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Published: 09/04/2014



There's a growing interest in understanding the behavior of rockfill dams facing overtopping, as a consequence of an insufficient discharge capacity of the spillway. Several countries, including Spain, are reviewing their dam design criteria in order to increase the safety in these extraordinary events. Furthermore, the latest studies on climate change indicate that, among other consequences, there will be a rise in the frequency and importance of events involving extreme rainfall. This would probably lead to review the calculation criteria for the design floods of spillways, making them even more conservative.


Figure 1. Dambreak due to overtopping. Left: experimental test at Norway. Right: breakdown of the cofferdam used to protect the Jerte Dam construction site (source: EUROESTUDIOS)

This is the core of the research undertaken in the XPRES project, carried out by the same partners, which produced relevant advances in the understanding of the phenomenon. However, in order to obtain practical criteria applicable to improve dam safety, it is essential to extend the objectives of the XPRES project, and analyze the behavior of the impervious element once the downstream shoulder has been swept. This is the main objective of eDAMS project. The failure of the impervious element (a clay core or an external concrete or asphaltic face) could be more fragile compared with the rest of the failure process, and thus could lead to a very high outflow. In any case, its understanding is completely necessary to obtain a complete characterization of the dams failure hydrograph.

Objectives of the project could be summarized as follows:

  • 1. Develop a mathematical model to make possible to simulate the evolution of the whole failure process during a overtopping event, taking into account both the behavior of the rockfill and the failure of the impervious element.
  • 2. Characterize and model the structural failure of the impervious element, whether it is a clay core made or an upstream face, with the different failure mechanisms that cause the destruction of the rockfill shoulder.
  • 3. Combine the failure processes of both the rockfill and the impervious core to provide the outflow hydrograph corresponding to each dam characteristics and typology.
  • 4. Develop design criteria for downstream toe protections in order to improve the failure endurance in case of overtopping both in existing and new dams.
  • 5. Acquire a deeper knowledge in some aspects referent to the downstream shoulder failure characterization: scale effects, compacting, dam geometry, granulometry and the incoming hydrograph.

To reach these objectives, the consortium inteds to continue with the plan followed in the XPRES Project. Both CEDEX and UPM will run experimental tests, field where they have broad experience.

CIMNE will develop a new code for numerical simulation, improving the existing one, allowing simulations of all the failure processes during the overtopping event: a) the loss of material in the downstream shoulder, and b) the failure of the impervious element. In case of clay core, it will take into account the possibility of erosion caused by water flow and the possibility of structural failure produced by the loss of the support of the downstream shoulder.

  Figure 2. Rockfill dam failure in overtopping scenario, physical and numerical tests examples.