| Author | Pornsak Suppataratarn |
| Call Number | AIT Diss. no. WA-90-02 |
| Subject(s) | Rivers--Mathematical models
|
| Note | A dissertation submitted in partial fulfillment of the requirements for
the degree of Doctor of Engineering, School of Engineering and Technology |
| Publisher | Asian Institute of Technology |
| Series Statement | Dissertation ; no. WA-90-02 |
| Abstract | The River Network model,a combination of the River model (dynamic
model) and the Cell-Link model (diffusion model) is capable of simulating both highly fluctuating flows in the rivers and slowly fluctuating
flows through the floodplains. Therefore, it is suitable to simulate
floods in deltaic regions such as the Chao Phraya delta, the Mekong
delta, the Ganges-Brahmaputra delta, etc.
The River model is basically formulated according to the one - dimensional de SAINT VENANT flow equation, the four-points implicit
finite difference scheme, and solved by the algorithm developed at SO- GREAH . The model has been firstly used to study various force terms of
momentum equation in the tidal reach of the Chao Phraya river and the
effect of the time weighting factor of the finite difference scheme.
The mod el has been further developed to incorporate t he effect of flow
interaction between the main channel and berm sections. The proposed
method to account for this effect provides correction for the overall
section discharge of the compound channel during the overbank flow
period. The Cell- Link model is based on the model formulated by
ZANOBETTI et al (1970). The River Network model has been successfully
applied to simulate flows for the Chao Phraya delta which covers an
area of 19,000 km . It is calibrated using the 1980 flood and then
verified with the 1983 flood. Good agreements between observed and
simulated water levels are obtained for both years. The model has further been applied to simulate the effect of 1980 flood on the present
diking system and assumed complete high dike along the rivers. Finally,
the mod el has been used to study the effects of flow interaction of the
rivers in the Chao Phraya delta.
(i) It is found that a breaking down of the momentum equation into
various force terms can explicitly identify the role of inertia term in
the flow equation. The local inertia force becomes significantly important during the peak water level period when the magnitude of pressure
and friction terms are small . Neglecting the local inertia term in the
computation of flow in the tidal reach will underestimate the peak water
levels, overestimate the reverse peak discharges and underestimate the
arrival time of the flood wave. For time weighting factor, 0 , of the
implicit finite difference scheme, it is found that by increasing this
factor , the peak and fluctuation of water levels and discharges become
lower.
(ii) The proposed formula for correcting the compound channel discharges
is found to be governed by depth, width and roughness but not longitudinal slope. The results of the simulation by incorporating the flow
interaction effect using the proposed formula show significant difference from those without the incorporated flow interaction.
(iii) The factors which are found to signifcantly effect the simulation
results of the Chao Phraya delta are the initial water levels in the
floodplains, Manning coefficient and gate operations. The role of floodplains in the study area is found to be very important in governing the
flood conditions and be a very effective natural measure in reducing
flood level in the river. The present diking alters slightly the 1980
flood conditions in the Chao Phraya river. However flood conditions in
(ii)
the Thachin river are significantly changed. The assumed complete high
dike increases considerably flood levels in the rivers. Both diking
cases can effectively reduce water levels in the floodplains. Finally by
incorporating the flow interactions be tween berm sections and main
channel in the mod el, the water level s and discharges in the Chao Phraya
delta is slightly changed for the 1980 flood, however water levels and
discharges in the Thachin river and adjacent area are significantly
reduced for the flood of 100 year rainfall. |
| Year | 1990 |
| Corresponding Series Added Entry | Asian Institute of Technology. Dissertation ; no. WA-90-02 |
| Type | Dissertation |
| School | School of Engineering and Technology |
| Department | Other Field of Studies (No Department) |
| Academic Program/FoS | Water Resources Research Engineering (WA) |
| Chairperson(s) | Suphat Vongvisessomjai; |
| Examination Committee(s) | Tawatchai Tingsanchali ;Gupta, Ashim Das ;Harboe, Ricardo ;Huynh, Ngoc Phien ;Vries, M. de ; |
| Scholarship Donor(s) | The Government of Japan; |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 1990 |