R&D highlights edition 2019

Delta infrastructure 43 R&D Highlights 2019 SHIFTING SANDS – MEASURING TOE SCOUR USING INNOVATIVE TECHNIQUES T oe structures are a common feature in coastal rock- armoured structures: they protect the structure from scour at the toe and provide support for the armour layer. The toe structure itself often includes rocks as well. Some form of scour protection, such as a filter layer or a geotextile, is therefore generally placed below the toe structure. There are currently no methods available for assessing the need for costly scour protection measures of this kind beneath the toe structure. Deltares is working with the commercial partners Van Oord, Boskalis and Royal HaskoningDHV in the Joint Industry Project (JIP) CoastalFoam with the aim of optimising the design of toe structures. This JIP project is drawing on physical model tests of scour at the toe of rock armoured structures to establish a unique dataset. Those tests were performed in the Deltares Scheldt Flume, where a rock- armoured structure was built on a live sand bed. During the physical model tests, the temporal development of the scour at the glass wall of the flume was measured using an innovative combination of video imagery and a deep-learning algorithm. The algorithm classifies which pixels in the image constitute the sand bed and converts their position into flume coordinates. In this way, the level of the sand bed can be tracked over time, even underneath the structure. Furthermore, changes in the bed level were measured after each test with a laser scanner covering the entire sand bed, including the section underneath the structure. This involves draining the flume after each test and the partial disassembly of the structure to expose the sand bed below. The laser and video data of the transect at the glass wall of the flume were cross-validated against each other. Scour was observed in all tests both in front and underneath the structure. The data was used to derive an expression to estimate scour below the toe structure and therefore establish a picture of the need for scour protection underneath toe structures and help to optimise the design process. Contact: Joost den Bieman, Joost.denBieman@deltares.nl , t +31 (0)6 4691 1198 Marcel van Gent, Marcel.vanGent@deltares.nl , t +31 (0)6 46911194 In this JIP, a unique dataset was gathered from physical model tests of scour at the toe of rock- armoured structures using a laser scanner and the combination of video imagery and deep-learning algorithms. These innovative measurement techniques produce unprecedented datasets and valuable new insights. Still frame from video with the sand bed (red) detected with the deep-learning algorithm Example of experimental setup before (above) and after (below) a test Normalised erosion volume underneath the toe structure Sedimentation (green) and erosion (red) patterns from laser scanner data