Overview

The Malpasset Dam was a concrete arch dam about 10 miles upstream of the town of Frejus on the Reyran River, France. At the time of completion in 1954, it was reported as the thinnest arch dam of its height (218 feet). Malpasset Dam failed on the night of December 2, 1959 at approximately 21:13 after the area experienced several days of heavy rain and high winds. The sudden failure of the dam resulted in the death of 421 people when emergency rescue attempts were thwarted due to the inaccessibility of the town’s flooded roadways and access routes (https://damfailures.org/case-study/malpasset-dam-france-1959/).
 

Data

The following provides a short description of the data sources used for validation. The data for this validation effort was provided by BC Hydro and Spatial Vision Group.

Hydraulics

The following excerpt was taken from Johnstone (2005): Between February 1998 and January 2000, a study of dam break modeling (CADAM – European Concerted Action on DAmbreak Modelling) was funded by the European Union. The purpose of the project was to investigate methods and their use for simulation and prediction of the effects of dam failures. The program’s scope of work included the application of 2-dimensional flood wave modelling tools to the Malpasset event. Under the direction of EDF-LNH (Electricité de France Laboratoire National d’Hydraulique), the breach was simulated using the 2D computer model TELEMAC-2D (a computation model that solves the Saint-Venant depth averaged flow equations) (EDF 1998). To model the Malpasset event, EDF derived a DEM using topographical mapping. However, due to the dramatic changes that occurred in the valley downstream of the Malpasset dam following the dam failure, old 1:20,000 Institut Géographique National (IGN) maps dated 1931 were used as they provided the only viable source of “pre-dam failure” topographical information. (Hervouet 1999)
 

Structure Inventory and Road Network

The structure inventory and road network were developed to represent their condition in 1959 Johnstone (2005). This was accomplished by taking the BD-TOPO data (reference year 2002), and performing a reverse change-detection to “back-cast” to a view of the Town of Fréjus and its local environs circa 1959. Additional evidence such as local maps, ground-based hand-held photos, and airborne oblique photos provided additional evidence of the actual building stock in 1959.
The structure inventory was defined with LifeSim’s default Wood-Anchored stability criteria. This decision was made based on review of the parameters used to define building type in Johnstone (2005) and the raw datasets provided by BC Hydro.

Emergency Planning Zones

There was no formal warning associated with the Malpasset dam failure. As the dam began to overtop, the guardian of the dam set out on his mobylette to warn the authorities, the phones not working because of a telephone-company strike. He wanted to open the valves to release some of the water pressure but, to prevent damage to the new bridge pylons being built for the autoroute, permission was refused. Because there was no formal warning, one emergency planning zone was entered for the entire study area. Due to a lack of information on warning and protective action, the default “Unknown” functions were selected. It is important to note that with no formal warning and little to no advanced notice the warning and protective action initiation functions have little impact on the overall results.

Destinations

Destinations were defined at primary exit points for the evacuation. However, due to the lack of evacuation the destination dataset has little impact on the overall results. Almost all population was caught by surprise with no time to evacuate.

Alternative

To simulate the lack of an official warning the imminent hazard identification time was set to 1 hour after the breach. No communication delay is assumed.

References

EDF (1998). TELEMAC Modelling System – TELEMAC-2D Version 5.1 User Manual, Electricité de France, August 1998.
 
Hervouet, J.M.; Petitjean, A. (1999). Malpasset Dam Break Revisited with Two-Dimensional Computations, Laboratoire National d’Hydraulique, Journal of Hydraulic Research, Vol. 34, 1999, No.6.
 
Johnstone, W.M. (2005). Verification and validation of the Life Safety Model Simulator using the Malpasset Dam Failure, Spatial Vision Group Inc report, North Vancouver, British Columbia

Questions

If you have any questions, please e-mail RMC.Software@usace.army.mil.