Scale variation in the controls of runoff response in northern Thailand catchments
Han She Lim
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Weir at the outlet of a small catchment at the RFD experimental station west of Mae Chaem |
The response of catchments to rainfall depends on a wide range of factors that may vary in their importance with the size of catchment. The aim of this project is to examine this issue in northern Thailand, in order to assess the scales at which changes of climate and land use may be most effective in altering runoff behaviour.
At the large scale (basins of the order of 1,000-10,000 km²), flood magnitudes of given frequency will be related to general catchment properties such as area, topographic indexes, land use statistics, etc. This will generate a database which can be subjected to multiple regression and principal components analyses in order to develop a predictive tool, in the form of a regional flood frequency model.
At an intermediate scale (a basin in the area range of 100-1,000 km²), rainfall-runoff data will be analysed using time series methods and lumped catchment modelling methods in order to assess the main controls of runoff and the changes in the runoff system. Finally, at spatial scales smaller than 1 km², catchments with different vegetation or land use will be monitored in order to examine the detailed control of the response of runoff and sediment yield following rainfall.
The third of these scale-dependent studies will be undertaken at an experimental station run by the Royal Forestry Department, to the west of the town of Mae Chaem. Here, two small catchments with weirs at their outlets have been instrumented using pressure transducers for water level data, turbidity sensors for suspended sediment data, and data loggers to capture records with a 15 minute time interval; continuous raingauge data is also available at this location.
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Some hydrograph data from the Weir (see above) |