Design and Monitoring of River Restoration Work

Abstract

Two experimental river restoration programs of the Agence de l’Eau Seine Normandie enabled to apply river restoration techniques on two small rivers tributary to the Marne. The concerned channel is about 5 km long. After the end of restoration work in 2013, 3 years of morphological and ecological monitoring were plan in order to verify and justify technical choices. One of the technical objective is to formulate hypothesis and bring elements in order to develop methods in order to proportion ambitious restoration projects answering the European laws. Second objective is to define interest and precision of numerical simulation in bed design. This simulation can be done in order to plan the evolution in the medium term of the river route and to guarantee the security of the goods and people. Different design methods have been tested such as empirical formula, 1D, 2D, and 3D hydro-morphological models. Those models are comparing to morphological and physical habitat. This work must allow choosing more accurate methods and describers for restoration process. First conclusion for river such as Pissancelle and Blaise is the restricted interest of complex models like 2D and 3D hydraulic models. Those models are limited to represent complex bed such as alternated shoal or complex curve. Furthermore, “natural” process like cyanobacterial benthic films or bank vegetation are impossible to simulate despite being dominant for bed evolution. Second lesson to learn to monitoring program is obligation of multi-scale approach for data assimilation and modeling: morphological evolution (final water depth, river bed mobility) require large study while fish habitat assessment require detail data