By Rehan Khan Khushik
SUKKUR: A case study of the Sediment transport dynamics during 2010 super flood at the Guddu Barrage on the Indus River published by the International Journal of Sediment Research and experts strongly recommended sediment management to ensure ecosystem maintenance for mitigating threats of sea water intrusion, reduce desilting cost, maintain flood carrying capacity and increase life of gated weir.
The study released recently, observed that sediment management could reduce the billion of rupees cost annually of desilting work and maintain the flood carrying capacity of hydraulic structures. The study was conducted by local and international researcher’s team from Project Management Office- Sindh Barrages Improvement Project, Irrigation department, West Florida Research & Education Centre, Watershed Management Lab, Soil, Water, and Ecosystem Science Department, University of Florida USA, and Mehran University of Engineering & Technology Jamshoro, led by Imran Aziz Tunio, PhD Scholar.
The study was conducted using 1D sediment transport model, made by Hydrologic Engineering Centre- River Analysis System (HEC-RAS) US Army Corps of Engineers, sediment transport was assessed for three months duration from July to September 2010. The analysis revealed that cumulative sediment mass inflow was about 320 million tons, and sediment transport aggradation was 155 million tons at Guddu Barrage.
This study can help local authorities, Federal Flood Commission, International Sediment Research Institute of Pakistan (ISRIP), and the Indus River System Authority (IRSA), policy and decision makers about the situations pertinent to understand the sediment transport dynamics and behavior of water spreading in the river through a gated weir and measure the effects of the climate change in the case of extreme floods, the high flood level may be exceed against the design flood carrying capacity at barrage. Additionally, this study can assist in the operation of gates managing sediment deposits that exist for Indus delta environments.
The study suggest 1D model can also provide quick intelligent estimation and visualization of sediment aggradation, degradation, flood depth, flood retention duration, inflow, outflow, along with water surface elevation, in comparison to manual calculations, which necessitate significant resource allocation.
The 1D model revealed that sediment accumulation could cause significant operational issues at the barrage. Model simulations indicate that barrage gates operation significantly impacts sediment management, standard operating practices can significantly minimize sediment deposition in the upstream of barrage and off taking canals, up to 60%. The effect of sedimentation on bed level rise would influence flood carrying capacity of barrage, high lag time, increasing maintenance costs and, flow delivery to the off taking canals, therefore restrict canal conveyance capacity, resulting an increase in pond/ water levels which can endangering system sustainability.
The model’s most significant feature was its capacity to display flow characteristics and sediment patterns throughout its cross-section, and in the longitudinal direction, gates operation, critical velocity, erosion, and deposition at each simulated section.
The findings and techniques applied in the study can be helpful to the improve barrage gate operation for regulation of water and remove sediment deposition at upstream of barrage. However, the use of advanced modelling techniques may also familiarize decision makers and enable them to assess the situation, allowing them to develop effective policies and timely decisions for sediment flushing operation and mitigating possible flood damages in vulnerable areas.
The study suggests that water surface elevation/ flood levels are very important to be vigilant to possibly unsafe levels of water so that corrective measures can be taken timely, and early warning can be issued in case of flooding conditions to safeguard vulnerable populated areas and resources. The lessons learned from the 2010 super floods underscore the significance of such preparation and stress the necessity of employing real-time monitoring and emergency preparedness plan to rescue and save vulnerable communities and public property.
The study indicates that the lower reach of the Indus River in Sindh province is characterized by a flatter slope terrain, while the upper reach extending from the Himalayas to Punjab features a steeper slope terrain, resulting high velocity carry more sediment load in the flow from upper reaches due to steeper terrain. As the river progresses towards the lower reach, the flatter terrain slope and low velocity contribute sediment aggradation in flatter terrain. Sediment will remain suspended in the river due to lack of minimal flow requirement for flushing during low water demand period and will not move to downstream; sediment flow will be required to initiate the flushing process. There is dire need to revisit the Water Apportionment Accord of 1991 and allocate sediment flow for the flat slope region, as sediment can be removed towards delta environments to combat sea water intrusion, ecosystem maintenance, reduce desilting cost and increase life of gated weir.
The study serves as a reminder that climate change projected to escalate the occurrence and intensify of floods and other severe weather occurrences in the years to come. As a result, the concerned authorities must be prepared to alleviate the consequences. Thus, the Federal and Provincial government needs to be ready for active flood monitoring and management in real-time basis. It is important to strategize how to flush out deposited sediments while low and peak water demand periods by implementing appropriate gate operation protocols.
Among its key recommendations to the use of a two-dimensional flood propagation model to enhance monitoring in anticipating areas at risk of flooding, the study recommended the use of hydrodynamic and sediment transport model to observe how sediments move, settle, and affect rivers and hydraulic structures to improve the accuracy of results.
