# Measurements of High-Froude Number Boat Wakes near a Seawall
## 4 Discussion and Conclusions  
A square array of pressure gauges was deployed in an urbanized estuary at a sheltered location with frequent small-boat traffic. The geometry of the array allowed for calculation  
Figure 13: Directional power spectrum from full deployment. of directional spectra, a capability that can be useful for coastal planning science and management. For example, directional spectra can help back-trace the origin of wave signals. Potential sources include open ocean or local open waters, structures, such as seawalls or flood control barriers, shipping channels, ports or marinas, or even specific vessels. Distinguishing these disparate sources is useful in adaptation and resilience planning. The directional spectrum can provide information to sort multiple sources by direction, and rank by frequency and intensity. Including additional parameters of time or weather conditions can help develop a dynamic picture of the wave environment, such as separating incoming swell from local wind waves or quantifying how wake propagation and potential reflection from hard boundaries is impacted by the tidal level. While directional wave studies have been common for many years, these have typically involved intermittent sampling bursts, separated by comparable periods without measurements. These limited sampling regimes were developed when battery power and data storage were at a premium but are still useful for very long-term deployments or when only gross wave statistics are needed. The use of continuous sampling at relatively high rates (compared to the ambient waves) necessary to fully measure ship wakes, as presented here, has not been widely performed. Wake durations are generally several minutes. Interrupting their measurements would result in degraded understanding of their forms and impact. In this study, wake from the personal craft were typically 5 min in duration. Wakes from larger commercial vessels will be significantly longer due to the much larger wavelengths and wave periods generated. Continuous, extended sampling is therefore essential to capture these signals. Such measurements help support management of coastal areas by providing quantitative measures of the wave environment and the effectiveness of any decisions or regulations such as changes to shoreline structures, vessel speed and size limitations, or coastline morphology. The study site examined here will soon have a living shoreline installed along the seawall to reduce wave impacts and enhance resilience of the region. New measurements using the same wave array at the same location are planned. Impacts of the installation on wave reflectivity (absorptivity) will be performed by computing changes to the energy spectrum from the direction of the seawall compared to the pre-installation spectrum (Figure 13). This will validate the effort associated with the project and provide information useful to future similar projects. Measurements of wake characteristics, such as amplitude, frequency, duration, and occurrence rates, are useful for designing shoreline protective measures, as these quantities impact the wave energy and their ability to resuspend sediments. In field studies of the wave environment, detecting wakes and separating them from wind-driven wave fields can be challenging [74; 75]. Separation has often been accomplished by estimating and then subtracting the nominal wind wave environment from the total signal. This typically required either a strong wake-to-wind wave signal, or a priori knowledge of approximate wake arrival time. The AWD developed here was able to identify wakes under a wide range of conditions and is robust under a range of conditions (Appendix A). The AWD was optimized for wave forms with dispersive signals, as is commonly found originating from boats operating at a high Froude number, as well as part of more complex wakes from lower Froude number boats. The algorithm was found to be skillful in the detection of primary wakes but not reflected wakes.