ISLAMABAD: The Indus River System Authority (Irsa) has reduced discharges from Tarbela dam to 30,000 cusec from 40,000 cusec owing to reduction in storage to a critical level of 1,382.96 feet, enough to meet crop watering requirements of about four days.
A senior Irsa official told Dawn on Friday that substantial variation in hydrological data that started about a week ago had not settled down yet, causing difficulties for water regulation and management.
He said water inflows at Tarbela dam were recorded at 38,000 cusec on Thursday and even though temperatures had surged in northern areas, the inflows at Tarbela dropped to about 32,000 cusec on Friday which should have gone up because of higher temperatures.
Over the past three days, river flows at Besham were shown stable at 30,000 cusec but inflows at Tarbela have been constantly showing variation. “When there is stability in flows at Besham, variation at Tarbela is difficult to understand,” the official said.
Irsa, therefore, has not been able to take a decision on changing water discharges except to increase share of Sindh by 5,000 cusec.
The Irsa official said Wapda was responsible for variation in water flows because it was required to implement Irsa instructions regarding water discharges, recording and monitoring of hydrological data.
He said Irsa had sought an explanation from Wapda’s executive engineer for huge variation in hydrological data at Chashma barrage that took place last week. The executive engineer was asked to explain why full flows had not reached Chashma and why higher discharges were made from Tarbela dam.
According to the Irsa official, the Wapda engineer had conceded the mistake over higher discharges and promised to follow Irsa instructions in letter and spirit in future.
However, a Wapda spokesman told Dawn that Irsa’s demand was placed and fulfilled on mean daily basis and the inflows and outflows were calculated on 24 hours average basis. He said the average inflows in River Indus at Tarbela on April 30 were 32,100 cusec, while on May 1 it was 33,500 cusec.
He said Irsa’s indent from Tarbela reservoir remained 40,000 cusec from April 10 to 29. On April 30, at 1635 hours, Hydrology Section of Tarbela Dam received a message that Irsa indent had been revised from 40,000 cusecs to 30,000 cusecs.
“As per decision taken by Irsa in its meeting held on Dec 19, 2011, the 36 hours margin may be availed to adjust the outflows,” said the Wapda’s spokesman and added that system requirements of outflows were reduced to 30,000 cusecs from 40,000 cusec within the allowed time margin. He said irrigation had always been the first priority and hence it was not correct to say that preference had been given to power generation.
An Irsa official explained that the 36-hour margin for discharge adjustment was restricted to normal circumstances and decided by Irsa on a case to case basis that was not the case last week when water level at Tarbela dam had reached a critical stage.
Wapda was given specific instructions to immediately reduce outflows but they availed of 36-hour margin at their own even though it was bound to implement the Irsa’s directive instantly.