A Study of River Mechanics in Lower Pasak River by Mathematical Model

บทคัดย่อ

Lower Pasak River between downstream portion of Rama VI Dam and ChaoPhraya junction was selected for river mechanics study in conjugate with an application of MIKE11 model. Both of Pasak and ChaoPhraya river cross section data were surveyed in the period of 2013 - 2015 in form of 50 m spacing. The model calibration and verification of MIKE11 was carried out with the data in the period of 2012 - 2013. It found that roughness coefficient along Pasak river has a range between 0.023 – 0.026 which was acceptable with the statistical indexs of R^2 and RMSE equal to 0.85 and 0.62 m respectively. The calibrated MIKE11 was then applied to analyst the low flow period by calculating the lowest depths in the period of 2007-2013. The result showed that there were almost water depths below 4.9 m were located nearby upstream portion of lower Pasak River from KM. 30+000 to KM. 51+900. However, the full river bank analyzed from the river capacity illustrated that downstream portion of lower Pasak River from KM. 10+000 to KM. 30+000 has an average capacity in the range of 517.64 - 630.17 m^3 s^-1 and was much lower than the overall average with 811.19 m^3 s^-1. Consequently, the determination of flow efficiency in both of low flow and high flow periods should consider the factors related to the river mechanics including water depth, river width, and river capacity in order to guideline as a basis for water management of government agencies involved.