Holistic hydro10 January 2008
A World Bank study is recommending basin-wide hydroelectric development to yield greater output from cascades, improve resource management and thereby help India achieve its social and economic development goals. Report by Sue Pritchard
The philosophy behind river basin development has evolved over recent years and more countries are taking up the challenge of a basin-wide approach to hydro power development. India is the latest contender to use such worldwide experience to its advantage, and two hydro-rich states believe that a holistic approach to river basin development can contribute to their, and the country's, development goals while promoting sustainable, equitable growth at local and regional levels.
Hydro power has significant potential when it is used to help meet national demands for more generating capacity, and the onus for such resource development rests with two Himalayan states. With the government estimating that hydroelectricity could increase its percentage of total generation from 26% to 40% by 2012, the state governments of Himachel Pradesh and Uttarakhand have put ambitious plans in place for the development of untapped capacity in their regions.
Himachal Pradesh has more than 20,000MW of identified hydro power potential (25% of the whole of India) but less than 7000MW has been installed to date. While Uttarakhand has potential hydro power resources of 15,000MW, the state has only harnessed 1000MW so far. At the request of the two states, the World Bank initiated a river basin development optimisation study to determine, and recommend, a framework for efficient hydroelectric development for river basins as a whole, which would naturally compare and contrast the experience of the project-by-project approach.
The Bank contracted Hydro Tasmania Consulting to undertake the study, which reviews the plans for developing the Satluj and Alaknanda river basins. Specifically, the study aimed to demonstrate how river basin development can help to achieve optimal energy production with minimal environmental and social impacts.
Rising in China, the Satluj river flows west through Himachel Pradesh and Punjab until it joins the Indus river in Pakistan. The Alaknanda basin is contained within Uttarakhand. Feasibility studies and related reports for hydro power projects in the river basins were analysed and simple mathematical and qualitative modelling was undertaken. Consultations were held with various stakeholders in the Satluj and Alaknanda basins, and experiences gained from international practice were drawn upon.
The collated information highlighted various shortcomings of the hydroelectric projects but illustrated how a framework for river basin development could overcome these with a positive effect on production. As highlighted by the findings of the study, the following factors are often associated with a project-only focus:
• Inaccurate estimates of energy production.
• A lack of upstream storage.
• Siltation problems.
• Poor flood risk assessment.
• Uncoordinated project construction and infrastructure.
• Social and environmental impacts.
Feasibility reports for the Satluj and Alaknanda basins indicate that current practice for analysing hydro power output only considers local site data for water yield. Although a significant part of both basins is covered by snow and glaciers (in some cases more than 50% of the catchment to a proposed dam site is snow covered), only a few considered yield estimates from these areas. For run-of-river hydro power projects this is an important issue due to the highly seasonal nature of snow and glacier runoff. Generally, upstream or downstream impacts of either water storage or operating rules are not considered in relation to yield. One report that was reviewed considered a power scheme immediately upstream but none considered the basin as a whole.
Hydrological yield estimations can be improved for river basin planning by the co-ordinated gathering, storage, and dissemination of hydrological and meteorological data to developers. The effects of climate change can also be estimated by central studies. To realistically assess run-of-river energy output, power projects immediately upstream should be considered as a minimum. Additionally, a cascade of run-of-river schemes could be optimised for total energy output if they are analysed together rather than in isolation. Ideally a basin-wide approach to energy yield is preferable.
For example, total energy output from a cascade system can be increased by optimising the scheduling of successive generators as the peak river flows progress downstream. However, current practice for energy production optimisation appears to be on an individual basis at the Satluj and Alaknanda projects, without regard to other projects in the cascade or indeed the entire basin. Therefore, it is seen that mathematical models of river basins should be developed to determine the effects of one project in a cascade on another, while the optimisation of the design and operation of a cascade of projects can be achieved.
Mathematical modelling in the Alaknanda river basin was carried out under the auspices of the optimising study. These models indicated that if the Alaknanda and Vishnuprayag plants were treated as a cascade, it could result in an increase in energy output of 230GWh/yr.
Upping the storage
Storage at the upstream end of a cascade can be beneficial in terms of controlling flows but needs to be large enough to allow proper regulation, otherwise the effect might be to reduce overall output due to peaking flows. Regulation provided by the storage would not only result in more energy from the cascade but also in less expensive projects due to fewer turbines and reduced installed capacity.
When incorporated into a river basin approach, studies for upstream storage must be carried out at a sufficiently early stage so that downstream projects can then be planned and designed accordingly. There would also be reduced environmental and social impacts due to the smaller footprint of the downstream projects. Such storage would also benefit downstream projects in terms of extending reservoir life and reducing downtime due to high silt loads.
Sedimentation issues have been prominent in the subject basins, with the Spiti river having a particularly high silt load. The Nathpa Jhakri plant has faced frequent shut downs due to very high concentrations of silt during the monsoons. On the Alaknanda, only two months after the Vishnu Prayag project started commercial production, two of the four turbines had to be taken out of service for repair following severe damage from the silt laden water. The number of upcoming projects in the Satluj and Alaknanda is likely to result in more sediment entering the rivers through soil erosion and construction spoils.
Silt loads can impact on hydro power projects in a number of ways. Storage can be lost over time due to siltation which can lead to the loss of daily and seasonal flow regulation and flexibility of operation (eg peaking power).
High silt loads can also damage turbine runners through pitting and erosion, resulting in reduced efficiency and a reduced operational life. Current practice is to incorporate desanders which remove silt particles greater than 0.2mm in size, and in times of high flow to close down the power station when the silt load exceeds 4000ppm. This problem could be reduced by having upstream storage to trap silt and more efficient desander designs. Costs could also be reduced by having the de-silted water from one project being directly fed to the downstream project, as is planned for the Raipur project downstream of Naptha Jhakri.
A basin-wide approach to hydro power development means that downstream users, including farmers who rely on sediments for terrace farming, must be considered if silt is taken from the river either through retained storage or by being completely removed from the river system.
Flood risk assessment
Current methods for preparing extreme flood estimation in the basins are not always consistent with the guidelines issued by the Central Water Commission. The guidelines suggest appropriate methods without actually being prescriptive and consultants generally try to adopt the simplest approach without exploring more appropriate methods.
With the amount of snow and glacier melt runoff contributing to baseflow, and the potential for increased flood runoff from extreme monsoon rain events falling on snow covered areas, it would be prudent to undertake a basin approach to flood estimation. The deterministic rainfall approach should be used with a unit hydrograph or hydrological modelled flood runoff.
The key advantage of flood risk assessment is in providing an accurate picture of risks upon which to base mitigation measures and emergency planning. An investment in a basin-wide assessment could be shared by governments and developers. A basin-wide flood forecasting and warning system should be implemented so that all downstream plants, local towns and villages can receive adequate and appropriate warning. Such a system is beyond any one individual developer and should be coordinated by both State and central agencies.
A new generation of river basin planning is emerging as the philosophy shifts from primarily engineering-based approaches to encompass biodiversity, non-structural means of improved water management, and stakeholder participation in sub-basin scale initiatives. The more holistic approach would seek to integrate potential environmental and social costs into the planning and implementation process.
However, at Satluj and Alaknanda the minimum flow requirements have not been developed with the ecology of the river basins, or the ‘carrying capacity’ of the rivers, in mind. Whilst the establishment of appropriate environmental flows continues to be a challenge everywhere, there is potential to improve its calculation and application in India. For example, given the high cultural importance of the Alaknanda as a tributary of the River Ganga, and being a heavily travelled pilgrimage route, it could be argued that a greater minimum flow is required.
International good practice points to the consideration of controlled water releases to support the ecology of the river being harnessed (and associated downstream tributaries) and/or social values associated with the river. Setting effective environmental flows requires a sound understanding of ecosystem function, and should be derived through a consultative process to establish the environmental and social values to be protected.
At present, a great deal of uncertainty surrounds the planned major development of hydro power in the Indian Himalayan region, which in itself creates social and economic impacts. People in the region do not have a clear understanding of the extent of the development and this makes investment in infrastructure and economic activity difficult. A river basin approach to environmental and social assessment would bring benefits at the planning stage for all parties.
A number of NGOs have supported the concept of river basin planning because it facilitates a strategic look at the natural, social and cultural assets or values in a basin and enables better plans to minimise impacts on vulnerable systems. This is particularly important for the Alaknanda region which has high cultural and ecological values and is relatively undeveloped. Three proposed projects (Deodi - 60MW, Rishi-Ganga I – 70MW and Rishi-Ganga II – 35MW) are located within the Nanda Devi National Park which is a designated World Heritage Area.
The report makes numerous recommendations and suggestions to enable hydro power development in India to move towards river basin level planning, design and operation. The underlying themes of these are the need for:
• data sharing amongst the developers and government authorities, particularly related to meteorology, hydrology and sedimentation;
• improved methods of yield estimation, which has a fundamental impact on project economics;
• significant improvement in coordination between developers in terms of shared infrastructure such as access roads, construction power, and power evacuation transmission lines;
• integrating communities and qualified third parties (NGOs) into aspects of project monitoring, such as the use of community forests and resettlement.
How the needs are to be answered remains a question. The many recommendations made in this report can be taken onboard as part of either improving current practice, or as steps toward the river basin planning approach. Implementing a completely new system via River Basin Authorities would require considerable time, and the report argues that positive actions should be taken as soon as possible without delaying the hydro power development programme.
A move towards river basin planning could include the informal, cooperative development of databases and tools which could be formalised through a central agency, the report suggests. It adds that establishing a new institution with the legal mechanisms to draw representative membership could deliver clear and transparent responsibility for river basin planning.
Further discussions are taking place on the report following its presentation last month to the governments of Himachal Pradesh and Uttarakhand, which had wanted the investigation to be undertaken. Going forward, representatives from the government, developers and affected communities can engage in debating the issues and deciding how the various recommendations might be implemented.
This article is based on the report ‘River Basin Development Optimisation Study’, October 2007, which was performed for the World Bank by Hydro Tasmania Consulting.
TablesSatluj Basin Project Details Summary of hydro power projects Alaknanda Basin Project Details