John Grimston, David Leong, Robin Dawson
The Angat Multipurpose Project, originally constructed in the 1960’s, is located 60 km north-east of Manila, and provides power, irrigation and domestic water supply and flood mitigation. The major water-retaining structures of the scheme are a 131 m high main rockfill dam and a 55 m high rockfill saddle dam.
Previous seismology studies have identified the presence of a possible branch of the West Valley Fault crossing under the saddle dam. If the fault dislocated, the branch under the saddle dam could produce horizontal and vertical shear displacements. Further, earthquake shaking poses a risk outside the fault zone. If the main dam/saddle dam were to fail in such an event, there would be major consequences in respect to both the water supply (serves a population of approximately 10 million) and the large population living below the dams. The dams are thus in the highest hazard category under any internationally accepted standard.
A study to investigate the dam safety aspects and identify remediation works which would bring the seismic performance of the main dam/saddle dam system up to an acceptable level was undertaken and included:
The main conclusions were:
Keywords: Dam, Remedial, Seismic, Fault, Spillway.
Robert Kingsland, Jamie Anderson, Andrew Russell, David Brooke
This paper presents the methods, observations and results from a programme of No-Erosion Filter (NEF) testing for the evaluation of a manufactured filter aggregate product that did not conform to normally accepted D15F grading limits. Base materials tested include both dispersive and non-dispersive soils. The results are compared against published no-erosion, excessive erosion and continuing erosion thresholds. The paper comments on the validity of the adopted thresholds and the effectiveness of the NEF test as a filter evaluation method.
Keywords: dam, filter, test, no-erosion
This paper highlights the importance of hydraulic diversion control structures during construction of large dams and the value of allocating sufficient resources during project planning and implementation.
The design of the diversion gate for construction of the Enlarged Cotter Dam presented various challenges, including operation for up to 38m head for discharge into a 3m diameter conduit and the need to serve as an upstream concrete form during eventual diversion closure.
The short duration of operation allowed acceptance of increased level of operational risk and a higher level of design uncertainty. The design used generally accepted gate design methods, but no hydraulic modelling. The hydrodynamic forces were estimated using published data. After installation, a 1 in 100 AEP flood event resulted in the gate being subjected to 90% of its design head while operating in conditions close to the maximum design down-pull force. Attempts to raise the gate succeeded only after increasing the hydraulic pressure above the design value.
Keywords: Guard gate design, outlet works, dam, construction.
Dr Andy Hughes
This paper will outline changes currently being implemented to the UK legislation via the Flood & Water Management Act 2010. This legislation has driven a change towards a risk based approach.
Significant consultation with the profession and owners has provided an interesting insight to the different and disparate views of owners, engineers and the public.
The guidance documents associated with the Act associated with floods and risk management are currently being rewritten and will be completed by the time of the conference in Perth and so progress with reformatting of those documents will be reported upon.
Keywords: Legislation, guidance, consultation
Louise Thomas, Graeme Mann, Alex Gower
Mundaring Weir is a 41m high concrete gravity dam that was built in c.1900 to supply water to the Western Australian goldfields towns of Coolgardie and Kalgoorlie. The dam was raised by 9.75 metres in c.1950 and impounds a reservoir of 63.5 GL. The c.1900 cast iron outlet works and c.1950 mild steel outlet works are still in operation without any significant modification or refurbishment since installation.
Mundaring Weir remains the principal storage for the Goldfields and Agricultural Water Supply (G&AWS). To meet the increasing demand and improve water quality in the G&AWS, the West Australian Water Corporation is upgrading the outlet works, constructing a new pump station and a water treatment plant.
The paper discusses: condition assessments undertaken; basis for refurbishment and the selection and design, including hydraulic modelling, of a staged upgrade of aged outlet structures; and ensuring these works can be undertaken without impacting on supply during the course of the works.
Keywords: Outlet Works, Asset Condition Assessment, Mundaring Weir
Krey Price, David Moore, John Palensky
Cold water pollution (CWP) occurs when dam releases draw from lower-temperature regions of a reservoir, potentially impacting fish survivability in downstream waterways. Declining fish populations along the Missouri River have prompted recent investigations into solutions for CWP prevention.
Fort Peck Dam is an 80-metre high, 7-kilometre long dam located along the Missouri River; completed in 1940, it is one of the world’s oldest and largest hydraulically filled earthen dams and is listed on the U.S. National Historic Register. Inflow temperatures to Fort Peck Reservoir are significantly warmer than the outflow temperatures through the dam during the months of March through August. A water temperature of 18°C has been identified as critical for spawning and recruitment of locally threatened fish species; however, downstream temperatures typically remain below 14°C during critical time periods. This difference is due to the current deep-water withdrawal from Fort Peck Reservoir.
Ten alternatives were proposed to increase the temperature of the discharge, and an options analysis narrowed the results to a single, preferred alternative that consisted of a flexible, submerged weir around the intake. This paper documents the design efforts undertaken for temperature control measures at Fort Peck Dam, including a description of the modelling methods, design criteria, and effectiveness of the submerged weir alternative.
The use of a submerged weir to increase discharge temperatures relies on the process of passing warmer water from the upper portion of the water column over the weir crest into the intake area, rather than drawing from the bottom of the reservoir. For reservoirs with fluctuating levels, such as those at Fort Peck Dam, a flexible curtain can be suspended a set distance from the water surface using a float system, with the bottom of the curtain anchored to the lake bottom with ballast and cables. The crest elevation is set relative to the thermocline; as the lake level fluctuates, the flexible curtain folds and unfolds in response.
The impacts of CWP are increasingly recognised as an environmental risk worldwide. This paper draws upon the results of similar, implemented projects around the world, including a comparison to cold water pollution prevention measures and costs that have been assessed by CSIRO for application to Australian reservoirs.
Keywords: Cold water pollution, reservoir stratification, thermocline, curtain, fish health