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Modern Processes
Though precipitation and temperature have varied throughout antiquity (cf.
Bar-Matthews, et al., 1998; Courty, et al., 2001; and Wilkinson, 2003), annual
precipitation currently averages between 300 and 400 mm annually. During the
late 1990s and early 2000s droughts decreased annual amounts to around 200 mm.
As a result, the flow of Wadis al-Mujib and al-Hasa are reduced to little more
than a trickle during the summer, with the Wadi al-Karak being completely dry.
A 1989 model developed by Montgomery and Dietrich proposed that basins with a
low relief require a large source area for channel initiation. Their work also
found that all else being equal, drier regions tend to have larger source areas.
Their findings are consistent with what we find on the plateau.
The total source (i.e., catchment/basin) area draining into the three major
wadis is 9,306 km2.7 Wadis al-Mujib
and al-Hasa together draw from over 87% of the total basin area east of the Dead
Sea with their reach extending nearly 120 km across the highland and plateau
(MacDonald, 1973 and Natural Resources Authority of Jordan, 1987 in Salameh,
1997). The basin is drained through a combination of runoff flowing directly
into the canyons, an extensive network of ephemeral channels, and sapping.
 Runoff Processes
Odeh and Salameh (1996) suggest "Much of the hydrology and geomorphology of the
study area can be attributed to the thunderstorms of the upper watershed
hill slopes and the plateau to the east which often leads to sudden and
high magnitude flash floods, accelerating stream work. This is consistent with
the results found in other areas by Bandara (1974), Smith (1994), Thornes
(1994), Chorley (1957), and Rinaldo (1995).
Even though the overall tilt of the plateau is away from the general direction
of the drainage flow (i.e., away from the Dead Sea), the overall topography is
such that it directs runoff into the channel heads of the major wadis. This is
especially true for the southward reaching channel head of the Wadi al-Mujib.
Ephemeral Processes
In addition to precipitation draining directly into the major wadis, there is
also an extensive network of ephemeral channels that feed the major wadis during
pluvial events. Ephemeral channels are particularly well developed near the head
of Wadi al-Mujib. [Figure 8  ]
Sapping Processes
 Though the majority of precipitation, both past and present, has drained
directly into the major wadis through runoff processes, sapping appears to be
the dominant shaping force at work along the rim of the plateau (See Luo, et.
al., (1997) for a discussion of sapping processes along the western desert of
Egypt, and cf. Oberlander’s (1965) discussion on sapping in the Zagros
Highlands).8 Evidence for sapping processes on
the plateau can be found in the numerous theater-headed valleys that are found
all along the sides of the major wadis. Given the high incidence
of fractures along the many faults of the plateau, it is suggested that the
source of the seepage is the subsurface flow of water along fractures in the
bedrock (cf. Anderson, et. al., 1997). This conclusion is supported by the
findings of MacDonald and the Natural Resources Authority of Jordan. Their
research (reported by Salameh, 1997) found that fractures in the sandstone
aquifers are the principle conduits for the transport of subsurface flow across
the plateau.
Conclusion
The Karak Plateau provides an ideal case-study for observing hydrological
processes and their impact on the development and preservation of drainage
networks on uplifted features. The plateau exhibits both ancient and modern
landforms associated with drainage systems and their morphology. The courses of
the Plateau’s channels were defined millions of years ago during periods of
increased geological and tectonic activity. The magnitude and expanse of its
channel canyons is the product of oceanic and pluvial events driven by
fluctuations in climate beginning 100 million years ago and continuing today.
The Karak Plateau stands today as witness to the ancient past that carved and
shaped it; a witness that is preserved and sustained today by processes common
to nearly all physical environments (i.e., overland flow and sapping).
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