In a letter, Humaira Alwani, an MPA from Thatta, has said that barrages not dams have depleted rivers and caused the severe water shortage in Sindh that is degrading the deltaic region severely. She has also opposed the building of Bhasha dam. In an amazing piece of logic, she thinks building Bhasha dam would add to the deterioration, and not help improve the situation. Dams dont consume water, nor do they deplete rivers. The canals of dams take only the water that is stored when river flows are high for three months. And they make this water available when the river flows are low for the remaining nine months. Without this mechanism working, there would be no water for the Rabi sowing in Pakistan. Being an MPA, it should be easy for Ms Alwani to check with the Sindh irrigation Department and note figures of the pre-Mangla (before 1967) canal flows in Sindh to compare them with the post-Tarbela (after 1974) canal flows. She would find an increase of about 6 million acre feet for Sindhher Sindh, alone. Of course, there is much more in the rest of the country too. The aggravation of the deltaic region is because of the demand and supply situation. The demand has increased over the years without any corresponding increase in the river flows because we built no dams, remember and only dams can add to the river flows. Apart from what is being consumed up country, thirteen big canals at Guddu, Sukkur and Kotri barrages are depleting the Indus River. Yes, it is the barrages that deplete rivers because they dont have any storage, and not the dams. About 20 million acre feet of water flows below Kotri into the sea during the three flood months, there is little or no flow during the remaining nine months. That allows sea incursion. Only 4.32 of the 20 maf, distributed over the twelve months, are sufficient to check this sea incursion. This can only be done by building new dams to store this amount in their reservoirs and release a monthly dose of 0.36 maf for the year round protection of the Indus Delta. Without more dams, the deltaic region would keep getting worse. -KHURSHID ANWER, Lahore, March 18.