River Training

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Posted by Pavan Vemula on January 29, 2010 at 5:38 AM Comments comments (2)

The training measures are planned with due regard to the limitations imposed by the type of

river. The various steps involved are as follows:

1. Alignment. Alignment of training work is generally based on the layout and number of training structures involved. A better way to arrive at radius of curve is to study the photographs of alignment of a stable stretch of river on a similar grade and soil conditions in the vicinity of the erosion site and from this stable section measure the radius of curves. An attempt is then made to develop an alignment with curves of similar radius to those measured. Once the proposed alignment is decided, the methods of control to stabilise the channel to its alignment are considered.

2. Cross Section. The cross section is that built by the river itself, i.e., when the channel is uniform and does not show signs of accretion or retrogression. The proposed section is either by river contraction or by river diversion and is compared with the normal cross section with regard to gauge and discharge relation, velocity of flow, and total sediment runoff. The section is modifled by successive analysis to bring it in line with the normal cross section as far as possible.




Posted by Pavan Vemula on January 29, 2010 at 5:37 AM Comments comments (0)

1. Classification Based on Purpose

1. High Water Training: River training aimed at flood protection is called high water training or training for discharge. It envisages provision of adequate waterway for safe passage of maximum flood by proper location, alignment and height of embankments for a given flood discharge without tending to change river bed conditions.

2. Low Water Training: Also termed as training for depth. It envisages to provide adequate water depths during low water periods in the river channel for navigation by concentrating flow in

a desired channel and closing other channels by the method of bandalling, i.e., contracting the width of the river channel with the help of groynes, etc.

3. Mean Water Training: Also termed as training for sediment. It is by far the most important type of river training. It envisages rectification of the river bed configuration and efficient movement of suspended and bed load for maintaining the channel in good condition. The maximum aggrading capacity of a stream occurs in the vicinity of mean water or dominant flood discharge, and as such tends to change the river bed in accordance with that stage of bed flow. Mean water training includes river training for efficient sand exclusion from canals by correcting adverse river curvature to locate the canal offtake.

2. Classification Based on Structure Alignment

1. Longitudinal structure: These aim at guiding the axis of flow at ordinary and low stages, protecting the banks from erosion, generally to improve their alignment, trapping bed load in the areas of superfluous width, and establishing channel boundaries where braiding has created too wide a section divided into small channels separated by islands. Longitudinal training works are preferred to projecting training works in rivers carrying small bed loads, and with narrow channels having steep slopes and swift currents. In rivers with unstable bed cQnditions, longitudinal works are susceptible to damage by undermining.

2. Projecting training works. Projecting training works aim to protect the bank from which they project into the river by deflecting the current away from the bank. They are more suitable in rivers with unstable bed conditions. Cross connecting dikes to the bank at intervals add strength to withstand flood action and promote sedimentation in the closed-off channel spaces.




Posted by Pavan Vemula on January 29, 2010 at 5:37 AM Comments comments (0)

The various objectives of river training are (i) To guide the axis of flow at ordinary and low stages and safe passage of floods without overtopping the banks, (ii) To protect the banks from erosion and generally improve their alignment by stabilising the river channel, (iii) To train the river flow along a safe course, thereby avoiding damage by flooding or erosion of valuable lands, habitations, crops, factories, etc., (iv) To prevent outfianking of a bridge, barrage or weir by directing the flow in a defined stretch of the river, (v) To prevent river from changing its course, (vi) To confine a river channel which has become too wide by swinging from side to side and to reclaim the land from river bed, (vii) To check certain devastations like that of flash torrents, (viii) To trap bed load in areas of superfluous width, (ix) To transport efficiently bed load and suspended sediment load, (x) To provide sufficient depth of flow for safe navigation, (xi) To establish channel boundaries where braiding has created too wide a section divided into small channels separated by islands, and (xii) To correct disorderly banks or flow conditions.




Posted by Pavan Vemula on January 29, 2010 at 5:35 AM Comments comments (2)

River training is an age-old practice resulting in incessant development and application of human ingenuity to correct vagaries of the rivers. It requires deep and precise study of river mechanism and behaviour discussed heretofore. River training has assumed considerable significance in India due to huge annual recurring damage caused by the floods; 80 per cent of which accounts for loss of crops. River training, in its broad aspects, covers all engineering works constructed on a river to guide and confine the flow to the river channel, and to control and regulate the river bed configuration for effective and safe movement of floods and river sediments. In essence, river training envisages training and stabilising a river within a suitable waterway and along a certain alignment for a variety of purposes. River training works involve large outlays and it is essential to select the type of the training work and materials of construction so as to make optimum utilisation of funds, and effective and economical utilisation of the available construction materials.