Effect of Water Withdrawal on Hydraulics and Morphology of Pumduang River, Thailand
Abstract The HEC-6 river morphological mathematical model is applied to predict the effect of water withdrawal from the Pumduang River on its water surface and bed profiles. The river is situated in the Surat Thani province in the south of Thailand. The HEC-6 model is calibrated and verified based on field data. After the model calibration and verification, the HEC-6 is applied to predict the effect of water withdrawal on changes in water level and bed level of the river. The predicted changes are compared with the results of a physical movable bed hydraulic model of scale 1:60. The agreement is found to be satisfactory. The equilibrium river bed and water surface profiles are determined for the annual average flow and the 2-, 10-, 25- and 100-year return period floods for the cases with and without water withdrawal. The water withdrawal of 16 percent of the average annual discharge of the Pumduang river is found to have no endangering effect on the flow and morphological condition of the river
Evolution of methods for evaluating the occurrence of floods
A brief summary is given of the history of methods of expressing flood potentialities, proceeding from simple flood formulas to statistical methods of flood-frequency analysis on a regional basis. Current techniques are described and evaluated. Long-term flood records in the United States show no justification for the adoption of a single type of theoretical distribution of floods. The significance and predictive values of flood-frequency relations are considered. Because of the length of flood records available and the interdependence of flood events within a region, the probable long-term average magnitudes of floods of a given recurrence interval are uncertain. However, if the magnitudes defined by the records available are accepted, the relative effects of drainage-basin characteristics and climatic variables can be determined with a reasonable degree of assurance.
Floods in North and South Dakota, frequency and magnitude
The magnitude of a flood of a selected frequency for any poftit in the two states may be determined by methods outlined in this report, with two limitations. These methods are not applicable for regulated streams or for small drainage areas (in general, less than 100 square miles). The determination of the magnitude of a flood of a selected frequency in the two-state area is accomplished by the use of composite frequency curves for 2 flood regions and curves showing variation of mean annual flood with drainage area for 9 hydrologic areas and 10 main-stem streams. These curves are based on all flood data collected in North and South Dakota with some use made of records from adjoining states. These data are tabulated in the report. Also included in the report is a tabulation of maximum flood experiences at gaging stations and outstanding floods at many miscellaneous sites.