ABSTRACT

Water surface and bottom boundary layer measurements and analyses are presented. These form a protocol to characterize wind driven surface gravity waves in shallow water near shorelines or in shallow open coastal waters and fluid mud movement in a bottom moving lutocline. Synthetic images predict wave patches and their energy (watts m−2). Space-time video imagery collected at ∼10 to 120 frames per second, hyperspectral imagery, wave gauges and line targets are presented. The scientific methods have applications related to management of coastal lagoons, estuaries, near coastal waters. Applications in coastal engineering such as wind farms, protection of structures (canals, seawalls, docks) and vegetated shorelines can benefit from improved understanding of wind driven gravity waves. Associated fluid mud movement in the bottom boundary layer is demonstrated.

INTRODUCTION

The measurement and statistical analysis of water surface gravity waves are important in ship design and operations, design of marine structures such as breakwaters, ports, harbors, seawalls, canals, and jetties. Waves also impact shorelines, oil and gas rigs and wind turbines located in coastal waters (Goda, 2000; Saha, et al, 2017). In coastal areas such as lagoons and estuaries, surface gravity waves and sea state conditions are responsible for shore erosion, resuspension and liquefaction of bottom sediments and the transport of muck and fluid mud in the bottom boundary layer (Bauer, Lorang and Sherman, 2002). Measurements of water wave and sea state conditions utilize wave buoys, pressure transducers, wave staff gauges, capacitance and resistance probes, optical imaging, high frequency radar, and even visual observations. Water wave variability, high wind and wave conditions present challenges to observation equipment and observation platforms (Shand and Bailey, 1995; Shand, Bailey, Shand, 2012). Disadvantages of in-situ methods include difficulty in the placement of instruments, maintenance costs due to biological fouling, corrosion, as well as to high risk to personal safety and equipment during field deployments. These risks and issues are offset by the value of characterizing wind driven water waves for use in engineering of ocean and coastal structures as well as in helping to understand the movement of cohesive and non-cohesive sediment regimes. Water surface gravity wave energy impacts the movement of fluid mud and lutoclines, especially in canals and waterways. The purpose of this paper is to present combined measurement techniques and an analysis protocol that utilizes optical and acoustic methods and inexpensive instrumentation compared to alternative approaches to measre surface and bottom boundary layers.

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