[Transcriber's note: This article has been extracted and prepared from
_The Geographical Journal_, v. 70, 1927.]
PROBLEMS OF THE LIBYAN DESERT
John Ball, O.B.E., D.Sc., M.Inst.C.E., F.G.S., Director of Desert
Surveys, Egypt
_Map following p._ 96.
THERE can be few tracts of the Earth’s surface which present such a
number and variety of interesting geographical problems as the Libyan
Desert. The following are some of the more puzzling of the questions
which have been asked at various times since I made my first
acquaintance with the desert thirty years ago:
1. Did the Nile, or a branch of it, ever flow through the Libyan
Desert to the west of the present Nile Valley?
2. By what natural agency were the great depressions in the Libyan
Desert excavated?
3. Can other depressions in this region, besides the much-discussed
Wadi Rayan, be considered possible of utilization in connection with
irrigation, flood-protection, or drainage of the Nile Delta, or as
sources of water-power for Egypt?
4. Whence comes the artesian water of the oases?
5. Why have not certain lakes, such as Sittra and Bahrein, situated as
they are in an almost rainless region, long since dried up?
6. Can the present scanty supplies of drinkable water derived from
local rainfall along the Egyptian Mediterranean Littoral be
supplemented by artesian borings?
7. Are the artesian water-supplies of the oases gradually diminishing?
8. Where shall we look for the mysterious “Zerzura,” or “Oasis of the
Blacks”? Are there any other “lost” oases remaining to be discovered?
9. Can the present difficulties of travel in the Libyan Desert, which
are chiefly due to scarcity of water, be alleviated by the sinking of
new wells?
10. Where are the “Tortoise Marshes” of Ptolemy?
11. What determined the peculiar distribution of the sand-dunes, some
of which extend in straight lines for hundreds of kilometres?
12. What is the full extent of the distribution of flint implements
and pottery, of which accumulations have been found in what are now
among the most desolate parts of the desert, and what light does this
throw on human history and climatic changes?
To most of these questions no completely satisfactory answers have as
yet been given, though several of them have been the subject of
painstaking investigations by many workers. Our knowledge of the facts
bearing on them has, however, increased considerably during the past few
years; and in the present paper I propose briefly to review the various
questions in the light of the latest available data concerning them.
The problems, though they concern a variety of subjects, are very much
interwoven with each other, and they are mostly alike in that the first
difficulty in any attempt to solve them has always been the
incompleteness of our geographical knowledge concerning the Libyan
Desert as a whole. If we possessed a series of detailed contour-maps
covering the whole of the desert, most of the problems would be in a
fair way of solution. But the surveys which would be necessary for such
a result are impracticable at present, mainly on the score of expense.
Some fifteen years ago I essayed the construction of a contoured map of
the Libyan Desert, in connection with the International “Million” map of
the world. But I had to give up the task, finding that there were vast
areas without a single observation for altitude, while such altitude-
data as did exist were open to errors of a magnitude intolerable for
even a preliminary contouring of the areas with which they were
concerned. The attempt however was not without its value, because it
drew attention to the great lack of reliable levels in the Libyan
Desert, and to the necessity of remedying this defect before even an
approximately true picture of the general relief could be obtained.
In the interval which has elapsed since my former attempt, a great deal
of surveying has been carried out in the Libyan Desert, and in most of
this work special attention has been paid to the matter of levels. Two
long chains of triangulation have been run westward from the Nile to
Siwa Oasis, one _viâ_ the Wadi Natrun and the other _viâ_ Baharia Oasis;
another chain has been completed along the coast westward from
Alexandria to Sollum, and a triangulation is now being carried out which
will eventually connect the oases of Kharga and Dakhla with the Nile
Valley. Small local triangulations have also been made in certain areas,
such as Dakhla Oasis and in the neighbourhood of Owenat. In all these
triangulations vertical as well as horizontal angles have been observed,
so that reliable trigonometric altitudes are now available for almost
all the points occupied or sighted. In the southern and central parts of
the desert, we are still dependent on barometric levels; but the old
determinations have mostly been replaced by later and better ones; and
the use of motor-car transport, by facilitating exploratory journeys in
hitherto untrodden regions, has permitted of a large number of
additional determinations being made in tracts where no previous
observations of any kind existed.[1]
Owing to the methods employed in the latest barometric determinations,
the resulting altitudes are of a much higher order of accuracy than
could be hoped for in previous measurements of the kind; in fact, it is
believed that they are not so very far behind trigonometric levels in
precision. This increased accuracy has been rendered possible by the
collaboration of the Egyptian Meteorological Service, which, thanks to
the abundant weather-data now received and dealt with by it, is in a
position to furnish a close approximation to the sea-level pressure at
any point in the deserts at any given instant. The aneroids used in the
desert explorations are compared with the standard barometer of the
Meteorological Service immediately before the start and immediately
after the return of each expedition. At each observation in the desert,
the date and time, and the temperature of the air, are noted, as well as
the approximate latitude and longitude of the place. On the return of
the expedition, the recorded reading is corrected for the error of the
aneroid on the standard barometer, and the Meteorological Service is
asked to supply the sea-level pressure at the particular place and time
of the observation. From the difference of the two pressures and the air
temperature, the height of the place above sea-level is then worked out
directly with the aid of Jordan’s table of “Barometrische Höhenstufen.”
If the place of observation lies considerably above sea-level, a small
correction is applied to the observed air-temperature to allow for the
temperature-gradient in the air; for of course it is the mean
temperature of the air column between the place and sea-level which
should be employed in the reduction.
It is unlikely that with this procedure either the sea-level pressures
or those observed at the places can be in error by much more than half a
millimetre; and consequently, even with some slight uncertainties in the
air-temperatures, the resulting altitudes may be expected to be accurate
to within about 15 metres when only a single observation has been made,
and to within much less than this when, as is usually the case at
important points, the altitudes have been calculated from a series of
readings spread over several days. That this degree of accuracy is
actually attained seems evident on comparison of the levels obtained for
the same places on different dates. Thus, for instance, at a camp close
to Bir Terfawi, during a stay of five days in January and two days in
March 1925, I made in all eighteen aneroid observations. The mean
altitude found was 244 metres; the average deviation of a single
observation from this mean was 8 metres, the maximum being 16. On the
assumption that all sources of error are accidental, the probable error
of the mean resulting altitude works out at less than 2 metres, which is
about the same as might be expected in trigonometric levelling to the
place from the Nile Valley.
The points in the interior of the Libyan Desert of which the levels are
fairly accurately known now number many hundreds, and with the exception
of a large blank in the unexplored west, and another between the Nile
and Merga in the Northern Sudan, they are fairly well distributed over
the country. It therefore seemed to me to be worth while to make another
attempt at a contoured map; for the levels now known (though still far
too few for contours to be drawn with any great precision) might suffice
for the construction of a map on a comparatively small scale and with
contours at fairly wide intervals; it was felt that a provisional map of
this kind, besides affording at least an approximate general view of the
relief, might help towards the solution of one or more of the problems
which I have mentioned above. I commenced by sketching in the contours
at 100-metre intervals on the original sheets of the 1:500,000 map of
Egypt, a revised edition of which is in preparation. They were then
reduced to the million scale, and afterwards still further reduced, with
additions from my own recent observations around Owenat, Gebel Kissu,
and Merga, from Hassanein Bey’s records of his journey between Jalo and
El Fasher, from the altitude-data obtained by the Anglo-French Boundary
Commission in the Sudan,[2] and from the maps of Prince Kemal el Din’s
expedition of 1926 to Owenat and Sarra Well,[3] to form the map
following p. 96. The attempt has, I think, fully justified itself, and
more than fulfilled the hopes that were entertained concerning it.
Probably the feature that will first strike the attention on glancing at
the contoured map is the series of depressions below sea-level
stretching westward from near Cairo to Jarabub. The following table
gives a list of the principal of these depressions, with the approximate
extent of the areas lying below sea-level, and also (where known) the
depths below sea-level of their deepest parts. Where the lowest part is
covered by a lake, the depth shown is that of the water-surface, not
that of the lake-bottom:
_Approximate area _Approximate
_Depression._ below sea-level depth of deepest
in sq. kiloms._ part below sea
in metres._
Wadi Natrun 220 23
Faiyum 700 45
Wadi Rayan 280 43
Qattara (including Moghara, 18,000 134
Qara, and Tebaghbagh)
Sittra (including Timata) 300 33
Bahrein (including Nuemisa) 150 15 (?)
Watiya 70 15
Areg 60 25
Siwa (including Maasir and 800 17
Maraqi)
Girba 20 (?)
Kheiba 40 (?)
Shiyata 20 (?)
Melfa (including Shebat, 260 18 (?)
Exabia, and Gagub)
As will be seen from the figures in the table, by far the largest and
deepest depression in this series—seven times as large, in fact, as all
the others put together—is that of Qattara, which has not been shown on
any previous map, and of which the existence was proved only last year.
That so deep a depression should exist comparatively near to the
Mediterranean and to Cairo, and have remained undiscovered until now, is
striking evidence of how much has still to be learned concerning the
configuration of the desert surface. The manner in which the discovery
was made is perhaps worth placing on record. Hearing early in 1917 that
a military patrol was about to operate in the Qattara region, I lent a
small aneroid to the officer in charge of the patrol, and asked him to
take readings with it at various points along his route, with the object
of getting some idea of the altitudes in that region. It was, of course,
certain that low-lying country existed along the foot of the Qattara
escarpment, but no idea was entertained that any great part of it might
be below the level of the sea. The officer brought back aneroid-readings
which seemed to indicate that the spring at the foot of the scarp at
Qattara was about 60 metres below sea-level; but the aneroid itself was
unfortunately lost during the return journey. The result was too
surprising for it to be accepted without evidence that the readings of
the instrument had not been vitiated by accidental rough treatment, and
consequently I refrained at the time from placing the levels found on
the maps. But I resolved to confirm them or otherwise on the first
opportunity.
That opportunity came last year, when it was possible to send a survey-
party to triangulate westwards from the Wadi Natrun so as to cross the
place where the aneroid readings had been taken. The work was entrusted
to Mr. G. F. Walpole, of the Survey of Egypt, who had already
distinguished himself by successfully carrying out a difficult
triangulation from the Nile across some 500 kilometres of the Libyan
Desert _viâ_ Baharia to Siwa. The result of Mr. Walpole’s work was not
only to confirm the substantial accuracy of the previous estimation of
the level of the Qattara spring, but to bring to light the existence of
a vast hollow, thousands of square kilometres of whose floor lie at even
lower levels, and which at one place descends to a depth of no less than
134 metres below the level of the sea.[4] This last-mentioned spot, some
100 kilometres south-south-west of the Qattara spring, is probably the
lowest-lying point on the land-surface of the African continent.
A scarcely less remarkable feature is the series of depressions
comprising the oases of Kharga, Dakhla, Abu Mungar, and Farafra; while
Baharia occupies a more isolated position about midway between Farafra
and the Faiyum. In contrast with those of the northern series, these
southern depressions do not penetrate to sea-level. The lowest points in
Kharga Oasis are probably at or just below the level of the sea, but the
general level of the Kharga floor is about 70 metres above that datum.
The lowest point of Farafra is somewhat higher than the general level of
Kharga; those of Dakhla and Abu Mungar are higher still, while in
Baharia, though it lies farther to the north, the floor-level averages
some 130 metres above sea.
A noteworthy thing about the larger depressions is that their northern
boundaries are formed by steep escarpments, while to the south the slope
is more gradual. This is the case, for instance, with the Faiyum,
Qattara, Siwa, Kharga, Dakhla, Abu Mungar, and Farafra. Baharia is
unique in being entirely surrounded by escarpments, as also in
containing a large number of hills approximating in height to that of
the bounding scarps. In the majority of cases the greater steepness of
the northern boundaries can be correlated with geological structure; the
northern walls of the Qattara and Siwa depressions, for instance, mark
the southern limit of certain Miocene strata, while those of Kharga and
Dakhla coincide with the southern limit of the Eocene limestones.
To the south-west of Dakhla Oasis there stretches a broad tract of
rising ground, with the Gilf Kebir and the peaks of Arkenu, Owenat, and
Kissu as conspicuous features. On either side of this tract the general
level falls, on the one hand towards Kufra and Cyrenaica, and on the
other hand towards the Nile. The Gilf Kebir is a great broken plateau of
sandstone, rising very nearly to the 1000-metre contour and stretching
in a direction a little west of south for over 100 kilometres. I saw the
south end of this plateau from several points on the way from Terfawi to
Owenat when travelling with Prince Kemal el Din in 1925, and fixed its
position by compass-bearings. As seen from the south, the plateau
appeared to be merely a flat-topped hill; its true form and extent were
discovered by the Prince in the following year, when he passed along its
eastern foot on his way from Pottery Hill to Owenat. The highest peak of
Arkenu, in about lat. 22° 17′, long. 24° 46′, I estimated to rise to
approximately 1410 metres above sea. The altitude of Gebel Owenat far
transcends Hassanein Bey’s previous estimate of 1100 metres; a
trigonometric measurement which I made in 1925 gave its summit as 1907
metres above sea. The general level of the ground at the foot of Owenat
I found to average about 600 metres, thus agreeing with Hassanein Bey’s
figures. Gebel Kissu, though lower than Gebel Owenat, is considerably
higher than Gebel Arkenu, and being an isolated mountain with a single
well-marked peak, it forms a very conspicuous landmark; my trigonometric
determination gave 1726 metres for the altitude of the peak above sea.
To the south-west of Kissu there are a few widely scattered isolated
hills, but the country in general forms a rolling plain of sand
extending to the north-east corner of French Equatorial Africa with a
nearly uniform level of about 700 metres. Beyond the French boundary the
ground rises towards the Erdi Hills, which attain over 1000 metres.
From the corner of French Equatorial Africa to Merga, a distance of 250
kilometres, the country consists of alternations of sand-plains and flat
stony tracts, with a very gradual fall to a level of about 560 metres at
the edge of the Merga depression.
Between Merga and Owenat the country consists of sandy plains
alternating with broken stony ground and occasional hills. The general
level rises from about 570 metres on the northern side of the Merga
depression to nearly 800 metres on the parallel of 20° 30′, then
gradually falls to about 600 metres at the foot of Gebel Owenat.
1. _Did the Nile, or a Branch of it, ever flow through the Libyan Desert
to the Mediterranean?_
The idea that a “dry river” exists in the Libyan Desert is a very old
one, and seems to have had its origin in the fact that barren
depressions in that region are sometimes called by the local Arabs _Bahr
bela ma_, that is, “sea without water.” But the Arabic word _bahr_,
which properly means a sea or a lake, as in Bahr Lot (the Dead Sea), is
also applied in Egypt and the Sudan to a river, as in Bahr el Nil (the
Nile) and Bahr el Azrak (the Blue Nile).[5]
The earliest depression to be discovered bearing the name of _Bahr bela
ma_ was the one now known as the Wadi Faregh (the “empty wadi”),
situated immediately south of the Wadi Natrun. Father Sicard, who
visited the place in 1712, correctly interpreted the Arabic name to mean
literally “sea without water,” and having discovered fossil trees there,
which he imagined to be the petrified remains of masts of ships, he
inferred that a narrow arm of the sea formerly extended from the
Mediterranean into the locality.[6] At a later date Sicard’s view that
the petrified trees were the masts of ships was recognized to be a
mistaken one; but a greater error was committed by changing the
translation of _Bahr bela ma_ from “sea without water” into “river
without water,” as was done by D’Anville in his ‘Mémoires sur l’Egypte,’
published at Paris in 1766. D’Anville was a great authority in his day,
and his translation was adopted by subsequent writers for over a hundred
years. General Andreossi, who commanded Napoleon’s artillery in the
expedition of 1798 and 1799, made a map of the “Dry River” and the
“Valley of the Natron Lakes,” in which both depressions are shown open
at both ends, instead of being closed in as they really are. Andreossi
considered that the “Bahr bela ma” was the dry bed of an ancient branch
of the Nile, which left the present Nile Valley somewhere in Middle
Egypt and entered the sea to the west of Alexandria; he also thought
that the ancient Lake Moeris was probably formed by the damming of the
“dry river” near its supposed offtake from the Nile.[7] Later on, after
Cailliaud and other early nineteenth-century travellers had discovered
that other depressions existed in widely separated localities and bore
the same Arabic name of _Bahr bela ma_, it seems to have been hastily
assumed by the cartographers of the time that all the depressions
bearing the same name were parts of a single dried-up river-channel.
Thus, on a large map of Egypt compiled by Colonel Lapin and published at
Paris in 1856, the “Bahar Belah-mah ou Fleuve sans eau” is stated to
come from the Congo and is depicted as coursing through the Oasis of
Dakhla, thence passing to the east of Baharia Oasis and on to the
Mediterranean. On another large map of Egypt, compiled by Muzzi Bey, the
then Director-General of Egyptian Posts, and published in Florence in
1876, a continuous valley is boldly shown leading from the mountains of
Darfur to the Mediterranean, while cross-valleys, labelled “Old Bed of
the Nile,” are depicted as connecting the main valley with that of the
Nile at Korosko and Dongola.
The Rohlfs expedition of 1874 proved that there was no such channel
running northwards through Dakhla Oasis; that the “Bahr bela ma” which
had been crossed by Cailliaud between Siwa and Baharia was merely a
closed-in local depression, and that the continuous empty river-beds
which were shown on the maps of that period had no real existence.[8]
But though the continuous “Bahr bela ma” channel of the old
cartographers has been shown to be purely imaginary, and has in
consequence disappeared from our modern maps, the belief that an old dry
river-bed _may_ exist _somewhere_ in the Libyan Desert has apparently
persisted in many minds even to our own day. Only a few years ago I was
called upon by the Government to discuss a suggestion, made in all
seriousness by a person of considerable eminence, that the Nile, or a
branch of it, must at one time have followed a course from somewhere
near Dongola through some of the Egyptian oases to the Mediterranean;
and that by tracing out the old channel, and deepening it artificially
where necessary, a part of the river might be taken off along this path
and its water utilized to irrigate the desert country on either side of
it. To the few scientific travellers who have journeyed extensively in
the Libyan Desert, it will doubtless appear incredible that such a
suggestion as this could be seriously made. But old traditions
concerning the geography of little-known regions die hard, and this
particular one has probably been fostered by the circumstance that on
most small-scale maps the oasis-depressions have been shown without any
precise indication of the altitude of the intervening ground, as well as
by the speculations of geologists as to the existence of a river in the
region in past geological ages. Blanckenhorn, for instance, published in
1902 a series of small-scale maps depicting the course of a hypothetical
river, the “Libyan Ur-Nile,” running northwards through the desert in
the Eocene and Oligocene periods, and ceasing to exist in the
Pliocene.[9]
That a river flowed during late Eocene or early Oligocene times in a
north-easterly direction through what is now the Libyan Desert, and
entered a sea near what is now the Faiyum, can scarcely be questioned;
for it is only by the existence of such a river that we can account for
the assemblage of fossil trees and curious remains of Eocene animals
(including the ancestors of the elephant) discovered by Mr. Beadnell
north of the Birket el Qarun and described by the late Dr. Andrews.[10]
As to the size, length, and exact position of this river of the
geological past there is very great doubt; but neither its situation nor
even its existence can be considered material to our present inquiry. No
one conversant with the known facts bearing on the general geological
history of Egypt during late Tertiary and Quaternary times could make
the mistake of thinking that the path of an Eocene river might be
traceable in the present desert relief. The evidences of such path must
be purely of a geological nature. In his endeavours to suggest what
might possibly have been the course of the river on whose banks the
Eocene animals lived, Mr. Beadnell found in two localities deposits
which might have been formed along the ancient drainage-line; and in
both these localities the deposits now occupy the summits of hills.
There is insufficient evidence of any kind to justify so exact a
location of the Eocene river as Blanckenhorn’s maps would suggest, and
none whatever of any relationship, either between the present surface-
configuration of the desert and Eocene or Oligocene drainage-lines, or
between those drainage-lines and the River Nile. The appellation “Ur-
Nile” of Blanckenhorn is thus a misleading one. If we are to look for
traces of a dried-up river in the surface-forms of the Libyan Desert of
to-day, it must be a river which, like the streams which eroded the
great wadis of the Eastern Desert, existed in geologically recent times,
and which became dry either through the continual deepening of the
present Nile-channel, with consequent capturing of the former drainage,
or through climatic changes causing a diminution of rainfall in the
collecting area.
A study of the contoured map seems to me to be absolutely conclusive on
the question at issue, for it indicates clearly that at no time within
the geologically recent period can there have been any such continuous
channel as has been supposed. Let us try and trace, with the aid of the
map, the most likely course along which the ancient Libyan Nile-branch,
if ever one existed, must have flowed. Starting from the Nile in the
neighbourhood of Dongola, we observe that the lowest possible track is
through Sheb towards Kharga. But Sheb can only be reached after passing
over some 350 kilometres of desert lying well above the level of the
Nile at Dongola, which is about 230 metres above sea. It is, of course,
quite conceivable that even within geologically recent times the Nile at
Dongola may have been considerably above its present level; so that we
may pass over this first difficulty as not being definitely conclusive
against the hypothesis we are pursuing. From Sheb to the south end of
the Kharga depression there is a drop of about 160 metres, so that up to
this point a channel may have been possible. But from here onwards,
difficulties come in. If we turn northwards, we soon encounter the north
wall of Kharga, rising to 300 metres above sea-level; so there is no
continuing that way. Instead, we turn westwards towards Dakhla. But from
Kharga we have to pass over ground reaching very nearly to the 200-metre
contour for some 80 kilometres to enter the Dakhla depression, where we
drop to a level of 119 metres. We have to traverse some 15 kilometres at
altitudes above 200 metres to reach Abu Mungar, where the level is 117
metres; then a further 12 kilometres lying above the 200-metre contour
to get to Farafra, where the level descends to about 90 metres. To get
out of Farafra, we have again to traverse country lying over 200 metres
above sea, whether we choose a north-westerly route _viâ_ Sittra to the
Qattara depression, or a north-westerly one _viâ_ Baharia to the Wadi
Rayan and the Faiyum. Taking the first of these alternatives as being
the shorter, we cross some 30 kilometres of ground above the 200-metre
level, and a further 120 kilometres lying between the 200- and 100-metre
contours, before reaching the Qattara depression. And once we are in the
Qattara depression (the lowest point of which is 134 metres below sea),
there is no possibility of reaching the Mediterranean except by crossing
a considerable tract where the ground-level is over 100 metres above
sea-level.
A section of the route described, with a comparison-line passing through
the present Nile-levels in corresponding latitudes, is shown in the
figure below:
[Illustration: _Profile from the Nile at Dongola through the depressions
of Kharga, Dakhla, Abu Mungar, Farafra, and Qattara to the
Mediterranean. Vertical scale 500 times the horizontal. Total length of
section about 1700 kilometres; for more than half this distance the
ground-level is seen to be above a line drawn through the levels of the
Nile in corresponding latitudes._]
Can any one believe that a course of this kind was ever that of a river?
To make a through channel would entail deep cutting for more than half
the total distance of 1700 kilometres, and would consequently involve
excavating hundreds of millions of cubic metres of rock, much of it of
considerable hardness. Moreover, it cannot be supposed, in the present
state of our knowledge of the region, that more favourable lines of
communication exist and have been overlooked. Many depressions doubtless
still remain to be discovered; but these, like those already known, will
surely prove to be merely local basins. So many cross-country journeys
have now been made in various directions through the desert, that it is
inconceivable that any continuous channel of the kind we are discussing
could possibly have escaped notice. Nor can we reasonably suppose that
recent earth-movements have produced the present severance of the
various depressions; such movements might perhaps be invoked to account
for one or two of the separating elevations, but certainly not for all.
We can therefore be absolutely certain that neither the Nile nor any
branch of it ever passed through the Libyan Desert to the sea.[11]
Even channels of tributary streams to the Nile, such as abundantly
survive in the great wadis which enter the Nile valley on its eastern
side, are markedly absent in the Libyan Desert. The contours on the map
suggest that possibly one such tributary stream may formerly have
drained the south-western faces of the great plateau in which the
depressions of Dakhla and Kharga form bays, and have entered the Nile
somewhere between Aswan and Halfa; but if such a channel ever did exist,
its actual traces have long since been obliterated by the smoothing
action of subsequent denudation, and only the great escarpment of the
plateau which it half encircled remains to tell the tale.
_Photographs by Prince Kemal el Din, Dr. Ball, and Mr. Walpole_
[Illustration: 1. _Desert exploration with the ordinary car, requiring
help even on flat ground in sandy tracts_]
[Illustration: 2. _Caterpillar cars carrying heavy loads over a sand-
dune between Bir Terfawi and Gebel Owenat_]
[Illustration: 3. _The western wall of the Qattara depression 35 km.
S.S.W. of Qara Oasis. Top of cliff about 3 m. and floor of depression
133 m. below sea-level_]
[Illustration: 4. _Ain el Hez, Baharia Oasis, irrigated by free flow
from well_]
[Illustration: 5. _Overlooking the Baharia depression from the pass at
its southern end: cars bound for Farafra_]
[Illustration: 6. _Northern end of Farafra depression: sandy ravine
cutting back into chalk plateau_]
2. _Origin of the Depressions._
It is a marked characteristic of almost all true deserts, that they are
regions of internal drainage; and the Libyan Desert is no exception to
the rule. There are a few gullies draining from the plateau to the sea
along its northern edge, and a few others draining into the Nile Valley
along its eastern border. But none of these external drainage-lines
extends for more than an insignificant distance backward into the
interior of the country. There is, in fact, in the Libyan Desert
(especially in its north-eastern portion) a marked absence of any
distinct drainage-lines at all; in their place we find extensive stony
plains, which either slope gradually down towards the various inland
depressions, or terminate in an abrupt fall where the depressions are
cut back into them. Even in the Pluvial epoch, when Europe was glaciated
and the deep wadis of the Eastern Desert on either side of the Nile were
being cut out by great streams, there cannot have been any external
drainage from a large part of the Libyan Desert; for if there had been,
we should find the Libyan plateau far more intensely dissected than is
actually the case. The rainfall in this region, even during the Pluvial
period, must have been far smaller than in the neighbouring tracts of
the Eastern Desert and Sinai; such rainfall as did occur was drained
into the series of depressions already described, and there either
formed lakes or was evaporated. But the action of inflowing drainage
waters, carrying sand and mud in suspension and salts in solution, is
not to _deepen_ the basins into which they flow, but rather to _fill
them up_. Hence we must look to some other cause for the formation of
the basins themselves. A possible cause is to be found in earth-
movements—either a local down-folding of the crust, or an upraising by
faulting of the surrounding tracts. It is not unlikely that such earth-
movements have to some extent conditioned the formation of the
depressions; but that the depressions are not simply faulted-down areas
or subsidences is abundantly clear from an examination of the bounding
scarps and the floors of the larger oases. Baharia is wholly, and Kharga
and Dakhla are partially, bounded by high escarpments, in many places
hundreds of metres high, and the floors of these oases are composed of
the same rocks as are exposed at the base of the bounding escarpments.
It is, in fact, obvious that these great hollows are natural
_excavations_, not subsidences. What was the excavating agency?
To the south-west of the limestone plateau which lies west of the Nile
and extends northwards from lat. 23° 30′ there is fairly open sandstone
country, and the oases of Dakhla and Kharga occupy great bays in the
escarpment which marks the south-west termination of the plateau. It
seems reasonable to suppose that the Eocene and Cretaceous seas had
their southern shores somewhere about the latitude of Wadi Halfa, for
the limestones do not extend far beyond the tropic; and to the south the
hard limestones of the plateau probably passed gradually into softer
shallow-water deposits, which would lend themselves easily to
degradation and to removal by the agency of streams whose traces have
long since disappeared. We can thus possibly invoke water-action to
account for the primitive formation of the “bays” in which Kharga and
Dakhla are situated. But we cannot in this way explain either the
further deepening of these oases, which converted them into basins, or
the excavation of the more northerly depressions such as Baharia and
Qattara.
The problem as to how the excavation of the northern depressions, and
the deepening of the southern ones, were accomplished is not altogether
an easy one. There is, of course, no doubt that wind has been the main
excavating agency. All the depressions occur in areas where soft rocks
are overlain by hard ones, and once the hard overlying rock was removed
at any place, the action of the wind on the softer beds would soon
excavate a hollow. The difficulty is only as to how the hard overlying
rock was first removed. To some who have studied the question, a
sufficient explanation is to be found in the general degradation,
combined with the tectonic disturbances—folds and faults—which are known
to have affected some of the oasis-areas, as, for instance, that of
Baharia. Given an anticlinal fold, a general lowering of the surface by
wind-degradation would eventually result in the exposure of the soft
underlying beds at the highest point of the fold, and subsequently
continued wind-erosion would proceed most rapidly on these soft
underlying rocks. Others, while admitting this explanation as partly
accounting for the formation of the depressions, consider that other
factors must have assisted to cause penetration of the hard overlying
beds, especially in the areas where folding is not very marked.
Of such other factors, I can only suggest what appears to me to be a
possible one. About twenty years ago I was mapping the Mediterranean
coastal area in the neighbourhood of Mersa Matruh, some 160 miles to the
west of Alexandria. In this area, which has about 6 inches of rainfall
in an average year, there are numerous closed-in basins a few miles long
and a few hundred yards in width, descending to a depth of 10 metres or
more in the rather soft limestone which forms the principal rock of the
locality. These basins, though called wadis on the maps, are more
usually known as _’ebs_ or “bosoms” by the local Arabs. I was at first
much puzzled to account for them; but eventually I arrived at what I
believe to be the true explanation of their formation. The basins, of
course, collect the surrounding rainfall in the winter, and the drainage
carries with it into the hollows a certain amount of fine loam and sand
from the disintegration of the surrounding surfaces. After the rains,
the bottoms of the basins become covered with vegetation, while the
surrounding rocky surfaces are left bare. In the hot dry summer,
however, the vegetation perishes, and much of the loam is removed by the
wind. We have only to assume (what seems indeed likely) that the
rootlets of the vegetation disintegrate the limestone floors of the
hollows to form fresh soil, and that more of this is removed each year
by the wind than is brought into the hollows by the drainage, to find an
adequate cause for a slow but progressive deepening of the basins. The
primitive hollow may well be a very slight depression of the surface,
such as might arise from greater local softness of the rock and
consequent more rapid weathering. Once vegetation has commenced to grow
in a slight hollow of this kind, the action would lead to a slow yet
steadily progressive deepening year by year, and sand-erosion would tend
towards an elongation of the depression in the direction of the
prevailing wind. Can such a process as this, continued through vast ages
during which the climate was somewhat less dry than at present, have
been active in the formation of Baharia and similar depressions?
3. _The Possibility of Utilization of Depressions in the Libyan Desert
for Irrigation, Drainage, or Hydraulic Power._
The depression known as the Wadi Rayan, discovered by Mr. Cope
Whitehouse about 1883, situated some 40 kilometres west of the Nile
Valley and about 100 kilometres south of the latitude of Cairo, has been
so frequently described and considered in regard to its utilization as a
reservoir or as a flood-protection for Lower Egypt, that I need say
little about it beyond a reference to the principal published works
dealing with it.[12] There is no other depression in the Libyan Desert
which has received so much attention from the economic standpoint. That
the Wadi Rayan has not already been utilized as a reservoir has depended
on a variety of considerations, of which one of the principal has been
the doubts always entertained as to whether there might not be an
underground leakage from it, resulting not only in a loss of part of the
stored water, but also in damage to the adjacent flourishing province of
the Faiyum. These doubts will not be lessened by the converging lines of
evidence which I shall bring forward in dealing with the artesian water-
supplies, all leading to the conclusion that there is an underground
water-connection between the various depressions of the Egyptian Libyan
Desert. Of late years, however, it has been proposed to make use of the
Wadi Rayan, not as a reservoir, but as a sump for disposing of the
drainage water of Upper Egypt by evaporation; and to this, in
consequence of the lower level at which the water would stand in the
depression, there is far less objection from the point of view of
possible leakage or damage to the Faiyum.
The Wadi Natrun, which, though considerably less deep, is not greatly
less in extent than the Wadi Rayan, has received some consideration as a
possible sump for disposing of some of the drainage water of the Behera
Province of the Delta. So long ago as 1895 the Public Works Department
studied the possibility of draining Lake Mariut into the Wadi Natrun,
and thus doing away with the increasing cost of keeping down the level
of the lake by pumping water from it into the sea.[13] The Wadi Natrun
has an area, even at the low contour of 10 metres below sea-level, of
nearly 100 square kilometres, and the average rate of evaporation from
an open water-surface within it could not well be much less than 3 mm.
per day; the wadi could therefore dispose annually of at least 100
million cubic metres of drainage water by evaporation alone, and
probably of a considerable additional quantity by seepage. But the high
cost of cutting a drainage channel from Lake Mariut to the wadi, and the
heavy maintenance charges which would be incurred in keeping the drain
open, were formidable objections to the scheme. From a reconnaissance
carried out in 1896, Mr. Verschoyle found that the length of the
proposed drain would have to be almost 80 kilometres, and for the
greater part of the way it would have to be a cutting 20 metres in depth
through desert and ridges of drifting sand; he remarked that if it were
an easy matter to make the connection, it would be no easy matter to
maintain it; and he concluded that the scheme was an impracticable
one.[14] A more recent proposal has been to construct a partly tunnelled
channel instead of an open drain; but this has likewise been found to be
impracticable, as involving too heavy an outlay for the benefits which
would result.[15]
[Illustration: 7. _Qasr Farafra, seen from the north over plain of
powdery chalk forming floor of depression_]
[Illustration: 8. _Escarpment and “Hattia” of Abu Mungar from the
south_]
[Illustration: 9. _The “Hattia” of Abu Mungar from the east: well on
earth-mound on right_]
[Illustration: 10. _The principal well at Qasr Farafra_]
[Illustration: 11. _A street in Qasr Farafra, with irrigation canal_]
When the great extent and depth of the Qattara depression were
established by Mr. Walpole’s explorations of last year, hopes were
immediately entertained that the depression might be made to serve some
useful economic purpose. Any idea of its being of use as a Nile
reservoir was of course at once cut out, not only by reason of its
position and distance from the Nile, but also by its immense size; for
even if we could turn the whole Nile flood into it, some twenty years or
more would be occupied in filling it to a sufficiently high level,[16]
and the loss by evaporation from so large an area would be enormous. As
a receptacle for drainage water from the Delta it appeared equally
impossible of consideration, because of the great length and depth of
the channels which would have to be cut to reach it. A more reasonable
prospect seemed to be that of admitting sea-water from the Mediterranean
into it by means of a navigable canal from the Arabs Gulf; this would
only have to be about 56 kilometres in length to reach the nearest point
of the depression; and once the canal was made and the depression
filled, ships might sail almost to Siwa. Other advantages which might
accrue from the formation of this inland sea were an increased humidity
of the climate along the Mediterranean Littoral of Egypt, leading to
increased rain-crops in that region, the establishment of a valuable
fishery, and a possible increase in the water-supply of the oases by the
causing of a slight rise in the static water-level there. Another idea,
which rapidly followed the first one, was to utilize the depression as a
source of electrical power for driving pumps by which the drainage of
the northern parts of the Nile Delta might be improved. At first sight
this latter prospect looked a very attractive one. The salt-marsh which
covers much of the floor of the depression appeared suggestive of a
former sea-connection, and if we could trace out this old connection,
the cutting of a canal along it might not, it was thought, be a very
expensive matter. Moreover, it was apparent that evaporation from an
inland sea or lake of so large an area would keep pace with quite a
large influx from the Mediterranean, so that if the influx were
restricted to such a quantity as would permit of the lake-surface being
maintained at a level considerably below that of the Mediterranean,
power could be generated continuously. Suppose, for instance, that we
maintained a permanent water-level in the lake of 50 metres below the
sea; the estimated area of the lake at this level being 9000 square
kilometres and the mean evaporation assumed to be 4 millimetres a day,
an influx of no less than 36 million cubic metres of water per day could
be passed into the lake without altering its level, and this with a fall
of 50 metres would suffice theoretically for the continuous generation
of over 270,000 horse-power. Of course the lake would gradually get more
and more saline, but the power might continue to be maintained for very
many years before the lake became as rich in salt as the Dead Sea.
But alas! an investigation of the northern borders of the depression
showed that the hoped-for traces of a former connection with the
Mediterranean Sea do not exist. The depression is entirely shut in from
the north, either by great cliffs, or by ground lying so high that the
cutting of a canal to the sea is utterly impracticable. Of the 56½
kilometres from the sea-level contour of the depression to the coast
along a line running 12° east of north from Moghara Lake (which is the
easiest line hitherto found for the cutting of a canal), only 16
kilometres are at less than 50 metres above sea; 31 kilometres lie at
altitudes between 50 and 100 metres; and 9½ kilometres are above the
100-metre level. An open channel being thus put out of the question, it
was next natural to inquire whether a tunnel, or a channel partly open
and partly tunnelled, could be excavated to serve for the conveyance of
sea-water into the depression. But even this, though perhaps not
impracticable, would be a very costly undertaking. The conveyance of the
requisite quantity of water, even at a relatively high velocity (which
of course implies a considerable slope), would necessitate a tunnel or
tunnels of very large dimensions. To convey 36 million cubic metres a
day at a velocity of 5 kilometres per hour would require a sectional
area of 300 square metres—_i.e._ if two tunnels were made, each would
have to be 14 metres in diameter. The cost of boring and lining such
tunnels would certainly be very great, and it is doubtful whether the
value of the power generated could justify the capital expenditure
involved in the excavation and other works which would be necessary.
Until more is known of the nature of the strata through which the
aqueduct would have to pass, and as to the length of tunnelling and
amount of open cutting which would be required, it is impossible to form
even an approximate estimate of the expense which the undertaking would
involve. All that can be said at present is that the utilization of the
Qattara Depression offers a possible means of obtaining power on a large
scale for the drainage of the low-lying lands of the Delta, with at the
same time a prospect of improving in some measure the agricultural
resources of the Mediterranean Littoral; much further investigation will
have to be accomplished before any judgment can be formed as to whether
such a project would be an economically sound one.
In formulating any scheme for improving the drainage of the Delta, it is
of course important to consider, not only the manner in which the
drainage water could be ultimately disposed of, but also the
modifications which would have to be made in the existing drains and
irrigation canals—modifications which would need to be carried out
without serious interruption to existing agriculture. A scheme which
otherwise appeared attractive might easily prove to be impracticable by
reason of the heavy expenses and inconveniences of the subsidiary works
which would be required to make it effective.
[Illustration: THE LIBYAN DESERT Showing Surface-Relief, Contours of
Static Underground Water-levels, Distribution of Sand-dunes, and Routes
of Principal Exploratory Expeditions in the West and South by Dr. JOHN
BALL
THE GEOGRAPHICAL JOURNAL JULY 1927]
4. _The Artesian Water Supplies._