Programme de bourses "Echanges Universitaires"
Hydrological Patterns in the Tha Chin River Basin, Thailand
This study lays the focus on the hydrological patterns in the Tha Chin River Basin in Thailand. The research shall contribute to understanding the hydrological system of the Tha Chin River, as basis for a Material Flow Analysis (MFA)1. Existing hydrological data sets are analyzed and complemented by own measured discharge data, in order to quantify the discharge and the water balance of the Tha Chin River. In addition, strategies governing the regulations of canal and main river discharges are explained.
The study is designed under the PhD project of Monika Schaffner: “Assessment of Water Quality Problems and Mitigation Potentials by using Material Flow Analysis - A Case Study in the Tha Chin River Catchment Area, Thailand". The project was realized in cooperation between the Hydrology Group of the Geographical Institute at the University of Bern, the National Centre of Competence in Research (NCCR) North-South, and the Asian Institute of Technology in Bangkok/Thailand.
The Tha Chin River Basin is a flat, intensively used area (mostly by agriculture, livestock, industry and urban areas) in a complex hydrological system. It is interspersed with water regulators and highly interlinked canals, which do not allow the river to flow any more according to its natural regime. In addition, the river is the most polluted river in Thailand andseveral projects are being implemented to recover the water quality (TCS and PCD, 2001).
The Tha Chin River lies within a greater hydrological system, starting from two large water storage dams in the north, down to the Central Plains of Thailand, with the capital Bangkok. In this setup the Tha Chin River is given the role of an “under dog”. During the dry season it has to ensure sufficient water for irrigation in its own catchment area, and in addition has to provide water to the Chao Phraya Basin in case this suffers water shortage. During the rainy season, Tha Chin River Basin has to receive all surplus water threatening Bangkok Metropolitan Area through Chao Phraya River floods.
As a result of this role in the basin, the high discharge variability is a key characteristic of Tha Chin River, especially in the Upper Basin. The river does not have a typical flow regime; its discharge pattern varies strongly from year to year. Looking at the spatial distribution, the discharge variability of the river increases on its way to the south. The amount of water, on contrary, decreases towards south, as it is extracted from the river for irrigation purposes. In the middle of the Tha Chin River Basin, due to the inflow of several canals from the neighboring basin in the west, the discharge increases again and keeps increasing continuously until the river reaches the Gulf of Thailand. The adjoining canals on the east side of the Tha Chin River can change their flow direction, depending on the hydrological situation in the Central Plains. In case of water shortage in the Chao Phraya Basin, water is taken out of the river to fill the water gap in the neighboring basin. On contrary, in case of flood, the Tha Chin River Basin has to collect the excessive water from the Chao Phraya Basin. Finally, the discharge of the river in the lower basin is strongly influenced by tidal fluctuations. Water is pushed backwards, resulting in periods of negative discharge and longer water retention time.
According to the water balance calculations there is a water deficit in the Tha Chin River Basin: evapotranspiration requirements and river outflow exceed the water supplied through rainfall and irrigation water inflow. However, with the large uncertainties regarding the countless in- and outflows inflows to the basin, further investigation would be required to assure this statement. Considering the decreasing rainfall and the increasing water use in Northern Thailand and the growing water consumption in Bangkok, these developments will accentuate the potential water shortage in the Central Plains. Thus, the Tha Chin River Basin may have to handle with severe water shortage in the future.
With the acquired data sets, the required input data for MFA could be estimated on different spatial scales (average and range of in- and outflow to the basin). In addition, it was possible to verify the nutrient load calculations in the Tha Chin River Basin by Bieri (2005).
Contact addresses
Claus Walcher
Waldstätterstrasse 23
3014 Bern
Switzerland
Email:cwalcher@gmail.com
Thammarat Koottatep, D.Eng.
Assistant Professor and Regional Coordinator of JACS-SEA
School of Environment, Resources and Development
Asian Institute of Technology
P.O.Box 4
Klong Luang
Pathumthani 12120
Thailand
Email: thamarat@ait.ac.th
1 Material flow analysis (MFA) is a promising tool for river water quality management. Based on orders-of-magnitude estimations, the approach provides an overview of pollution problems and their dimensions in a river system. This allows to identify key sources and pathways of pollution, and to evaluate mitigation priorities. (Baccini and Bader, 1996).