The Occurrence of Ridge-and-Runnel Beach Morphology Associated with Deep-Water Wave Steepness on New York's Ocean Coast

The occurrences of ridge-and-runnels were documented along the ocean shoreline of New York. These ephemeral beach morphologies represent the post-storm recovery period as sand eroded from the subaerial beach makes its way back on shore. Daily images from a camera in East Hampton, NY (40.964;-72.185) were examined to look for the occurrence and duration of ridge-and-runnel events between October 2010 to November 2012 and again from February 2014 to July 2016. Seventy-five ridge-and-runnel events were seen lasting between one to seven days, and representing about 16% of the time. Deep-water wave steepness has long been used as a parameter to determine beach erosion and accretion, because steep waves remove sand from the subaerial beach and deposit it as an offshore bar which remains until waves of low steepness return it. The time series of wave steepness (NOAA Buoy 44017) was found to be dominated by rapid increases to values of about 0.06 followed by gradual decays to about 0.012. Wave steepness is positively correlated to wind speed representing the passage of mesoscale weather systems. These cycles occurred about every five days; when ridge-and runnels occurred, they appeared, on average, 2.7 days after the peak in wave steepness.