Surf Zone Observations
Part of the reason for choosing Kill Devil Hills as the study location is because of the willingness of KDH Ocean Rescue to help gather observational data. Rip currents are ephemeral in nature, which makes measuring them very difficult, especially when you are trying to cover about 5 miles of shoreline. KDH presents us with a very unique opportunity to observe the nearshore and surf zone as there are 19 guard chairs covering the 5 miles or about 8km or coastline. That equates to an observer for every 400m of beach. In addition the guards are there 7 days a week for about 8 hours a day from the end of May to the first week in September.
Google Earth image of the guard chair locations in KDH
For this initial pilot study we will not have any hard velocity measurements indicating the presence of rip currents. However, we have incredible observational beach coverage to indicate if rips or a strong shorebreak is present and its estimated intensity. To catalog this data the guards are using a daily surf condition report sheet. At each chair location the guards will make visual observations of the nearshore conditions and report the time at which the observations were made. In addition they will make notes if there were rip or shorebreak related rescues on that day or if rip curring warning flags or if red flags (beach closed to swimming) were used.
An example of the observational report sheets the guards are using at KDH
The final observation the guards will be making is estimating the distance and depth of the nearshore bar about every third day. To accomplish this they work in pairs with depth rods and laser range finders to get a general idea of the distance and depth of the center of the nearshore bar. This data will provide us with at least some indication of the extent of the nearshore bar, or if it is significant at all and how it varies both spatially and temporally. This data will also supplement the other bathymetry data as it can be done much more frequently.
Once all of this observational data of the surf zone is collected, it will be put into an excel database for the summer of 2008. It will provide us with a good indication for how surf zone conditions varied both temporally and alongshore. This database will then be correlated with the bathymetry data and the directional wave data. One of the instances that will be of the most interest will be those times in which there was significant alongshore variability in surf zone conditions.
An example of the database of surf zone observations for 3 days in June. wY represents waves breaking over the bar, sM= medium shorebreak, sS=strong shorebreak, rW= weak rips, rM = medium strength rips.