Techniques for evaluating the size of potential dam-break floods from natural dams

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Manville, V. 2001 Techniques for evaluating the size of potential dam-break floods from natural dams . Lower Hutt: Institute of Geological & Nuclear Sciences.Institute of Geological & Nuclear Sciences science report 2001/28 72 p.

Abstract: Floods generated by failures of natural or artificial dams constitute a widespread hazard to people and property because of both their large size and their unpredictability. Natural dams may be formed by a variety of barriers including landslides, glacial ice, moraines, and volcanic deposits. Those formed rapidly, i.e. by landslides or volcanic activity are the most unpredictable and represent the greatest threat to life and property. Consequently both the stability of the dam and the likely peak discharge of the potential dam-break flood require rapid assessment. This is particularly important in New Zealand due to its combination of high topographic relief, frequent large earthquakes, and episodic volcanic activity. However, estimation of the potential flood hydrograph from a failing dam is complicated by its dependence on four inter-related factors: the volume of the lake, the height of the dam (or depth of the lake), the average width of the breach, and the breach development time. Four main techniques have been developed by various workers to assess the magnitude of potential dambreak floods: (i) empirical regression relationships; (ii) parametric models; (iii) dimensionless analysis; and (iv) computerised physically-based dam erosion models. This report briefly describes and assesses each of these techniques and their respective advantages and disadvantages. The appendices contain a number of Excel spreadsheets (on an enclosed CD-ROM), designed as tools to partially automate analysis of potential dambreak flood hazards, including landslide dam datasheets, peak discharge, outflow hydrograph, and breach dimension calculators and dam and lake volume calculators. (auth)