A 2km stretch of the Nara Canal, the largest channel in Sindh`s irrigation network, has been lined to restore its original parameters, which were disturbed due to soil erosion. Nara Canal emanates from the Sukkur barrage, the oldest barrage in Sindh. The lining aims to improve water productivity in the Nara canal system that feeds the lower Sindh region and touches the desert region of Tharparkar.

From an engineering point of view, the lining was a work of important nature to ensure efficient flows with a gross cultivable area of 2.17 million acres and a cultivable command area of 2.1m acres. Nara`s main canal stretches over 226 miles, according to irrigation department figures, bringing water to major left bank districts like Sanghar, Mirpurkhas and Umerkot a hub of mango orchards and sugarcane.

Nara Canal is part of the irrigation system managed by the Sindh Irrigation and Drainage Authority (Sida), a body that seeks to promote a participatory irrigation system. Sida has executed the project out of provincial government funding at a revised cost of Rs 4.25 billion the project was initially planned at a costof Rs 2.89 bn.

During the ongoing Rabi crop season, the channel was closed on Jan 6 this year ahead of the Sukkur barrage`s closure. Water supply in the canal resumed on Feb 4 with a discharge of 1,800 cusecs to enable growers to start preparing for Kharif season, which begins early in this region compared to the rest of Sindh.

Depending on water availability in the Indus River, the Nara Canal can draw a maximum discharge of 18,00019,000 cusecs, even though its designed discharge is 13,649 cusecs.

`The area of the pit is located downstream between RD0+315 to RD0+955,` said Qamar Hussain, resident engineer of National Engineering Services of Pakistan (Nespak) while talking to Dawn at the site before the canal was to be opened for regular flows. Nespak was Sida`s project consultant.

According to Mr Hussain, considerable scouring occurred in the canal`s earthen bed; this lining methodology would address it now. Lining work was done between RD1+160 to RD7+050.

A drainage system has been installed in the bed to protect the lined structure. Sheet piles were installed at 28ft depth inside the bed coupled with a sloppy design to help block siltupstream in the pit, he added.

Sida`s General Manager of Operations, Sajjad Soomro, observed that the sheet piles would dissipate energy in the current of water and travelling time would increase. He said the soil in the canal remained sandy as the Nara Canal used to be a natural waterway in the pre-Sukkur Barrage era. `Flows were not uniform in the canal due to pit,` he said.Between the lined and earthen bed of the canal, a 15ft fall occurs. At this point (RD7+050), an RCC slope is added to withstand high water pressures. It is also backed by stone dumping at 250ft in length to avoid ditch formations in the bed, thus ensuring canal safety, explained executive engineer Khurram Parvez Rid.

Resultantly, the upper surface of the water at the canal head wouldmove faster while silt-laden flows would remain trapped to cause silt deposition eventually in the same pit that is invariably 40-50ft in depth. This process would take a year or so.

The pit`s creation at Nara`s head made the canal water flow turbulent, prompting Sida to find a solution.

During a rotation programme coupled with this chronic problem, water shortage complaints had increased.

Sida`s Managing Director, Pritam Das, believed that noticeable soil erosion was witnessed at a fast pace in the canal, which necessitated this work that meanders at certain locations. He pointed out that the lining would help improve efficiency in the canal`s regulations.

`Water productivity will certainly improve, and the canal will be channelised up to RD-13. The canal has witnessed major interventions and due to its capacity for carrying more water, projects like twin Jamrao were also executed,` he said. Mr Das pointed out that the lining would help restore the canal`s original parameters and address the pit issue.

Before Nara, a certain reach, around a 10km area, of Rohri canal was lined about a decade back. Rohri, being the second largest canal of Sukkur barrage, also feeds the lowerSindh districts, including Tando Allahyar, Matiari, Badin, Sukkur, etc. It was lined by the irrigation department in Benazirabad district ostensibly though to benefit a construction tycoon`s private housing scheme to control seepage in the land located adjacent to the scheme.

Nara Canal has witnessed a few essential interventions to achieve water productivity. Multibillion rupee expenditures were witnessed over the canal`s re-alignment. Construction of fall structures was another major task achieved on the canal. The Makhi Farash complex in Sanghar, Pakistan`s largest cotton-producing district, was a huge intervention.

The complex led to provisions of freshwater through Thar carrier to energy project in coal-rich Tharparkar district`s Islamkot taluka, where power generation has been taking place for the past several years to feed the national grid. Construction of the Makhi-Farash Complex has three heads and one cross regulator for the Thar, Khipro and Mithrao canals.

Three of five fall structures were built by Sida at a cost of Rs1.25 billion to remove meandering in the canal and ensure uniform flows under the World Bank-funded Water Sector Improvement Project through Sida. •