Administration Report of the Irrigation and Civil Works, Part-1 1935-36

Abstract

The Province of Sind is situated beyond the influence of the south west and the north-east monsoons, and in consequence its rainfall is normally scanty and unreliable. Unlike the greater part of India, therefore, the area of cultivation in Sind that depends solely or mainly upon rainfall is insignificant. The River Indus, however, brings down abundant supplies of water, the minimum discharge at Sukkur during the last 10 years being 16,800 cusecs, while the average has been as high as 1,45,000 cusecs. From where it enters the Province of Sind, the river is generally in deltaic formation, flowing along an elevated ridge formed by its own alluvial deposits. The indigenous system of irrigation by inundation canals took advantage of this physical pecularity. The device was primitive ; a channel was' cut from the river approximately at right angles to its course; after a short distance the canal deviated to an alignment parallel to the river and cpmmanded the low-lying lands falling away from the marginal ridge. These old irrigation works have been improved and extended while scientific methods have been introduced into the design and control of these canals, and they haVe.been provided with head regulators. There are, however, inherent defects in this method of irrigation. The cultivation dependent on river inundation is principally kharif, and even this is subject to uncertainty of supply owing to fluctuations in the river levels. The low water supplies available during the Winter season can be tapped only to a small extent and therefore this water largely runs to waste in the sea. As a result of the vagaries of a constantly changing river, the inundation canals frequently suffer from deficiency of supply during critical irrigation periods. The above inherent defects in irrigation have been remedied in Central Sind with effect from the year 1932 by the construction of the Lloyd Barrage at Sukkur and the opening of the perennial canals taking off above it. It is only in parts of Upper and Lower Sind, which are outside the sphere of influence of the Barrage, that only a ‘ kharif’ water-supply continues to be available from the inundation canals. ‘ Bosi-Rabi ’ crops (Rabi crops grown dfi waterings given prior to sowing and before the inundation canals cease to flow), however, are grown to a considerable extent in these areas, especially if the ‘ abkalani ’ happens to be a long and high one.