Mohammad Albishi, Jarbou Bahrawi and Amro Elfeki (2016). Derivation of the Unit Hydrograph of Allith Basin in the South West of Saudi Arabia. 7 International Conference on Water Resources and the Arid Environments (ICWRAE 7): 621-628 4-6 December 2016, Riyadh, Saudi Arabia. Abstract: Most studies on unit hydrograph theory is developed for temperate regions and to the best of the authors’ knowledge, there is no studies on this topic in arid regions because of the lack of runoff measurements. This paper presents the derivation of a unit hydrograph of a Allith basin and its S-curve in the south western part of Saudi Arabia to be used to predict flash flood more accurately in this region. The derivation is based on the method of stream flow data that has been collected from measured rainfall and runoff storms in the region. The study resulted in the unit hydrograph of 1 hr duration and the S-curve that is used to transfer the hydrograph to any other durations. This unit hydrograph can be used to predict flash floods in Allith basin and similar watersheds.

1. Derivation of Unit Hydrograph of Allith basin in South-
West of Saudi Arabia
By: Mohammad Abdullah Al-Bishi (maalbeshi@kau.edu.sa)
Prof. Amro Mohamed Elfeki (aelfeki@kau.edu.sa)
Dr. Jarbou Abdullah Bahrawi (jbahrawi@kau.edu.sa)

2. Outlines
• Introduction to the problem.
• Objective.
• Literature Review.
• Study Area & Data collection.
• Methodology.
• Results and Discussions.
• Conclusions.
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3. Introduction to the problem
Most studies on unit hydrograph theory is
developed for temperate regions and to the best
of the authors’ knowledge, there is no studies on
this topic in arid regions because of the lack of
runoff measurements.
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4. Objective
The main objective of this paper is to derive a
unit hydrograph from stream flow data.
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5. Literature Review
The basic ways to derive unit hydrograph:
- Using stream flow data.
- Synthetic methods.
- Statistical distribution methods.
- Geomorphological instantaneous unit hydrograph.
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6. Study Area
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7. Digital Elevation
Model (DEM) for
Allith basin
Properties of Allith Basin
3079.00km2Area
586.57kmPerimeter
113.00kmBasin Length
0.0232Basin Slope
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8. Data Collection
The data used in this study relied on reports from
Dams & Moore Co. (1984 - 1987).
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9. Methodology
• Storms selection:
– The hydrograph has a single peak.
– The flow caused by a connected excess rainstorm
without gaps.
– The rainstorm occurs after a dry period.
• Steps of deriving the unit hydrograph:
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10. Methodology cont.
1 2
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11. Methodology cont.
3
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12. Methodology cont.
Abstraction
4
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13. Methodology cont.
5
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14. Methodology cont.
6
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Hunt, B. (1985)
𝑄 = 𝑥 1 − 𝑒−𝑏𝑡

15. Results & Discussions
1) Station J-415:
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16. Results & Discussions cont.
1) Station J-415:
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17. Results & Discussions cont.
2) Station J-416:
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18. Results & Discussions cont.
2) Station J-416:
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19. Results & Discussions cont.
3) Station J-417:
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20. Results & Discussions cont.
3) Station J-417:
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21. Results & Discussions cont.
4) Unit hydrograph and S-curve for Al-Lith basin:
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22. Results & Discussions cont.
4) Unit hydrograph and S-curve for Al-Lith basin:
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23. Conclusions
This paper presents the application of the stream flow data
method to derive a unit hydrograph of a Allith basin and its S-
curve in the south western part of Saudi Arabia to be used to
predict flash flood more accurately in this region. Most studies
on unit hydrograph theory is developed for temperate regions and
to the best of the authors’ knowledge, there is no studies on this
topic in arid regions. The study resulted in unit hydrograph of 1-
hr duration and the S-curve that is used to transfer the hydrograph
to any other duration. This unit hydrograph can be used to predict
flash floods in Allith basin and similar watersheds.
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