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Much useful information as to the preparation of drainage projects, and tables of discharges of different sections, will be found in Practical Instructions in Surface Drainage, by Mr. H. A. Gubbay, Executive Engineer, Public Works Department, published by the Government of Bengal.

In most cases, when designing a system of drainage, it is advisable merely to take the general surface level of the bazaar as the level to be drained, leaving artificially caused depressions to be filled up with the débris of old buildings, and any available suitable material as opportunity occurs. It is also generally unnecessary to provide for a very heavy rainfall. The usual provision in this part of India is for a run off due to ½ an inch of rainfall per hour from densely built over, and ¼th of an inch from suburban areas.

It is more scientific to design the drains with reference to the possible flushing power and facilities available, rather than that of the maximum rainfall.

The importance of proper drainage, especially in connection with checking the spread of malarial fever by anopheles mosquitoes has, owing to recent researches, been fully recognised. These are found to breed most extensively in the earth-lined drains alongside streets. Where brick-lined, the current should be strong enough to wash away the larvæ, but it is quite otherwise on the numerous kutcha ones in every bazaar. It is also essential, in Bengal, to make use of the powers conferred by the Municipal Act (Section 195) to compel owners to fill up small depressions which, during the rains, form extensive and numerous breeding-grounds. Every attempt should be made each year to brick-line a section of the roadside drains as money is available, where funds do not admit of much being done. Grass and weeds in the earthen drains must be cleared out at regular intervals during the rains, and the oftener the better. Mosquitoes of the culex tribe cannot also be disregarded, as these have been proved to convey elephantiasis and other diseases, and stegomyia, which abound in Lower Bengal, are the hosts of yellow fever.