WD.1368 RevC WCD dam break assessment report with appendices

Waimea Community Dam: Dam Break Analysis
Waimea Water Ltd
2.2 Methodology
The process for the dam breach analysis was made up of five stages.
i. Data collection: Reviewing available information required for analysis.
ii. Dam breach outflow: Estimated the dam breach parameters, geometry, and
development rate to construct outflow hydrographs for the considered scenarios. This
was done using a one-dimensional unsteady HEC-RAS model.
iii. Downstream flood wave: Routing the dam breach outflow on its downstream flood path
to the sea. Model flood depth and velocity to develop inundation maps for the failure
scenarios.
iv. Comparison of results: Using historic flood data and previous analysis results to assess
model stability and accuracy and verify updated scenario findings.
v. Flood mapping of each breach scenario for use in emergency planning.
Another important difference from the T&T study was that their analysis focused on the dam hazard
assessment, and therefore only considered incremental hazards. This was done to categorize the
potential impact of the project. Only incremental flood depths of above 0.5 m were used for the
2009 hazard assessment.
This updated dam break analysis serves the purpose of providing the inundation maps for the EAP,
requiring, therefore, all range of flood depths be considered in the model.
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