Sindh Irrigation & Drainage Authority

Sedimentation: An operational problem of Mithrao Canal

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Courtesy of Sindh Irrigation & Drainage Authority

Mithrao Canal off-takes from Nara Canal, which off-takes from the left bank of Sukkur Barrage. The participation irrigation management was introduced in Sindh Province with the establishment of Nara Canal Area Water Board in 1999. Mithrao Canal Division is divided into four administrative sub-divisions (please refer Annexures – II & III). They are as following;
a. Sangahr Sub-Division.
b. Samaro Sub-Division.
c. Nabisar Sub-Division.
d. Naukot Sub-Division.

There are 55 minor & distributaries in Mithrao Canal and many direct outlets. The system is considered to be efficient for its high cut-off since it helps in smooth gravitational flow of canal water.


The irrigation channels in Indo-Pakistan were designed on regime theory after tedious research by some renowned Irrigation Engineers like Mr. Inglis, Mr. Kennedy, Mr. Lacey. As such, regime channels are supposed to be non-silting and non-scouring. However, some channels undergo problems of erosion or deposition of sediment at some reaches. This creates regulation and management problem and at times leads to breaches and morphological changes with the channel. Currently Mithrao Canal is facing the problem of sediment deposition at some reaches especially between RD-175 and RD-230.


There are three canals off-taking namely: Lower Nara Canal, Khipro Canal and Mithrao Canal. The Lower Nara Canal has been provided with silt ejectors in the form of pipes at glacis during the construction of new head regulator. This was constructed few years back by the Chinese Engineers at about one thousand feet (i.e. 1 RD) downstream of the old head regulator. The new head regulator was constructed to increase the discharge capacity of Lower Nara. The new head regulator is provided with silt ejectors in the form of circulator pipes. Since the silt ejectors on the right side are not functioning well, as reported at site, therefore, sediment is depositing on the left side just 350 ft downstream (as shown in photo-6) and it is likely to become a silt bar in due course of time. Khipro Canal has little cut-off and as such does not carry any additional sediment load. Mithrao Canal has a huge cut-off of 08 ft, which means that velocity of incoming water would be very high at the intake. This view is validated by the fact that a scour hole is developed just at the downstream of gates (where friction blocks are erected to dissipate the energy) and, therefore, section has widened (as shown in photos 1, 2&3). To control the situation, jhuck work has been done. Due to high cut-off, Mithrao Canal carries more sediment load and it is further increased due to erosion of the bed immediately downstream of the head regulator.

It has been reported by the operational staff that this year Mithrao Canal was immediately opened after the end of closure period (every year irrigation canals are closed for about 15 days to carry out necessary repair/maintenance works) while Lower Nara Canal and Khipro Canal were opened after a week. Therefore, bulk of the sediment load entered into Mithrao Canal’s system. Although formation of silt bar is a slow process, however, this factor could have also helped in aggravating the situation.

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