Development of Alternative Overtopping-Resistant Sea Defences

Abstract

The present proposal deals with a presentation of three potentially feasible concepts for strengthening of the sea defences as to allow for increased wave overtopping, within the framework of ComCoast. In addition, for each concept an indicative proposal is given for a further theoretical study (Phase 2) and an indicative approach is shown for further testing. This proposal is denoted Phase 1: generation of alternative concepts. For the present proposal and the activities involved, as well as possible future assignments within Phase 2, a consortium has been formed between Royal Haskoning and INFRAM (Royal Haskoning, being the leading party), the two partners that also participated in the Inventory Study that preceded this proposal. We think that this combination brings about the outstanding expertise from both firms, which we hope is reflected in the present proposal. The three alternative concepts focus on different types of innovative reinforcement measures, i.e.: reduction of the wave overtopping flow attack, strengthening of the present grass revetments and strengthening of the subsoil. After an introductory chapter, Chapter 1, the relevant failure phenomena are indicated in Chapter 2. The Concepts A (low hedges), B (application of innovative grass reinforcement) and C (application of Smartsoils techniques) developed to cope with these phenomena are presented in Appendices A, B and C and are summarized and discussed briefly in Chapter 3. Chapter 4 presents the indicative set-up for the further theoretical studies of Phase 2 for each concept, whereas in Chapter 5 the approach for testing of the concepts is indicated. The Concepts A and B are highly promising solutions, and we think that they only need limited elaboration and research. The costs are very competitive as compared to the costs for traditional raising of a dike crest (=Reference). The savings can be so big, that further in-depth research on optimization seems anyhow to be useful. Concept C is still highly experimental for application on sea defences and clayey soils. Nevertheless, it would be an interesting option to further explore The charm of these Concepts is that they can also be combined in an economical way (A and B together being still much more economical as the Reference) as to cope with increasing Sea Level Rise in future in a flexible way).