North Wales Tides

As SCUBA divers we plan our diving many months in advance. Of particular importance is the occurrence of Spring and Neap tides, as they generally offer the longest slack windows, best suited for diving. Obtaining tidal predictions that far in advance is a real challenge, as most sites allow free access a mere 7 days in advance. A few offer 28 day predictions, but we really need 12 months. The National Oceanography Centre Poltips software would gives us that, but it's beyond the budget of a small volunteer dive club. It would be a violation of copyright to scan (or otherwise copy) printed tide tables, despite their being very reasonably priced.

Fortunately Bangor University Centre for Applied Marine Science generously share their annual tidal predictions for a selection of ports around North Wales - Liverpool, Conwy, Beaumaris, Menai Bridge, Port Dinorwic, and Caernarfon.

This module supports the creation of calendars of Spring and Neap tides based on the Bangor tables, though the generation of ICS files. The code can also be imported into AppScript to manipulate a Google calendar directly.

The author is not in any way associated with Bangor University, and is not aware of any copyright or other restriction on the public data downloaded from the Bangor University CAMS website.

Generating a .ics file

Clone the repository and install dependencies. Then run the bin script:

git clone https://github.com/cdot/Tides.git
cd Tides
npm install
node bin/gen_ics.js

This will output ICS data for neap and spring tides to the console. Redirect it into a file, and import it to your calendar app.

Running in Appscript

You can create a script that will automatically update a Google Calendar. Clone the repository as described above, then

npm run appscript

• In Google Drive, create a new AppScript file.
• Use Files + in the left bar to create a new Script file.
• Call it "TideCalendar"
• Replace the contents with the content of the local file appscript/TideCalendar.gs
• Switch to Code.gs, delete everything there and paste:

function createCalendar() {
  createTideCalendar({
    site: "Liverpool",
    // Replace the calender ID with your own calendar
    calendar_id: "eq470fggslkdf44ff5098silf4o@group.calendar.google.com",
    year: new Date().getUTCFullYear(),
    nsOnly: true // Neaps and Springs only
  });
}

• Replace the second parameter to updateTideCalendar with your calendar ID.
• Click Run in the top bar