Tidal Flooding Awareness

One of the things that the Office of Emergency Management is concerned with is Tidal Flooding Awareness, that is residents knowing what predicted tidal flooding means to their neighborhood and property.   The County Office of Emergency Management has developed a tool that the resident’s in Cape May County can use.  The website is located HERE (click to go) before you go there it would be helpful to have a better understand how it works and what it’s based on.  The county mapping office and an outside vendor came up with this webpage which uses elevation data obtained by LIDAR readings which were taken several years ago by a over flight of the area where radio beams were bounced off the ground and the difference in micro-seconds of the beam bouncing back determines the elevation of the surface.    As the LIDAR measurements were in the NAVD88 datum to get them in the MLLW references you have to use the local National Geological Survey reference point which gives you the differences between datums.   North Wildwood uses the NGS Tide Elevation Benchmark for Station 8535835 which is located at the Wildwood Crest Fishing Pier.

Because the county website uses live data it depends on being connected to a NGS online tide gage the County has divided all the municipalities into three groups and North Wildwood is in the South Group which uses the Cape May tide gauge for it’s reference point.   With that the county uses Cape May’s NWS heights for Minor / Moderate / Major tidal flooding, which from our past posts you know that those designations vary from town to town.  For example they show minor flooding at 6.2 feet while the NWS shows it at 6.7 feet for North Wildwood.

To use the website click on the above link, click on the tab that says “What will the flood look like?”, a new page opens  and once you get past the disclaimers the map opens up,    next zoom into your neighborhood.   Once you have your neighborhood centered on your map,  on the right hand side of the page click on the Inundation Layers – South,  which will open to show different heights.  Check the box of one of the heights.     Start with the lowest which is 5.7 feet (above MLLW) at the Cape May Tide Gage. It will show several areas in town in blue with means it may be water covered at a tide of 5.7 feet above MLLW.   As many of us that have been around for a while we know that elevation is not always the best prediction of flooding  as you can see most areas in blue are not usually water covered at 5.7 feet above MLLW.   Looking at the different heights you can see that it shows a larger area than we usually see at the listed tide heights.   We know from watching the tides from over the years that you can two flood tides at the same height and you can have two different areas flooded.   Tidal flooding is affected by wind speed, wind direction, rate of tide rising, associated low pressure, residual tidal water from the last tide, and rain fall.    Flooding by using elevation is affected by bulkheads,  storm drain tideflex valves, wind, height of crown of cross streets and rain.    Is the map still relevant – YES just remember the areas indicated are at an elevation that will not always be flooded but may get flooded at the indicated tide height.