Patrice Mériaux

Tree root architecture: new insights from a comprehensive study on dikes

AimsThis study aimed at disentangling the respective influence of species, environment, root size and root type in tree root architecture.MethodThe root system of 106 adult trees from ten species was carefully extracted from French dikes. Root length and proximal diameter, length and diameter of root segments and branch insertion diameter were measured. Root branching and tapering rates, segment taper, classical (P) and new architectural parameters related to branching patterns were computed.ResultsTwo contrasting root types called “running” (R) and “short” (S), were identified from growth and architectural parameters. Compared to S roots, R roots were longer for an equivalent proximal diameter and singled out with lower tapering rate, branching rate and segment taper and with smaller branches. Their main axis lost less in diameter at branching point for branches of the same size. Tree species had little influence on these architectural parameters. The effect of soil material (coarse vs fine) was significant mainly on root size, on branching rate in fine material, and only secondarily on some branching patterns for running roots and on segment taper. The new architectural parameters describe branching patterns more accurately than classical ones.ConclusionThis study provides an original insight in tree root architectural analysis, proposing a new root typology and innovative parameters for the description and modeling of root architecture.

Methodology Applied to the Diagnosis and Monitoring of Dikes and Dams

The recent and dramatic floods of the last years in Europe (Windstorm Xynthia, February 2010) and United-States (Hurricane Katrina, August 2005) showed the vulnerability of flood defence systems. The first key point for avoiding these dramatic damages and the high cost of a failure and its consequences lies in the conception and construction of the dams and dikes, taking into account the past flooding events. A well-designed dike with the correct height avoids failure and overtopping.

Modular assessment of the performance of embankment dams

The performance assessment of embankment dams in respect to main deterioration mechanisms is a major challenge for managers in charge of their security. One model developed knowledge-based models for assessing the performance of embankment dams. They have three hierarchical levels: performance of the analysed component (embankment, foundations), performance of the functions and status indicators. However, while these dams are frequently located upstream elements at risk, small dams are rarely equipped with drains and monitoring instruments, and woody vegetation is often present. These features were partially or not dealt with in the previous models. To cope with them, we propose to firstly, identify the specific status indicators linked with woody vegetation and secondly, adapt and complete the existing models. A modular approach is notably proposed in order to evaluate different types of dam. The approach was applied to a group of seven French and Italian dams and showed its relevance.