ON THE CANAL AS IT IS TO BE
BETWEEN Colon and Panama the American Isthmus is about 36 miles across
as the crow flies, and is therefore nearly, though not quite, at its
narrowest. In this portion of its sinuous course both coasts trend north
of east and Panama lies nearly south-east of Colon. The Isthmus in
general is a very confused mass of hills and mountains. It is crossed by
no transverse trench (such as sometimes occurs in mountainous regions),
neither by the trough provided by down-folded strata, nor the rift
valley produced by fracture and foundering of rock. A low-level
transverse can only be found by following up the course of a river,
crossing the divide, and following the course of another river
downwards to the other ocean. From the vicinity of Colon, by following
up the valley of the River Chagres, we are led in precisely the required
direction, _i.e._, directly towards the Pacific, for nearly two-thirds
of the way. The distance from the head of Limon Bay, following the
curves of the valley, is 26 miles to this place, Obispo, and for the
greater part of the distance the river flows in a broad valley of deep
alluvial deposits.
[Illustration: FRENCH DREDGER LAID UP.]
[Illustration: FRENCH TRUCKS PARTLY COVERED WITH FOREST GROWTH]
At the point mentioned, the Chagres abruptly changes its course, and, if
followed towards its source, will be found to be flowing from north-east
to south-west. Moreover, it is now confined to a narrow valley, with
steep hills of rocky substance on either side, and its gradient becomes
much greater than hitherto. The course of the Canal cannot therefore
follow the Chagres valley further. Fortunately, the valley has led us
not only a long distance towards the Pacific, but to a place where the
dividing ridge only attains an elevation of about 300 feet above
sea-level. Striking from Obispo straight for the Bay of Panama, we come
in 9 miles to the low alluvial plain of the Rio Grande, which leads
straight to the sea in another 6 miles. Thus, from shore to shore, the
course of the Canal along this route is 41 miles; but to reach deep
water 4-1/2 miles must be dredged beneath the sea at either end, so that
the total length of the artificial waterway is 50 miles. Of the
land-course less than a quarter, or about 9 miles, is hill country, and
most of this is less than 200 feet above the sea. The United States has
been committed to this route by the long chain of circumstances already
narrated.
Whatever type of canal was to be constructed along this route, there
were certain excavations which must necessarily be done. These were,
firstly, dredging the sea channels, and secondly, making a cut through
the solid rocks of the divide. Thus, although de Lesseps started
operations upon inadequate data, yet most of the work done by the first
Panama Canal Company is available, either for the tide-level canal
proposed by de Lesseps or for the 85-foot-level canal now being made by
the United States. Similarly, the New Panama Canal Company, although
hampered by many uncertainties, continued to work at the Culebra Cut, as
it is called, that is to say, the trench through the rocky hills which
separate the alluvial valleys of the Chagres and the Rio Grande.
Thus the works taken over by the United States in 1904 were available
for any type of canal, and the decision to adopt the 85-foot-level was
not taken until 1906. Even now, or in April, 1908, at the time of my
visit, when so much work has been done upon the locks, many of the rank
and file of the employees still cherish the hope of a tide-level canal,
and there are not wanting well-informed people, both on the Isthmus and
in the States, who, while accepting the high-level scheme as inevitable,
regard a tide-level canal as essentially a better thing.
Let us resume our description of the Isthmus, in order that we may be in
a position to understand the conditions with which the engineers have
to deal. The practicability of the Panama route is due to the fact that
rivers have already done a great part of the excavation, and if desert
conditions had supervened--if there were, as at Suez, practically no
rainfall--the construction of a tide-level canal would be simply the
excavation of a trench in dry material, which would be filled by the
inflowing waters of the sea. A tidal lock being added to regulate the
ebb and flow at Panama (for the Atlantic side is tideless), the canal
would be complete.
But as things actually are, the rainfall on the Isthmus is very heavy,
particularly on the Atlantic side, where it reaches 140 inches[5] per
annum, and the rivers have at all times considerable bodies of water,
and during the rainy season (commencing in May) are subject to sudden
and violent freshets. The Chagres at Gamboa has been known to rise
35-1/2 feet in 24 hours.[6] Suppose then that a tide-level trench were
suddenly formed across the Isthmus, as by a convulsion of nature. We
should then see the rivers pouring into this fjord in a number of
cascades of various height. Of these the greatest would be the Chagres
cascade, entering from the east near Gamboa and Obispo. The height of
the waterfall would be 46 feet in the driest season and as much as 80
feet in occasional floods.[7]
[5] Abbot, "Problems of the Panama Canal," p. 96.
[6] _Loc. cit._, p. 146.
[7] Abbot, _loc. cit._, p. 116.
[Illustration: EXCAVATION NEAR TAVERNILLA.]
[Illustration: RIVER CHAGRES AND RAILWAY NEAR GORGONA.]
In order therefore to make a tide-level canal, some means must be found
for disposing of the waters of the Chagres and other rivers. De
Lesseps's tide-level project was rather an aspiration than a plan. He
proposed to conduct the waters of the Chagres to the sea by other
channels. The magnitude of this task would be scarcely less than that of
cutting the Canal itself. The other rivers on both sides of the Canal
would likewise require diversion channels, so that the final result
would be roughly the formation of three channels, of which the centre
one would be for navigation. The Board of Consulting Engineers summoned
by President Roosevelt in 1905 to advise the Isthmian Canal Commission
recommended, in a majority report, a tide-level canal as practicable and
best fulfilling the national requirements, defined by the Spooner Act of
1902. But whereas they had detailed schemes for high-level canals before
them, they were in the matter of the sea-level project at the
disadvantage of having to act in a constructive capacity and elaborate
the details of a scheme before they could criticise it. Moreover, five
of the eight who constituted the majority were European engineers, who
returned to their duties as soon as the report was drafted. The report
of the minority in favour of the 85-foot-level scheme having been
adopted by Congress in 1906, all available engineering talent has for
the last two years been devoted to improving the details of this scheme.
The tide-level project of the majority of the Board has had no such
advantage, and the difficulty of estimating the relative advantages of
the two schemes is therefore all the greater.
Both schemes depend for their success upon the security of dams.
The tide-level scheme has a dam at Gamboa, near Obispo, thus making a
lake of the upper waters of the Chagres, whose surface would be 200 feet
above sea-level.[8] The floodwater would partly be accommodated in the
lake by reason of the great height of the dam above low-water stage, and
partly by running the excess into the Canal, by which it would escape to
the sea, generating currents which the Board calculated would not attain
an injurious velocity.
[8] Report, Board of Consulting Engineers, p. 205.
Streams entering the Chagres in its lower reaches would be dammed back
or diverted--a considerable, but not momentous, undertaking. The three
great objections to the scheme appeared to be:--
1. The extra cost, and above all the extra time, required to complete
the immensely greater quantity of excavation required for the last 85
feet;
2. The fact that the artificial lake was to be above the Canal, so that,
if the dam burst, the Canal might be ruined; and,
3. That the velocity of currents in the Canal due to discharge of the
surplus waters might perhaps be a serious drawback to navigation in a
narrow channel.
It will be seen presently that the second disadvantage is offset by
corresponding disadvantages in the dam required for the high-level
canal.
As for the cost, that has always been an unknown quantity, and, I think,
has always been a secondary consideration. The fear of undue delay seems
to have been the principal deciding factor in favour of the high-level
scheme. Rival expert opinions that the majority of the Board of
Engineers had under-estimated the time required for the tide-level canal
were adopted by those in authority, and mainly on this account, I think,
the high-level scheme became law.
Since visiting the Isthmus a second time, and inspecting the work in the
great Cut between Empire and Paraiso, it has seemed to me that there is
an objection to the tide-level project which did not fully appear in
the early stages of the work, viz., that the behaviour of the rock
might involve the engineers in ever-increasing difficulties as the
depths increased. The opinion which had been held by many that the
difficulties would diminish with the depth did not seem to me to be
justified up to that time.
[Illustration: LIDGERWOOD UNLOADER, WINDING APPARATUS.]
[Illustration: _ANOPHELES_ BRIGADE OILING A DITCH.]
Next let us see what are the special difficulties of the high-level
project.
This also depends for its success mainly on the efficacy of one dam,
which is now being made at Gatun. It will hold up the waters not only of
the Chagres but of its tributaries, to a level of 85 feet above mean
tide, and the area of the lake thus to be formed is shown on the map.
The Chagres will be ponded back far above the point where it enters the
Canal, and thus will be effectually tamed. The flood-waters will be
spread over an area of about 164 square miles--for Lake Gatun will be
twice the size of Lago Maggiore and about four-fifths that of the Lake
of Geneva,[9] and ships, in the ample waterway, will not be troubled by
currents.
[9] The size, in fact, will not differ greatly from that of the
principal basin of the Lake of Geneva, all above the _petit lac_, or
narrow part at the Geneva end. A good idea of this area is obtained by
recalling the well-known view over the waters of this lake from the
_quai_ at Ouchy.
A flight of three locks at Gatun will raise ships to the level of this
lake in coming from the Atlantic, and one lock at Pedro Miguel and two
at Milaflores will lower them to the level of the Pacific.
It has been claimed that if the Gatun dam burst the consequences would
be less disastrous than if the Gamboa dam burst, but there is in reality
little to choose between the two catastrophes.
The great blot on the high-level scheme is that the great Gatun dam is
not founded on solid rock. The Gamboa dam of the tide-level project
would have been founded throughout on hard rock, from which it could
have been built up of masonry so that the structure should be part and
parcel of the rocky framework of the globe itself. The Gatun dam as
recommended in the minority report, on the other hand, was designed to
consist essentially of a mass of earth dumped upon an alluvial plain so
as to fill up a gap of 2,000 yards between two ranges of hills, the gap
through which the Chagres escapes to the Atlantic. Thus the Gatun lake
was to be held up as a glacier lake is held by a moraine blocking a
valley.
We shall presently describe the high-level canal as it is to be, from
which it will be seen that it will provide a magnificent waterway, but
before concluding the present section I must mention the special point
in which it will be inferior to a tide-level canal. This is for purposes
of defence. A fortress has to be preserved from capture, but not from
damage. The locks, however, must be preserved from serious damage, which
demands far more elaborate protection. Such protection, moreover, has to
be provided at two positions (Gatun and Milaflores) about 30 miles
apart.
_The High-level Canal as it is to be._
The Spooner Act, the law under which the Canal is being constructed,
enacts that it shall be "of sufficient capacity and depth as shall
afford convenient passage for vessels of the largest tonnage and
greatest draft now in use, and such as may reasonably be expected."
Accordingly the following dimensions have been selected:--
1. A minimum depth of 41 feet.
The Suez Canal has a depth of 31 feet[10] admitting of the passage of
ships with a draft of 27 feet.[11] The channel of this canal is now
being deepened, so that by 1915 it is hoped that a depth of 36 feet[12]
will be obtained. The Kiel Canal has a depth of 30 feet. The average
draft of the Cunard s.s. _Mauretania_, the largest ship now afloat, is
about 32 feet, but she is stated to draw, when fully laden, about 37
feet, and there are comparatively few harbours in the world which she
could enter fully loaded.
[10] Report, Board of Consulting Engineers, p. 175.
[11] "Four Centuries of the Panama Canal," p. 436.
[12] _Daily Telegraph_, June 18, 1908.
2. A minimum bottom width of 200 feet in the Culebra Cut.
The minimum bottom width, or width at a depth of 31 feet, in the Suez
Canal is 108 feet.
The bottom width of the Kiel Canal is 72 feet.[13]
[13] Report, Board of Consulting Engineers, p. 173.
3. Each lock will have a usable length of 1,000 feet and a width of 110
feet.
The locks of the Kiel Canal have an available length of 492 feet and
width of 82 feet.
The _Mauretania_ has a length of 790 feet and beam of 88 feet.
4. The minimum radius of the curves is 5,577 feet (1,700 metres).[14]
This curve, however, does not come in the Culebra Cut, where the bottom
width is to be 200 feet, but north of Bas Obispo, where the bottom width
is 500 feet. Most of the curves have a radius of 9,842 feet (3,000
metres).
[14] _Vide_ p. 205 of General Abbot's "Problems of the Panama Canal"
(1907). Slight changes in the projected course are made from time to
time, so that this figure is subject to slight modification.
In the Suez Canal,[15] outside Lake Timsah, there are five curves with a
radius of 2,000 metres, or a little more, which are being enlarged to
2,500 metres (8,202 feet). The usual bottom width in these curves was
184 feet, but this is being increased to about 230 feet. The Kiel Canal
has four curves with a radius of 1,000 metres (3,284 feet).
[15] Report, Board of Consulting Engineers, p. 178.
A reference to the accompanying plan (_vide_ Map, end of volume) of the
Panama Canal will show that most of the curves are situate in Gatun
lake, where the width of the canal proper is large, and where the spread
of shallower waters secures better steerage.
Thus the high-level Canal is not only deep and wide, but also much freer
from troublesome curves than might be supposed from a casual inspection
of its course. The details of the bottom width of the high-level Canal
in its different parts are as follows:--
Feet.
From the Atlantic entrance to Juan Grande (27 miles) 1,000
Juan Grande to Bas Obispo 500
Bas Obispo to a point about half-way between Empire and Culebra 300
Culebra Cut nearly to Pedro Miguel lock (about 4 miles) 200
Pedro Miguel to Pacific entrance 500
[Illustration: 100-TON WRECKING CRANE, GORGONA.]
[Illustration: INTERIOR OF MACHINE SHOP, GORGONA.]
Limon Bay being shallow, the deep water where a battleship can freely
navigate or manoeuvre lies outside a line joining Colon Lighthouse
with Toro Point, and at a distance of 7-1/2 miles from Gatun locks. From
this distance the lock-excavation can now be plainly discerned from the
deck of a ship without the aid of a glass. Here, when the Canal is
complete, a ship will enter the buoyed channel of the submarine portion
of the Canal, but this part of the channel does not lead directly
towards the locks, which are not visible upon the face of the water.
Moreover, they are presently hidden altogether by the land. Not until
Mile 5, near Mindi, is reached does the course of the Canal, by a slight
bend, open up the locks to uninterrupted view, and at this point the
ship is already confined between banks. When the foot of the flight of
three locks is reached a vessel will no longer proceed under her own
steam, but be warped through.
The length and width of the locks has already been stated. The maximum
lift will be 32 feet, or about 4 feet more than in any other locks at
present in use. As the width (110 feet) is much greater than that of
existing locks, it follows that the lock gates will be far larger than
any now in use. The vessel has to pass through a flight of three
succeeding locks. Parallel with this is a second flight of three locks,
so that two ships could be simultaneously put through either flight in
the same, or in opposite, directions. Each lock through which the vessel
passes on her upward course is provided with two pairs of mitre gates,
_i.e._, double-swinging doors, but the uppermost lock has in addition a
rolling gate near the lower end. This is a precaution against the
breaking through of the upper folding doors by a ship coming down,
_i.e._, from the Pacific side. An emergency gate is also being designed,
a sort of swing bridge, to close the upper entrance to the flight of
locks, for Gatun, Pedro Miguel, and Milaflores. It is hoped that a
vessel will be put through all three locks at Gatun in 50 minutes, to
which must be added some delay in approaching. Coming from the Atlantic
the water of the Canal will be smooth, and the vessel somewhat
sheltered, so that there should be no difficulty. Approaching from the
lake there may be some roughness, but anything more than a fresh breeze
is rare, and the lake will be practically free from currents, so that
the approach should present little difficulty. The Pacific side is
always calm, so that no difficulty of approach or exit is to be
anticipated there on account of either winds, waves, or currents.
Our vessel, having been locked up to the broad surface of Lake Gatun,
proceeds under her own steam and at a fair rate of speed across that
lake, slowing down to about 4-1/2 miles per hour for the 9 miles of
Culebra Cut, which will thus occupy two of the 8 or 10 hours in which it
is hoped to accomplish the whole transit. On this basis it is calculated
that 40 ships could be put through in 24 hours from the Atlantic to the
Pacific, or two fleets of 20 ships if passing simultaneously in opposite
directions.
A 10-hour transit of the 50-mile channel is about the same rate of
progress as that in the Suez Canal, where, though there are no locks,
the speed has to be kept low on account of the friable nature of the
banks.
It is evident that the time of transit cannot yet be certainly known to
an hour or two, but a considerable margin beyond the above estimate
would enable the passage to be made between dawn and dusk of the
tropical day.
At Pedro Miguel our vessel passes through one lock on her way down to
the Pacific, and at Milaflores through two locks. Each of these three
locks has, of course, a duplicate alongside, permitting, as at Gatun,
the simultaneous passage of a companion vessel, or of one passing in the
opposite direction. In case of repairs to one set of locks the parallel
set would maintain the waterway.
The lift of the lower lock at Milaflores is variable, depending upon the
level of the tidal water in the last reach of the Canal. The extreme
range of the tide at La Boca, the Pacific entrance to the Canal, is 20
feet; that is to say, low water during "spring" tides is 10 feet below
the average sea-level. During low tide on the Pacific side, therefore,
the water in the Canal stands 95, instead of 85, feet above that sea.
Hence the maximum lift of 32 feet already stated, for
32 x 3 = 96.
[Illustration: MACHINE SHOPS, GORGONA.]
[Illustration: CLUB HOUSE FOR EMPLOYEES, GORGONA.]
Beyond the Milaflores locks our vessel enters a reach of the Canal which
is exposed to the ebb and flow of the tide and _which will be confined
within banks or levees as far as La Boca_. In this respect the plan and
the section are both, unfortunately, misleading. The La Boca lock and
dam have been abandoned, and no Sosa lake will therefore come into
existence, the lowest lock being, as I have said, at Milaflores. I have
thought it better to reproduce the existing maps as they stand rather
than to attempt a re-draught which would necessarily be imperfect. Our
vessel, then, below Milaflores is in a tidal channel and will be subject
to some tidal current. By designing this channel so as to avoid a bottle
neck, and by giving it a width of 500 feet, the calculated current will,
however, not exceed 1 foot per second.
The La Boca site for locks was found to be much too exposed to gun fire
and other modes of attack from the sea, whereas the Milaflores site is
not only distant about 5 miles from the shore, but is well sheltered
both by hills near it and by the position of the hilly eminences of the
shore line.
It will be seen from the map that the dredged sea channel by which our
vessel will reach deep water on the Pacific passes to the west of the
Isle of Naos instead of to the east, as was proposed in the earlier
plans.
* * * * *
Returning now to the Gatun locks. The mitre sill of the top lock is 37
feet above mean sea-level, _i.e._, 48 feet below the surface of the
lake, which is 85 feet above mean sea-level. But the bottom of the lake
here is only about 5 feet above sea-level, the total depth of water
immediately above the locks and dam being 80 feet. It follows that, in
the extreme case of both gates of one of the top locks (as well as the
roller gate) being wrecked, the level of the water in the lake can only
fall to the level of +37, which would leave a depth of 32 feet
immediately above the dam. Ships of large draft could therefore lie
there without being stranded. Moreover, the lake is so large that the
outflow through the broken locks would only lower the level 2 feet _per
diem_, so that more than three weeks would elapse before the water sank
to the level of the mitre sill.
Again, the channel provided by the broken lock would be so small that in
the Canal below the calculated current which would result from the
outflow would have a velocity of only 3-1/2 miles per hour.
Above the Pedro Miguel and Milaflores locks there is not the same
surplus depth of water, so that vessels might be grounded if the locks
were broken. Moreover, as there is no wide-spreading lake above Pedro
Miguel, the outflow of water would generate a somewhat swift current
above the lock, which might be a source of danger to ships.
This circumstance serves to enforce the apparent paradox that the great
area of Lake Gatun is in several respects an element of safety, not, as
the layman might suppose, of danger. The hydrostatic pressure upon the
dam depends, of course, solely upon the depth of water, not upon the
area of the lake, while the greater the contents of the reservoir the
more nearly stagnant are its waters.
As there is to be no lock at La Boca, the dams shown there on the plan
and profile will not have to be constructed, so that it is not necessary
to deal with the questions to which they formerly gave rise.
In the vicinity of the locks at Pedro Miguel and Milaflores, however,
dams have to be constructed to hold up the water. At both places the
dams will be short, and will be founded upon hard rock,[16] and in each
case the head of water to be held up will only be about 40 feet, instead
of 80, as at Gatun. The construction of the dams at Pedro Miguel and
Milaflores is not, therefore, regarded with anxiety.
[16] "Canal Zone Pilot," pp. 316-317.
The great Gatun dam remains the one important experiment in the whole
scheme of the high-level Canal, and much attention is being devoted to
the planning of this work. The alluvial foundation is a disadvantage
shared by the Bohio site formerly chosen, and all other sites in the
lower Chagres valley; so that, having decided upon the Panama route, and
a high-level canal, there appears to be no alternative to the
construction of a dam upon this kind of bottom. The details of the
proposed structure, as elaborated in April, 1908, were as follows:--
The length of the great earthen dam at Gatun is 7,700 feet, its breadth
no less than 2,060 feet. The weight of the dam per linear foot is more
than 60 times the horizontal pressure of the water in the lake, so that
the pressure could not move the whole mass; and the weight of the dam is
spread over such a great width that it is not thought that the ground
will sink beneath it. The form of the plan and section is shown on the
map, and an idea of the topography may be obtained from the
photographs, which I took in April, 1908. The south-eastern end of the
dam abuts on the hill of hard, fine-grained, argillaceous sandstone in
which the lock-site is being excavated.
The dam, according to these plans, is not to be merely superposed upon
the surface, as originally proposed in 1905. Embedded in its earthy mass
there is to be a puddled core, and a trench will be excavated to a level
of 40 feet below the sea (-40 feet) for the lower part of this core. Nor
is this all that is to be done to check seepage beneath the earthen dam.
From the bottom of the trench excavated for the puddled core, sheet
piling, made of 4-inch timbers, is to be driven down for another 40
feet, so that sheet piling and puddled core together will form an
impervious barrier to -80 feet; that is to say, 80 feet below the
surface-level of the sea, or about 85 feet below the lowest natural
surface of the ground. The puddled core is carried up through the
earthen dam to the level of +90, that is to say, 5 feet above the level
of the lake, which is to be 85 feet above sea. The crest of the dam will
be +135 feet, _i.e._, 50 feet above the level of the lake; this excess
of height being to provide top weight for increased stability of the
whole structure, and also for the purpose of compacting the underlying
material. The underwater slopes of the earthy materials have been
reduced from the 1:3 of 1905 to 1:5. On the other hand, it has been
decided that the width of 2,625 feet given in 1905 was in excess of
utility, and that a reduction of between 500 and 600 feet can be made
without loss of strength or efficiency.
[Illustration: EXCAVATION IN THE CUT.]
[Illustration: PIPE FOR DIVERSION OF A RIVER, NEAR EMPIRE.]
About half way across the valley occurs a low hill, on which a house is
shown in the photograph. This hill is on the crest-line of the dam, and
is useful as giving support to the sides of the regulating channel which
will be excavated in it. The material of the hill, however, is not the
hard argillaceous sandstone of the lock site, but merely alluvial. The
regulating works themselves will be built of concrete: a solid mass
built up to +69 feet, and on this piers will be constructed 8 feet in
thickness, between which will be the sluice-gates. By their means the
level of the lake will be prevented from rising unduly in flood time.
The capability of the dam to maintain the waters of the lake at a
sufficient level in the dry season depends upon their not finding a
ready way either through the dam itself or below it. The construction of
the dam is believed to guarantee its own practical impermeability. Not
only is there a puddled core, but the mud, sand, and rocks of which the
principal mass will be composed will be laid down in the manner best
calculated to secure compactness. With regard to underground flow, there
is an underlying bed of indurated clay which is regarded as sufficiently
impervious, and wherever the puddled core and piling are imbedded in
that clay it may, I think, be assumed with some confidence that the
leakage will be unimportant. On referring to the section (map), however,
it will be seen that there are in the valley two old river gorges, which
to a depth of 200 and 260 feet are filled only with gravel, sand; sand,
shells, and wood; clayey sand, and so forth. These gorges, measured on
the section shown in the figure, have widths of about 1,200 and 500 feet
respectively at the depth to which the sheet piling goes, and extend
about 120 and 180 feet below. How much water may escape by these gorges
it is difficult to say. This leads us to the next division of our
subject.
_On the Supply of Water Available for the Needs of the High-level
Canal._
The construction of the Suez Canal was a work of excavation pure and
simple. The construction of any kind of canal across the Isthmus of
Panama involves another task, second only in importance to the primary
work of excavation, viz., that of regulating the rivers.
In the case of a sea-level canal the problem would have been how to get
rid of their waters, particularly in the rainy season.
In the actual case of an 85-foot-level canal, the regulation of the
rivers, particularly of the Chagres, presents two aspects, viz.:--
(1) In the wet season, disposing of the surplus waters.
(2) In the dry season, conserving water supplied by the rains so as to
meet the waste caused (_a_) by locking, (_b_) by evaporation, (_c_) by
percolation.
The arrangements for taming the torrents of the Chagres and its
tributaries have already been described. They are, briefly, the
construction of the Gatun dam and its spillway.
Turning to the other aspect of the problem, I have to answer the
question, What is the guarantee that there will be sufficient water in
the dry season?
[Illustration: IN THE CUT, WIDTH 500 FEET.]
[Illustration: IN THE CUT, LOOKING SOUTH TOWARDS CULEBRA.]
Probably there is no problem of the Panama Canal which has received more
prolonged and careful study than this. From the outset the French
engineers commenced collecting data relating to the hydrology of the
Isthmus, and when funds grew low, and the proposed level of the canal
began to rise, the matter received ever-increasing attention. The
_Comite Technique_ of the New Panama Canal Company commenced in 1894
elaborate investigations to determine the catchment area, the amount of
rainfall, and the discharge of rivers. Brigadier-General Henry L. Abbot
(late Corps of Engineers, U.S.A.), whose investigations upon the
Mississippi are known the world over, was a member of this Committee of
the New Panama Company until the work was taken over by the Government
of the United States, for whom he continued to act; and he was a member
of the Board of Consulting Engineers, signing the minority report in
favour of an 85-foot-level canal in January, 1906. A continuous study
for seven years is an advantage enjoyed by few of the American
engineers, and the book on "Problems of the Panama Canal" published by
General Abbot in 1905 (new edition 1907) deals very fully and ably with
the hydrology and meteorology of the Isthmus. The observations were
continued under the direction of Don Ricardo M. Arango, who has also a
long experience on the Isthmus. I shall not attempt to summarise the
mass of data upon which the authorities rely in their calculation that
there is a sufficient water supply for the needs of the Canal during the
dry season, contenting myself with showing, as above, that in this
department of study, which more than all others connected with the Canal
demands long experience, this requisite has in fact been secured. Yet
whatever depends upon climate is liable to unexpected accidents, and
personally I regard as an important safeguard the fact that at
Alhajuela, on the Chagres, 9 or 10 miles above Obispo, there is an
excellent site for a dam, which would form a reservoir where some of the
surplus water of the wet season could be stored, and supplied to the
Canal as required. The details for such a dam were elaborated in
connection with one of the earlier plans of the Canal, so that the
necessary data would be immediately available in case its construction
should become necessary in the future.
_Harbours and Fortifications._
There are no storms in the Bay of Panama, and but little additional
protection from weather is needed there for shipping. The entrance to
the Canal being at La Boca, a new city will grow up there. This will be
the second westward migration of the terminal port, the present city of
Panama lying between Old Panama and La Boca.
Colon is exposed to northers, and protection against the heavy sea which
then rolls in will have to be provided. Whether this will be done by
breakwaters or by forming an interior basin is not yet decided, and the
cost of this part of the Canal works is therefore not yet known.
The Canal, as already stated, is to be fortified; but I made no
inquiries as to the location or character of the proposed
fortifications, a matter which I regarded as outside my province. The
cost of fortifications is included in the provision made by Congress for
the Canal.