Using natural foreshores instead of traditional dike re-enforcements: a field pilot in the large shallow lake Markermeer, the Netherlands

Ellis Penning, Henk Steetzel, Jasper Fiselier, Marieke de Lange, Vincent Vuik, Jaap van Thiel de Vries, Robbin van Santen, Sonja Ouwerkerk

Chair(s): Mark van Koningsveld

Monday 29 june 2015

14:35 - 14:50h at Antarctica (level 0)

Themes: (T) Special session, (ST) Building with nature

Parallel session: 2D. Special Session: Building with Nature

Increasingly, natural foreshores are seen as a valuable alternative for, or addition to conventional dikes. Natural foreshores consist of shallow zones and beaches with a gradual slope and a (near-) natural vegetation, e.g. freshwater reedbeds and wetlands, willow forests, salt marshes and mangroves. They create an additional protection against flooding and wave attack on the dikes or can even protect the dike completely from being attacked. Using wide beaches and dunes is common practice in the coastal flood defense of the Netherlands. This is so far not the case for the larger delta lakes in the Netherlands. The shorelines of these lakes are at present protected by dikes, some several centuries old and important cultural historic monuments. There are several locations where the use of a soft defense in considered for various reasons. One is to spare the older dikes which otherwise would have to be completely rebuilt because of problems with macroinstability. In some places a soft defense may offer a more cost-effective and also more flexible alternative. A soft defense along these larger lakes is however a novelty. Many processes work differently from those at the coast. There are no tides, wave length is much shorter and vegetation will play a larger role in shore line development. The design of these defenses and also the expectations regarding related maintenance can therefore not be based on experiences gained over the past centuries on the coastal dunes and beaches. In order to better understand the crucial aspects of designing, constructing and maintaining a natural, vegetated foreshore, a pilot is being carried out along the ‘Houtribdijk’ dike between Lake Markermeer and Lake IJsselmeer (the Netherlands). This dike needs reinforcement since it no longer complies with Dutch safety standards. The pilot was constructed in summer 2014, and consists of a 500 m long stretch of sandy foreshore along the dike. Monitoring takes place from 2014-2018 for aspects of hydrodynamic forcing, morphodynamics in relation to vegetation development. We will present the process of design, implementation and the monitoring results of the first year after implementation.