Rainfall – Runoff Module in Tapee Basin, Surat Thani.

Tapee Basin is a watershed in the southern part of the country where has an area of ​​approximately 13,454.51 square kilometers. Most of the watershed areas are located in Surat Thani, consisting of 8 tributaries: Upper Tapi River, Canal Chandi, Canal Sinpun, Canal Ipan, and Lower Tapee River, Khlong Sok, Khlong Phra Saeng, and Lower Phum Duang Canal. Upstream are mountains in the west and south, covering almost all areas of Surat Thani and some parts of Nakhon Si Thammarat and Krabi.

Walailak University and Regional Environmental Office 14 (Surat Thani) created a model of rainwater and runoff in the Tapee River Basin (lower part) of Surat Thani province, from Sinpun, Phra Saeng to Krut, Phunphin, Surat Thani, a distance of about 81 kilometers. The resulting model can be further modified to increase accuracy by adding current information, developing a mathematical model, and creating a geographic information database for the show. A mathematical model of the Tapee Basin in connection with the model development. By using the program (software) MIKE11, which the Regional Environmental Office 14 (Surat Thani) has licensed, the preparation of a rain-water runoff model (MIKE11 RR, Rainfall-Runoff Model), a stream flow model (MIKE11 HD, Hydrodynamic Model), a convection-dispersion model (MIKE 11 AD, Advection-Dispersion Model), and a water quality model (MIKE 11 Ecolab, Water Quality Model) can be used for forecasting the quality of the Tapee River (lower part) in the future.

The MIKE11 HD model is a hydraulic model with a visualization of the physical characteristics. of the watershed in the form of a mathematical model to calculate the water level, flow rate, and others in a river and watershed. The required physical data consists of four main factors:

• The size of the watershed and the sub-watershed to use for calculating the side flow factor

• Schematic Diagram of a River Network for simulating river network data. Upstream, downstream, and various connection points between rivers

• Cross Section is the data from surveying the cross-section of the river at different stations along the river. In addition, the shape of the river can also tell the width of the river and the slope of the river bank.   

• Hydraulic structures in some rivers, reservoirs, weirs, or sluices may be constructed to block the direction of water flow in order to simulate the flow using a mathematical model. It is also necessary to import this data.

Modeling of rainwater-runoff in the Tapee Basin (lower part), Surat Thani. The goal is to analyze and forecast the occurrence of water in the area by calculating the movement of water from upstream to downstream and forecasting the amount and water level. To describe the water quality of the Tapee Basin area (lower part), Surat Thani affected by human activities and to predict the amount and level of water in the future.