Anat Arbhabhirama

CHARACTERISTICS OF A CIRCULAR JUMP IN A RADIAL WALL JET

The characteristics of a circular hydraulic jump created by the radial flow from a circular jet which spreads as a thin layer on a smooth flat plate were studied. The characteristics considered were: the profiles of the approaching laminar and turbulent flow; variation of the free-surface velocity; boundary-layer development; applicability of the circular jump equation; energy dissipation, and the length, height, and location of the jump. The analysis is an extension of a previous investigation which made use of the boundary layer theory of an axisymmetric flow. Experiments were conducted to verify the theoretical equations.

A statistical analysis of the sediment volume accumulated in reservoirs

Abstract A statistical method is used to investigate the reservoir sedimentation problem by: (1) correlating the annual sediment discharge and the annual river discharge; (2) using the resulting correlation either to generate a sediment sequence having the same length as the river discharge, or to obtain the distribution of the sediment discharge by means of a transformation of variable; and (3) expressing the accumulated volume as the cumulative sum of a sequence of random variables. Assuming a reservoir trap efficiency equal to unity, this cumulative sum is the partial sum of annual sediment discharges. The investigation then concentrates on the derivation of the mean and variance of the sediment volume accumulated in the design lifetime of the reservoir.

Rainfall distribution in northeastern Thailand / Sur la distribution de pluie dans le nord-est de Thailande

Abstract Rainfall is the main source of irrigation water in the northeastern part of Thailand where the inhabitants derive their income primarily from farming. In order to improve their economic conditions, the efficient use of available water is essential and this requires a sound understanding of the distribution of rainfall in space and in time. The present study aims at providing basic information on rainfall sequences in the region, such as their amount and their distribution in space and time. Several other statistical properties such as the persistence, the periodicity and the degree of irregularity of rainfall and the transition probabilities between rainy and non-rainy days are presented. An assessment of the availability of water for irrigation is also made.

Range analysis for reservoir storage with independent inflows

Abstract Range analysis has been used to investigate the storage problem of an infinite reservoir where the annual inflows are independent and identically distributed either as normal or as gamma variables. The distribution of the water content in the reservoir for a specified year has been derived and given in a closed form. The first few moments of the maximum amounts of water in surplus and in deficit over the reservoir life are obtained, and their distributions are approximated by the Pearson type-I curve. The distribution of the reservoir storage capacity is approximated by the type-III curve which is completely determined by its first two moments. In addition, it has been found that when the skewness coefficient of the inflows increases: (1) the maximum amount of water in surplus fluctuates more and approaches the zero value more frequently, while that in deficit fluctuates less and approaches the zero value less frequently; and (2) the reservoir size becomes smaller but its distribution becomes less stable.