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FloodProBE: Internal Erosion - 27 July 2011

FloodProBE: Internal Erosion Image

By the European Working Group on Internal Erosion of Large Dams (ICOLD), internal erosion is defined as "downstream transport of soil particles within an embankment dam or its foundation by seepage flow". The definition is a collective term for several mechanisms including suffosion, contact erosion, backward erosion and concentrated leak erosion. The relevance of the different mechanisms depend on geological conditions. These conditions may vary locally and across countries in Europe.

The Netherlands

In the Netherlands, backward erosion, or piping, is a dominant type of internal erosion. In January 2011, during a once every 10 year flood, dozens of sand boils were observed (see image). These observations indicate the beginning of failure by backward erosion. It is for that reason, not surprisingly, that in recent years much research has been done on backward erosion. In the Netherlands, this research has resulted in a new mathematical model and a new safety philosophy for backward erosion.


In France, suffusion and concentrated leak erosion are much larger problems. Suffusion involves selective erosion of fine particles from the matrix of coarser particles. It occurs when water flows through widely graded materials. Concentrated leakage involves the enlargement of pre-existing cracks or holes (e.g. along pipes in the levee) by detachment of soil particles due to seepage forces. In the Netherlands, little attention is paid to these mechanisms. In recent years, in France, calculation models and testing equipment have been developed for these types of internal erosion.

FloodProBE, Work Package 3

In FloodProBE workpackage 3, an overview of conditions under which the various failure mechanisms of internal erosion occur are being developed. This overview includes an array of significant geotechnical properties and methods to determine these properties in the field as well as the available empirical and physical-based models to assess their probability of occurrence. Furthermore, it describes observations that may indicate the occurrence of a particular mechanism. For the different European countries, the overview can be used to assess the relevance of possible modes of internal erosion.

Author: Han Knoeff