ABSTRACT
Sukkur Barrage was constructed between 1923 and 1932 and is located on the River Indus in Pakistan. The barrage has suffered from sediment management issues since its construction and as a result the so called ‘approach/tail channel’ was installed on the right bank to induce secondary currents with the aim to reduce sediment intake into the right pocket and the canals. An island was created between the tail channel and the right pocket which has led to the closure of 10 gates. For some years this approach was perceived as successful but over time the canals on the right bank have experienced significant sediment build-up. In addition to this there is significant build-up of sediment in the river channel, both upstream and downstream of the barrage, and the pockets.
The sedimentation problem was investigated as part of a wider project adding significant complexity to the possible solutions and improvement measures. One of the other major concerns at the barrage was flood risk. The original barrage configuration had 55 main river spans. This number was reduced to 36 main river gate to allow the construction of the approach/tail channel with 8 gates and closure of 10 gates as part of the sediment management improvements. This has led to concerns about the flood capacity of the barrage in particular following the 2010 floods in Pakistan. The sediment management of the barrage and the flood capacity can therefore be perceived as competing concerns.
The barrage is of great significance to the agriculture in Sindh Province supplying irrigation water to over 8 million acres on both banks of the Indus. The command area of the barrage is the largest of the three barrages in Sindh Province. As such, the safety of the barrage and the continued performance attracts huge public interest.
Since the construction of the barrage significant further development has taken place on the Indus upstream with construction of a large number of dams and barrages on the Indus and its tributaries. This has significantly altered the flow arriving at the barrage and has also influenced the sediment transport in the river system.
Furthermore, climate change is likely to have played a part in the reduced dry season flows experienced particularly between 2002 and 2011.
As a result the solutions had to balance the requirements of both the sediment management and the flood capacity of the barrage.
The paper sets out how the project addresses the risks to the barrage from droughts, flooding and climate change and how the team have approached the identification of solutions in the context of the competing requirements for flood capacity and irrigation performance. The challenges faced on the project provide lessons learnt for other projects and demonstrates the need for engineers and scientists to understand the wider picture beyond the science of sediment management.
