Optimal design of alluvial irrigation canal system with respect to aggradation and degradation | |
| Author | Lal, Narendra Kumar |
| Call Number | AIT Diss. no. WA-92-01 |
| Subject(s) | Sedimentation and deposition--Nepal Channels (Hydraulic engineering)--Nepal |
| Note | A dissertation submitted in partial fulfillment of the degree of Doctor of Engineering, School of Engineering and Technology |
| Publisher | Asian Institute of Technology |
| Series Statement | Dissertation ; no. WA-92-01 |
| Abstract | This study develops a new approach to design an alluvial channel considering varying discharges and sediment load. The Chatra main canal of the Sunsari Morang Irrigation Project in Nepal is considered as an example for application. The basic design variables considered are the bed width and bed slope of a trapezoidal channel given a fixed bank slope. Their values are I determined by a simulation optimization technique based on the minimum annual sediment deposition in the canal. The input variables in the design are the annual patterns of daily sediment concentration entering into the canal from the Kosi river and monthly irrigation demand for each set of design variables. The design also considers the effects of sediment removal through the sediment ejectors in the canal and sediment extraction at the canal intake. A morphological mathematical model is used to simulate the bed level changes for the given input variables and assumed bed width and slope of the irrigation canal including all types of structures. The model is developed on the basis of a simplified set of governing equations and non-equilibrium sediment transport formula. The calibration and verification of the model is carried out using the observed data of the Chatra main canal in 1985 and 1990 respectively. Good agreement between observed and calculated bed levels and the sediment deposition volume is found. The model is then used to evaluate the bed level changes in the Chatra main canal for varying entering sediment concentration. The expected annual volume of sediment deposited in and ejected out of each reach is calculated for various bed widths and bed slopes. A method of classifying the annual patterns of daily sediment concentration and determination of its probability of occurrence is presented. Five categories (so called classes) of annual pattern of daily sediment concentration and their probability of occurrence are determined for input to the design calculation. These five classes are determined based on the 80 years generated sediment concentration data calculated from the generated discharge data and a sediment concentration-discharge relationship. The 80 years generated discharge data is obtained from a data generation model developed by using the observed discharge data of 17 years (1960- 1976) while the sediment concentration-discharge relationship is developed by using the observed data of 7 years (1970-76). Within the range of possible variation of bed slope used in the simulation for optimization of the Chatra main canal geometry, it is found that the bed slope effect is not significant in reducing the annual sediment deposition volume. On the other hand, the bed width has a remarkable effect in reducing sediment deposition in the canal. A narrower and deeper canal - ii - would have less deposition compared to a wider and shallower canal for the same annual flow and sediment concentration input condition. The effect of the reduction of sediment concentration at the intake from the river using a sediment removing device is also studied. The results show that the bed width reduction would not be necessary if the entering sediment concentration is equal to or less than 20 % of the river sediment concentration. However, the effect of bed width reduction becomes more significant in reducing the sediment deposition when the percentage of sediment concentration entering into the canal is increased above 20%. According to the results of design, recommendations on the modification of the irrigation canal cross-sections and sediment extracting devices are given. |
| Year | 1992 |
| Corresponding Series Added Entry | Asian Institute of Technology. Dissertation ; no. WA-92-01 |
| 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) | Tawatchai Tingsanchali ; |
| Examination Committee(s) | Harboe, Ricardo ;Paudyal, Guna N. ;Worsak Kanok-Nukulchai ;Plate, -Ing. Eric ; |
| Scholarship Donor(s) | Government of Australia. ; |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 1992 |