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Title: EARTH AND ROCK SURFACE SPILLWAY EROSION RISK ASSESSMENT

Author
item WIBOWO, JOHANNES - USACE
item YULE, DONALD - USACE
item VILLANUEVA, EVELYN - USACE
item Temple, Darrel

Submitted to: Workshop Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 3/1/2005
Publication Date: 6/6/2005
Citation: Wibowo, J.L., Yule, D.E., Villanueva, E., Temple, D.M. 2005. Earth and rock surface spillway erosion risk assessment. Proceedings of the American Rock Mechanics Association Rock Mechanics Symposium, Anchorage, Alaska. Available: http://www.armrocks.org.

Interpretive Summary: Recent advances in understanding the erosion process for earth spillways has resulted in software that may be used to predict extent expected spillway erosion during extreme floods. This software was used in combination with regression analysis to develop generalized relations for estimating extent of expected spillway damage for use in risk analysis applications. This approach allows application of the spillway erosion technology in risk analysis without requiring application of the full computer model.

Technical Abstract: The outlet works are a critical element in the safe operation of a dam that must be protected from damage that could lead to complete failure from earth and rock surface spillway erosion. However, since there are several critical elements that comprise a dam each with associated high costs in maintenance, especially for a portfolio of dams, there is an economical necessity for employing risk assessments to aid optimum decision making in safety assurance activities. Therefore there is a strong need for developing procedures and tools that support spillway risk assessment procedures and prioritizing spillway channel remediation projects. The spillway erosion risk assessment process discussed provides procedures for estimating the probability and level of spillway damage for a given flood event. The assessment is based on an erosion model which considers two basic macro-parameters in developing a threshold line dividing spillway performance between no erosion and erosion: These basic macro-parameters allow the common engineering concept of comparing the load – hydraulic attack expressed as Stream Power to resistance-material properties expressed as Erodibility Index (a unique classification for earth and rock mass in resisting erosion). The assessment process was further extended to enable quantifying the amount of spillway erosion (damage) by using the threshold line as a constitutive relation in the SITES model to simulate system response for a given flood event.