English abstract
Al-Khoud dam, like many other dams in the world, face siltation problem. Siltation is
the accumulation of fine soil particles on the soil surface. This layer of accumulated
sediments reduces soil infiltration rates. The soil particles are carried with sediment rich flash floods after rainfall events. To combat this layer, the responsible authority
in Oman removes the silt layer by mechanical scraping. However, this process is
tedious, costly, and requires action after each flash flood. Moreover, the scrapping
process does not solve the problem completely. That's because the saturated hydraulic
conductivity of the dams' original coarse matrix is already reduced. This reduction is
caused by clogging of large pores of the subsoils by fine sediments. Fine sediments
migrate and translocate from the soil suspension into large pores in the soil matrix. In
addition, because of its fine texture, the silt layer stores water. The stored water either
evaporates or penetrates the deeper bottom soil layers of dam's reservoir. If the stored
water evaporates, it's considered as a loss. Moreover, stored water remains ponded for
longer time with the presence of silt layer. As a result, evaporation losses increase.
Therefore, another solution is required to mitigate this problem and reduce water loss
through evaporation and runoff. A suggested method is the cultivation of trees in the
dam area. Trees' roots create cracks in the soil. These cracks provide preferential
channels for water to seep through. In this study, Sidr trees are used as an infiltration inducing bioengineering in the Al-Khoud dam bed. Sidr tree was chosen because it's
an indigenous (in Oman and other Gulf countries) tree that can survive under heat
stress, water stress, and flooding. However, as a phreatophyte, Sidr trees in the dam
area use groundwater as their main water source. Therefore, the quantification of the
amount of water used by Sidr trees in the dam is required. This was done in the research
using the sap flow meter. For an optimal cultivation of Sidr trees in the dam bed, the
water balance in the dam should be evaluated. Based on the water balance in the dam
reservoir, some scenarios are suggested for the optimal number of cultivated Sidr trees
in the dam reservoir.
