| Author | Nguyen Huu-Thoi |
| Call Number | AIT Diss. no.WA-94-01 |
| Subject(s) | Water use--Mekong River Delta (Vietnam and Cambodia)
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| Note | A dissertation submitted in partial fulfillment for the requirements of the degree of Doctor of Engineering, School of Engineering and Technology |
| Publisher | Asian Institute of Technology |
| Series Statement | Dissertation ; no. WA-94-01 |
| Abstract | This dissertation deals with the problem of water resources utilization in tidal areas. The main objective of the study is to develop the methodology of conducting the assessment of available water resources and integrating the use of these resources for agricultural development. Since the surface water system is under tidal effects and salinity intrusion, its hydrodynamic aspects are very important and are studied in detail in the present study. Three water resources; rain water, surface (river) water and ground water; are assessed and analyzed for their utilization in the agricultural development in the delta. A rainfall generation model in which the first order Markov chain with two states is employed has been developed to generate daily rainfall sequences that are used in the computation of crop water requirements. A new three-step approach has been developed to assess the surface water resources in tidal areas. The first step of this approach is to establish a mathematical hydrodynamic model to simulate the flow and salinity intrusion in the surface water system. Having successfully calibrated and verified, the developed hydrodynamic model is used in the second step to conduct a number of typical simulations with different boundary conditions in order to produce more data of the distribution of flow and water salinity in the river network. The simulated data of flow and water salinity at different locations in the river network are then decomposed into various harmonic constituents by means of harmonic analysis. Finally, the relationships between the boundary conditions and the tidal constituents obtained from harmonic analysis are established. Using these relationships, the harmonic parameters of flow and water salinity at a location under study can be determined under the different known boundary conditions and thus, the flow as well as water salinity at the location can be predicted much faster than using numerical hydrodynamic model. This enables to incorporate the hydrodynamic factors of the surface water system into the Water Resources Utilization Model (WARUM) which can be used for the purpose of water resources planning and management in tidal areas. The W ARUM has been developed to integrate the use of water resources available for agricultural development. The controllable factors considered in the W ARUM are crop types, cropping patterns, cropping schedules and water extraction from the rivers and I or aquifers while the objective is to maximize the total net benefit from agricultural production. In principle, the set-up problem can be formulated in dynamic programming context. It is, however, almost impossible to solve it by dynamic programming technique due to the curse of dimensionality. In this study, a procedure to solve the problem has been developed. Particular application of the present research is given to the Mekong delta in Viet Nam which is selected as a case study area. The results obtained from the analysis of rainfall show that the daily rainfall amounts on wet days can be fitted by the three-parameter lognormal distribution and thus, this distribution is used in the generation of daily rainfall sequences which are used in the computation of crop water requirements in the delta. Since the crop water requirements are not zero for most of periods in the rainy season, the irrigation is needed even forrainfed agricultural areas. The developed three-step approach has been successfully used to assess the surface water resources. The results obtained from the calibration and verification of the hydrodynamic model indicated that the one-dimensional model is applicable to reflect the flow and salinity intrusion in the Mekong delta. A clear picture on the characteristics of flow and salinity intrusion in the river system has been obtained. The functional relationship with total upstream discharge is found to be linear formean discharge, while exponential formean salinity. The relationships of amplitude and phase of each harmonic constituent are approximated to the power function of degree three. The results also show that the effects of changing mean downstream boundary water level on the salinity intrusion in the river system are less and the salinity intrusion in the Mekong is more severe than one in the Bas sac. A preliminary assessment of ground water resources in the Mekong delta indicates that the use of ground water for agricultural production is possible and the ground water can be used in the supplementary irrigation. The ground water for this purpose should be exploited from the Upper Pleistocene aquifer which is the most productive one. It is recommended that only the brackish ground water which is not suitable for domestic water supply but good enough for irrigation should be used for this purpose. The results obtained from the application of WARUM to the Mekong delta show that a higher total agricultural production as well as a higher cropping intensity compared to the present ones can be obtained under the proper water allocation. The results also reveal that the double and triple cropping are possible for number of subareas but not for all subareas in the delta. The results obtained from the sensitivity analysis show that a half-month period is sufficiently short to use in the developed model. They also reveal that the surf ace water resources play the most important role while the ground water resources can be used as supplementary ones in order to assure a stable agricultural production in the delta up to its potential. Another finding from the obtained results is that planting only rice in the delta is not the best strategy on agricultural development and the diversified agricultural production systems will result in a higher cropping intensity and better benefit. |
| Year | 1994 |
| Corresponding Series Added Entry | Asian Institute of Technology. Dissertation ; no. WA-94-01 |
| Type | Dissertation |
| School | School of Engineering and Technology |
| Department | Department of Civil and Infrastucture Engineering (DCIE) |
| Academic Program/FoS | Water Resources Research Engineering (WA) |
| Chairperson(s) | Gupta, Ashim Das; |
| Examination Committee(s) | Harboe, Ricardo;Suphat Vongvisessomjai;Huynh Ngoc Phien;Dam, J. C. van; |
| Scholarship Donor(s) | Division of Water Resources Engineering Asian Institute of Technology; |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 1994 |