This paper presents the application, and implications of line arrays of light emitting diodes (LEDs) as an illumination source for planar particle image velocimetry (PIV) measurements in large-scale hydraulic laboratories. The use of class 4 lasers, commonly applied as illumination source in these PIV measurements, requires strict safety precautions (i.e. to prevent safety hazards for people working in their vicinity), specifically when applied at hydraulic experimental setups that are not located in a laser lab. To examine the applicability of an alternative light source, differences between LED- and laser-based illumination for PIV are analyzed. A theoretical analysis, in which a so-called motion blur parameter ((Formula presented) ) is introduced, shows that for moderate flow velocities in large-scale setups, image blur can be avoided, even for relatively long (millisecond) pulse widths. The light sheet thickness, width and intensity of a pulsed laser and a line array of both continuous and pulsed LEDs are measured and compared. Based on these properties a safety assessment is made, from which it is concluded that the application of arrays of LEDs for PIV measurements applied in liquid flows requires significantly less safety precautions than in case a class 4 PIV laser is used. Planar (2D) PIV measurements have been performed with both a pulsed and a continuous LED as light source for two testcases in large hydraulic scale-models. Time-averaged velocity field results from the LED-based PIV measurements show good resemblance to both PIV measurements obtained with a class 4 laser as well as to pitot tube measurements. It is shown that the time-averaged PIV vector fields are influenced by motion blur, resulting in a distinct bias towards smaller velocities when increasing motion blur. The two testcases show that linear LED arrays can serve as a suitable alternative illumination source for planar PIV measurements in large-scale hydraulic laboratories in case motion blur remains limited. Specifically, LED line arrays are considered useful for the time-average quantification of predominantly 2D, low to moderate flows in a relatively large domain.

Remote sensing technologies have the potential to support monitoring of floating plastic litter in aquatic environments. An experimental campaign was carried out in a large-scale hydrodynamic test facility to explore the detectability of floating plastics in ocean waves, comparing and contrasting different microwave and optical remote sensing technologies. The extensive experiments revealed that detection of plastics was feasible with microwave measurement techniques using X and Ku-bands with VV polarization at a plastic threshold concentration of 1 item/m² or 1–10 g/m². The optical measurements further revealed that spectral and polarization properties in the visible and infrared spectrum had diagnostic information unique to the floating plastics. This assessment presents a crucial step towards enabling the detection of aquatic plastics using advanced remote sensing technologies. We demonstrate that remote sensing has the potential for global targeting of plastic litter hotspots, which is needed for supporting effective clean-up efforts and scientific evidence-based policy making.

Hydraulic structures can be a promising place for tidal energy extraction due to the high flow velocities, easy access to the power grid and easy access for maintenance. However, quantification of the impacts of a tidal power plant in a hydraulic structure is not straight forward. In 2015 a pilot plant consisting of an array of five Tocardo tidal turbines was installed in the Eastern Scheldt Storm Surge Barrier in the Netherlands. This pilot was accompanied by monitoring studies to verify that the operation of the plant had no adverse impact on the barrier and its surroundings. This paper presents the assessment of the hydraulic impact of the tidal power plant in the storm surge barrier based on an analysis of water level and current measurements, combined with numerical modeling and followed by an assessment of the environmental impact with emphasis on the effects on the intertidal areas in the estuary. This validation approach by a pilot plant is imperative to understand the interaction between tidal turbines and the hydraulic structure on the local scale. This understanding gives extra credibility to the predictions of the extrapolated large-scale and large array assessments which will always be fully numerical.

Salt water intrusion through the New Sea Lock of IJmuiden, Netherlands requires mitigation to ensure availability of enough fresh water further inland. For this purpose, a salt screen has been proposed for selective withdrawal of salt water from the Noordzeekanaal in the vicinity of the lock complex. Formulas to assess the withdrawal rate of selective withdrawal are based on idealized layouts and conditions. In the case of IJmuiden, the flow surrounding a salt screen has a strong nonuniform character, such that these formulas are not applicable to predict the correct withdrawal rate and the effectiveness of selective withdrawal accurately. In this case physical scale modeling or computational fluid dynamics (CFD) modeling can be applied. This article discusses the limitations of the formulas for a three-dimensional (3D) flow application near the locks of IJmuiden and presents the use of CFD and physical scale model research to assess the flow patterns around the salt screen and the effectiveness of selective withdrawal. The CFD model was validated against the physical scale model and represented the complex flow fields around the salt screen to within acceptable deviations for both steady and transient states. This gives confidence in applying these more advanced modeling tools for the design and positioning of salt screens in confined complex 3D flow areas.