Determination of land slope and computtion of the flow rate of the Chao Phraya River using GNSS | |
| Author | Prapas Wanthong |
| Call Number | AIT Thesis no.RS-16-01 |
| Subject(s) | Slopes Flow of water--Chao Phraya River |
| Note | A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering in Remote Sensing and Geographic Information Systems |
| Publisher | Asian Institute of Technology |
| Series Statement | Thesis;no. RS-16-01 |
| Abstract | The determination of heights above the terrains can be done by the classical method called differential leveling but it is time consuming especially in a large area. GNSS system is one of a powerful and effective tool to determine the heights of the terrain but the heights derived from GNSS is called ellipsoid height. It is the height which has the ellipsoid called WGS84 as the datum. The heights in practical purposes is orthometric height, it means ellipsoid heights cannot be represented the heights of the real terrain. Thus, the ellipsoid heights cannot be applied to determine the heights of the terrains. They have to be transformed to orthometric height by adding the values of geoid undulation. Online Precise Point Positioning by the Canadian Spatial Reference System gives the most accurate heights differential computation compared to differential leveling results in the range of 0.010 - 0.084 m., while the error from GNSS Analysis and Positioning Software (GAPS-PPP) is in the range of 0.051-0.531 m. The other techniques give the errors in the range of 0.136 to 0.834 m, 0.047 to 1.532 m for RTKLib-PPP and static positioning, respectively. The worst results are from single positioning technique, the error is in the range of 1.394 to 6.553 meters. In term of elevation above geoid, the orthometric heights derived from PPP technique are approximately one meter above the real terrain this is because the orthometric height from GNSS based on the global geoid while the ortometric height from differential leveling based on local geoid but it does not affect the height differences. The slope of the Chao Phraya river basin is 1 :33333 after determined by GNSS with online PPP technique. Since the slope of the area is known, then the Manning roughness coefficient (n) can be determined by back-calculation. Discharge observed station of the Chao Phraya river at station C35, C36, and C37 in Ayuthaya province were selected to determine the Manning's coefficient roughness for further discharge computation. The Manning's coefficient roughness of station C35 in Banpom Phranakornsriayuthaya, C36 in Bangbal Ayuthaya, and C37 in Bangbal Ayuthaya are 0.030, 0.053, and 0.084, respectively. The discharge of the river at each station can be determined if the n value as well as the relations between cross section parameters e.g. cross sectional area and hydraulic radius are known. Finally, the discharges can be simply determined directly from water depth. The comparison between the actual discharges and the computed discharges at C35 station, the difference is in the range of 0.04- 59.83 ems. During the summer and winter season, the difference between the actual and the computed discharges are very high but during rainy season (August to November) the differences are lower and getting closer to the actual data. The average discharges in summer (March to July) and winter (November to April) is approximately 200 and 250 cms., respectively while the highest discharge was occurred in rainy season in August with the highest discharge of 700 ems. The computed discharges at C36 and C37 are quite close to the actual discharges, the differences are in the range of 0.02 - 11.76 ems. and 0.03 to 3.17 ems. at C36 and C37, respectively. The the average discharges at C36 and C37 in summer and winter are approximately 50 ems. and 18 ems., respectively. The maximum discharges were occurred in rainy season in August as well as at C35 station. The maximum discharges at C36 and C37 are 350 ems. and 90 ems., respectively. The amount of the water at C36 and C37 are approximately two times and eight times less than the discharges at C35. It can be seen that the discharges at C36 and C37 are very much low compared to C35 station because at C36 and C37 are the Chao Phraya river branches while C35 is the main channel of the Chao Phraya river. The computed velocities from Manning's formula and the velocities computed from the relation shows that the difference is approximately 0.01 m/s at every observed station. It is very valuable information for determine the remaining time to evacuating during the high amount of the water or in the flooding situation. The velocity of the Chao Phraya river at station C35 has the velocity about 0.4 (34.56 km/day) in summer and 0.5 m/s (43.2 km/day) in winter but in the rainy season (August to November) the velocity is not constant, it varies with the changing of discharge. At station C36 and C37, the velocities of both stations are quite similar. In summer and winter, the velocities are about 0.1 (8.64 km/day) and 0.2 m/s (17.28 km/day) and the velocities vary in the rainy season as at station C35. The velocity at C35 is faster than at C36 and C37 approximately 3 times and 5 times, respectively. |
| Year | 2016 |
| Corresponding Series Added Entry | Asian Institute of Technology. Thesis;no. RS-16-01 |
| Type | Thesis |
| School | School of Engineering and Technology |
| Department | Department of Information and Communications Technologies (DICT) |
| Academic Program/FoS | Remote Sensing (RS) |
| Chairperson(s) | Shinichi Nakamura |
| Examination Committee(s) | Nagai, Masahiko;Sarawut Ninsawat |
| Scholarship Donor(s) | RTG Fellowship |
| Degree | Thesis (M.Eng.) - Asian Institute of Technology, 2016 |