STRIVAN - Storage and Risk Value Analysis - water and hydro reservoirs

The project has developed a decision support tool which dam owners and water authorities can use to quantify the benefit of the reservoir volume (storage volume) that is lost due to sedimentation. Reservoirs store water so that the water is available for use when the need for water/energy is greatest, for example for agricultural water during cultivation periods or for energy production. Drained reservoirs help to reduce flooding downstream and can thus contribute to less flood damage during heavy flooding episodes. Reservoirs therefore have great value both from a social economic and a business economic perspective. It is estimated that around 1% of the volume of the world's water reservoirs is lost annually due to sedimentation and this loss is considered one of the biggest sustainability challenges for the dam and hydropower industry. The project has further developed quantitative reliability analytical methods (including failure modelling) in combination with hydrology and sediment science. A separate GIS tool has been developed for estimating flood costs. In combination, these methods will be able to analyze and value loss of volume and risk of damage due to large flood and sediment events, as well as to analyze the socio-economic and business economic benefits of alternative technical solutions. The project has used plants from the Philippines and two plants from Albania as example plants where the method has been applied. For both of these examples, results show that "hydro-suction", i.e. sediment suction with gravity solution, was the most profitable future single solution to reduce future sediment risk for the facilities.

Sedimentation in hydropower storage reservoirs is a major and increasing problem in the world and for the future energy market. The value of stored water in reservoirs in terms of revenues from power and energy production has increased rapidly due to recent market conditions. It is therefore increasingly important that plant owners secure and maintain this valuable reservoir storage. The application of STRIVAN methodology has improved the understanding of sediment-related risks and costs throughout the dam owner’s organisation (owner of both cases). This in turn has formed a broader consensus from management to O&M staff on what measures are to be applied and when. Using the STRIVAN approach to analyze sediment risks for an asset requires a multidisciplinary team of experts as well as the technical O&M/Asset Owner experience. A full STRIVAN process will make sense and be beneficial for large reservoirs and high-income hydropower assets in catchments with heavy sediment yields. The sediment hydro-suction solution has been analysed and was found to be the most profitable measure for protecting power intakes in both test cases. The approval process of solutions like hydro-suction can be long and needs to start early to achieve an optimal timing of solutions. It is important to note that, if the two test cases studied were not part of a cascade but were “stand-alone” reservoirs, the NPV results would have been significantly different, and the analyses would have resulted in higher profitability of mitigation measures implemented earlier in the lifespan of reservoirs.

The research project will provide dam owners with decision-support tools which quantify loss of reservoir storage due to sedimentation and enable them to prolong the lives of their existing reservoirs as well as build in true life cycle analysis and sustainable design into their decisions on future projects. The products of this research project are designed to be taken into broad use by the project beneficiaries, thus enabling reservoir storage to be optimized from a broader society viewpoint and enabling measures to reduce sediment deposition to be given full attention and appropriate weighting in the design of new dams. Loss of storage volume due to siltation is one of the main factors which prevents the dam industry being viewed as truly sustainable. Despite this growing need for more water storage, research into what the full cost of loss of reservoir storage is to the dam owner and society at large is very sparse. Techniques for valuation of storage are lacking on a global scale both in terms of the reduced damage due to flooding and due to loss of income due to power production losses and failure to deliver the original services the reservoir was designed for. The objective of project is also to develop a statistical method for estimation of economic risk associated with flood events combining the science and approach of reliability engineering with sediment science. The conceptual framework will be developed in parallel with using a pilot case. The starting point of the method is estimating the probability function of clogging of intake etc. under different future floods and scenarios. The focus is on high to extreme events, i.e. floods that cause extraordinary sedimentation that may result in a failure (unplanned downtime). The method can be used in the process to optimize technical hydraulic solutions and to guide decision makers on the optimal timing of the measures.