Potentially Dangerous St Helens Fort Walk!

This yearly tradition is certainly something that people look forward to, with a 25-30 minute walk to reach the fort and usually around about a 30 minute walk to get back, taking roughly an hour for most people. Approximately half an hour before low tide is the best time to start as the tide usually stays at its lowest position for around an hour. Any earlier and there is usually still a fair amount of water draining from the surround beach area, but that said during fine weather you can often safely navigate the walk from an hour before low tide, so lets talk about why this changes and then why this year is likely to be so dangerous.

Water is very sensitive to air pressure, so if you change the air pressure above water, the water will rise as the pressure decreases and then be pushed back downwards as the pressure increases, this means that during unsettled weather the water level is likely to be significantly higher than when the weather is fine because fine weather is often brought about by high pressure in the atmosphere, whereas unsettled weather is usually brought about by areas of low pressure. Another factor is wind. We can use the example here of sweeping water away with a broom. As you push the water from one side, you are able to push it up over slightly higher ground to sweep it away and this is simply because of the force that you are applying to the water.

The wind can produce the same effect as it blows on the waters surface, it quite simply begins to push the water along with the wind, so when it comes to an obstacle blocking its way such as a ridge in the seabed or an island, the water piles up against the windward side and makes that water deeper, and if the pressure is hard enough and the wind strong enough it can push the water right over that island or ridge. The most dangerous part however isn't the water breaching the the ridge or island, it is in fact because the water is forced to keep its momentum but over a much narrower area, so the water actually then speeds up. So just imagine we have some water flowing along in a stream that is 1 meter deep at a speed of say......2mph, then what happens if that water flows over an area of 1/4 meter deep? Well the water is still keeps flowing, but it now must speed up because the water upstream isn't going to slow down for it, so you end up with a rapidly moving, turbulent stretch of shallow water moving at potentially 6-8mph or more, at least before it becomes deeper once again and slows down. Well, this exact thing takes place in the sea when a current is present, especially when the current is being forced by the wind.

So to summarise that all, the water is likely to be deeper than usual due to an area of low pressure affecting the UK and IOW, combined with a strong wind that will increase water movement and will likely push the water up on one side of the ridge that everyone walks on, meaning that we will likely see water flowing across the walkway, and that combined with wind driven waves means that Today (Thursday) the conditions will be extremely hazardous. Tomorrow (Friday) we still have the low pressure present and it will still be quite breezy, so whilst the worst of the weather will have cleared through during the morning, the conditions will still be far from perfect by the evening, and that combined with a low tide that is ever so slightly higher than the previous day, there will likely still be water on some parts of the route. Here at IW Met we will never suggest taking any risks, but we will always explain to you the dangers of any weather impacts on various events, so our advice is to avoid taking part in any events that haven't been officially organised, and if you take part you do so at your own risk.