Jeffrey A. Schaefer, Ph.D., P.E., P.G. and David M. Schaaf, P.E.
In 2005 the U.S. Army Corps of Engineers (USACE) developed and implemented a Screening Portfolio Risk Assessment (SPRA) process for Dam Safety. The screening process considered loading frequency, an engineering rating to estimate a relative probability of failure, and both human life and economic consequences of failure. The results were utilized as a tool to help prioritize funding for dam safety modification projects and required studies. Three multidisciplinary cadres evaluated what was considered the worst 10% of the USACE’s dam projects in 2005 and the next worst 10% in 2006. The dams evaluated included flood control, navigation, and multi-purpose dams. Approximately seventy facilities were evaluated each year.
As a result of the aging of the USACE’s dam portfolio and the state of the art at the time of design and construction (mostly 1940’s-50’s), significant dam safety deficiencies exist at many USACE dams. This paper summarizes the major deficiencies identified from the SPRA process. Examples, including foundation seepage, karst development, embankment stability, gate deterioration, liquefiable foundations, and inadequate spillway capacity are provided along with discussion on which deficiencies contribute the greatest risk.
N. Vitharana, G. McNally, C. Johnson, A. Thomas, K. Dart and P. Russell
Millbrook Reservoir is an offline storage with an earthen embankment dam containing a puddle clay core and a moderately sized upstream catchment. The dam is 31m high and has a capacity of 16.5 GL when the storage water level is at the Full SupplyLevel (FSL). The reservoir is 25km NE of Adelaide on Chain of Ponds Creek, a tributary of the River Torrens. The dam was constructed during the years 1914-1918. Earthworks were carried out only during summer as the five winters during the construction period were very wet.
Dam safety reviews and geotechnical investigations, undertaken between 2001 and 2004 by SKM, showed that these winter recesses would have created weak layers, increasing the potential for piping due to the lack of a filter. This was highlighted by the large deformations which occurred at the end of construction in 1918. The spillway was assessed as able to pass a flood event with AEP of 1:1,300,000. Given the location of the dam, ANCOLD(2000b) Guidelines suggest the dam should be able to safely pass the PMF flood event. Accordingly, the dam required upgrading to modern guidelines.
The 2005 detailed design of the upgrade included the construction of a 70m wide unlined spillway, construction of filters on the downstream face of the dam with a stabilisation (weighting) fill, installation of instrumentation and seismic protection of the outlet tower. The construction of these works is currently underway.
SunWater manages its portfolio of 29 major dams through 6 business centres each responsible for the Dam Safety Program for the dams under its management control.
The effectiveness of responses during an emergency depends on the amount of planning and training performed. Management must show its support for dam safety programs and the importance of emergency planning.
If management is not interested in community protection and in minimising property loss, little can be done to promote dam safety. It is therefore management’s responsibility to see that a program is instituted and that it is frequently reviewed and updated.
The input and support of all communities must be obtained to ensure an effective program. The emergency response plan should be developed locally and should be comprehensive enough to deal with all types of emergencies specific to that site.
SunWater is a responsible dam owner and has recently upgraded all its emergency action plans in consultation with emergency services of Queensland. This paper details the basic steps to handle emergencies of water infrastructure. These emergencies include inflow floods, rapid drawdown, earthquake, sunny day failure, changes in reservoir water quality and terrorist attacks including hoax.
This paper is intended to assist small dam owners that do not have dam safety programs in place. It is not intended as an all inclusive safety program but rather a provision of guidelines for planning for emergencies.
For many years most emergency management agencies in Australia have used a framework called Prevention, Preparedness, Response and Recovery (PPRR). This approach has worked very well in the past and has been incorporated into the more recent framework of Emergency Risk Management.
While Emergency Management Agencies use practice sessions in the form of Desktop/Tabletop Exercises and Field Exercises as part of Preparedness (the 2nd P in PPRR) these activities can suffer from a lack of engagement with the community.
State Water Corporation, a dam owner in NSW, has installed warning systems to trigger plans written by the SES to warn affected residents of possible dam failure. Although the systems are maintained and tested regularly in a technical sense, the next logical step is to encourage the affected communities to understand their role in the event of evacuation.
A joint exercise involving the NSW State Emergency Service (SES), State Water Corporation and the community, was conducted in a town in the Namoi valley in 2005 and has provided an opportunity to explore this concept. State Water Corporation is now confident that not only will the technical side of the warning system work but that residents should be more aware of their role and that of the SES and State Water Corporation.
Other benefits from the exercise are: the opportunity for improving general flood awareness in the community; the SES identifying community representatives; fine tuning procedures between and within the SES and State Water Corporation; allaying fears within the community about what is required of them in a dam failure; and demonstrating the dam owner’s duty of care to affected residents.
Peter Hill, Rory Nathan, Phillip Jordan, Mark Pearse
This paper outlines the development and application of the Risk Analysis Prioritisation Tool (RAPT) which has been developed as an interactive tool to aid dam safety risk management. RAPT allows the risk profile and prioritisation of upgrades to be incrementally updated as inputs are refined. The paper outlines some of the requirements of a risk management tool and the resulting functionality of RAPT and the lessons learnt from its application to more than 75 dams.
Issues covered include:
Verbund – Austrian Hydro Power (AHP) is the owner and operator of 27 large dams. The highest dam is the 200 m high Koelnbrein arch dam and the highest embankment dam is the 83 m high Durlass-boden dam. Instrumentation of the dams of AHP comprises almost all kinds of instruments employed in dam monitoring. Manual measurements are carried out with the help of portable terminals. Auto-matic monitoring with an early warning system is implemented at all dams. Besides a description of the monitoring system and some “interesting” measurement results the article also deals with organisational aspects of dam surveillance.
The case study of Koelnbrein arch dam is appended to the article. It contains a brief description of the original dam and the encountered problems as well as of the main elements of the remedial works. Dam surveillance and the performance up to now are also dealt with.