Simulation of downstream flooding due to an assumed breaching of the Bang Lang Dam, Thailand | |
| Author | Naris Sinthananopakhun |
| Call Number | AIT Thesis no. WA-91-12 |
| Subject(s) | Flood routing Dam failures--Thailand--Yala Bang Lang Dam |
| Note | A thesis submitted in partial fulfillment of the requirements for the Degree of Master in Engineering, School of Engineering and Technology |
| Publisher | Asian Institute of Technology |
| Abstract | The Bang Lang dam is an earth rockfilled darn built across the Pattani river in South Thailand. The dam is 40 m high and has a maximum storage capacity of 1,403 million m3 • The sudden flooding due to an assumed failure of Bang Lang dam is predicted by using two · computer models namely : dam breach erosion model and the MIKE-11 flood routing model. The dam breach erosion model predicts the enlargement of the dam breaching section considering two possible shapes of breaching, namely : trapezoidal and triangular. The erosion control coefficient of the model is determined from model calibration based on the breaching time of 2.5 hours according to the records of previous earth dam failure statistics. The flood routing downstream of the dam is carried out up to the river mouth at the sea over a distance of 110 km. Two methods of river channel and flood plain schematization are considered. In the first method so called the single reach model, the river and flood plain cross-sections are considered as a compound cross-section. In the second method so ·called the channel network model, the 'river channel and flood plain are represented by a channel network. The values of Manning n roughness coefficients used for flood routing are determined by trial and error model calibration based on the previous flood data in 1969 which is one of the largest flood in the river. After model calibration, the flood prediction is carried out using the computed dam breaching outflow hydrograph from the dam breach erosion model. The results of the prediction are presented in terms of the envelope of peak flood level, the arrival times of flood wave front and flood peak along the river. The channel network model gives a more accurate and more detail information of flooding condition. The results of the present study are compared with the results of the previous study by the Electricity Generating Authority of Thailand (EGA'I) in which the .BOSS-DAMBRK computer model is used. The comparison shows that the results are not significantly different. The discrepancy is due to the use of different values of Manning n and river cross-section geometry. Finally, it is concluded that the dam . break flood wave front will reach the Bannang Sata district which is 16 kilometers downstream from the dam in 1.5 hours after the dam breaching starts and will reach Y ala province, which is 72 kilometers downstream from the dam is 6.5 hours. The maximum flood depth of 59 m MSL will occur at Bannang Sara district at 5 hours after the dam breaching starts and the flooding duration in 26.5 hours. For Yala province, the maximum flood depth of 20 m MSL will occur at 12.5 hours after the dam breaching starts and the flooding duration is 25.5 hours. Sensitivity analysis of the erosivity coefficient of the dam breaching model and of the Manning n for river and flood plain is carried out to determine their effects on the computed flooding conditions. |
| Year | 1991 |
| Type | Thesis |
| School | School of Engineering and Technology (SET) |
| Department | Other Field of Studies (No Department) |
| Academic Program/FoS | Water Resources Research Engineering (WA) |
| Chairperson(s) | Tawatchai Tingsanchali |
| Examination Committee(s) | Gupta, Ashim Das ;Paudyal, Guna N. |
| Scholarship Donor(s) | The Government of Denmark |
| Degree | Thesis (M.Eng.) - Asian Institute of Technology, 1991 |