title: Sensor technologies for measuring coastal hydrodynamics and morphological change
Creators: name: Knight, Philip
Publisher: name: University of Liverpool Repository
Year: 2023

description: This research has focused on development of cost-effective sea-level and wave measuring technologies for implementation alongside X-band radar monitoring programmes. These data are important for two reasons: firstly, sea-level data are required for deriving the morphological maps from the X-band radar images; these maps can inform coastal managers of critical lowering of beach levels that might compromise sea-defences, or high beach levels that might exacerbate run-up and overtopping hazard, and secondly, sea-level and wave data can be used to understand the role of tides, storm surges and waves in shaping beaches and tidal flats. While there are numerous commercial devices capable of measuring sea level and waves, many are not suitable for the intertidal zone and those that can are generally too expensive to deploy for long durations or to implement at scale as part of a near-real time system. This research is based upon taking ideas and developed products from other sectors and transferring these advances to create low-cost devices. This research has successfully produced and evaluated two devices with field experiments; a low-cost GNSS buoy capable of deployment from a small boat or from the beach at low water, and an Internet of Things (IoT) tide gauge capable of scaling up to provide a network of near/real time devices. A comparison of tidal heights between the GNSS buoy and a reference tide gauge at Holyhead harbour (located 1.5 km away) produced a mean difference of -1.1cm and a RMSE of 1.4 cm, indicating its suitability for sea level measurement. Likewise, a comparison between the IoT tide gauge and a reference tide at Gladstone Lock, Liverpool (located 2.6 km upstream), produced a mean difference of 0.2 cm and a RMSE 3.5 cm, showing that acceptable data can also be obtained using low-cost pressure sensors. The research also sets out to develop a method of using temporal X-band derived Digital Elevation Models (DEMs) (which contain spatial elevation errors), alongside more accurate annual LiDAR data, to characterise morphological changes of a tide flat. Analysis of DEMs over a three-year period shows the importance of regular monitoring of beach morphology over annual surveys. The results indicate the presence and shoreward movement of small sand ridges situated between the mean-sea-level and mean-low-water-springs. There are also regular cycles of erosion and deposition and these appear to be related to both the tidal height and stormy periods. The two-week X-band radar composite maps of the intertidal zone are not at a resolution capable of analysing the effect of individual storm events, or to separate parts of the tidal cycle e.g., neap tides over seven days. Future surveys with the X-band radar would benefit from the instrumentation developed as part of this research. This would improve the data quality, allow for increased temporal output i.e., more maps, and thus provide the additional data necessary to solve some of the issues encountered with analysis of the historical data.