Document Details
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Document Type |
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Thesis |
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Document Title |
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MODELLING OF FLASH FLOODS IN ARID REGIONS نمذجة الفيضانات الفجائية في المناطق الجافة |
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Subject |
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Faculty of Meteorology Environment and Arid Land Agriculture |
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Document Language |
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Arabic |
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Abstract |
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The impacts of flash floods are catastrophic and devastating. They can destroy anything that comes in their way and are mostly noticeable in arid regions. Therefore, arid regions are more susceptible to such devastating events. The purpose of this study is to assess and analyze the impacts of flash floods in arid regions from the hydraulic perspective that takes into account the understanding of the dynamic behavior of flash flood events. The objectives of this work are classified into two broad categories. One of the main objectives is to investigate a one dimension diffusive wave (1D DW) equation using the Hayami analytical solution and another main objective of this study is to investigate a two dimension (2D) DW equation based on the new stochastic approach; i.e. the stochastic random walk particle tracking (RWPT) technique.
This study is comprised of: (1) the development and generalization of the Hayami solution (Analytical solution) for a 1D diffusive flood wave (DFW) case, and (2) the development of the numerical algorithm for the simulation of a 2D DFW case using the RWPT.
A Hayami analytical solution for the propagation of a 1D diffusive flood wave is developed and generalized. This developed solution takes into account an additional term, known as the ‘Decay Coefficient’ which plays a significant role in the arid regions that can influence the shape and the peak of a flood hydrograph while passing in an ephemeral stream. The Hayami solution is generalized in the sense that it can handle any shape of the inflow storm hydrograph. Furthermore, a spreadsheet model of the developed and generalized Hayami solution referred as ‘SMHS’ is proposed and presented. The model takes an inflow flood hydrograph, comprising of ten unit floods (Pulses). It is tested on two Hayami examples that show identical results. Moreover, sensitivity analysis is performed for the selection of a number of pulses that can influence and sway the accuracy of the simulated results. Taking 10 pulses as a reference case, RMSE converges from 0.7 at one pulse to 0.03 at eight pulses. In addition, the flexibility and the significance of this model is proven by its application on the real field data of Yiba catchment, located in Saudi Arabia where the diffusion coefficient larger than 400 m^2/s shows the divergence of the RMSE and the values between 50 m^2/s and 400 m^2/s are the fair estimates.
The RWPT (a stochastic method) is used in this study for the solution of a 2D non-linear DW equation. The novelty of this approach has been discussed. In literature, the traditional deterministic numerical methods are usually applied for the investigation of a DFW studies. These numerical methods incurred different pitfalls; for instance, numerical diffusion and artificial oscillations that lead to instability issues. However, on the other hand, the stochastic methods are free from such pitfalls and add more realistic behavior to the transformation of the physical appearance of nature to the numerical equations. In the RWPT method, each particle carries a fixed amount of water volume. The superposition of the convective movement and the diffusive movement of these particles in the flow domain provide an analogy with the movement of a diffusive flood wave in the same flow domain and hence the solution of RWPT leads to the solution of a DW equation. The proposed model was first applied to a hypothetical urbanized city in order to assess its capabilities, behavior, and performance. The algorithm for the RWPT model is modified in phases. First, the algorithm is modified for handling the different shapes of hydrographs for a single pulse case. These different shapes are represented by different types of pulses. They are: (1) a pulse with an instantaneous duration, (2) a pulse with an infinite duration, and (3) a pulse with a finite duration. Then, the algorithm is further improved to handle any complex shape of inflow hydrographs, represented by a number of pulses having different strengths. The model is validated based on two approaches: (1) validation based on experimental data, and (2) validation based on the data of a real flood event. Both validations show that the model produces plausible and commendable results. It is also applied for modelling the flash flood event that occurred in Jeddah in 2009. The simulations produce reliable and convincing results. |
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Supervisor |
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Dr. Amro Elfeki |
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Thesis Type |
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Master Thesis |
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Publishing Year |
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1439 AH
2017 AD |
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Added Date |
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Tuesday, November 14, 2017 |
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Researchers
| كاشف نور مالك | Malik, Kashif Noor | Researcher | Master | |
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