C16

Assessment of Reservoir Sedimentation Induced by Extreme Flash Flood at Wadi System:
Case Study Asarrin Upstream dam, Oman

〇 Tahani AL-Harrasi, Sameh KANTOUSH, Tetsuya SUMI, Mohamed Saber

2019 and Aug. 2019 were conducted in order to study

INTRODUCTION
Sedimentation is the most serious environmental

the sedimentation issues and its impacts on theproblem in reservoirs management, especially in arid

reservoir capacity and identify the flash floods marks.

regions

withincreasing

extremeflashfloods.

Several procedures have been implemented; such as

Monitoring the sediments coming from upstream

sediments scale bars measurements, pedons to study

reaches of Wadi basins during the flash floods isthe vertical layers of sedimentation at the reservoir

extremely difficult and scarce in arid regions (Saber,and drone survey. The sedimentation volume at the2018). Huge quantity of sediments usually comes withreservoir along Wadi Mijlas was measured from thethe flash floods. Sediment quantities are controlled bysedimentation scale bars installed in the reservoir

serval factors, such as geological and topographicalbefore the dam constructions (Fig. 2).

features of the basins, along with the land uses andsoil types variability, as well as the intensity andfrequency of extreme rainfall. Therefore, the aim of
this study is to quantify the sediment yield andreservoir sedimentation in the upstream dam of Wadi
Mijlas in Oman (Fig. 1) by using field investigation
and remote sensing techniques, then to link thesediment yield with the discharge.
Fig.2 Sediments bars in the reservoir

Investigation of the morphological changes along
Wadi channels is required to understand the sedimentyield, transport and erodability at the basins. We have
tried to assess and investigate the depositions anderosions along Wadi channel using remote sensingtechniques.

Previous works in remote sensing

indicated that the DEM derived from Google Earth isrelatively as acceptable as DEMs from other sources.
Currently, several methods are available for obtaining
the elevation data. El-Ashmawy, (2016), proved thatFig.1 Study area, including dam locations

DATA AND METHODS
Four field surveys on Dec 2017, Sept 2018, Mar.

Google Earth elevation data can be used forinvestigation and preliminary studies with low costand acceptable accuracy.

Fig. 3 Erosion and deposition polygons showing areas of sediment reworked for the period between 2017 and 2019.

The change in elevation at any point during a period

Earth images (Fig.3).

of time (e.g. between i and j) can be calculated

The sediment volume calculated from the fieldaccording to Ghoshal (2010), using the following

measurements for the two last events between 2017

formula:and 2019, was about 5,667m3 (fig. 4), while theΔDi,j = DEMj − DEMi

(1)resulted volume from remote sensing method using

where ΔDi,j is the change in elevations between i

Eq.2, was 4,129m3 for the same two events which isand j. While the change in the sediment volume (ΔSi,j)around 75% of the observed volume. This study

can be calculated using the following formula:concluded that remote sensing method can give

ΔSi,j = [ΔDi,j] × [A]acceptable accuracy for calculating the sediment yield(2)

where A is the area of the reservoir.

and reservoir sedimentation in Arid regions.

In order to enhance the understanding of thesediments mechanism associated with rainfall andrunoff, the deposition and erosion was studied along
the Wadi channel.
RESULTS AND DISCUSSIONSThis study shows how remote sensing methods canbe used to quantitatively document the deposition anderosions in the channel morphology and the extent ofsediment reworking by extreme floods with an

Fig.4 Sediments bars in the reservoir

acceptable accuracy. The sedimentation volume at theREFERENCES

reservoir along Wadi Mijlas was calculated from theEl-Ashmawy, K.L., 2016. Investigation of theaccuracy of google earth elevation data. Artificial
Satellites, 51(3), pp.89-97.
Ghoshal, S., James, L.A., Singer, M.B. and Aalto, R.,
2010. Channel and floodplain change analysis
over a 100-year period: Lower Yuba River,California. Remote Sensing, 2(7), pp.1797-1825.
Saber, M., Ogiso, Y., Kantoush, S., Sumi,andAlharrasi, T., Reservoir Sedimentation in Arid
regions: Challenges, field investigation andSediment Transport Modelingsedimentation scale bars installed in the reservoir
before the dam construction. It was found that theestimated accumulative sedimentation volume from 9flash floods events over 8 years (From 2011 to 2019)is equal to 37,137 m3 at the Upstream Dam.
Volumetric analysis of the changes in sedimentdeposited and eroded in the period from 2017 to 2019was calculated from the derived DEM from Google