- The Underwater Domain Awareness (UDA) Framework is increasingly necessary for effective sedimentation management.
- Controlling erosion is one of the best methods to reduce large amounts of sediment.
- Sediment management in rivers should be the way forward for sustainable management of sediments.
- Sediment management in rivers should be the way forward for sustainable management of sediments.
Sediment management is a multilevel challenge that is necessary for collaboration among diverse stakeholders to ensure policy formation effectively. Annual monsoon of a year causes excessive siltation due to the high speed of the water. Thus, sediment management is very important to reduce the damage caused to the national economy.
In a 2022 article published in National Framework for Sediment Management, former Union Minister for Jal Shakti, Gajendra Singh Shekhawat noted, “In present times, due to rapid urbanization and development, many new issues are coming up, leading to a change in the river dynamics. Reservoirs are also losing their storage capacity because of sedimentation. Hence, comprehensive sediment management has now become the need of the hour for the sustainable development of the country’s water resources.”
Effect of Erosion on Sediment Management
Erosion and aggradations are the most important geological processes that are responsible for bringing down large amounts of sediment from higher elevations to plains. Sediment carrying capacity is directly proportional to the kinetic energy of water, as the river flows from a higher altitude to a lower, the speed of the flow is reduced as energy is being utilized by sediments with the suspension of coarser particles midway, thereby silt deposition in route. It may cause the widening of rivers which can further cause erosion of river banks and embankments. Sedimentation in rivers leads to a decrease in navigable depth and causes riverbeds to rise, resulting in drainage congestion. To address this issue, it becomes essential to remove sediment from specific locations strategically. In reservoirs, the removal of sediment can increase its life and minimize downstream stakeholder risk.
The key physical processes of rivers are mainly sediment transport, bank erosion, and associated channel mobility. Hence, their understanding plays a crucial role in defining river restoration and management strategies. The main causes of increased sedimentation in rivers are being studied and they mostly include rapid urbanization and industrialization in flood plains, encroachment of river beds, changes caused due to various human activities, and deforestation in the catchment area of river, etc.
Currently, sediment management in reservoirs and dams is becoming crucial for the development of water resources and management. Reservoirs have been used globally and have provided reliable water supply for irrigation, domestic, industrial, hydropower generation, flood management, etc. The Union Ministry of Jal Shakti is actively involved with the framework of sediment management, for holistically managing the sediment. This framework will involve concerned stakeholders such as state governments, other ministries, and various departments, etc.
Classification of Sediment
Sediment transport is the movement of organic and inorganic particles by water. Fine organic and inorganic material erodes from land surfaces, flows downhill to the river, and is then transported downstream as suspended sediment. Sediment is classified based on the size of the particle. Sediment is called coarse if its diameter is greater than 0.25mm while it is medium-sized if its diameter is ranged between 0.062mm to 0.25mm and is called fine sediment if its diameter is less than 0.062mm. The total sediment load includes bed load, suspended load, and wash load.
Sediment deposition in rivers at any place depends on their catchment/watershed characteristics, size, geological disposition along the course of the river, and other human interventions. Alterations in sediment quality and quantity can significantly affect both rivers and reservoirs. These changes serve as valuable resources but can also pose challenges in their unique ways.
Stakeholders Involved in Transport Study
Sediment management plays a crucial role in conducting transport studies. It is an essential aspect that cannot be neglected when studying sediment movement and its impact on natural systems. A few applications of sediment management are water resource management, port management, inland water transport, ecosystem management, etc. Each stakeholder has a different point of view and has a different aspect of each problem. The stakeholder process, therefore, deserves a lot of attention. A few stakeholders interested in the sediment transport study are:
- Government Agencies: These include local, regional, and national agencies responsible for environmental protection, water resources management, and infrastructure development. They set policies, monitor river health, and manage sediment-related projects.
- Environmental Organizations: Non-governmental organizations (NGOs) and advocacy groups focus on preserving habitats, improving water quality, and maintaining ecological balance.
- Local Communities: Residents who live near rivers are directly affected by sediment transport as it impacts water quality, flood risks, and recreational opportunities. They may also depend on the rivers for fishing, agriculture, and transportation.
Sediment Management in Rivers and Watersheds
Minimizing the sediment intake is very important to ensure the optimal functionality and longevity of a dam or reservoir. This requires a two-pronged approach: catchment area treatment and appropriate land practices planning to address unsustainable land use to reduce sediment production and soil erosion. If sediment is not removed from run-of-river facilities before it enters canal turbines, heavy siltation in canals may cause clogging of water intakes. It is important to prioritize catchment area interventions because they arrest silt within the boundary of a watershed which helps in minimizing siltation in river beds and reservoirs.
For rivers, it is important to incorporate sediment management into an integrated river basin management plan. Regular sediment budgeting should be performed for all basins, especially those that are affected by heavy siltation problems. During the lean season, removing sediments from the river bed may aid in the channelization of river flow and improve navigability, but it may not have a significant effect on flood levels.
Effect of De-siltation in Reducing Floods
De-silting of rivers does significantly affect flood levels. Stakeholders aimed to identify the causes and extent of river siltation, recommend ways to minimize it and assess if de-silting is a viable method to reduce flood severity in rivers. Additionally, they were to suggest the best technologies and methods for de-silting, propose a realistic, time-bound operational program, and consider other related aspects. Here are the findings and recommendations of the involved stakeholders:
- De-silting of rivers for flood control is not a very economical solution.
- De-silting of rivers can minimize the magnitude of floods to some extent and could be effective only for a short period.
However, selective need-based dredging of certain reaches of rivers along with structural and non-structural measures could be considered to protect habitation, agricultural land, airports, industrial and institutional installations, etc.
Measures to Minimize Sediment Deposition in Reservoirs
It is possible to successfully manage reservoir sedimentation by using a sediment management strategy. This involves implementing measures to reduce sediment yield from the watershed, diverting sediments around or through storage, and restoring lost reservoir capacity through desilting. None of the single measures can be 100% effective for ensuring the long-term sustainability of sediment management in reservoirs.
Catchment erosion is the main source of incoming sediment to any reservoir. Hence, the first step in tackling the main cause of incoming sediment is watershed management through various engineering and bio-engineering techniques to address sediment erosion effectively. The next step is to manage the sediment deposited in the river by routing the sediment around or through the storage by different kinds of sediment by-pass and sediment pass-through interventions. Sediment Bypass includes Flood Bypass Channels or Tunnels and off-stream reservoirs for bypassing sediment inflows away from reservoirs. Strategies such as draw-down flushing (complete and partial), pressure flushing, sluicing, and venting turbid density currents are sediment pass-through techniques. These non-structural interventions involve operational methods aimed at removing sediment from reservoirs.
Conclusion and Summary
Various techniques for sediment routing use temporal variation in sediment discharge to manage flows during periods of highest sediment yield to reduce sediment trapping in the reservoir. The basic strategy is to restrain the clear water and release the sediment-laden flood flows. Sediment routing techniques require a part of the river inflow and storage volume for transporting sediment around or through the reservoir. At their optimum operational levels, bypass tunnels can reduce sedimentation by 80-90 percent, according to studies by researchers.
Pradnaya Kumbhare, IIT Bombay
About Author
Pradnya has recently completed her internship with the Maritime Research Center, Pune. She is a third-year undergraduate at the Indian Institute of Technology (IIT) Bombay in the Electrical Engineering Department. She also worked as a Marketing Associate in one of the recent technical teams at IITB, named Spart.