This reproduction Copyrighted, 2004, by J. Johnson (jj@scn.org).
See notes for information about this document, or excerpts for the pertinent parts.
R E P O R T
O N
C E D A R R I V E R P R O J E C T
F O R T H E
C I T Y O F S E A T T L E
B y
JOSEPH JACOBS,
E. H. BALDWIN,
GLOVER F. PERRIN,
BOARD OF ENGINEERS.
TABLE OF CONTENTS.
SUBJECT PAGE
Introduction . . . . . . . . . . . . . . . . . . . . . . . . 1
Description of Project . . . . . . . . . . . . . . . . . . . 2
Water Supply . . . . . . . . . . . . . . . . . . . . . . . . 3
Storage. . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Dam Site . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Foundation . . . . . . . . . . . . . . . . . . . . . . . . . 9
Plan of Dam as Proposed by City Engineer . . . . . . . . . .10
Modifications suggested by Board . . . . . . . . . . . . . . 11
Comparative Costs . . . . . . . . . . . . . . . . . . . . . 11
Replies to Specific Inquiries : . . . . . . . . . . . . . . 12
Question (a) Suitability of Dam Location . . . . . . . 12
" (b) Type of Dam . . . . . . . . . . . . . . . 15
" (c) Stability of Foundation . . . . . . . . . 17
" (d) Seepage through North Bank . . . . . . . . 18
" (e) Economy of Pressure Tunnel . . . . . . . . 21
" (f) Line Revision at Landsburg . . . . . . . . 22
" (g) Future Pipe Lines . . . . . . . . . . . . . 26
Some General Features :-
Final Instruction . . . . . . . . . . . . . . . . . . . . 27
Complete Project . . . . . . . . . . . . . . . . . . . .. 27
Cedar River Alternatives . . . . . . . . . . . . . . . . .28
Swan Lake . . . . . . . . . . . . . . . . . . . . . . . . 30
Recommendations . . . . . . . . . . . . . . . . . . . . . 33
Acknowledgments . . . . . . . . . . . . . . . . . . . . . 34
[Following appendices not reproduced here.]
Runoff of Cedar River at Cedar Lake . . . . . . . . . . A
" " " " " " Landsburg . . . . . . . . . . B
Precipitation at Cedar Lake . . . . . . . . . . .. . . C
Tests of Foundation rock . . . . . . . . . . . . . . . . D
Reservoir Areas and Capacities . . . . . . . . . . . . . E
Power and Storage Data . . . . . . . . . . . . . . . . . F
Chemical Analyses of Swan Lake Water #1. . . . . . . .. G-1
" " " " " " #2 . . . . . . . . G-2
Bacteriological Analyses of Swan Lake Water . . . . . . G-3
Cost Estimate of Cedar River Dam per Plan of City Engr.. H
" " " " " " " " " Board . . . I
Cost Estimate Complete Project . . . . . . . . . . . . . J
PLATES [not available]
GENERAL Map of Dam Site and Dam Layouts . . . . . . . . .I
Sections of Earth Dike and Core-wall . . . . . . . . . II
General Profile of dam site . . . . . . . . . . . . . . III
#1
Seattle, May 6, 1912.
To the Mayor and Council,
of the City of Seattle.
Gentlemen:
By virtue of Ordinance No. 29025, approved March 5,1912, and
your letter of instructions dated March 6,1919, the undersigned were
appointed a Board of Engineers "to investigate and report on the con-
struction of the new Cedar RIVER Dam, pipe lines and other matters in
connection with the maintenance and protection of the light, power
and water systems of the City of Seattle."
The questions which we were specifically directed to con-
sider and report upon were as follows:
(a) Is proposed location of the dam suitable for
such a structure, and if not, what location should be
selected?
(b) Do the general plans and designs for the pro-
posed structure conform to the best engineering practice
for dams of this magnitude; if not, what type should be
adopted?
(c) Is the foundation of the dam sufficient to stand
the load to be placed upon it, and sufficiently impervious
to prevent undue leakage?
(d) Is there danger of seepage through the north bank
with water at an elevation of 1590 feet if the lake be
raised by gradual stages covering a series of years?
(e) Is the proposed plan for the pressure tunnel
and the location of the new power house to be preferred
to the construction of additional pipe lines down the
canyon of the river to the present power house site?
(f) Is the plan proposed by the City Engineer for
taking the pipe lines from the vicinity of Cedar River be-
low Landsburg by the construction of a tunnel, the best
and most practical method of securing the protection re-
quired, or should steel pipes be constructed beneath the
bed of the river crossings?
(g) What method should be adopted by the City in
future construction of pipe lines or other facilities for
bringing water into the city from intake?
Also the said engineers by the terms of the contract
shall submit to the Council, in addition to the information
and recommendations on matters above enummerated, anything
that such investigation, or their or his judgment may sug-
gest to them , or to any of them, concerning the entire
lighting, power and water project."
#2
In compliance with the above instructions, therefore, we would
submit the following report:
Before proceeding with the several questions involved in
in this inquiry, in order that a better understanding may be had
of our comments thereon, it is desireable to present here a brief
outline of what the project contemplates.
It is proposed to construct upon Cedar River at a point
situate about two miles below the present outlet of Cedar Lake,
or be more exact, in the Northeast quarter of the Northwest
quarter of Section II, Township 22 North, Range 8 East W.M., a
Masonry dam of the so-called gravity type, to a height of about
175 feet above present stream bed, 218 above bed rock in
mid channel and probably 240 feet above ultimate foundation at
maximum section of dam.
With spillway at elevation 1605 ft. above mean sea level
or 10 ft. below the proposed crest of dam, there would be created
by the construction of this dam a reservoir of 162,500 acre-feet
capacity, this being sufficient to store the entire run-off of
Cedar River for two successive high years, provided the simul-
taneous draft from reservoir was not less than the mean run-off
of the stream.
From this reservoir it is proposed to construct a pressure
tunnel 9,000 feet in length along the left bank of the river to a
point just below the present Municipal Power Plant where a new
power house is to be constructed capable of developing the entire
discharge of Cedar River as regulated by the reservoir construc-
tion above described.
The effective head available at this proposed power station
is approximately 585 feet and the water, after passing through the
water wheels of the station should be discharged back into Cedar
River whence it would follow the natural channel of that stream
#3
to Landsburg, at which point as much of it as may be required would
be taken into the supply mains which deliver domestic water to the
city of Seattle as is done with respect to the water passing through
the present power station.
Attention should be called to the fact that the normal run-off
of Cedar River at Landsburg is sufficient, at its lowest stage, to
provide ample domestic water supply for a population of 600,000,
the lowest discharge of record being 148 cu.ft. per second, or
95,904,00 gallons per day. This discharge occured in October,
1902, and again in August,1903, both being prior to the construc-
tion of the present crib dam at the outlet of Cedar Lake and there-
fore fairly indicative of the low water discharge of the stream
unaffected by storage operations above. Until the City of Seattle
reaches a population of 600,000,therefore, no storage will be re-
quired for domestic water supply, and when it reaches the 1,000,000
mark, not to exceeed 4000 acre-feet of storage will be required to
supplement the deficient flow during low water periods.
The entire new development proposed should therefore be regard-
ed practically as for power purposes alone and its commercial justi-
fication must proceed from that premise.
Water Supply: The amount of power that can be developed
at the proposed power station is dependent primarily upon the
water supply and the determination of the amount of this water sup-
ply is therefore all important.
The run-off of the Cedar River watershed has been observed
for varying periods at two stations, viz. at the outlet of Cedar
Lake or intake of present power pipe lines, and at Landsburg, or
intake of present city water main. A complete list of the avail-
able records for these two stations is as follows:
1. At Landsburg for the period September 27th, 1902,
#4
to date, as maintained by the United States Geological
Survey and published regularly in its reports (See
Appendix B.) This record is made up from a computed dis-
charge over the Landsburg weir, based upon actual gage heights
plus an allowance for the amount taken into the city water mains.
This record is regarded as dependable.
2. At Cedar Lake for the period October 17,1902, to
August 8,1903, as maintained by the United States Geological
Survey, and published in its WATER SUPPLY AND IRRIGATION
PAPER NO.100. (See Appendix A) The record is regarded as
dependable but unfortunately covers only a few months of each
year.
3. At Cedar Lake,for the period 1896, to 1904, inclusive,
as maintained by the City of Seattle. The run-off for this
period appears to have been deducted wholly from a precipitation
record at the same station and the apparent ratio of run-off
to precipitation for the short period of actual stream flow
observation of 1902 and 1903, referred to in previous paragraph,
the assumption being made that this ratio would be a constant.
Such an assumption we regard as untenable for even
though the topographic and cultural or forest cover conditions
of a watershed remain unchanged, the run-off ratio would still
be variable, depending as it does largely upon the rate and
endurance of the precipation for individual storms. This
is indicated in the actual ratios which obtained (50.6% to 78.7%
mean 61.1%) for the period 1905 to 1911, during which period
both run-off and precipitation had been continuously observed.
The constant ratio adopted for the period 1896 to 1904, appears
to have been ± 80%, as referred to the present known drain-
age area of basin, resulting in an indicated run-off which we
consider unjustifiably high. The record for this period
#5
we have therefore disregarded as not dependable though it may
be noted that if the more likely mean run-off ratio of 60%
were applied for the entire period it would result in a
mean run-off, as expressed in acre feet per year, almost ex-
actly that shown for the succeeding period 1905 to 1911.
4. At Cedar Lake for the period 1905 to 1911 inclusive, as
maintained by the City of Seattle. The record run-off
for this station is made up from actual discharge through present
power pipe lines as determined at power house, plus the dis-
charge over wier portion of present crib dam as deduced from
daily readings of lake guage. The estimate of flow over this
weir was based upon the well known Francis formula [illegible]
which, on account of the form of weir crest obtaining in this
instance, we believe gives results somewhat too low.. The
formula Q = 3.50 1 h 3/2 was therefore adopted by us, as more
nearly correct, the revised discharge, which is about 5% in
excess of that indicated by the City record, being shown in
tabluar form in Appendix A.
In view of all the above, and because that station
is in the immediate vicinity of the proposed new dam location,
we have regarded the record of the Cedar Lake Station for the
period 1905 to 1911 inclusive, as the best available and the
one which should now control in studies for power development
and storage needs.
It will be noted from Appendix A that the following
annual runoffs obtained for the Cedar River watershed at
Cedar Lake Station.
In years of Mean Runoff, 281,500 Acre feet,
" " " Maximum " 352,400 Acre feet,= 125% of Mean
" " " Minimum " 225,400 Acre feet,= 80% " "
#6
A comparison of the runoffs at Landsburg and at Cedar
Lake with reference to their respective drainage areas would
seem to indicate that the runoff at the lake station should
somewhat larger than the record indicates. There is unquestion-
ably some leakage around the present crib dam and we are advised
that there have been occasional unrecorded wastages from the
pipe lines die to breaks. The latter would be negligible and
the leakage around the dam, which in our opinion is not heavy,
would be offset in part if not in whole by leakage around any
new dam that might be constructed, and it would be further off-
set by the fact that no deductions have been made, in power esti-
mates, for evaporation from the lake surface which in itself
would amount to from 4000 acre feet to 6000 acre feet per year
depending on height of storage maintained.
Although our estimate of the amount of water avail
able for storage and power purposes is appreciably less than any
figures which we understand have heretofore been considered, we
regard them as reasonable and conservative and would not feel
justified in rejecting the record for 1905 to 1911 upon which
they are based, in favor of any more or less arbitrary assump-
tions or deductions as to what the runoff should be.
Storage: The amount of storage required, from which
follows the height of dam required, is dependent upon three
factors, as follows:
(a) Upon the total amount and the month to month
distribution of the actual runoff of the watershed. This
has already been considered in the preceding discussion of
Water Supply.
(b) Upon assumption as to losses due to seepage
and evaporation. These too have been referred to in the
#7
preceding discussion and seepage will be more particularly
considered in reply to your inquiry "d" further on.
(c) Upon the assumption as to whether storage pro-
vision shall be made to tide over years of minimum runoff,
thus requiring maximum storage capacity and providing an all
hydro-electric plant, or whether provision shall be made
only for years of mean runoff, thus permitting reduced stor-
age capacity but requiring the installation of a steam aux-
iliary plant to supply the deficiency of mininum years. In
fact a careful analysis of the problem, with sufficient
data at hand to warrant such analysis, should be made to
determine the point at which storage ceased to be profit-
able and steam installation became the more economical.
The amount of seepage loss from the reservoir, if
there be seepage loss at all, will depend upon the height to
which storage is maintained and such loss will be greater and,
within certain limits, the amount of water available for power
will be less under a condition of high storage than under one
of low storage.
Assuming no seepage loss from reservoir and taking
the two actual relatively high years of 1906 and 1907 we find
that the storage capacity required to have conserved this sup-
ply with simultaneous normal draft from reservoir for power
purposes, would be 159,000 acre feet, requiring a dam practically
to the height proposed by the City Engineer, i.e. a dam with
spillway crest at elevation 1605. On this assumption too the
power that could be developed at proposed new power station
would be 25,860 continuous water horse-power for a mean discharge of
389 S.F., but requiring a penstock capacity of 1200 S.F. to meet
peak load demands, and the power that could be delivered to City
sub-station would be equivalent to 11,640 continuous K.W.
#8
Considering seepage loss however, and we believe such
seepage loss will occur ( see subsequent discussion), less stor-
age would be required and less power could be developed than
above indicated. From our assumptions as to the runoff and pro-
able seepage loss, the tabulation shown as Appendix F was pre-
pared, giving storage and power data for varying heights of dam.
From this tabulation it will be noted that with full
provision for minimum years,i.e., an all hydro-electric plant,
the maximum power that could be developed would be 19900 W.H.P
requiring a dam with spillway crest at elevation 1595 or 10'
lower than that proposed, and that with no provision for mini-
mum years the spillway crest could be placed at elevation 1564,
thereby storing sufficient water to develop 21,000 W.H.F. but
requiring a steam auxiliary installation in the City of 6,900
K.W. capacity.
Refined accuracy is not claimed for the above figures,
but we believe them to be the best estimate that can be made
from present available data and are intended chiefly to indi-
cate the character of study that must be made before the economic
installation can be determined.
Dam site: The dam site selected by the City Engi-
neer is at a point where Cedar River has cut through a rocky
ridge, leaving a narrow wedge-shaped canyon, which has been
filled to a height of about 40 ft. with sand,gravel and boul-
ders. The rock formation on the south side rises with a fairly
uniform slope of about 1 to 1, to a height of several hundred
feet above the bed of the river. On the north side, the slope
of the rock above the river bed is more gradual and at a dis-
tance of about 300' from the river flattens out, at elevations
1535 which is about 95' above present stream bed, and continues
nearly level for some 400',rising again to elevation 1560 in
#9
the next 100'. From this point the rock probably extends in a
general northwesterly direction for a distance which has not been
determined but presumably a considerable distance beyond the extreme
northerly and of the proposed dam. The limited number of borings
taken indicate that the rock on the north side of river slopes rather
steeply downward toward the east.
Foundation:- The bed rock in the vicinity of the proposed dam
site has been classified by Professors Henry Landes and Milnor Roberts,
of the University of Washington, in their report to the City Engineer
dated July 12,1910, as quartsite and andesite, the latter predomin-
ating. Quoting from the above report:-
"The andesite is an ingenous rock but occurs as layers
stratified or interbedded with quartzite. During the time of
deposition of the sandstone (from which the quartzites were later
derived by complete cementation) the andesite appeared in the
nature of flows of molten material, or extrusions. Some portions
of the andesite layers are made up of rounded fragments, produced
by the flowage of molten rock over a sea beach or other places
where rounded rocks might occur. Such a rock composed of water-worn
boulders and gravels, but held together by a matrix of igneous
material is called an agglomerate. In other portions of the andesite
the original rock (when molten)contained much steam and very many
pores or cavities were produced when the rock cooled. Since that
time nearly all such cavities have become filled with calcite and
opal and an amygdeloid is the result. In yet other portions of the
andesite the whole mass seems to be made up of angular fragments,
composing a breccia, made by the continued movement of the rock after
it had practically congealed."
A careful examination of the exposed rock was made. On the south
side of the river the conditions for determining the character of the
rock were excellent as the superimposed earth had been sluiced off and
much of the loose rock removed. The exposed rock is much broken and
shows numerous seams of varying thickness, generally pitching downstream
at an angle of about 40° with the horizontal. Some of these seams are
nearly tight and filled with a film of clay while others have a thick-
ness of several feet, filled with alternate layers of clay and stone,
the latter being generally of low specific gravity,unsound and in
many cases much broken. In general, the surface of the rock, above
the highest water in the river, is weathered to a considerable depth,
but where it has been exposed to the running water of the river the
weathered parts have been removed and it appears firm and solid.
This apparently sound rock, however, is impregnated with seams which
#10
generally are fairly tight, but whch are often underlaid or backed by
a mud seam.
The cores taken from a diamond drill (A-8),driven horizontally
for a distance of 400' into the south slope, show conclusively that
the rock at this point is reasonably sound after a sufficient dis-
tance from the exposed face has been reached. A tunnel driven
100' feet horizontally into this slope, about 20' above the river bed,
shows three distinct transverse seams varying in thickness from 3"
to 12",filled with clay and fragments of rock which might permit
of some seepage unless rendered impervious by grouting.
The rock under the river bed is being further explored with the
diamond drill and diagonal holes, intersecting beneath the river bed,
show continuous rock of the same character as that described above.
Just north of the river the surface rock is somewhat better,
but even here most of it is unsound and underbedded with seams. At
north end of dam site there is a large overburden of earth so that
the only indication of its character was necessarily determined by an ex-
amination of the cores from the drill holes. These indicate the
rock to be of about the same general character as that already des-
cribed , the short lengths of core and the frequest fragments con-
clusively demonstrating its seamy nature.
Plan of Dam as Proposed by City Engineer: The plans prepared
by the City Engineer's office contemplated the construction of a
masonry dam of gravity type, arched up-stream with radius of 900',
crest elevation at 1615, top width of 15' and length of about 900'.
At the south end a natural abutment can be secured but at the
northerly end, where bed rock is not sufficiently high for the pur-
pose, it is intended to construct a massive concrete abutment to
take up the arch thrust.`
A spillway with capacity of 20,000 sec.ft., crest elevation
at 1605, and crest length of 200' is to be excavated in the rock
around the southerly end of the dam and discharge into the river a
short distance below the toe of the dam, From the north end of
dam,following up the right bank of river to the 1620 contour, to
prevent erosion around the northerly end of dam and to cut off a
#11
certain amount of seepage from the reservoir, a dike, with crest
elevation at 1602 and top width of 40 ft., with puddle core to
elevation 1535 and sheet piling to elevation 1480, is contemplated.
Modifications suggested by Board:- On account of the absence
of a natural abutment at the north end, compelling entire dependence
on the gravity section without assistance from arch action, we
believe, if the dam is to be carried to the height proposed (elev.
1615) the site is better suited to a straight than a curved dam.
If a dam be built here at all to the height proposed we suggest
a straight dam, the dam proper terminating in a solid masonry abut-
ment at north end, which abutment would also act as a retaining wall
for an earth dam which would extend, in line with the main dam, a dis-
tance of about 100', thence curving to right and continuing parallel
with river bank, but well back from its edge, a distance of 1000'
to an intersection with contour 1620.
In the central portion of the first 125' of this earth dam a
concrete core-wall would be built connecting with the abutment and
extending well into the bed rock, thus affectively preventing per-
colation, and beyond this to end of earth dam, instead of a concrete
core-wall we would provide a deep cut-off trench filled with selected
material beneath which sheet piling could be driven to elevation
1480.
This construction would materially decrease the total volume of
masonry and the amount of excavation that would be required in the
scheme proposed by the City Engineer.
The spillway would be of same capacity and location as that pro-
proposed by the City Engineeer, but contemplates carrying the water over
a ridge some 400' down-stream from the dam and discharging into the
river at a safe distance below it.
Comparative Costs:- The general plan of these two schemes is
shwon in Plates I and II [n/a] and comparative cost estimates, prepared
from such data as are now available, are shown in Appendices H and I.
From these Appendices it will be noted that the estimated cost of
construction of Cedar River Dam and Reservoir for the two schemes is as
follows:-
#12
Per plan as now proposed by City . . . . . . . . . . . . $3,001,725
" " " Suggested " Board . . . . . . . . . . . . 2,490.310
---------
Difference in favor of latter plan . . . . .. $ 511,415.
This indicated saving of approximately $500,000 results from the
proposed changes at north end of dam, from the shorter length of dam
resulting from the substitution of a straight for a curved dam in
plan, and about $75,000 results from a reduced section of dam, a
feature which will be discussed more particularly in a subsequent
paragraph.
We would here, however, specifically emphasize that the above
comments are not to be construed as a recommendation by us that a
dam be built either to the height or at the location above proposed,
and that it is intended merely to show, in event the City does
proceed with the present plans, how a modified treatment would in
our opinion secure a more rational design and effect a material saving
in cost.
REPLIES TO SPECIFIC INQUIRIES
We now proceed to a consideration of the specific inquires
contained in your general letter of instructions.
Question (a):- "Is the proposed location of dam suitable for
such a structure, and if not, what location should be selected?"
This question must be considered not only with respect to phys-
ical fitness, but as well from the view point of securing the most
oconomical storage obtainable on the stream.
Concerning physical fitness would say that the matters of type
of dam, character of foundation and danger of seepage through the
north bank, are discussed in detail under inquires "b", "c" and "d",
which follows. We may say here, however, that we do not by any
means regard this site as an ideal one for the height of dam proposed,
not only because there must be an excessive amount of stripping of
unsound rock from the dam foundation and that extensive grouting will
be required to secure an impervious cut-off around the dam, but
chiefly because the situation at the north end is one that requires
very careful treatment. It is our opinion,however, that a stable and
secure dam can be built at this site even to the height proposed by
the City Engineer.
#13
At the northerly end of dam the highest bed rock elevation at-
tained is 1568 or 47' below the proposed top of masonry dam and this
can be reached only by extending the dam an undue length beyond the
normal rim of the river bank. Within the dam limits, in fact,the
highest bed rock elevation attained is only 1535 or 80' below top of
dam.
To prevent danger of actual washout around this northerly end of
dam through this over-burden of porous earth, it is necessary to con-
struct a practically impervious cut-off extending well beyond the dam
abutment and well back from the rim of river bank. We believe such
cut-off can be provide in the form of a concrete core-wall extending
from the dam abutment back as far as rock foundation, within feasible
depth, will permit, after which such concrete core-wall would be re-
placed with a puddle trench carried to greater depth, beneath which
sheet piling would be driven to a depth of 30' or 40' or more.
The purpose of this cut-off is not primarily to prevent the water
loss which results from seepage, but to prevent the seepage which may
ultimately lead to an actual failure of the embankment or earth dike
at northerly end of dam. The general features of this earth dam or
dike and the cut-off above described are shown in Plate II. [n/a]
The matter of economic height and of economic location of dam is
a far more intricate problem, and no sufficient time and no sufficient
data have been available to us to dully solve it. We can only convey
here our general impressions which are as follows:
We examined Cedar River from the present crib dam to the present
power house and believe that the first available dam site above the
power house that could be considered is the one that has been selected
by the City Engineer. Between this site, however, and the present crib
dam, there is at least one site that appealed to us strongly, and
which we believe should be surveyed and carefully considered in the
light of well prepared comparative estimates before adopting the lower
site as the ultimate location for a dam to impound water on this stream.
The site referred to is at a point about 2000' below the present crib dam,
where a spur from the hills on the south side extends down to the river,
this being opposed on the opposite side by an abrupt bank which rises
approximately to elevation 1590.
#14
Apparently no detail survey has yet been made at this site, nor have
any borings or test pits been put down.
So far as may be judged from surface indications there is a con-
siderable depth of sand and gravel in this river bed and probably bed
rock lies at a great depth, though this can only be ascertained by
actual borings. The indications, however, are that the type of dam to
be constructed here would be either an earth dam or an earth and rock
fill dam, both of which have ample precedent and both of which may be
regarded as safe types of dam construction. They can be made reasonab-
ly tight against seepage losses, and the principal feature to be consid-
ered in their adoption for this location is that of securing a proper
cut-off in the river channel.
The advantage of this location is, that to secure the same amount
of storage as would be obtained by the construction of a dam at the
lower site, i.e., with flow line of reservoir at elevation 1605, it
would require a maximum height of only 100' as against a maximum height
of not less than 225' and possibly 240' at the lower site. It seems to
us almost unquestionable that this upper site will prove far cheaper than
the lower, such rough estimates as we have been able to make from data
now available indicating, in fact, that there might be a difference of
$1,400,000 in first cost of the two structures, in which estimate an
allowance has been made of $350,000 for the extension of power tunnel
from the lower to the upper site.
A further advantage of this upper site is that it would in measure
reduce seepage losses resultant from high storage by reason of the
long exposure of high river bank between this site and the proposed lower
site, this being a bank having an average height of 90' and a length of
about 5000', or, excluding lenght of proposed dike at lower site, which
would cut off some seepage, a length of at least 4000'.
Our present opinion is that a safe, substantial and permament dam of
earth, or of earth and loose rock combined, can be constructed at this
point, though the exact method of treatment of the foundation and cut-off
would need be matter of further and more careful study, based upon the re-
sults shown by actual borings.
The final phase of this entire question that must be considered,
is the actual height to which any dam should be built on Cedar River
#15
to secure the maximum or at least the most [?? missing in the source].
From our general study of storage conditions, as hereinbefore dis-
cussed and our deductions as to seepage losses, as hereinafter discussed,
it is clear to us that some height less than that now proposed is the
most economic and every change in the direction of lowering the height
of this dam renders the upper site more advantageous and indicates a
greater disparity in its favor in the matter of first cost.
Question. (b):- "Do the general plans and designs for the pro-
posed structure conform to the best engineering practice for dams of
this magnitude; if not, what type should be adopted?"
In our opinion the general type of structure proposed, namely, a
masonry dam of gravity type, does conform to the best engineering pract-
ice for dams of this magnitude and upon the character of foundation
that here obtain.
As will be noted elsewhere in this report we have suggested the
substitution of a straight dam for a curved dam, also a modification in
the treatment of the northerly abutment and our present comments there-
fore relate only to type of dam proposed.
A dam of the magnitude proposed at this location and bearing the
relationship that it does to the cultural and town and city develop-
ments along the valley of the Cedar River below the dam, must, in our
opinion, satisfy the following conditions:-
(a) It must within a reasonable factor of safety resist all ex-
ternal forces that can be exerted against it tending to produce failure.
(b) It must be of absolutely permanent construction.
The type of dam proposed by the City Engineer, in our opinion,
best meets the above requirements.
We have carefully computed the stresses that would obtain in this
dam under conditions of reservoir full and reservoir empty, and for
hydrostatic uplift considered and hydrostatic uplift ignored, and find
the section to be amply safe, in fact, over-conservative.
We believe that the seamy condition of the foundation, despite
the fact that this may be largely overcome by grouting, clearly im-
#16
poses the necessity of considering uplift in designing this dame, and
in doing this we have considered the uplift at heel of dam should
be that due to full hydrostatic pressure for reservoir full, tapering
to a zero hydrostatic pressure at toe of dam.
The only other unusual force that might be considered
is that of ice thrust, but we believe the conditions here do not at
all warrant its inclusion.
A careful mathematical determination of the section that should
be adopted, and this should by all means be done, we believe will in-
dicate that the very wholesome section proposed by the City Engineer
may be reduced to such an extent as to effect a saving in total voluem
of masonry of at least 5% and possibly 10%, our own computations in-
dicating a base width of 188' instead of 200', to be sufficient.
Comparing the section proposed by the City Engineer with that
for other high dams, particularly the Wachusett dam in Massachusetts
and the Olive Bridge dam in New York, both of which are above populous
distircts and both of which are designed to resist uplift and, at
least in the Wachusett dam, ice thrust as well, the justification for
reducting the section, as suggested above, becomes apparent.
Features which in our opinion should be provided and which are
not indicated in the plan proposed by the City Engineer are an in-
spection gallery extending longitudinally through the dame, which
would serve also as a drainage channel for any water that might pene-
trate the face of dam, weep holes or smaller conduits connecting with
this gallery both from top and base of dam, and outlet conduits ex-
tending from said gallery to the down-stream face of dam. It may also
be well to provde a few expansion joints in the upper portion of dam,
though considering the climate of that locality and the general ab-
sence of extremes of temperature, we do not regard this of prime import-
ance.
In this connection we would again call attention to the fact that
we are not recommending that a dam be built at this location, or to
this height, but are now only considering type of dam, should the city
decide to proceed with its present plan to build at this site.
#17
Question (c):- "Is the foundation of the dam sufficient to stand
the load to placed upon it, and sufficiently impervious to prevent
undue leakage?"
The general geology and character of rock formation at this site
has already been discussed and the conditions indicated by test pits
and diamond drill borings have already been described. There can be
no question as to the stability of this foundation, provided there
be ample stripping of the surface rock which latter is of a particu-
larly soft, shattered and unfit character. A very considerable extent
of this stripping will need to be done and we have in our estimates of
cost assumed that the average for the entire dambase would be not
less than 10', although at certain points a much greater stripping
would be required. We refer here particularly to the south canyon
wall and more particularly to the upper portion of same where a broad
seam may need to be followed to a depth of from 25' to 50' to insure
anchorage in sound rock.
To further guide our judgment as to the character of this found-
dation we had a series of tests made upon six samples of rock taken
both from the river bed and from the end of exploring tunnel into
the south slope. The results of these tests (see Appendix D) were
very gratifying, showing the rock in fact to be of greater specific
gravity and greater crushing strength than we had anticipated. It
will be noted that the average of the six tests showed for this rock
a specific gravity of 2.7 (168 lbs. per cu.ft.) and a crushing
strength in excess of 17500 pounds per square inch.
That this rock compares favorably with the best building stones
is indicated in the following tabulation.
Average Crushing Strength of Building Stones.
----------------------------------------------------------------------
Wt.per Crushing strength
Kind Sp.Cr. Cu.Ft. in lbs. per sq.in.
----------------------------------------------------------------------
Cedar River Andesite 2.70 168. 17500
Granite 2.70 168. 15000
Lime Stone 2.60 162. 10000
Trap 2.70 168. 17000
Sand Stone 2.35 146 8000
----------------------------------------------------------------------
#18
As the maximum pressure to be imposed upon this foundation is
but 210 pound per sq.in., it will be able to resist this load with a
safety factor of 83, against crushing.
As to the perviousness of this foundation would say that the rock
material itself, as may be plainly inferred from its general character,
as indicated above, is absolutely impervious, but the extremely seamy
nature of the rock at least for depths of from 10' to 50' below the
surface makes the general material quite pervious, unless precaution
be taken to counteract it. Hydraulic pressure tests, of which there
were unfortunately only too few, indicate, if visual observation were
not sufficient, the general seamy character of their formation.
These tests showed comparatively free movement of water under
pressure, and also showed intercommunication between holes 23' apart.
To afford an impervious cutoff, therby preventing seepage through
the rock material, around and under the dam and particularly to reduce
hydrostatic pressure on base of dam to a minimum, the upstream portion
of the foundation will need be thoroughly grouted and efficient drain-
age provided for the down stream portion. This grouting is car-
ried well up the sides of the canyon and tu such depth as tests at the
time show to be necessary but which we believe should not be less than
50 feet.
QUESTION (d):- Is there danger of seepage through the north bank
with water at an elevation of 1590 feet if the lake be raised by
gradual stages covering a series of years?"
This is indeed one of the important questions to be considered in
connection with this development, for the amount of seepage loss that
may be suffered, directly effects not only the amount of storage that
need be provided, but as well the amount of power that can be developed.
The right bank of Cedar River between the present crib dam and
the proposed new dam, rises abruptly from the river bed to a general
elevation of 1600, which means a bank approximately 80' high at crib
dam and 150' high at side of proposed new dam. The brow of this bank
forms the southerly edge of a morainal plateau extending northerly to
the Snoqualmie River, the general elevation of 1600 being maintained
for a distance of about one and one-half miles, thence dropping rapidly
#19
to the Snoqulamie River at an elevation of approximately 600' feet,which
it reaches in another one and one half miles.
So far as is disclosed by surface exposure along the creek bank
along the cuts of the C.M. & P.S.Ry., which cross it and from such
test wells as have been put down at Camp 2, this entire plateau was
formed by glacial action and is made up of intermixed sand, gravel and
clay of a highly porous character.
That the formation is highly porous is indicated in several ways,
as follows:
1st. By visual observation and examination of the material itself
in so far as that was possible, there being no general deep borings
from which samples could be obtained.
2nd. By the fact, that no surface drainage channels are revealed
until the lower and steeper stretches of the plateau toward the Snoqual-
mie River are reached, although the mean annual precipitation at its
upper end is 110" and the mean annual precipitation for the entire
plateau about 93", thus indicating the highly absorbent nature of the
materials upon which this moisture falls.
3rd. The fact that water moves freely through the material, as
can be plainly seen along the excavations of the C.M.& P.S.Ry.
already referred to, and more definitely in the little stream which
empties into the Snoqualmie River at the North Bend Lumber Co's mill
which stream is in fact the gathering channel for all the water which
ultimately comes to the surface from this plateau. Weir measurements
made of the discharge of this stream during the progress of our inves-
tigation indicate its present flow to be about 20 cu.ft. per second,
which flow we are informed by the mill people is at times somewhat
smaller than this, but also at times materially larger. Assuming 20
second feet as the mean runoff its per annum yield would amount to
14600 acre feet, which for a precipitation of 93" per annum over its
small water shed of about 6 square miles means a ratio of seepage runoff
to precipitation of 50% which may be regarded as high.
It may be admitted at once that any attempt short of actual test
measurements to determine the rate of ground water movement through
#20
these soils is more or less a conjecture. In the absence, however, of
any such actual experiments, and in view of the many physical indica-
tions of high porosity of the soil, it becomes necessary to make evalua-
tions of the rate of such ground water movement, basing our deductions
of course upon actual experiments in other localities and upon such
theory as has been already been deduced in relation thereto.
The two factors which particularly control the velocity of water
through soils is the effective size of the soil particles and the hy-
draulic gradient of the water plans. Velocities from 1' to 64' per day
have actually been measured in various places in the United States and
Europe, as for instance in the Mojava River gravels in California where
the latter velocity was attained, but the actual field experiments thus
far made in river beds have been where only light hydraulic gradients
obtain, as compared with that which presumably obtains in this instance.
Considering the character of material of which this plateau is formed
and applying formulae as deduced from the very careful experiments of
Hazen and Slichter, and considering also the long and broad exposure
of river bank that would be subjected to seepage, in the reservoir con-
templated, we are led to believe that not less than from 50,000 to 55,000
acre feet of storage would be lost per annum, depending on the actual
stage of water maintained in reservoir. A loss of such an amount means
a 20% depletion of the power possibilities, based upon total runoff; and
we conceive it to be entirely possible that the seepage losses may be
greater than above estimated.
We regard the matter of such vital importance, in any event, that
in our opinion no definite work should be done in the way of actual dam
construction until this matter has been satisfactorily solved by actual
tests and by actual tests we mean the putting down of a series of test
wells to determine the position of the ground water plane between the
proposed dam site and Snoqualmie River, actual measurements of the move-
ment of ground water between these test wells and numerous mechanical
analyses of the materials derived at different depths from said wells.
Such a series of experiments would form a fairly secure basis for esti-
mating probably seepage losses from the proposed reservoir and should
#21
by all means be made before further construction expense be incurred.
As to the suggestion that the exposed right bank of the river
would gradually silt up under a plan of raising the water surface in
reservoir by slow successive annual stages, we would say that in our
opinion no such result may be reasonably expected under the condi-
tions which prevail here. We are entirely cognizant of the fact that
in canals and rivers charge with silt there is a tendency to seal up
sides and bottom of such channels, often to the complete prevention
of seepage losses. It should be noted, however, that the head under
which such sealing usually occurs is extremely small. And furthermore,
it is unlikely that any appreciable quantity of silt bearing water
would each this particular bank, all such material having practically
been precipitated in the main Cedar Lake above, which acts as a large
settling basin. Practically the only silt that could be picked up for
such a process would be the silt contained in the bank itself and it is
not believed that the velocity which seepage water would attain in
moving through this soil (perhaps 30' per day) would be such as to
either pick up or deposit sufficient silt to form an effective seal.
Under the high pressure which would obtain against this bank and
with the apparent steep hydraulic gradient of the water plane toward
Snoqualmie River, we believe nothing short of a very thick and a very
well compacted mat of clay puddle would be effective against seepage
and such provision would be abnormally expensive.
When one considers that in the construction of an earth dam,
whose base width is usually five times its height, that undue seepage
can be prevented only by first carefully selecting the earth materials
of which the dam is built, and then compacting these material in 6"
layers under a process of heavy rolling, the fallacy of the motion of
sealing up this bank under heads at full reservoir varying from 80' to
150', by a mere surface coating of silt, becomes apparent.
Question (e):- "Is the proposed plan for pressure tunnel and
the location of the new power house to be preferred to the construction
of additional pipe lines down the canyon of the river to the present
power house site?"
We would answer this question in the affirmative and for the fol-
lowing reasons:
#22
The tunnel route including tunnel proper, penstocks, surge tower,
surge tanks and other auxiliaries, in fact everything between the dam
and power house, we estimate to cost $994,000, or allowing 20% for en-
gineering contingencies $814,500.
In this route, however, the wood pipes would need to be renewed prob-
ably within 15 years at a cost of $600,000, and for this renewal an amor-
tization fund of $27,800. per annum would be required, which capitalized
at 5% would be equivalent to a present investment of $556,000. A fur-
ther charge against this route results from the fact that by reason of
a decreased effective head of 30' it develops 1300 to 2060 continu-
ous water H.P. less than the tunnel route, depending on whether or not
seepage loss from reservoir be considered.
Assuming an annual profit of $6. per water H.P.(it is at the present
time much more), and capitalizing same at 5%, the loss represented in
this decreased power amounts to from $156,000 if seepage loss be con-
sidered, to $247,000 if it be assumed that there will be no seepage
loss. Assuming the former, however, a fair comparison of these two
routes would be $1,192,900. for the tunnel route as against $1,427,500.
for the wood pipe route, or a difference of $234,700. in favor of the
former, although in initial expenditures there is an apparent advantage
of $378,300. in favor of the latter.
A further advantage of the tunnel route other than that indicated
by cost comparison, is the fact that it insures a practically uninter-
rupted service, whereas an wood pipe construction would be more or
less subject to breaks.
Question (f):- "Is the plan proposed by the City Engineer for
taking the pipe lines from the vicinity of the Cedar River below
Landsburg by the construction of a tunnel the best and most practicable
method of securing the protection required, or should steel pipe be
constructed beneath the bed of the river crossing?"
#23
In reply to this question we would say that this entire matter
seems already to have been all considered by the City Engineer's
office, and we take pleasure in commending the careful surveys and
estimates and the very excellent report prepared in relation thereto.
(See Carver's report to City Engineer, dated Feb.27,1912) to all
of which you are respectfully referred.
With the findings of that report we are in general accord, the
five alternative schemes proposed therein and our comments thereon
being as follows:
Scheme 1. To maintain the present combination spans which carry
the pipe lines over Cedar River, strengthening them as may be necessary
from time to time.
This scheme we think may be immediately rejected as being at best
but a temporary make-shift that would sooner or later have to give way
to one of the more permanent alternative schemes offered. The shallow
depth to which piling can be driven through the coarse gravel, boulders
and hard pan of the river bed at these crossings will always threaten
the stability of these structures in time of flood.
Pending the actual adoption and putting into effect of one of the
several other schemes we are of the opinion that immediate repairs should
be made as follows:
(a) To cut off a low channel and thereby in times of flood, to
prevent scour behind the cribbing and under the trestle approach
at easterly end of the first crossing, a small dike should be construct-
ed to a height well above high water, this dike to connect the pipe
line embankment at trestle bulkhead with the high ground on left
bank at upper end of cribbing.
(b) As a protection against scour around the pile piers sup-
porting the bridge, we would suggest that instead of concrete en-
casement of the piling as proposed, there be substituted heavy
rock carefully placed around the piles, which rock would settle
and afford maximum protection to the piling when scour occurred.
Scheme 2. To replace present bridge with steel structures sup-
ported upon masonry piers. This scheme is estimated by the city to
cost $62,000.
#24
There is no question that substantial steel structures supported
upon substantial concrete piers could be constructed at these crossings
and be regarded as reasonably permanent. Cedar River, however, is
subject to heavy freshets resulting from violent scouring action on the
river bed which necessitates carrying to great depth, any structure
founded in this channel. The undermining of the concrete piers of the
several crossings of this river by the C.M. & P.S.Ry. is ample evi-
dence of the violent action of this stream in flood. Piers for such
bridges as are here contemplated, therefore, would need be very deep,
probably not less than 20 feet below river bed, thereby becoming rela-
tively expensive. The additional cost involved in making these piers
entirely secure, plus the cost of additional pipe lines to meet the
growing demands of the city, would in all probability entirely offset
the apparent difference in cost as indicated by the City Engineer's
estimates between this scheme and scheme No.5, which latter is the
one finally recommended.
Scheme 3. To cut a channel through the ridge immediately north of
the C.M. & P.S.Ry. tunnel, to move the railroad bridge from its
present position below the tunnel to a point near the upper end of pro-
posed change, where it would span an opening to be made through the rail-
way embankment restoring the stream to its original channel, thence car-
rying it through the proposed new cut completely clear of the pipe lines.
This scheme is estimated by the city to cost $144,000.
We have no hesitancy in condemning this scheme, not only as in-
volving greater expense than any of the other schemes offered, but also
because it introduces a situation that at once becomes a menace to the
railroad and also threatens trouble at upper end where it is proposed
to sharply turn the channel across the railway into its original course.
We further believe that the size of channel proposed through the ridge
paralleling the railway tunnel will need be materially widened in order
that excessive velocities be not attained in times of flood. To put
a narrow channel through this ridge as proposed, depending upon high
flood velocities to erode it to such size that cutting would cease,
would in our opinion inevitably endanger the railway track and tunnel.
The enlargement of this cut would increase and only the more
#25
tend to eliminate it from consideration as a possibility of permanent
relief.
Scheme 4. To place the pipe lines below the bed of the river, in-
volving their relocation for a total distance of 3500' and the sub-
stitution of steel pipe for wood pipe for the portion immediately under
the river. This scheme is estimated by the City to cost $77,000.
We concur in the opinion expressed in the report of Mr. Carver to
the City Engineer hereinabove referred to, namely, that if the pipe
line location is to remain practically unchanged, Scheme 2, as already
described,is to be preferred.
Scheme 5. To re-locate the pipe lines, carrying them entirely
clear of the river via the so-called tunnel route lying immediately
to the south of Cedar River, replacing 6600' of old line with 5700'
of new line. This scheme is estimated by the city to cost, for tunnel
of 72" diameter $77,000, and for tunnel of 86" diameter $95,000.
We regard this as by all means the scheme to be adopted, the only
modifications suggested being as follows:
(a) That instead of putting through a tunnel of 7'-2" diameter
and 155.8 S.F. capaciy as proposed, it be made of 8'-4" diameter and
of 232. S.F. capacity, or sufficient to server a population of 1,000,000.
After the tunnel equipment is once on the ground the increased cost
due to the slight enlargement of tunnel is relatively small. The unit
prices upon which the City Engineer's estimates are based are $10 per
cu.yd. for concrete lining, which we would increase to $12 per cu.yd.
and tunnel excavation at $4 per cu.yd. which we would increase to $4.50
per cu.yd anticpating, as we do, that more or less timbering will be
required.
Making allowance for these increased unit prices and for the
tunnel enlargement proposed we estimate the total cost of this improve-
ment to be $132,000 as against $95,000 estimated by the City Engineer.
As proposed by the City Engineer, this tunnel lies at its nearest
point about 200 ft. from the river, at which point the river bank
rises to a height of about 90'. The river makes a sharp bend at this
location, already showing some evidence of erosion, and although
#26
the formation here is of fairly indurated clay and gravel we think
there is a possibility of the river cutting still further into the bank,
and we therefore recommend that the tunnel be moved back a further dis-
tance of about 100 ft. This change we believe will practically involve
no additional expense and would in fact make the final total length of
conduit to be maintained by City somewhat shorter. An added advantage
of this change is that the connection at its upper end with the exist-
ing lines is more favorably located, being about 250' further upstream
where the danger of river erosion is less threatening.
We not only recommend the adoption of Scheme 5 but also urge that
it be put into effect immediately.
Question (g):- "What method should be adopted by the city in fu-
ture construction of pipe lines or other facilities for bringing the
water into the city from intake?"
We assume that this question in fact relates to type rather than
method of construction, and upon this understanding we would say as
follows:
No form of pipe conduit construction can be regarded as permanent
and the choice of type of construction to be adopted depends largely
upon the economics of the situation at the particular time the con-
struction is put into effect.
Wherever tunnel construction can be employed within reasonable
limits of cost, as has been suggested for instance, in the proposed
line revision near Landsburg, that type of construction should be
adopted, for it secures not only the maximum permanency but involves
a minimum maintenance cost as well. Where topographic conditions ren-
der tunnel construction impracticable and a grade conduit is feasible,
as may be the case near upper end of line, then in our opinion cut and
cover construction should be employed. By cut and cover construction
is meant open excavation with concrete lining carried to just above
flow-line of conduit over which is placed a concrete cover, which in
turn is covered with a back filling of 2' or 3' of earth.
As soon as pressure conduit becomes necessary and speaking in a
general way and for conditions as they are today, we believe that where
the static head does not exceed 100', reinforced concrete pipe will
#27
prove the most economical and the most satisfactory.
For heads between 100' and 200' and for the size of conduits that
will be required here, either wood pipe or steel pipe will need be
employed and while the latter is somewhat more expensive it has a some-
what longer life under ordinary conditions. Wood pipe, however, we re-
gard as entirely good construction, provided due caution be exercised
in the character of soul used for back filling the trenches, good clean
sand or gravel, devoid of vegetable matter being the best for this
purpose. If such material can not be obtained at reasonable cost, the
pipe line should be laid upon cradles and kept entirely free of contact
with soil.
For heads in excess of 200' steel pipe should be employed.
Final instructions:- "Also the said engineers by the terms of the
contract shall submit to the Council, in addition to the information
and recommendations on matters above enumerated, anything that such
investigation or their or his judgment may suggest to them, or to any
one of them, concerning the entire lighting, power and water project."
This appears to be a sort of "general welfare" clause that opens
up a broader field for discussion than our investigations would warrant
and we will, therefore, confine ourselves to a few major features, as
follows:
Complete project:- Besides the construction of the storage works
and the power station at Cedar Falls, as hereinbefore described, there
is required, before such power can be made available for market, the
construction of about 40 miles of transmission line and also the con-
struction of sub-station and distribution system in the City of Seattle.
We have estimated that the cost of developing and delivering this
power to the Seattle sub-station, i.e. to and including the step-down
transformers of the transmisssion line (see Appendix J) would be
$6,681,325. or $157 per K.W. of generator capacity installed. We also
find, that on the basis of no seepage loss from reservoir as has appar-
ently been assumed by the City, the installation cost per continuous
K.W. dleiverance to sub-station would be $579, whereas if seepage losses
develop as we have assumed, this cost would be $747.
#28
While an installation at the above figures can not be regarded as
of low cost it is not unduly high, and we believe that such an invest-
ment would be warranted on the basis of the prices for electric power
which now prevail and which are likely to prevail here in the future.
It does, however, raise the question as to whether or not a more
oconomical development is possible, i.e. a lesser and cheaper storage
development as has already been discussed, with small steam auxiliary
in the City, or indeed whether power development on some other stream
might not prove more economical as an initial installation than would
the Cedar River project. As to the former, there are several advantages
in having a small steam auxiliary in the City, and considering the
greatly reduced cost for storage that would result therefrom, we believe
such a combined installation would prove as cheap if not cheaper than
an all hydro-electric plan. As to the latter, i.e. power development
on other streams, we, of course, have no data whatever upon which to
base an opinion.
Cedar River Alternatives:- In our general investigation of this
project, a number of alternative possibilities suggested themselves to
us, most of which have already been referred to and all of which, in
our opinion, should be given due consideration before actual construction
is decided upon. These several alternatives may be recapitulated, as
follows:
Scheme 1. To build a masonry dam at the site now proposed and to
an elevation of 1615, either along the lines proposed by the City Engi-
neer or the modifications therof suggested by ourselves.
Scheme 2. To construct a solid masonry dam to an an elevation of 1605
thereby securing all the water which we believe can be secured, seepage
losses considered, such storage providing an ample supply to take care
of years of minimum runoff, thereby securing continuous power from a
single hydro-electric plant.
Scheme 3. To build a solid masonry dam at site now proposed to
elevation 1575, such storage to provide only for years of mean runnoff,
the deficiency in years of minimum runoff to be cared for by the con-
#29
struction of an auxiliary steam plant located in the City of Seattle.
Based upon our assumption as to probable seepage losses from the
reservoir, we find this scheme will in fact develop more continuous
power by reason of there being less seepage loss than will Scheme 2,
though it will of course, involve as already indicated, the operation
of the steam plant during such seasons as the runoff falls below the
mean.
Scheme 4. To consider the same alternatives as listed above
with reference to an earth or earth and rock-fill dam as suggested
by us for the upper site.
In this connection it should be stated that the adoption of the
upper site will involve the extension of the proposed power tunnel a
distance up-stream of about 5200' and in weighing the difference be-
tween the two locations the cost of such extension should operate as
a credit to the lower site or a charge against the upper site.
The possible difference in value between the least expensive and
the most expensive of these alternative schemes, considering actual
first cost of construction and the power that may be developed there-
from, may in our opinion reach as high a figure as $1,500,000, and
therefore indicates clearly how unwarranted it would be to proceed
with this development without having first thoroughly investigated
the possibilities suggested above.
The whole subject, in fact, of power development in this region,
whether municipal or private, is of such vital importance to Seattle's
future growth as to be worthy of far more careful study than it has
yet received. As we can conceive of no better investment the City could
make than to place at the disposal of such department as is best
equipped to handle the work, funds sufficient to institute and to carry
on for several years if necessary, exhaustive surveys and investiga-
tions of all the as yet undeveloped power possibilities tributary to
the City. The results of such surveys and investigations, properly
compiled, would be invaluable, not only to indicated what the City
could and ought to do in the matter of future power development, but,
what is equally essential, to indicate what it ought not to do, and
#30
to point the way for securing the maximum sufficiency from its
future expenditures for those purposes.
Swan Lake:- We were verbally requested to express an
opinion as to the possible utilization of Swan Lake in connection
with the city water system and in compliance therewith we spent
a portion of one day at that Lake, examning the character of its
watershed, its shores and outlet, and also looked for indications
of seepage from the lake to the north toward Cedar River.
Swan Lake is a body of water having a maximum depth of
about 75', a water surface area of about 550 acres and a total
drainage area of about 3200 acres, of which 242 acres (largely
shore lands) are now owned by the City of Seattle. Its outlet
is to the south through Little Soos Creek, the discharge of this
outlet at the time of our visit being estimated at from 8 to 10
S.F. The lake surface elevation is about 472', this being 16'
below the highest point in present pipe lines immediately below
the temporary pumping station installed last winter, the hydrau-
lic grade line being but slightly above that, for the maximum
capacities of these pipes.
If there is any seepage from lake, it could be toward
a swamp about a mile to the westward and approximately 70' below
the lake, but more likely the greater portion of such seepage
would be toward Cedar River about 2 miles to the north and about
350' below the Lake. We examined the territory between the lake
and the station of Elliott on Cedar River and found more or less
evidence of seepage all along the bluff facing the river at this point.
We believe, however, that seepage loss would not in fact be
heavy, and that 2000 acre feet per year would be a fair estimate
of same, even if the lake were raised.
In the absence of any definite rain fall data for the
drainage basin, or discharge record for Little Soos Creek, noth-
#31
ing more than a fairly intelligent guess, based upon probable
rainfall and drainage area, can be made, as to runoff. On such
basis, however, we have estimated that the total yield of this
basin might be 8800 acre feet per annum, or allowing 2000 acre
feet for seepage loss, say a net yield of 6800 acre feet per annum.
To conserve this supply would require the construction
of a small dam at outlet of lake that would permit a 10' raise
in lake surface, and, if run-off assumptions be correct this
would afford a two months water supply for the City of Seattle
at is present population, the lake itself being supplied wholly
from its own runoff.
If an earth dam were built to elevation 500 we estimate
that the lake would conserve a supply of about 18,000acre feet, an
amount sufficient to serve our present population for a period
of 157 days, and it is probable in this case too that the lake's own
runoff would furnish this supply, for such emergencies as would
call the lake into use, would only occur at long intervals, the
interim between such demands affording ample time for replenish-
ment.
To utilize the lake, however, for emergent use in case
of break down of lines between the lake and the Landsburg intake,
would necessitate the construction of an outlet from the lake to
connect with the pipe lines at some point north of lake. We find
that an 8' circular conduit taking out from the north end of lake
opposite Station #507 of pipe line and joining said pipe line at
about Station 623, would be able to deliver to present pipe lines
and such additional pipe lines as may hereafter be required,
sufficient water to serve a population of 1,000,000 when lake
was at maximum or normal storage, and about a two-thirds supply
#32
for same population when lake was at is minimum stage of 472.
The present pipe lines could of course be maintained,
the lake route being used merely as an alternative in case of
emergency, but if the lake be included at all in the system it
would appear to be far more economical to cut out all future pipe
lines between Station 455 where pipe lines could discharge into
the lake and Station 623, or a total distance of 16,800'.
As to the purity of the Swan Lake water, would say that
analyses made during the past week, by the Health Department at
our solicitation, indicate its entire freedom from bacilli coli
and its entire potability at the present time, as will be noted
in Appendices C-1, C-2 and C-3. With an increased depth of
water we belive its purity is likely to be enhanced, particu-
larly if the water were kept in motion by the actual constant
passage of the city water supply through the lake. The lake
would also act as an efficient sedimentation basin, a feature
which is lacking in the present system. It goes without saying,
that, should the city incorporate this lake in its water system, it
would need acquire for proper sanitary control, the entire
watershed of the lake, involving the purchase of about 2400
acres of land not now owned by the City.
Without actual surveys of dam site and of drainage
area and a more detailed study of the many features involved,
no definite estimate can be prepared of the cost of this develop-
ment. Such rough estimates as we have been able to make, indi-
cate that the cost, exclusive of land purchases, would be in
the neighborhood of $350,000. The elimination of future pipe
lines between Stations 455 and 623 would, however, effect a sav-
ings of about $250,000., thus indicating a net cost, if such sav-
ing be regarded as a present credit, of about $100,000 plus the
purchase price of the watershed.
#33
A reservoir, situated as is Swan Lake, about midway
between the head of our supply mains and the south boundary of
the City, and with a storage capacity sufficient to tide over
an emergent period of nearly two months for a population of
1,000,000 appeals to us strongly as a most desireable adjunct
to a city water supply system, and the expense that it apparently
involves also appeals to us as trivial considering the safety
and protection it would afford. Despite its apparent desirability,
however, our hurried investigation would not warrant a recommen-
dation further than that the City Engineer have prepared, detail-
ed estimates based upon actual surveys, with a view to the possi-
ble acquirement of this lake and its inclusion in the city water
system.
Recommendations:- Our final recommendations concern-
ing this project are as follows:
1. That the present crib dam be immediately repaired
to serve for a period of three or four years, or to cover the
time that may elapse before construction of a permanent dam at
one of the lower sites can be completed. No expense should be
spared to make these repairs in a thoroughly wholesome manner.
2. That the present pipe lines in the vicinity of
the two Cedar River crossings below Landsburg be reconstructed
to conform to the so-called "Tunnel Route" and that this work
be begun immediately and pushed to prompt completion.
3. That a series of well drill holes be put down
along the line extending from Camp 2 easterly to foot of moun-
tains just opposite present crib dam, for the purpose of deter-
mining character of material penetrated, position of ground water
plane, and, if practicable, the depth to bed rock.
4. That a series of well drill holes be put down along
#34
the line extending from a point say midway between Camp 1 and
Camp 2 across the morainal plateau between that point and Sno-
qualmie River, for the same purpose named in the paragraph above,
and for the additional purpose of determining by actual experi-
ments the rate of movement of ground water between those holes.
5. That further diamond drill borings be made imme-
diately up-stream and down-stream from the line of of holes now put
in at Camp 2 dam site.
6. That the upper dam side, hereinbefore described,
be explored by putting down a few test pits at the higher eleva-
tions along a line of dam and sufficient test drill wells and if
need be diamond drill borings in river bed to determine the prox-
imity or absence of bed rock.
7. That an accurate topographic survey of upper dam
site be mde and that careful comparative estimates be made of
the several alternative possibilities for dams of different
heights, both at this location and at the Camp 2 location before
adopting any scheme for final construction.
8. Our chiefest recommendation, and this is without
qualification, is that constructive operations in connection
with the building of a dam at Camp 2 be suspended until such
time as a thorough investigation of the possibilities suggested
in this report shall have demonstrated the best plan to pur-
sure and that such investigation be commenced at once.
Acknowledgements:- For courtesies shown and assistance
rendered we desire, in closing, to make acknowledgements to the
following gentelmen:
To His Honor, Mayor George F. Cotterill, to City Engi-
neer, Mr. A.H. Dimock and his several assistants who cheerfully
provided all data information available in their office, and
to former City Engineer, Mr. R.H. Thompson, to Professor Henry
#35
Landes of the State University, to Mr. R.H. Ober of the Build-
ing Department and to Mr. M.T. Stevens of the Health Department,
all of whome attended sessions of our Board and furnished valuable
information.
Respectfully submitted,
(Signed) Joseph Jacobs,
" E R Baldwin,
" Glover F. Perrin,
Board of Engineers.
Notes on the document:
The physical document reproduced here is a typewritten "carbon
copy" at the Seattle Public Library. The original copy is
presumably somewhere in the City of Seattle archives.
The source document reproduced here will seem somewhat peculiar to
modern readers in several respects. This is due partly to changes
in grammatical style in the past ninety some years, and partly to
the nature of using a manual typewriter, where what you typed was
what you got, revision was difficult, and there wasn't the same
striving to emulate the perfection of set-type as is typical today.
This reproduction has been done in a fixed format to retain some
flavor of the original physical document. (If your browser over-
rides that the results will be more peculiar than the original.)
"Improvements" have been limited to correction of obvious spelling
and formatting errors (I believe the original authors would concur
in that), addition of horizontal rules to indicate page breaks in
the original, and addition of hyper-links and anchors for readier
referencing.
The appendices have not been reproduced. They are largely tabular
data of little interest, and having been produced sideways on 14
inch long paper they presented significant formatting challenges
of little benefit. The plates (site map, etc.) have not yet been
found.
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