12.5.5. Pitched Islands A pitched island is an artificially created island in the river bed. It is protected by stone pitching on all sides. A pitched island is constructed with sand core and boulder lining. To protect it from scouring, a launching apron is also provided. The location, size, and shape of pitched islands are usually decided on the basis of model studies. Pitched islands serve the following purposes (3):
(i) Correcting an oblique approach upstream of weirs, barrages, and bridges by training the river to be axial,
(ii) Rectifying adverse curvature for effective sediment exclusion,
(iii) Redistributing harmful concentration of flow for relieving attack on marginal bunds, guide banks, river bends, etc., and
(iv) Improving the channel for navigation.
A pitched island causes scour around it and, thus, redistributes the discharge on its two sides. Pitched islands upstream of barrages and weirs have been found to be quite effective.
