463 Comprehensive Flood Risk Management – Klijn & Schweckendiek (eds) © 2013 Taylor & Francis Group, London, ISBN 978-0-415-62144-1 Quality of peat dykes evaluated by remote sensing Sharon Cundill, Robert Hack & Mark van der Meijde University Twente, Faculty of Geo-Information Science and Earth Observation (ITC), Enschede, The Netherlands Joost van der Schrier Royal Haskoning, Nijmegen, The Netherlands Dominique Ngan-Tillard Technical University Delft, Faculty of Civil Engineering and Geosciences, Geo-engineering Section, Delft, The Netherlands ABSTRACT: Dykes are increasingly becoming structures of major importance in view of sea level changes. Dyke inspectors monitor dykes visually whilst walking the dyke. It has been proposed that remote sensing could be used to make dyke inspection faster and cheaper. This paper presents the results of a study that investigates remote sensing for evaluating the soil moisture as a means to investigate the quality of a peat dyke. Correlations were found between soil moisture and thermal remote sensing data. Remote sensing provides useful information for soil moisture evaluation for dyke inspection and may be useful for dyke quality inspection. half of The Netherlands from being flooded (Van Baars, 2005). To maintain the groundwater level and drain the precipitation of the low lands that are below sea level, water is pumped from the low-lying areas into canals and from there into the sea. 1.3 Peat dykes Peat for fuel has been excavated in large parts of the Western Netherlands from the early Middle Ages until the early 20th century. The remaining low-lying excavated areas either have been left flooded and still exist as lakes today, or are drained to use as agricultural areas (‘polder’). For the latter a system of canals has been dug surrounding the excavated area and the water is pumped from the excavated area into the canals (Fig. 1). The canals 1 INTRODUCTION 1.1 Dykes In view of expected sea level rise, dykes will become of increasing importance for the protection against flooding of densely populated low land areas, such as coastal zones and deltas. Dykes are a flooding protection mechanism in The Netherlands and many other countries, e.g. the USA, Thailand, and Bang- ladesh. Unfortunately, it is not easy to predict the occurrence of flooding and hence dykes should be ready at any time to safely cope with the design flood should these occur. It is important to monitor dyke quality regularly to ensure proper dyke function- ing under design conditions. Unfortunately, moni- toring of dyke constructions is not easy, certainly not at times that the design loads are still absent. Currently, dyke owners rely heavily on visual dyke inspection at regular intervals, and according to an intensified monitoring regime when water levels are high and flooding may be imminent. The focus in a visual dyke inspection is on anomalous dyke behav- ior such as shown by, among others, crack develop- ment, occurrence of wetter or dryer spots, boiling points, and seepage and leakage quantities. 1.2 Dykes in The Netherlands In The Netherlands, 3,200 km length of primary and 14,000 km length of secondary dykes protect about Figure 1. Sketch peat excavation (vertical scale exaggerated).