'THE GEOLOGY AND MINERAL RESOURCES OF DHUFAR PROVINCE, MUSCAT AND OMAN' [‎17r] (23/96)

2
9
RainfaUv and Run-off
stem of the
tial, judged
ranean flow
lied in the
Jr. Bertram
:rom about
, with two
wadi A seasonal or intermittent watercourse, or the valley in which it flows. from
Mughagha
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id another
are dry in
he pool of
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rtant wadi A seasonal or intermittent watercourse, or the valley in which it flows.
s’ Danka).
ich Hamm
a Thomas’
ed a large
not under
the wadi A seasonal or intermittent watercourse, or the valley in which it flows.
ire is an
shows the
i be called
> discover,
low a dry
dan wadi A seasonal or intermittent watercourse, or the valley in which it flows.
wadi A seasonal or intermittent watercourse, or the valley in which it flows. in
front of a
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it on the
ley opens
:h-flowing
ielow the
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i of over
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the scour
et camps
own their
15. There are no reliable rainfall records for the Qara high
lands, but it is estimated that the average rainfall is approximately
30 inches, falling mainly in the wet or monsoon period between
June and September. In the plains to the south, along the coast,
the rainfall is probably not more than 5 to 6 inches annually, again
restricted to the wet months, but in addition to rain the plains are
very subject to wet mists during the rainy weather. In the Qara
highlands a heavy dew is also to be reckoned with during the early
part of the winter months. North of the highlands and over the
drainage into the Qam Shaiba and onwards to the Nejd, the rainfall
is uncertain and I was given to understand that there might some
times be no rain for two or three years. While this o might be true
as regards the actual fall of rain on the ground surface, I find it very
difficult to believe that floods do not come down the wadi A seasonal or intermittent watercourse, or the valley in which it flows. courses
every year. The evidence of heavy floods is too clear to be mistaken,
and the fact that these wadis have their sources well up the northern
slopes of the A 1 Qutun makes it certain that they tap large volumes
of run-off rainfall from the rain-belt of the Jabal Qara.
16. It is difficult to assess what proportion of the rainfall
flows north, but assuming equality of precipitation on the A1 Qutun
(watershed) and the presence of deeper valleys into the mountains
from the south, my observations incline me to the view that, while
there is a considerable run-off to the north, the losses by evaporation
and actual percolation into the ground are greater on the northern
slopes. On the other hand, seeing that the limestones are almost
flat and full of joints and solution cracks and holes; and that the
slopes and hillsides carry grass or light forest, and also that the
valleys are deep and well into the highlands, large quantities of
water will sink into strata and re-appear as springs (that is without
very serious losses by evaporation and percolation). The percolating
water, by dissolving the limestone and enlarging the cracks and
subterranean channels, has converted the flat tops of the A1 Qutun
into a typical karstland. The emerging spring and seepage water
carries much carbonate of lime which is precipitated, as calcareous
tufa or travertine, in almost every southern valley. The Dahaq in
the Darbat wadi A seasonal or intermittent watercourse, or the valley in which it flows. is in fact a natural dam of tufa, and the valley
above it is now also filled up with this material.
Springs and Lakes or Khors
17. All the water-holes I saw in the Qarn Shaiba tract to the
north, except the spring under the cliff at Thenot camp, are pools
under dry waterfalls (and usually associated with caves). In flood
time the hollows must be well scoured, and indeed at the dry waterfall