Abstract:
Many arid region Wadi catchments are facing increasing water scarcity due to
the unsustainable human practises such as the over expansion of irrigated
agriculture and over exploitation of their groundwater aquifers.
The “Soil and Water Assessment Tool” (SWAT) model, which is a
comprehensive conceptual, semi-distributed watershed scale model, was
selected after a review of the hydrological processes occurring in arid region
catchments to simulate the hydrological processes of the Wadi Ham catchment
in northeast United Arab Emirates.
A sensitivity analysis conducted for SWAT for the total runoff, maximum runoff
and days of runoff showed that a DEM resolution of no more than 100 m should
be used for proper representation of such mountainous arid catchments. The
appropriate size of defined sub-basins was found to be about 18 km
2
. The
sensitivity analysis also demonstrated that the most sensitive parameters that
affect the ephemeral streamflow are mainly related to the soil and channel
properties of the catchment soil depth, soil available water capacity, soil bulk
density, soil clay percentage, soil curve number, baseflow recession constant
and channel effective hydraulic conductivity.
SWAT simulated the ephemeral streamflow in Wadi Ham acceptably. For the
calibration period of 1981 and 1982, the performance statistics for DRMS,
PBIAS, NSE and PEM were 1.10 m
3
/s, 27.12%, 0.78 and 0.80 respectively.
During the validation period between 1983 and 1988, the DRMS, PBIAS, NSE
and PEM were 0.93 m
3
/s, -27.30%, 0.57 and 0.70 respectively. SWAT showed
very plausible behaviour for reservoir sedimentation, plant growth, irrigation abstraction and groundwater recharge via the transmission losses mechanism.
However, SWAT was not able to adequately simulate the recharge from the
bottom of the recharge dam reservoir due to an inappropriate maximum
effective hydraulic conductivity defined by the model.
Two management scenarios were simulated. The first scenario related to the
construction of an additional dam upstream and its effect on sedimentation rate
in the main reservoir. The second scenario found that the recharge volumes
could be enhanced through the construction of a discharge inlet point into the
main stream channel for the treated wastewater from the principal town
upstream of the catchment.
The successful simulation of Wadi Ham represents the first use of SWAT in a
truly arid climate. This research has therefore established the feasibility of
using SWAT as a tool for integrated catchment modelling in arid region data-
poor Wadi catchments and to support improved water resources management
in this water stressed environment.
