STUDY OF METHODS OF WATER SURFACE PROFILE CALCULATION IN GRADUALLY VARIED FLOW

BY

TAN SHI NGIN

ABSTRACT

It has become widely accepted among water resource planners that the most cost effective way to reduce future flood damages is to restrict development in areas that are subject to flooding. The process of identifying and napping such areas involves, first, the selection of a design flood. The second step in this process consists of a hydrologic analysis that provides estimates of the discharge of this design flood at points along the stream system. The next step is a hydraulic analysis in which the elevation of the water surface associated with the design flood is computed. Finally, the computed elevations are used in conjunction with topographic maps to identify those areas lying below the elevation of the design flood.

In this report, I will be concerned in part 3- the hydraulic analysis that provides estimates of the water surface elevation associated with a given discharge in a given stream reach. This analysis is based on the one-dimensional energy equation for steady flows. In order to apply this equation, we assume that each cross section of the channel is characterized by a single velocity, depth, slope and resistance. We also assume that the follow is gradually varied flow.

When the depth of flow in an open-channel flow varied with longitudinal distance, the flow is termed gradually varied flow. Such situations are found both upstream and downstream of control sections. This definition signifies two conditions: (1) that the flow is steady; that is, that hydraulic characteristic of flow remain constant for the time interval under consideration; and (2) that the streamlines are practically parallel; that is, that hydrostatic distribution of pressure prevails over the channel section.

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Diploma in Civil Engineering

April 2000

Number: 15 – 19