North Wildwood’s Emergency Preparedness website

2302, 2021

Why aren’t elevations of Land and water the same?

A question we some times receive is “My home’s first floor is supposed to be at 10 feet so when we get a seven foot flood tide will the water be three feet below my floor level?”  The simple answer is No,  but to understand why we must first look at the different ways that land and tidal water is measured.    Because land is static, that is never changes,  there is a datum or reference point that is called the North America Vertical Datum 1988 or NAVD88.   This datum is where “zero” is using NAVD88 reference point.   As tidal water height changes depending on the tide the datum or reference point used is the Mean Lower Low Water or MLLW datum.   This is the point where “zero” in the vertical measurement using the MLLW reference point.   MLLW water is the average of the lower low water heights of each tidal day over a specific 19 year period (currently 1983 to 2001).   The distance the tide rises from low tide to high tide is different at different Latitudes.  for example in Florida the tide will only rise about a foot  from low to high whereas in Maine the tide will rise over 14 feet every low to high tides.   This means that the MLLW is different at every location.   That is why we have different tide tables for each different location.  As not every location has a tide predictions you have to use the closest for your location, so for North Wildwood’s back bay tide we use the West Wildwood tide predictions.   To see tide predictions for different locations (click here) .   Now that we know that land and tidal water are measured using different reference points we need to figure out what the relationship  between MLLW and NAVD88  for our specific area.   To determine the relationship we to look for a National Geodetic Survey or NGS benchmark.   There are many of these located around the area.  One is located on the entrance way to City Hall.   Most show only vertical elevation of the marker that is put there by the NGS.   Only a few have the relationships to tidal water.   The closest one with tidal water is Benchmark Station #8535835.   Looking at the information (see below) we learn that for our area zero feet NVGD88 is equal to 2.75 feet MLLW. So to convert a MLLW height in our area to a NAVD88 height just subtract 2.75 feet or conversely to change a NAVD88 height to MLLW height you add 2.75 feet. Each town will have a different
relationship and number to add/subtract from either MLLW or NAVD88, for example in Ocean City you use 2.06 feet and in Stone Harbor you use 2.66 feet.  Now to answer the original question   “My home’s first floor is supposed to be at 10 feet so when we get a seven foot flood tide will the water be three feet below my floor level?”   As buildings are on land NAVD88  reference point was used to obtain your homes first floor height of 10 feet which after you do the math is equivalent to 12.75 feet above MLLW.      Working from the flood water height of 7.0 feet using the MLLW reference point you find that the water height is equivalent to 4.25 feet NAVD88 or 5.75 feet below your 10 foot floor height.   Even though the water will not enter your house you still have to be concerned with your yard, garage, sheds, etc.  As landscaping, curb heights, driveways can change your yards elevation it is important that you make note of where the water comes up when it is at a specific height.   As wind driven water and at times of heavy rain with flooding can raise the height of water so  it is important to add this information to your notes.   NWOEM posts the tide heights after each flood on the OEM Facebook page.   You can also get the tide heights from the weather station and tide gauge using the link on the left of this page or clicking (HERE)  Remember that the National Weather Service uses the MLLW datum when predicting heights in their Coastal Flood Warnings and Watches.  Also as it is important to boaters to know how much water is below them tide charts are in MLLW datum.   Surveyors use the NAVD88 for land elevations.   A handout with the same information in this post is available on the left hand side of this page at the link called “Vertical Elevations Explained” it also contains a reference chart comparing both datum.    Coming up next year is NAVD22 which will be the first datum using measurement taken by satellite.  Below is a screenshot of the benchmark#8535835

2212, 2020

Keeping up on the weather, Tide Charts and Snow Emergency Routes

The winter season brings many weather related events that will affect our area such as rain, snow, ice and an occasional tidal flooding. The good thing for us is there never has been a time that there is more detailed information on weather from readily accessible satellite pictures, animated forecast models, online weather stations and Nexrad weather radar images that are available on your smart phone or Internet connected computer. For some there is too much information and they are just satisfied with a weather reporter reading off of a published forecast during the nightly news. Others like to have advance notice of a storm when it is in the “possible” stage and follow it as it evolves into the storm that will affect our area. Whatever type of person you are there is one thing that needs to be done and that is you get into an everyday routine to check the weather. To learn more about the weather visit the links on the left hand side of this page listed under IMPORTANT LINKS. From time to time we have gone over these links in detail on this page to see previous posts scroll down on this page until you see “Click here for archive notices” and you can see the past posts.

You may notice the 2021 Tide Charts or tide tables are already posted. Click on the link and download the tide predictions for our area for the entire year. Lastly one thing we like to mention before each winter is the Snow Emergency Routes. North Wildwood has designated that New Jersey Avenue and Atlantic Avenue are the snow emergency routes. We ask that if there is a forecast of snow coming to move your vehicle to a side street so that the roadway can be plowed curb to curb. There is a specific Code Red message that has been created to notify residents on Atlantic and New Jersey Avenues of the Snow Emergency Route. The message is a reminder not an alert that the snow emergency route has been activated – once snow covers the street the snow emergency route is active so please do not wait until you get a message to move your car.

2310, 2020

Winter Preparedness . . .

As we enjoy the nice October weather, which many of us  think is the best time of the year at the shore,  it is time to begin to prepare for the upcoming winter weather.   Looking at the long range winter predictions of the National Weather Service, Farmer’s Almanac and various other YouTube weather forecasters we could be in for a cold mixed winter.    With the upper mid-west seeing an early winter, with snow and unusually cold weather perhaps some of the forecasts that are calling for snow and coastal storms for our area might be correct.   With that in mind now is the time we should be making preparations for the winter.    As we have pointed out before many of the things you do to be prepared for one event, such as a hurricane, can be carried over to another event, such as a snow storm.  For example the same food supplies you had stored to use during a hurricane can be used during a snow storm where you can’t get out.   If you are on top of your preparedness all you have to do is to prepare for what is different from one event to the other, that is, in the winter we have freezing temperatures along with snow or ice that you wouldn’t prepare for other times of the year.     Taking that in to consideration you should have only a few things to do to be prepared.      If you are new to preparedness you are urged to visit the many resources that are on our BE PREPARED page which can be accessed at the link at the top of this page or the link on the Right Hand Column.    Take a few minutes before the winter weather arrives in our area to see if you’re prepared.

As we are already a month into  the new hurricane season and our first tropical storm has been named it is time to check our emergency plans and preparation.   We urge everyone to visit the links on the left hand side of this page.   They are links listed under BE PREPARED.    Preparation is not hard and while most  preparation needs will be the same for everyone each person will have to come up with his or her own plan.    By visiting the suggested websites and tailoring the information to your specific situation you can check your plans and ultimately will be better prepared. 

Also today due to the many requests to be added to the flood notification list we have expanded the flood notification to all residents west of New York Avenue from Spruce to 26th Avenues.     Phones in these areas will be called and a recorded message will played.   There are two messages that can be sent one known as the initial call sent when it appears that flooding will take place and one sent when the siren has been sounded.     These phone calls are sent via the CODE RED Community Alert System.  Read below to how to add your cell or other phone numbers.    REMEMBER this system is used city wide for other notifications so if you are not in the flood prone area you still should visit the CODE RED website and add your alternate phone numbers. 

Currently the Code Red Community Alert System will dial every Verizon and Comcast Phone in North Wildwood.   However with many people relying on Cellular phones the system will enable you to add phones to your address.   Remember this system is based on North Wildwood addresses so when you sign up you need to attach your out of town phone to your North Wildwood address.    Being addressed based the city will be using the system to alert those in flood prone areas of flood warnings, those on the snow emergency routes to move their cars and on occasion when there is a natural gas leak or police emergency a circular area around the incident will be notified.   Those of you visiting this page can follow this link to get a head start on signing up your “other” phones (Click on the CODE RED LOGO)

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On the Code Red website you will be asked if you want to add your email address or receive text messages.   We have the ability to duplicate the contents of the voice message into an email and truncated text message.    As this will only be used in an emergency why not add all your contact preferences and methods so you can keep informed.    Also those with “smart” phones will have the capability to download the Code Red App. 

At the  North Wildwood Office of Emergency Management we feel our central job is to keep communications when the normal systems are failing.   Therefore we don’t put one form of communication above another.   At times some may seem simplistic in these times of technology however when normal systems fail we will fall back on them.   That  is why we depend on a fire siren,  AM radio and telephone as basic methods of notification.   We will be using North Wildwood’s AM1640 as the method of communication that can put the most information out.   Please get your self a good AM radio.   Remember when there are no emergencies AM 1640 broadcasts special event information – ever wondered what time the free concert starts and who is playing? it is on AM 1640;  want to know what the start and end times of the festival in the entertainment district?  it’s on AM 1640 as well as the upcoming events for the next several weeks.