TORRENTIAL rains and floods in 2022 have been a blessing in disguise, at least for the otherwise dying Manchhar Lake. The lake is lately witnessing development works aimed at rehabilitating its bank and system comprising Aral and Danister canals at a cost of multi-billion rupees over a decade.
These works are being executed under the Sindh Flood Emergency Relief Project (SFERP), a World Bank funded programme. SFERP aims to rehabilitate the flood protective (FP) bund, which ensures the safe passage of flows of hill torrents in upper Sindh right up to the lake. Such excessive flows in the event of extreme weather events eventually end up in Manchhar Lake.
Last year’s floodwaters from Balochistan and heavy rainfall in Sindh ended up in Manchhar, as did the water in the 2010 super floods. But last year’s floodwaters didn’t burst Manchhar Lake’s banks. However, given the precarious condition of its dyke, the provincial government decided to give relief cuts — as happened in the floods of 2010 — in the lake’s embankment following advice from serving and retired engineers.
So, two back-to-back controlled cuts, one falling between RD-13 and RD-14 and the second at RD-52, were given on Sept 4 and Sept 5, 2022, with the government’s sanction. The lake falls in the provincial constituency of outgoing Sindh Chief Minister Syed Murad Ali Shah in Jamshoro district’s Sehwan taluka. Cuts, however, widened to several hundred feet in measurement due to gushing flows from Manchhar.
After the execution of the ongoing works, it will be able to release 83,500 cusecs of water, an increase of 47,000 cusecs from its previous capacity
Water flows from two cuts inundated a vast area downstream of Manchhar Lake, leading to massive displacement of communities. It then necessitated development works at the lake’s dyke called Manchhar Containing Bund (MCB), Aral head, Aral tail and Danister canals’ tail regulators.
“MCB’s entire motorable path is being widened from 20ft width to 30ft,” said Zahid Shaikh, a retired chief engineer in the Sindh irrigation department and Water Resources Specialist in SFERP. “These are major works being executed ‘under build back better concept’ after 2010 devastations when similar cuts were given to the empty lake, which allowed it to receive flows of Tori dyke breach Guddu barrage upstream [Aug 2010],” said the former chief engineer, who had spent considerable time of his service at Manchhar lake.
Aral tail regulator is not undergoing any work for want of a pending study. Such study’s terms of reference are being prepared by Dutch and Spanish experts who visited the site early this month. The study would help the irrigation department see what kind of work should be taken to ensure better performance of Manchhar’s overall system.
Aral tail regulator currently ensures a discharge of 25,000 cusecs of water from Manchhar, and Mr Sheikh believed its capacity could be enhanced up to 100,000 cusecs.
According to him, Manchhar presently has the capacity to discharge around 36,500 cusecs of water cumulatively. After the execution of the ongoing works, it will easily be able to release 83,500 cusecs of water — up by 47,000 cusecs from the previous capacity — because capacities of the Aral head and Danister tail regulators are increased substantially.
“Likewise, the bed of Aral wah has been widened to have more flows. Aral head regulator now has 14 gates to have 52,500 cusecs discharge in future — up by 42,000 cusecs — from the previous 10,500 cusecs discharge. Structure of the Aral head regulator has been relocated around 2,300ft upstream from its previous location off Indus highway near Sehwan city,” said Mr Sheikh.
Insofar as the Danister tail regulator [located at RD-62 of MCB) was concerned, it would now have 6,000 cusecs of discharge against its previous 1,500 cusecs discharge, given the lessons of the 2022 floods and rainfall.
The tail regulator at RD-62 was damaged due to flows from the lake. Until last year, it worked with three gates of 10ft each, but now it will have two gates with 20ft width each. Gates have been installed, and the regulator will become functional soon, as observed in a visit to the site last week. Danister canal’s head regulator, located at the Larkana-Sehwan (LS) dyke of the Indus River, was last upgraded in 2010 to have 10,000 cusecs discharge.
Floodwaters and rainfall in 2022 had, in fact, upset all estimates of irrigation officials. The quantum of flows reaching Manchhar Lake had become a guessing game for them. Even the former chief minister, an engineer by profession himself, looked worried and disturbed during visits on handling these exceptional flows in this part of Sindh, which were equal to more than one Tarbela dam’s capacity, according to his assessment.
In view of these flows, a forensic and satellite survey/analysis of 2022 floodwaters, according to Zahid Sheikh, was needed for Indus Right Bank flood management to know/determine the generation of possible flows in the area upstream of Manchhar to enable authorities to handle it accordingly.
Considering these issues, Manchhar Lake’s bund’s 100 RDs, or 20 miles in length, was rehabilitated because the lake also serves as a reservoir to store water. This capacity is key for the entire system as well. Its embankment width has been revised from 20ft to 30ft now. Similarly, around 150km long FP Bund that goes up to Qambar-Shahdadkot district is being rehabilitated. FP Bund also witnessed damages last year.
Unusual flows are seen during flood season in the Indus River and in the lake. Officials note that the lake — located from the Sukkur barrage — could store around one million acre-feet quantum of water if the Indus River allowed space for carrying additional water from Manchhar due to higher floodwater levels downstream of Sukkur barrage.
Similarly, Hamal Lake in the Qambar-Shahdadkot district was another potential source for storing floodwaters before being released downstream, provided its upkeep is ensured.
Manchhar Lake used to get fresh water from hill torrents in its catchment. The lake works both ways — fed from the Indus River and releases water to the river, if need be.
Its ecology was destroyed by unending toxic flows from upper Sindh and Balochistan through the Right Bank Outfall Drain (RBOD). Revival of the lake’s ecology eludes Manchhar for drainage-related initiatives — Right Bank Outfall Drain system — remain incomplete even after two decades. The lake is still the principal source of farming for communities. The revival looks like a distant dream.
Published in Dawn, The Business and Finance Weekly, September 25th, 2023