ABSTRACT
Morphometric
analysis and flash floods assessment were conducted for the watersheds of Ras
En Naqb escarpment, south Jordan. The study area comprises of twelve small
watersheds occupying the faulted-erosional slopes, and the dip slopes. The
drainage network shows that dendritic and sub-dendritic patterns dominated the
dip slopes, whereas trellis pattern characterized the faulted-erosional
slopes. Stream orders range from fourth to sixth order. The mean bifurcation
ratios vary between 4.2 and 5.38 for the dip slope basins, and between 3.5 and
5.0 for the faulted-erosional slope watersheds, indicating a noticeable
influence of structural disturbances (i.e.,
faulting and uplifting), and rejuvenation of drainage networks. All watersheds
have short basin lengths, ranging from 23.8 km to 42.2 km for the dip slope
basins, and between 15.3 km and 45.4 km for the faulted-erosional slope
catchments. This is indicative of high flooding susceptibility associated with
heavy rainstorms of short duration. The circularity ratios range from 0.177 to
0.704 which denote that the catchments are moderately circular on the
faulted-erosional slopes, and to some extent elongated on the dip slopes. The
length of overland flow values ranges from 0.854 to 0.924 for the dip slope
catchments, whereas LO values for the faulted-erosional slopes vary
from 0.793 to 0.945 denoting steep slopes and shorter paths on both dip slope
and faulted-erosional slope watersheds. Values of stream frequency range from
1.509 to 1.692 for the dip slope, and from 1.688 to 2.0 for the
faulted-erosional slope catchments. FS values are also indicative of
slope steepness, low infiltration rate, and high flooding potential. The
watersheds of the dip slopes show lower values of form factor varying from
0.079 to 0.364, indicating elongated shape and suggesting a relatively flat hydrograph
peak for longer duration. Similarly, values of Dd are high for
catchments on the dip slope basins (1.709 - 1.85) and the faulted-erosional
slope watersheds (1.587 - 2.0) indicating highly dissected topography, high
surface runoff, low infiltration rate, and consequently high flooding
potential. Furthermore, high relief values exist, ranging from 388 m to 714 m
for the dip slope basins, and from 421 m to 846 m for the faulted-erosional
slope catchments indicting high relief and steep slopes. Morphometric analysis,
and flash flood assessment suggest that ten watersheds (83.3%) are categorized
under high and intermediate flooding susceptibility, and the faulted-erosional
slope catchments are more hazardous in terms of flooding. Thus the protection
of Ma’an, El Jafr rural Bedouin settlements, and Amman-Aqaba highway from
recurrent flooding is essential to ensure sustainable future development in Ras
En Naqb-Ma’an area.