SCOURING AND LOADING OF IDEALIZED BEACHFRONT BUILDING DURING OVERLAND FLOODING

The coastlines of the United States are susceptible to tsunamis, windstorms, and other types of flooding hazards. In the past few years, extreme events such as Hurricane Katrina and Hurricane Sandy resulted in the loss of lives and properties, costing the nation billions of dollars (The Office for Coastal Management, 2019). Despite the elevated risk of extreme coastal events, the population in coastal communities has been steadily increasing (Nicholls and Small, 2002; NOAA, 2013). To develop resilient coastal communities, buildings and infrastructures must be designed and constructed such that they are able to withstand extreme flooding. Achieving such an objective necessitates understanding and prediction of flood-induced damages to structures and infrastructures in coastal areas. The existing literature mainly focuses on the current-induced and wave-induced scouring around slender structures. However, structures having dimensions on the scale of incident wave lengths cannot be treated as slender structures. Few studies concentrated on the scour and local hydrodynamics of large bodies, mainly large cylindrical structures (e.g. Katsui, Toue, and others 1993; Sumer and Fredsøe 2001; Toue, Katsui, and Nadaoka 1993).

The coastlines of the United States are susceptible to tsunamis, windstorms, and other types of flooding hazards. In the past few years, extreme events such as Hurricane Katrina and Hurricane Sandy resulted in the loss of lives and properties, costing the nation billions of dollars (The Office for Coastal Management, 2019). Despite the elevated risk of extreme coastal events, the population in coastal communities has been steadily increasing (Nicholls and Small, 2002;NOAA, 2013). To develop resilient coastal communities, buildings and infrastructures must be designed and constructed such that they are able to withstand extreme flooding. Achieving such an objective necessitates understanding and prediction of flood-induced damages to structures and infrastructures in coastal areas. The existing literature mainly focuses on the current-induced and wave-induced scouring around slender structures. However, structures having dimensions on the scale of incident wave lengths cannot be treated as slender structures. Few studies concentrated on the scour and local hydrodynamics of large bodies, mainly large cylindrical structures (e.g. Katsui, Toue, and others 1993;Sumer and Fredsøe 2001;Toue, Katsui, and Nadaoka 1993).
The main objective of the present study is to investigate the morphodynamics of flooding around near-coast structures. Experimental work has been undertaken to characterize the initiation and development of scour around an idealized building on an erodible berm, during the interaction of a solitary wave with the structure.

METHODOLOGY
A series of flume experiments were carried out for an idealized building with a square cross-section configured in two different layouts (side and center) and exposed to various wave and water level conditions. The experiments were executed at the Coastal and Hydraulic Research Laboratory (CHERL) of Stony Brook University (Fig.1). The experimental conditions are summarized in Table 1 in which the variables h and h are water depths in front of the wave paddle and on the beach berm, respectively; H and T are the wave height, and period in front of the wave paddle, respectively; U represents the maximum undisturbed near-bottom flow velocity, measured at ~2mm above the sand layer; KC = U T D ⁄ is the Keulegan-Carpenter number, and D is the structure width. The structures and the corresponding flows were selected to represent λ=1:40 length scale according to the Froude similitude.
The free surface elevations were measured at various locations along the flume and around the structures with Edinburgh Designs WG8USB resistive wave gauges (WG) with a sampling capacity of 128 Hz. Undisturbed near bottom velocities (U ) were recorded before placing the structure on the berm, using a Vectrino Profiler with 25Hz sampling frequency. On the other hand, the velocity field during the test was measured using three Nortek Vectrino Acoustic Doppler Velocimeters (ADV) placed at one-third the still water depth above the berm with a sampling rate of 25 Hz.
The bed was scanned with a HR-Wallingford's HRBP-1070 bed profiler system, equipped with a traverser system for adjusting the position of the profiler in the two or three-dimension setting, before and after each test. Before each test, the surface of the berm was leveled at 0.18m above the flume bottom, the water level gradually rose to the target level and the profiler was calibrated to eliminate potential reading error caused by lab temperature variations. A total length of 4.5D of the berm, 2D upstream and 2D downstream of the structure, was scanned by the profiler in each test. The maneuvering restrictions of the probe created a blind zone of ~2 cm around the structure. The bed profile in these zones were manually measured after each test. Figure 2 shows the plan view of the bed elevation variation (S) with respect to the initial bed, and the diameter of the footprint of the scour holes (R ), both normalized by the structure dimension (D). The scour holes are observed to form around the sharp edges both on the seaside and leeside of the structure in both layouts (Fig. 2). Although the scour hole is deeper on the seaside of the structure, the diameter of the footprint of the scour hole is significantly larger on the leeside. The wake vortices whose trajectories are marked with green spiral curves (Fig. 2) are the driving mechanism in the formation of the scour around this non-slender structure.

RESULTS AND DISCUSSIONS
The wake vortices, discussed by the authors (Sogut et al., 2020(Sogut et al., , 2019, tend to entrap and transport suspended sediment along their trajectories until they dissipate. Furthermore, it is observed that both depth and diameter of the scour holes significantly depend on the structure layout. Although a deeper scour hole is formed when the structure is positioned on the side, symmetric but relatively shallower scour holes are formed when the structure is positioned in the center. The variations of the maximum S/D, R /D, and V /V with respect to KC are shown in Figure 3. The figure demonstrates that the maximum depth, width, and volume of the scour hole increase more rapidly with KC when the structure is positioned on the side. is the characteristic volume which product of cross-sectional area of structure and unit height.