Impact of Structural Interventions on Sediment Management of Large Canals: A Case Study of Marala Barrage, Pakistan

Abstract

Marala Barrage was constructed in 1968 on River Chenab as a replacement of old Marala weir, which was constructed in 1912. Two canals, Marala Ravi Link (MRL) Canal and Upper Chenab Canal (UCC) off-take from left side of the barrage. It has an old history of varying sediment problems in both of these canals. Several attempts were made to investigate the problems and suggest remedial measures in the past and some of them were partially implemented as well. This paper reviews the major sediment management problems at Marala Barrage and their possible causes. The previous interventions are critically examined for their suitability and effectiveness in general and the effect of raising crest of MR Link canal in particular. The paper concludes that some of the past interventions have a positive effect on silt control entry in the off-taking canals. The analysis of data regarding sediment entry at the head of the canals indicate that the raising of crest of MR Link in the year 2000–2001 has improved the sediment intake in this canal to some extent, but its effect on the UCC is almost negligible. The data regarding sediment entry at the head of the UCC which had a scouring tendency, does not show any significant effect of this intervention as was perceived at the implementation stage. However, it is worth mentioning that analysis of data related to cross-sections and L-sections of the head reaches of these canals show a different trend, which makes it difficult to assess the long term and sustainable effect of this intervention on both of the canals. A critical review of data collection process and effective monitoring of the system is compulsory for meaningful analysis and future course of action if the present tendency seems to be changing, the possibility of which does exist.