COMPARISON OF MEASURED AND CALCULATED WAVE RUN-UP ELEVATIONS ON A MICROTIDAL PARAGLACIAL COASTLINE USING BEACH PROFILES

The approach outlined by Stockdon et al., (2006) is commonly used to calculate the 2% wave run-up exceedance probability (ƞ₉₈) and is helpful for anticipating storm impacts. The original work was developed in a mixture of settings and has been applied on both bluff and barrier coastlines. This study expands the analysis to the paraglacial New England coast using Real-time Kinematic GPS (RTK-GPS) beach profiles (n = 494) collected at three sites over 10 years to compare the predicted wave runup compares to measured wave runup. Profiles were from three locations along the paraglacial Rhode Island south shore, a microtidal, mixed-energy wave dominated shoreline. The beach slope between the dune toe and mean high water was calculated from the profiles. The field surveys, conducted at Napatree Point barrier (NAP; 5 profiles) and South Kingstown Town Beach (low bluff) (profile SK-TB) and the Charlestown Barrier (profile CHA-EZ) recorded the position and elevation of the last high-tide swash (LHTS). The ƞ₉₈ value was calculated using the offshore wave heights at the Block Island Buoy (50 km southeast of the study area) and water levels recorded at the Newport, RI Tide gage (35 km east of the study area). We find that the Stockdon equation overestimates the wave run-up at NAP and SK-TB and underestimates at CHA-EZ. The mean difference at the Napatree profiles is 0.2 m, while at the SK-TB profile it is 0.1 m. The CHA-EZ profile saw a mean difference of -0.2 m; positive values indicate the equation overestimates run-up, while negative values underestimate run-up. These results are similar to the uncertainty of the original study. Some overestimation may be expected as the ƞ₉₈ represents the 2% exceedance probability. These results demonstrate how the storm impact regime that a shoreline experiences during a storm may be different than what Stockdon predicts; however, the difference in LHTS and ƞ₉₈ seems to have no correlation with the beach slope. One limitation here is that these recorded wave runup elevations largely represent fair-weather wave conditions. Understanding this equation and where and when it may be most accurate will help with calculating potential dune and shoreline erosion particularly in modelling future studies and we are continuing to examine the factors that impact the results and variations found here.