This paper explores the role of the Lenders’ Technical Advisor (LTA) in identifying and mitigating risks in hydropower dam projects on behalf of the project lenders. It describes the LTA services that are required to manage the pre-financial close, construction and financing periods.
There are differing types of risk in both large and small hydropower projects (contractual, commercial, participant, completion, country, technology, reputational, environmental and social, etc.) and these are discussed with regard to how the lenders may be exposed if the risk eventuates either during dam construction or in operation.
Whereas a large dam for water supply would in its own right be a major project, the dam(s) associated with large hydropower will likely represent less than 25% of the total project cost and with this imbalance comes competing drivers for the other components (tunnels, waterways, powerhouse, M&E equipment, transmission lines, substations, etc).
The paper discusses the typical process whereby a hydropower developer has procured a feasibility study and is working towards financial close — covering both large and small types, i.e. storage dams and run-of-river diversion weir types, and the noticeable trend for fast-tracked developments to make a single large step from feasibility study through to engineer-procure-construct (EPC) contracting. This scenario presents some challenges for the initial due diligence when assessing in the pre-financial close stage.
The paper draws on case studies from the Asia Pacific region to illustrate the key elements in hydropower project financing from the LTA’s perspective, together with the author’s recent and current experience on multiple hydropower projects across Asia and Africa in the run-of-river, storage reservoir and pumped storage type of plants. It also brings together findings from the author’s own recent papers on the subjects of hydropower feasibility studies, the roles of lenders, owners and advisors, and tailored for an ANCOLD audience where the focus is on the dams component of hydropower.
Keywords: Lenders’ Technical Advisor, Dams, Hydropower.
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Chriselyn Meneses, Simon Lang, Peter Hill, Mark Arnold
Risk is the product of likelihood and consequences. Much effort is put into the risk assessment process for large dams to ensure there is a consistent approach to estimating failure likelihoods across an owner’s portfolio. For example, the use of common peer review teams and methods like the ‘piping toolbox’ allow the risk assessment team to apply repeatable logic and processes when estimating failure likelihoods. However, the methods for estimating life safety consequences are often not applied consistently. This inconsistency leads to estimates of potential loss of life (PLL) that vary between dams in unexpected ways, because results from the most commonly applied method (Graham, 1999) are sensitive to threshold changes in flood severity and dam failure warning time.
The recently released Reclamation Consequence Estimating Methodology (RCEM) is intended to supersede Graham (1999). RCEM varies fatality rates continuously with DV, and is therefore less sensitive to changes in flood severity. In this paper, estimates of PLL from RCEM are compared with results from Graham (1999) for five dams. Results from the latest US Army Corps of Engineers model for estimating the consequences of dam failure (HEC-FIA 3.0) are also compared with RCEM and Graham (1999) for one dam. Comment is then made about the important considerations for applying RCEM consistently across a portfolio of dams.
Keywords: potential loss of life, dam safety, risk analysis
Jiri Herza and John Phillips
The design of dams for mining projects requires processes and technology that are unfamiliar to many mine owners and managers. Dam designers rely on ANCOLD assessments of Consequence Category, commonly leading to a High rating for mining dams due to a combination of potential loss of life, impact on environment and damage to assets such as mine voids, process plants, workshops, offices, roads, railways etc.
From this High Consequence Category the relevant annual exceedance probabilities for design parameters and loading conditions such as earthquakes and floods are selected.
Mining companies have sophisticated methods available for assessing risk, yet for their assets they often adopt an order of magnitude lower security for earthquake and floods even though the consequences in terms of lives at risk and impact on project are similar.
The discrepancies in the design standards lead to situations where extreme dam loads are adopted to prevent damage and loss of life in assets that theoretically would have already collapsed under much lower loads.
One difference may be that some mining dams exist in an environment which is controlled by a single entity. Unlike other dams, failure of these mining dams would therefore impact only individuals and assets which fall under the responsibility of the same entity.
This paper discusses the discrepancies between the design of mining dams and the design of other mine infrastructure. The paper considers the impact of discrepancies on the overall risk to the mine and compares the degree of protection offered by a factor of safety and the influence of reliability of design input parameters, alternate load paths and design redundancy.
Keywords: Dams, tailings dams, mining, acceptable risk, factors of safety
Vicki-Ann Dimas, Wayne Peck, Gary Gibson and Russell Cuthbertson
Globally, reservoir triggered seismicity (RTS) is a phenomenon sometimes observed in newly constructed large dams worldwide, for over 50 years now. Over 95 sites have been identified to have caused RTS by the infilling of water reservoirs upon completion of their constructions worldwide. In Australia, there are seven confirmed sites with observed RTS phenomenon that are summarized by temporal and spatial means.
With almost 40 years of seismic monitoring, primarily within eastern Australia, several of Australia’s largest dams have monitored and recorded many RTS events. At present, twelve dams are 100 metres and above in height as possible candidates, with seven of these actually causing RTS and a disputed possible eighth dam.
Important factors of RTS are reservoir characteristics (depth of the water column and reservoir volume), geological and tectonic features (how active nearby faults are and how close to the next cycle of stress release they are temporally) and ground water pore pressure (decrease in pore volume under compaction of weight of reservoir and diffusion of reservoir water through porous rock beneath). RTS is an adjustment process often delayed for several years after infilling of reservoir before eventually subsiding within 10 to 30 years, when seismic activity then returns to its prior state of stress.
Generally there are two type of RTS events, either a major fault near the reservoir most likely leading to an earthquake exceeding magnitude 5.0 to 6.0, or more commonly, a series of small shallow earthquakes.
Seismic monitoring of all dams (except for Ord River) are presented with spatial and temporal series of maps and cross sections, showing the largest earthquake, build-up and decay of RTS events.
Keywords: Seismic monitoring, reservoir triggered seismicity (RTS), earthquake cycle
Peyman Bozorgmehr, Sarah McComber, David Harrigan, Erik F R Bollaert
Boondooma Dam is a concrete-faced rockfill dam with an unlined, uncontrolled spillway chute. The Acceptable Flood Capacity of Boondooma Dam is 1:60,000 AEP (equal to the Dam Crest Flood (DCF) and has a maximum inflow of 14,330 m3/s.
Significant rainfall events during 2010/11 and 2013 subjected the spillway to moderate discharges over the crest which caused significant scour to the spillway chute.
Following these events, a 3D physical hydraulic model was constructed at a 1:80 scale to investigate repair options. Originally the spillway chute was modelled using a mobile bed set up which showed that that future scour could occur. However, the model could not determine the rate and characteristics of this damage.
In order to determine how future scour may occur, the 3D model was modified using laser survey mapping of the spillway chute after each flood event. Using milled aluminium and concrete capping the model was able to accurately portray the damage profile sustained by the spillway in the 2010/11 and 2013 flood events.
Transient pressure, static pressure, water elevation, velocity and jet measurements of the model were used in a Comprehensive Scour Model to help inform how damage to the chute may progress in future flood events.
Keywords: Boondooma Dam, flood damage, 3D physical hydraulic modelling, comprehensive scour assessment
Richard Herweynen, Tim Griggs, Alan White
The Ministry of Public Utilities, Sarawak, Malaysia used an independent dam safety consultant to advise them on whether the Murum Dam was ready for impoundment. They were looking for a holistic assessment of the dam from a dam safety perspective. As a result, a risk framework was adopted to identify the key issues that needed to be addressed prior to impoundment of the Murum Dam. The process adopted which is presented in this paper, was transparent and defensible; and provided a reasoned approach for which items must be completed prior to the commencement of impoundment. As a result effort was focused on the key activities required prior to impoundment – whether this was the completion of specific works, the availability of key instrumentation to monitor the dams performance, the availability and operation of key dam safety systems, or the appropriate emergency preparedness should a dam safety incident occur during first filling. This systematic process based on a risk based approach, was a useful method of determining the dam’s readiness for impoundment, and provided an excellent way of communicating the importance of activities to the key stakeholders. The authors believe that this method is transferable to other dam projects, for an assessment of a dam’s readiness for impoundment.
Keywords: Dam safety, risk, impoundment, reservoir filling.