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Kent Estuary Tidal Bore, Arnside Cumbria

A cache by flipflopnick Send Message to Owner Message this owner
Hidden : 05/29/2007
1 out of 5
1 out of 5

Size: Size:   other (other)

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Geocache Description:

Morecambe Bay is a large flat area of tidal mud flats. When the almost diurnal tide comes in, it creates a tidal bore. On spring tides this is a visible wave between Silverdale and Arnside from the shoreline. Walk along raised walkway from above coordinates. Be aware that an Event Cache in the form of a Cross Bay walk is mutually exclusive, unless you are unlucky.

Morecambe Bay has the right shape of narrowing shoreline and shallow slope profile to generate a tidal bore in each river estuary, on a spring tide. When the tide gets funnelled by the narrowing channels, the tidal bore is more evident, as in the Kent Estuary. A bore wave can be seen in the nearby Leven estuary, but it is less obvious, even on a spring tide. High tide is roughly every 13 hours, and the tide comes in faster than a running person. On really good spring tides, kayakers will surf the bore wave all the way to the railway viaduct. Tides follow a 2 week cycle, with the height varying on a sinusoidal pattern. Spring tides are the maxim height. Neap tides are the lowest. Both neap and spring tides occur every fortnight.

So for safety stick to the shore. If anyone would like to join the author surfing the bore wave, please contact author of this Earthcache through Groundspeak personal profile. Parking is free.

The bore wave can form way out in the bay on springs, as the incoming tide rushes up the channels. The only ways to see the bore safely out in the bay are to use a boat or kayak, helicopter or hovercraft. Although the bore's affect can be seen through binoculars when the wading birds rise from feeding on the mud flats. Bring binoculars. The birds will rise any time between 2 and 4 hours before High Water (HW).

Conditions for best sighting:

  1. Spring tide rather than neap tide. Ideally Equinox spring tide for maximal range. Late March and late September
  2. Low pressure over Irish Sea.
  3. South westerly wind less than Force Three.
  4. Recent rain in river Kent to cut a good channel through the mud flats.
  5. Preferably visit prior to a spring tide so there is not too much standing water in the channels.
  6. None of the above will guarantee a good sighting, but may help.
Tide times:
Tidal predictions can be got from many sources, and are usually printed using GMT.
  1. Morecambe Bay (Barrow-in-Furness Ramsden Dock) tide tables. Available from newsagents around the bay.
  2. Online (only 2 months ahead).
  3. or View Barrow (Ramsden Dock) Annual Tide Tables from for free.
  4. Newspapers, local and national. Use Tidal difference to correct for local time of High Water.
  5. Each month's tide table is posted near a public access points. E.g. Arnside pier, Canal Foot Ulverston.

Tidal Difference
Tide times need to be adjusted for Arnside. Add 15 minutes to High Water Barrow-in-Furness for Arnside. Add 20 minutes to High Water Liverpool for Barrow-in-Furness.

ExampleSo if High Water Liverpool is 12.10 GMT on June 16.

Add one hour for British Summer Time (BST), add 35 minutes for Arnside. Thus High Water Arnside will be 13.45. You need to be there 2 hours before High Water Arnside.

Knowing time of High Water work back to time to expect the bore wave.

Either side of High Water the tide is slack.

1 hour 30 minutes before High Water, the bore wave is visible between Blackstone Point and railway viaduct. To be sure be ready 1 hour 45 minutes before High Water Arnside.

To log, perhaps walk from above parking coordinates out to sea along the shoreline walkway. Measure the distance between two points and wait.

Please answer as many of these questions as you can IN YOUR LOG. As Cache owner I will receive your log by email. A photo with the log of the fun you had doing the sums, or the sunset, is always appreciated. No need to log and send an email separately. A LOG will suffice. It's an Earthcache, they are educational.


  1. What time did you see the feeding birds rise from the mud flats?
  2. What time was HIGH WATER at Arnside predicted or actual time wave passed you?
  3. And which port did you use to work out High Water time?
  4. Did you see a bore wave? If so estimate its height and speed. If no visible wave, what did you see?
To estimate the speed, measure the distance between two fixed points in metres using your GPSr and time the bore wave using timer on your watch or mobile phone in seconds. Speed = distance divided by time. S=D/T
Your answer will be in metres per second (m/s).

Everyone's answers will be different.

Tidal information explained
Runner's account

This cache is located on a GeoHike.

Arnside Round (Cumbria)
Geohikes: Taking Walking and Geocaching to a New Level - Wednesday, 06 May 2009

The Bore Forum

Additional Hints (Decrypt)

Shegure bhg, orggre vg hfhnyyl vf.

Decryption Key


(letter above equals below, and vice versa)

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