharge in cubic feet per second (cfs)
with corresponding exceedance percentages. These values
were plotted directly on a flow-duration curve of flow
versus exceedance percentage. The six curves for the
gaged basins are shown on Plates 3 through 8.
Next, the six curves were plotted together for
comparison. The plots are shown on Plate 9. As shown,
the curve shapes are quite similar. From this composite,
and the annual average flow (AAF) for the gaged basins
also given in the U.S.G.S. data, parametric duration
curves were plotted. These curves show average daily flow
versus AAF values as shown on Plate 10 (see Heitz 1978 for
a detailed description of procedure). This graph has
12 -
<pbn="20"/>
daily flow plotted against AAF. Values of seven different
exceedance percentages were plotted for each of the six
streams, and the best-f,it curve was developed for each of
the exceedance values. With this graph and a value of
AAF, flow duration curves of ungaged streams can be
constructed.
Finally, curves for the remaining basins were
prepared from the parametric curves and estimates of AAF.
The values of AAF are most readily determined
from streamflow data or from an isophyetal map. However,
no such map has been developed for American Samoa, as
there are only two official long-term rain gages on the
island. The estimated AAP values from Table 1 were used
for this portion and are listed below.
BASIN NO. AAF, CFS
2, Maloata 6.2
6, Leafu 6.9
10, Papa 5.1
15, Maga 3.7
13 -
<pbn="21"/>
These AAF values were then used to enter the
parametric duration curves on Plate 10. Values of the
seven exceedance percentages were read from the curves for
each of the three ungaged basins. The resultant flow
duration curves for Basins 2-Maloata, 6-Leafu, 10-Papa,
and 15-Maga, are shown on Plates 11, 12, 13, and 14.
Examination of the composite flow-duration curve
on Plate 9 shows a marked similarity of flow pattern in
all the gaged basins. This similarity inspires confidence
in employing the parametric duration curve and annual flow
to prepare flow-duration curves for the ungaged basins.
It would appear from the curves that there is little
variation in flow pattern from basin to basin, throughout
the island, at least as far as can be deduced from the
data available.
MASS CURVE ANALYSIS AND STORAGE-YIELD PROBABILITY
A flow-duration curve will give a good idea of
the persistence of streamflow, and of the low-flow values
that may be expected during dry periods. Low-flow fre-
quency tables or graphs are also helpful, especially when
considering direct diversion, or "run of the river"
development without storage.
14
<pbn="22"/>
In the small drainage basins on Tutuila, however,
low-flow values approach zero in most cases, and storage
would be required for any reasonable development for water
supply or hydropower. For storage evaluation, then, a
mass curve analysis is required.
There are several ways of analyzing storage
requirements with mass-curve techniques. The first
method, sometimes called a Rippl diagram, is a cumulative
plot of flow values for the period of record. Its
advantage is that it shows the effect of carryover
storage, and portrays more realistically how the reservoir
would actually operate. Its principal weakness is that
little can be said about the probability of yield because
of the lack of certainty that the historical record will
occur again in the same way.
The second method (Riggs and others, 1971),
involves a way to estimate the probability of the storage
reservoir being able to yield a selected draft rate, but
does so by calculating the storage required to refill the
reservoir.each year, thereby sacrificing evaluation of the
carryover storage.
15
<pbn="23"/>
A third method, probability routing, is based on
a distribution of annual inflows and involves calculating
the probability of the reservoir being empty at year-end
under a given draft rate. This method combines the advan-
tages of the first and second methods, but only uses
annual values, and is expensive and cumbersome to use.
The first method was used to evaluate the
probable flow persistence with storage in this study
because it gives a better idea of how the reservoir would
actually operate. Another consideration was that it is
not very meaningful to compute the 50 and 100-year proba-
bilities, required in the second method, with only 18
years of record. In addition to being cumbersome, the
third method was not used because of the limited years of
record available.
Plot of Annual Values - Annual values for each of
the six stations with significant years of record were
taken from U.S.G.S. records, accumulated, and plotted
against time. The plot of these curves for the six
stations are shown on Plate 15. From this plot, it was
apparent that all six streams exhibit similar annual flow
16 -
<pbn="24"/>
patterns, which would be expected from the similarity in
shape of their flow-duration curves. Also, a relatively
dry period from 1971 through 1974 can be noted. The rest
of the years recorded exhibited more normal flows, so the
period of 1971 through 1975 was utilized, to ensure that
the selected draft rates would permit recovery after each
dry period.
The selected draft rates appear as the regulated
flows of 1 through 5 cfs in Plate 16.
Plot of Monthly Values - Monthly values for each
stream-gaging station, taken from the U.S.G.S. records,
were accumulated and plotted for each of the six
stations. The plotted data indicated that 1974 was the
more severe dry period.
Because of the five basins to be analyzed, only
Basin 16-Pago, has records of suitable length for
analysis, the next step was to select one or more sets of
monthly values as representative of the ungaged basins.
After examining the monthly plots of the six stations with
long-term records, Atauloma and Basin 7-Aasu, both with
good records, were considered further. Basin 14-Afuelo,
17
<pbn="25"/>
was discarded because of only fair records. Data from
Basin 11-Leele, was discarded because of the relatively
short period of record of 10 years. Basin 19-Alega, was
also used for guidance. Comparison of Basin 7-Aasu, one
of the largest basins, and Atauloma, a small one, showed
little difference in flow pattern, and when adjusted for
basin size, were virtually identical. The six basins with
long record flow showed an estimated average yield of 6
cfs per square mile. Therefore, these basins, and the
estimated average yield of 6 cfs per square mile of basin
area, were used to develop monthly flow data for Basins
2-Maloata, 6-Leafu, 10-Papa, and 15-Maga.
Gaging Station Data - The first step in the
analysis is to examine available stream-flow records. A
summary of gaging station data is given in Table 2. As
shown, seven U.S.G.S. stream-gaging stations are listed,
with their name, U.S.G.S. number, drainage area, average
discharge, and period of record. Also, the basin number,
corresponding to the basin map on Plate 2, is given for
all stations except Atauloma, which was not delineated as
one of the 23 basins to be considered in this study.
<pbn="26"/>
As noted in Table 2, two of the stream gages,
10-Papa, and 11-Leele, have been discontinued, and have
shorter periods of record than the rest. Also, it is
noted that 10-Papa, has records of fair to poor quality.
For these reasons, the records from Basins 10-Papa, and
11-Leele, were discarded, and the analysis was based on
the remaining five sets of records. These five sets of
flow data, plus the flow data from Basin 16-Pago, were
then accumulated and plotted in mass-curve format.
It is of interest to note that the flow rates for
Basins 15-Maga, and 16-Pago, were almost exactly the same,
exhibiting but little difference in pattern and magni-
tude. These two basins are virtually the same size, but
on opposite sides of Pioa Mountain. Basin 16-Pago had its
own streamflow records, while the ungaged Basin 15-Maga
values were obtained by correlation from gaged basins to
the west.
Based on three preliminary findings, it appears
that the basins on Tutuila are very similar in flow
pattern, irrespective of location or orientation, and
until more data is gathered, flows and yields can be based
on drainage basin size. Thus, basin size, and the esti-
19 -
<pbn="27"/>
mated average yield of 6 cfs per square mile can be used,
with caution, as a crude method of estimating yield from
any of the other drainage basins on Tutuila.
ReAuired Storage - Values of required storage to
sustain different rates of regulated flow through the 1974
dry period were determined graphically from the mass curve
plot for each basin. The maximum draft rate in each case
was a rate that would permit refilling in 1975. With only
19 years of record and two dry periods for analysis, it
must be noted that these maximum values should be used
with caution, as considerably more storage may be required
to sustain these draft rates through drier periods in the
future. The draft, or regulated flow, and required
storages are listed in Table 3.
As shown in Table 3 and Plate 16, Basin 6-Leafu,
the largest, will yield a regulated flow of 5 cfs, about
70 percent of it long-term average flow, with about 1,650
acre-feet of storage. Basins 2-Maloata, 10-Papa, and
15-Maga, are smaller in size, and hence have propor-
tionately lower sustainable regulated flows.
20
<pbn="28"/>
Basin 16-Pago, however, is somewhat different.
Although its flow pattern is very similar to the other
basins, as previously noted, it did not receive as much
rainfall in mid-1975, and therefore, by the criteria of
permitting refilling in the relatively dry year of 1975,
cannot sustain as high a draft rate, in proportion to its
size, as the other basins do. It is for this reason that
the Basin 16 curve, shown on Plate 16, is shaped differ-
ently than the others.
STORAGE SITES SELECTION
In 1971, large-scale topographic maps for the
entire island, 1 inch to 200 feet, were prepared by the
American Samoa Government Public Works Department. These
maps were used to select the most suitable storage site in
each basin.
As noted previously, the basins on Tutuila are
characteristically small and steep; few storage sites are
available. Nevertheless, a site was selected for each
basin, as far downstream as possible, to provide maximum
reservoir storage capacity. Upstream reaches of each
basin were examined as well, to see whether any sites
21 -
<pbn="29"/>
might exist in the valleys at higher elevations, so that
water supply by gravity could be more easily accom-
plished. Unfortunately, no upstream sites of storage size
sufficient to sustain the selected draft rate were found,
and the lower downstream site was used in each case.
At the location which appeared most suitable in
each of the five basins, an earth embankment was sketched
in. These preliminary layouts are shown on Plates 16, 17,
18, 19, and 20. The embankments are shown with 20-foot
wide crests and slopes of 3 horizontal to 1 vertical, both
upstream and downstream.
As can be seen from the plates, the embankment
itself occupies a considerable portion of the storage
volume in each reservoir. This fact was taken into
account by planimetering around the embankment at each
site in the measuring and computing of the
elevation-storage relationships, shown for each site on
Plate 22, Storage Volumes.
As shown on Plate 22, Basins 6-Leafu, and
10-Papa, have the best storage characteristics; more than
2,500 acre-feet of storage could be obtained at either
site with an embankment 150 feet high (200 feet above mean
22 -
<pbn="30"/>
sea level). Basins 2-Maloata, 15-Maga, and 16-Pago, are
less desirable for storage since only about 1,500
acre-feet could be obtained with an embankment of the same
height.
This very preliminary storage evaluation was
conducted on the basis of topography only, as shown on the
large-scale maps. Foundation conditions, availability of
construction materials, land acquisition, sediment
problems, and all the other factors involved in damsite
selection were not considered at this time.
CONCLUSIONS
HYDROPOWER POTENTIAL
Examination of the storage-regulated flow curves
and the storage-elevation curves given on Plates 16 and 22
permits computing a rough estimate of the hydropower
potential in each basin. As shown in Table 3, Basin
6-Leafu is the most efficient storage site and will yield
about 5 cfs of regulated flow with about 1,650 acre-feet
of storage.
23 -
<pbn="31"/>
If an embankment were to be built in Basin
6-Leafu, to Elevation 180, about 1,650 acre-feet of live
storage could be provided between Elevations 100 and 180.
Assuming an average pool of Elevation 150, and a tailwater
at Elevation 50, 100 feet of gross head would be avail-
able. At 70 percent overall efficiency, and using the
formula: KW = QH (e)
11.8
where KW kilowatts generated
Q flow in cfs
H available head
e efficiency,
11.8 engineering constant,
about 30 KW of continuous power would be generated.
This procedure was used to estimate corresponding
estimates of hydropower potential for each of the other
four basins. Table 4 lists the comparable results for all
five basins. Comparing the values from Table 4 with the
amount of power and energy generated on Tutuila, we find
that even by assuming a 25 percent plant factor in Basin
6-Leafu, and installing 120 KW of capacity, only about 1
percent would be added to the system capacity.
24
<pbn="32"/>
From a brief review of the drainage basin charac-
teristics presented in Table 1, it is unlikely that any of
the -other basins could contribute significantly more
hydropower than the five basins studied. The combined
annual energy-contribution of the five basins studied
would likewise be small. The total contribution of all
five basins, about 972,000 KWh, is only about 2 percent of
last year's gross generation of 61,963,700 KWh (OSI,
1977).
WATER SUPPLY POTENTIAL
A recent study prepared in August 1978 (URS,
1978), provides estimates of water supply demand on
Tutuila. Table 11-6 of that report estimates the average
day water demand in the Year 2000 to be about 11.9 mgd.
These average system flow rates are further subdivided
into service area values ranging from about 0.1 mgd to
over 1.7 mgd. Even without detailed examination of the
service areas and distribution systems, it would appear
that the quantities of water from the five basins could
provide for a substantial portion of this demand. Table 5
25
<pbn="33"/>
shows the same storage and regulated flow values for each
basin, from Table 4, but expressed in water-supply units
of million gallon (mg) and million gallons per day (mgd).
As shown in Table 5, each basin would yield more
than 1 mgd, with the largest, Basin 6-Leafu, yielding 3.3
mgd if the required storage were provided. The total of
12.1 mgd shows that all five basins together could provide
all of Tutuila's estimated water demand in the Year 2000.
There is much more to evaluating Tutuila's water
supply situation than the preliminary sizing of a few
catchments (see URS, 1978 for a complete discussion).
Based on the findings of this preliminary investigation
however, estimates show that surface water supplies are
available in reasonable quantities for future develop-
ment.
26
<pbn="34"/>
mom= m m m m m m
T A B L E I D R A I N A G E B A S I N C 1-1 A R A C T E R 1 5 T I C S
RECORDED EST614ATEo AvuRA6E
DRA INA GE U.S. G. t;. PERIOD of AvERAGE RECORDED ANNUAL YIELD (9)
BASIN BASIN NAME SQ. AREA ST AT I ON RLCORD, YIELD CFS CF"/SQ.mI J-DAY Q10
NUMBER Mi. 0) NumucH YHS. (61 (8) CFS ACRE-fT
UNNAMED o.36 NONE Notic 2.2 1,500
2 MALOATA 1.03 925o 4) o.48 6.2 11,500
3 MAYAVAI 0.28 92,10 ()1) 0.o6 1.7 1,200
11 VAILOLO 1.13 9220 0.10 6.8 )1,900
2')
5 AsILI o.64 9 j4 -
3? 0.40 3.8 2,800
6 LEAFU 1.1
93
0.40 6.9 ow
AASU 1.00 9205 (2) 18 6.03 5.85 0.33 6.o 11,300
8 LEAVEAVE 1.17 gigo (4) 0.23 7.0 @'100
9 VIAPUNA 0.37 9330 (5) 0.02 2.2 i,6oo
10 PAPA o.85 9442 (3) 0.29 5.1
31100
11 LEELE 0.32 9175 (4) 10 1.50 6.52 o.oli 1.9 1,400
12 ___VAIMA 0.92 ____ -9505 ('1) 0.03 5.5 4, ow
CIT00- I'.
N) 91 4-1
13 FAGAALU 049 14) NONE 11.7 3,400
AFUCLO 0.31 948o (2) 19 1.42 5.68 0.07 1.9 1,300
15 MAGA o.61
9565 '1) 0.22 3.7 ?,6oo
16 PAGO o.69 9120 (2) 18 3.20 5.33 0.29 11.1 3,000
17 TAGAU 0.70 9100 (4) NONE 11.2 3, CK)()
18 -MULOOLEVAI 0.38 ___961o (4) oA 2.3 N
- 9 ALLGA 0. 2 6 9600 (4) 18 1.21 6.37 0.25 1.6 1,100--.
20 VAITOLU 0.25 9060 (5) 0.01 1.5 1,100
21- LcPA 0.21 905 0 02 1 .3- 900
22 VAILOA 0.31 9000 (5) 0.00 1.9 1,300
23 MuLiVAITELL 96,jo OIL 0-03 2.1-
-, -) - L' 800
UNNUMBEHLU ATAULOMA 1 0.27 9@1 0 (?). -T 18 1.42 1 5.92 0.10 1.6 1,200
NOTES: (1). By PLANIMETRY FROM USGS 72" TOPo, 1963, 014 BASINS
DESIGNATED uy U.S. ARMY.
(2j. CONT:NUOUS RECORD: ACTIVE;'..@U.
CONT'.UOUl ECORU 015 ON
1) Low- LOW, PARTIAL RECORD, ACFIVE.
OW FLOW, PARTIAL RECORD, DISCONTINUED.
Foom.USGS RECORDS.
BASED ON USGS GAGED CATCHMENT AREA.
lJNPUbL 1. S'if 0USGSTDATA -
BASED U PLANIMF ERED DRAINAGE A14EA A140 RECORDED AVERAVE YIELDS FROM GAGED BASINS.
<pbn="35"/>
TABLE 2
GAGING STATION DATA
PERIOD
GAGED AVG. CFS OF
USGS BASIN AREA DISCH. PER RECORD
NAME NO. NO. (SQ-MI.) (CFS) SQ.Mi. (YRS) REMARK
Aasu 9205 7 1.03 6.03 5.85 18 Record
Papa 9442 10 0.78 4.18 5.36 8 Record
to Poo
discon
Leele 9175 11 0.23 1.50 6.52 10 Discon
Afuelo 9480 14 0.25 1.42 6.58 19 Record
Pago 9120 16 0.60 3.20 5.33 18 Record
Alega 9600 19 0.19 1.21 6.32 18 Record
discon
Atauloma 9310 None 0.24 1.42 5.92 18 Record
<pbn="36"/>
" m m wo am so rm
TABLE 3
REQUIRED STORAGE VS REGULATED FLOW
REGULATED FLOW
AVERAGE PERCENT
ACRE- DISCHG. OF AVG.
BASIN CFS GPM FT/YR MGD (CFS) DISCHG.
2-Maloata 4.5 2020 3258 2.9 6.2 73
6-Leafu 5.0 2245 3620 3.3 6.9 72
10-Papa 3.8 1706 2751 2.5 5.1 75
15-Maga 2.7 1212 1955 1.8 3.1 73
16-Pago 2.5 1122 1810 1.6. 4.1 61
SM. an as sm so No
TABLE 5
WATER SUPPLY POTENTIAL
BASIN STORAGE, MG REGULATED FLO
2-Maloata 521 2.9
6-Leafu 544 3.3
10-Papa 396 2.5
15-Maga 330 1.8
16-Pago 198 1.6
TOTALS 1,989 12.1
<pbn="39"/>
som
HYDROLOGIC INVESTIGATION OF SURFACE WATER
TUTUILA, AMERICAN SAMOA
U.S. ARMY ENGINEER DISTRICT
HONOLULU, OAHU, HAWAII
SAN FRANCISCO
TOKYO
P A CIFI C OCEAN
19 HONOLULU
MANILA
GUAM
LOCATION MA
WATER SUPPLY AND HYDRO
TUTUILA, AMERICAN
FIJI TAHITI SAMOA ISLANDS - SOUT
(NOT TO SCALE)
WESTERN SAMOA
S@AVAUI. --'IUPOLU IS.
is
TUTUILA
STUDY AREA-/ `AUNU!U
GOT TO SCALE) '&-RICAN
<pbn="40"/>
N
Pago If Lepa
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Vaimo
19
Vailolo Aosu Leele 12 - %-- Muliolevoi
Motavoi 13 Alega
Mago
Malouto /f Fagoolu
Papa Aluelo
(Unnamed)
Leoveave
a 9 6
Leofu
lauloma
Asib
Viapuno
DRAINAGE BASINS
TUTUILA ISLAND
AMERICAN SAMOA
SAMI&EI-11. 1.11 rl.., HYDROLOGIC IN
... ... ... TUTUI
U.S. AR
FROM US. ENGREER OtSIRHIT. HAWAII "ON(
<pbn="41"/>
DISCHARGE IN CUBIC FEET PER SECOND (CFS)
IQ 4%
@4 W
/000@
x0
0
fn
00
-LL
F
HYDROLOGIC INVESTIGATION OF
FLOW. DURATION CURVE TUTUILA, AMERICAN
m ATAULOMA STREAM AT AFAO) TUTUILA., AMERICAN SAMOA
WEST OF BASIN NUMBER 5 (YEARS OF RECORD: 196o - 1977) U.S. ARMY ENGINEER D
HONOLULU, OAHU, 1-
<pbn="42"/>
DISCHARGE IN CUBIC FEET PER SECOND (CFS)
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0 0 0
to m -4 wwo
0
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rn
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in
rn
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C-)0
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FLOW DURATION CURVE HYDROLOGIC INVESTIGATION 0
AASU STREAM AT AASU., TUTUILA., AMERICAN SAMOA TUTUILA, AMERICA
BASIN NUMBER 7 (YEARS OF RECORD: 196o - 1977) U.S. ARMY ENGINEER
HONOLULU, OAHU,
<pbn="43"/>
904MI" ads* in m"mmoom "ll" "'m
DISCHARGE IN CUBIC FEET PER SECOND (CFS)
N fQ
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_0
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rn
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0)
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FLOW DURATION CURVE HYDROLOGIC INVESTIGATION 0
LEELE STREAM AT MOUTH, AT FAGASA, TUTUILA, AMERICAN SAMOA TUTUILA, AMERICA
BASIN NUMBER 11 (YEARS OF RECORD: 1961 - 1976) U.S. ARMY ENGINEER
HONOLULU, OAHU,
<pbn="44"/>
"""WOO m
DISCHARGE IN CUBIC FEET PER SECOND (CFS)
L%
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FLOW DURATION CURVE HYDROLOGIC INVESTIGATION 0
AFUELO STREAM AT MATUU., TUTUILA, AMERICAN SAMOA TUTUILA, AMERICA
BASIN NUMBER 14 (YEARS OF RECORD: 1959 - 1977) U.S. ARMY ENGINEER
HONOLULU, OAHU,
<pbn="45"/>
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DISCHARGE IN CUBIC FEET PER SECOND (CFS)
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FLOW DURATION CURVE HYDROLOGIC INVESTIGATION 0
PAGO STREAM AT AFONO, TUTUILA., AMERICAN SAMOA TUTUILA, AMERICA
BASIN NUMBER 16 (YEARS OF RECORD: I 96o - I gly) U.S. ARMY ENGINEER
HONOLULU, OAHU,
<pbn="46"/>
Mae "so" ",No
DISCHARGE IN CUBIC FEET PER SECOND WFS)
to La LA
0 0 0
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HYDROLOGIC INVESTIGATION OF
FLOW DURATION CURVE
ALEGA STREAM AT ALEGA, TUTUILA, AMERICAN SAMOA TUTUILA, AMERICAN
00 BASIN NUMBER 19 (YEARS OF RECORD: 1959 - 1976) U.S. ARMY ENGINEER D
HONOLULU, OAHU, 1-
<pbn="47"/>
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DISCHARGE IN CUBIC FEET PER SECOND (CFS)
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x cn cn -1
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ANNUAL AvERAGE FLOW, CFS
PARAMETRIC DURATION CURVES
VALUES FROM 'GAGED STATIONS ON AME71CAN SAMOA
HYDROLOGIC INVESTIGATION OF SURFACE WATERI
TUTUILA, AMERICAN SAMOA
U.S. ARMY ENGINEER DISTRICT
HONOLULU, OAHU, HAWAII
41 PLATE 10
<pbn="49"/>
"MOM"
DISCHARGE IN CUBIC FEET PER SECOND (CFS)
0
0 0 0 0
X
rq
0
M
or
M
HYDROLOGIC INVESTIGATION 0
FLOW DURATION CURVE
BASIN #2 MALOATA TUTUILA, AMERICA
U.S. ARMY ENGINEER
HONOLULU, OAHU,
<pbn="50"/>
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DISCHARGE IN CUBIC FEET PER SECOND (CFS)
rv
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FLOW DURATION CURVE HYDROLOGIC INVESTIGATION OF
BASIN # 6 - LEAFU TUTUILA, AMERICAN
U.S. ARMY ENGINEER D
HONOLULU, OAHU, H
<pbn="51"/>
DISCHARGE IN CUBIC FEET PER SECOND (CFS)
Lo tx
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FLOW DURATION CURVE HYDROLOGIC INVESTIGATION 0
BASIN #10 - PAPA TUTUILA, AMERICA
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<pbn="52"/>
mIIWIWaw"m"m ""SNOW
DISCHARGE IN CUBIC FEET PER SECOND (CFS)
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FLW DURATION CURVE HYDROLOGIC INVESTIGATION 0
BASIN #15 - MAGA TUTUILA, AMERICA
U.S. ARMY ENGINEER
HONOLULU, OAHU,
<pbn="53"/>
HYDROLOGIC INVESTIGATION OF SURFACE WATER
TUTUILA, AMERICAN SAMOA
U.S. ARMY ENGINEER DISTRICT
HONOLULU, OAHU, HAWAII
100,000
8o'Ooo
6o,ooo
4o,ooo
sip'.
20,000 P,7rAULOMA
NoJELO LEELE
S-fR.
ACEGA
0
", @@S'3
'61 '62 19' '64 1 '66 19'67 19'68 1169 1 1 1
1 -9 0 19 19 63 19 1 '65 9 970 1971 1972
91r,:9 19 9 9 1973
T I M E Y E A R S
MASS CURVES FOR SIX BASINS
<pbn="54"/>
sm so m m m m " m SOON m 4w m
HYDROLOGIC INVESTIGATION OF SURFACE WATER
TUTUILA, AMERICAN SAMOA
U.S. ARMY ENGINEER DISTRICT
HONOLULU, OAHU, HAWAII
5
0-
4
0
(n
3
"oooool
00'e
c2l
I-le _'0000
2
.00
00 200 )too 6oo 800 1000 1200 1 4oo
REQUIRED STORAULP ACRE-FEET
REQUIRED STORAGE vs. REGULATED FLOW
<pbn="55"/>
MALOATA BAY
EL. 200
iT5
i3o
75
el
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SAMOA HYDROPOWER STUDY
STORAGE SITE - BASIN NO. 2
MALOATA
$CALL IN FEET
FROM PWO TOPOGRAPHIC MAP, SHEETS 25 & 36
HYDROLOGIC INVESTIGATION OF SURFACE WATER'
TUTUILA, AMERICAN SAMOA
U.S. ARMY ENGINEER DISTRICT
HONOLULU, OAHU, HAWAII
48 - PLATE 17
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100
SAMOA HYDROPOWER STUDY
BASIN NO. 6
LEAFU
200-%@@- m@*'Zo
SCALE IN FEET
FROM PWO TOPOGRAPHIC MAP, SHEETS 45
HYDROLOGIC INVESTIGATION OF SURFACE WATER
It
TUTUILA, AMERICAN SAMOA
U.S. ARMY ENGINEER DISTRICT
HONOLULU, OAHU, HAWAII
49 - PLATE 18
<pbn="57"/>
1011
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ISO
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.pal 175
200
12
-125
-100 --200
-173
-.Z-,
QAcIo
76" 75 75
50 so
t 25
r-'L/ In
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SAMOA HYDROPOWER STbDY
BASIN NO. 10
wo PAPA
SCALE 114 fEET
FROM MAID 70@0135RAPHM MAP, SHEET NO. 3-5
HYDROLOGIC INVESTIGATION OF SURFACE WATER
TUTUILA, AMERICAN SAMOA
U.S. ARMY ENGINEER DISTRICT
HONOLULU, OAHU, HAWAII
PLATE IQ
so -
<pbn="58"/>
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N
SAMOA HYDROPOWER STUDY
BASIN NO. 15
MAGA
SCALE iN FEET
FROM PWO MPOGRAPHIC MAP. SHEET NO. 23
HYDROLOGIC INVESTIGATION OF SURFACE WATER
TUTUILA, AMERICAN SAMOA
U.S. ARMY ENGINEER DISTRICT
HONOLULU, OAHU, HAWAII
51 - PLATE 20
<pbn="59"/>
J.
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N 100
N-1
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SAMOA HYDROPOWER STUDY
BASIN NO. 16
PAGO
FMM PW'l TOPOGRAPHC MP, SHEET NO. 12
HYDROLOGIC INVES71GATION OF SURFACE INATER!
TUTUILA, AMERICAN SAMOA
U.S. ARMY ENGINEER DISTRICT
HONOLULU, OAHU, HAWAII
52 PLATF_ 21
<pbn="60"/>
300
2@0
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200
LA
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2
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0 x i=
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c
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x 0 Z 0 jOO 1000 1500 2000 2@00 3000
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0 0
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rn STORAGE VOLUMES FOR FIVE BASINS.
1>
<pbn="61"/>
HYDROLOGIC INVESTIGATION OF SURFACE WATER
FOR WATER SUPPLY AND HYDROPOWER
TUTUILA, AMERICAN SAMOA
BIBLIOGRAPHY
1. Austin, Smith & Associates, Inc., Report Covering a
Master Planned Water Supply and istribution Syste
foF__thePago Pago and Tafuna Areas, prepared for the
Government of American Samoa, February 1963.
2. Austin, Smith & Associates, Inc., Report Updating the
1963 Master Planned Water Supply and Distribution
System for the Pago Pago and Tafuna Areas and
Including the Leone Plain, prepared for the Department
of Public Works, Government of American Samoa, April
1972.
3. Austin, Smith & Associates, Inc. Water Supply and
Distribution Systems Pago Pago anU-Tafuna Areas, April
1966.
4. CH2M Hill, Water System Study: Western Portion of
Tutuila Island, November 1975.
5. Government of American Samoa, Office of Samoan
Information, Annual Report, 1977.
6. Heitz, L.F. Maximum Stream Potential for Hydroelectric
Power Production, Universi y of Idaho, Moscow, Idaho,
June 7, 1978.
7. Linsley, R.K., M.A. Kohler and J.L.H. Paulhus,
Hydrology for Engineers, McGraw-Hill Book Company,
1958.
8. Riggs & Hardison, Techniques of Water Resources
Investigations, 1971.
9. Stearns, H.T., "Geology of the Samoan Islands,"
Geological Society of America, Bulletin, 1944, volume
55, pp. 1279-1332.
54 -
<pbn="62"/>
10. URS, Draft Report, Assessment of Water Systems,
prepared for the Department of the Army, 197F
11. U.S. Army Engineer District, Honolulu, American Samoa
Water Resources Study Plan of Study, December 1977.
12. U.S. Geological Survey, Flow Characteristics of
Streams in Tutuila, AmerTc-ansamoa, prepared in'
cooperation with the Government of American Samoa,
Draft Report, (unpublished) March 1978.
13. U.S. Geological Survey, Water Resources Data for
Hawaii and other Pacific Areas, 1960 through 1978.
55
<pbn="63"/>
INIOAA COASTAL SERVICES CTR LIBRARY I
"I
r
3 6668 1411OD94 3 1
L@-