gradually varied flow (gvf, steady) occurs in many situations · pdf file 2018. 8....

 Gradually Varied Flow (GVF, Steady) Occurs in many situations like upstream of a barrier, downstream of a sluice gate, due to change of slopes of a channel etc. Therefore, study on this type of flow is important from particle point of view. To study this flow and its profiles knowledge of normal depth and critical depth is essential.

 The Gradually Varied Flow (GVF) is the steady flow whose depth varies gradually along the length of the channel. The definition signifies two conditions. The flow steady means hydraulic characteristics of flow does not change for the time interval under consideration and streamlines remain practically parallel; that is, hydrostatic pressure distribution prevails over the channel section.

Learning Objectives  Dynamic Equation  Profiles of Gradually Varied Flow  Computations of Profiles  Computation Methods

Introduction

Assumption

Dynamic Equation of Gradually Varied Flow

Classification of Flow Profile

The Channel bed slopes are classified five categories: Critical Slope Sc: For given discharge and channel shape critical depth yc of flow exists. From this known critical dept yc, corresponding slope may be computed and this computed slope is called Critical Slope and is denoted as sc. Hence in this situation sb = sc and normal depth yn=yc, i.e., NDL and CDL coincide. Mild Slope: When the channel bottom slope sb is less than the critical slope sc, i.e., < sc, slope is called Mild. Application of Manning’s or Chezy’s equation indicates that in mild slope, yn>yc. Steep Slope: The channel slope is called steep slope if sb>sc and yn

Table 4.2 Types of GVF Profiles

Fig. 4.3. Various GVF profiles

Method of Computation

1- Direct Step Method

Steps of Computation

EXAMPLE

 A rectangular channel 8 m wide carries discharge of

11m3/sec (Manning’s n = 0.0025, bed slope of 0.0016).

Compute the length of back water profile created by a

dam which backs up a depth 2 m immediately behind

the dam by direct step method. Take at least 3 steps

to compute the profile.

SOLUTION