It is a misconception that dams deplete rivers and reduce their flow. Dams actually store and save surplus flood waters and add these to the flow of the rivers. Dams are built to overcome shortage of water, and not to increase it.It is at the barrages that the canals taking off from them deplete the rivers. On the Indus river, there are 5 canals in Punjab taking off from Jinnah, Chashma and Taunsa barrages. In Sindh there are 15 canals taking off from Guddu, Sukkur and Kotri barrages. In fact the flow to the Indus delta decreased to the present low level when Kotri barrage was built and four canals taken off from it. No reduction can be made in the number of these canals which are essential for the ever growing demand for irrigation water for Punjab, Sindh and Balochistan. However, a better managed and more efficient irrigation system can bring improvement in the ratio between water-input and crop-yield, which is very poor at present.KHURSHID ANWER, Lahore, January 15.