BANK PROTECTION AND WADI TRAINING

Lesson 2

IanMcAnderson@aol.com

Bank protection and Wadi training

High flow velocities during spates often erode Wadi banks

meander patterns to develop and migrate downstream

Wadi beds can be significantly lowered during the passage of large floods

traditional intakes to be left stranded

Providing engineered structures to control bed levels

Farmers give bank protection work a high priority

training and back protection works that cause damage elsewhere

River training and bank protection approached in a holistic manner

blocks Vs. crated boulders

The subject has been well debated. General experience, which has served

successfully for over 100 years, is to use crated boulders in alluvium deposits for launching aprons.

The size of crate is determined on the basis of water velocity to prevent it being swept and lifted away.

The basic principle of the launching apron is best described as the one of a carpet which takes the shape of the scoured bed.

The bottom of the apron is normally placed at LWL.

It is not possible to lay the apron below knee deep water because of difficult manual working.

In such cases, it is best to fill the area, if necessary by using suction dredgers

Crated boulders launch smoothly and being flexible, easily take the shape of the scoured beds and are not lost as in case of concrete blocks

For pitching guide bunds, slopes also, boulders in the form of grids are used.

gabion apron

Require minimal excavation and grade work. Generally the gabion apron is placed directly on

the ground utilizing a geotextile filter fabric between the gabion apron soil interface to prevent and leaching of soils from underneath the apron.

Gabions or reno mattresses may also be connected together filled and then placed into the water with a sling arrangement. This method is frequently used for building scour-resisting mats around bridge piers etc