GUNTUR : Bad designing of canals in the delta region of Andhra Pradesh are leading to collapse of several bunds and there was enormous damage to the Krishna Western Delta canal and drainage system.

Improper slopes maintained for the kind of soils available in Krishna Delta region was the major cause of damage to the canal walls and what adds to the woes is the unscientific maintenance carried out either by Irrigation Department or Water Users' Association, Roads and Buildings Superintending Engineer D. Bhavanna Rao told The Hindu.

In a presentation to be made to engineers of the Irrigation, Panchayat Raj and R&B departments, on the cause of frequent damage to the roads formed on the bunds of the canals, he emphatically says: "no canal bund in Andhra Pradesh is capable of taking the load of a road as they were not designed for that, we got greedy and formed roads for maintenance vehicle to run/people to travel on it."

The canals were dug and black cotton soil from the dug portion put on the bunds with improper compaction and slope for the soil quality.

Conversion

These bunds were slowly converted into motorable roads and later on got transformed into blacktopped road. Such roads never had proper base preparation/compaction to take the load of vehicle plying on it, he explains. During rainy season when Cyclone Ogni struck Guntur coast, all the canals were flowing to their brim and outside fields were full of water, so the irrigation officials suddenly brought down the water levels leading to the outside water pressure increasing on soil.

This led to sides caving in at many places and flooding of several villages.

Generally a 3:1 slope was needed for such BC soils, but it was reduced to 2:1 while construction of canals and during unscientific desilting by WUAs and Irrigation Department, the slope comes down to 1:1, he observed.

Canal water drawdown also should be properly planned to reduce adverse impact, Mr. Rao said.

The growth of grass on sides, and the silt to some extent work as natural lining or strengthening of canal bunds, but with frequent desilting due to lack of scientific comprehension of the water flow dynamics, even the stones from the walls got scourged during heavy flow.

Lining of all canals in a phased manner was the only comprehensive solution and not the widening of canals as that would leading to damage to other structures like culverts and bridges on them. Some bridges had collapsed on Nallamalla drain when it was widened from 50 feet to 100 feet.

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