Deben entrance 2024

[DougTheMac]

Further to my earlier post and Johnah's reply, I think Johnah slightly missed my point. I was wondering if the bar as a whole, not the deep channel through it, is shallower/higher than in previous years. The behaviour of the water inside the river depends on flow over the bar - and near HW, most of the volume of flow will be over the wide area of shallow sandbanks, not through the narrow deep channel. Think about the difference in the strength of the tidal stream in the channel by the groynes compared with in the bar channel itself. If the bar generally is more restricted (ie shallower) than usual, then the rise and fall of water inside will be less and later than usual. (Consider the theoretical example of a near-infinite lake connected to a tidal ocean through a narrow channel - the level of water in the lake will never change, but will always be at mean tide level; peak flow rate (ie tidal stream) in the entrance channel will be at HW and LW.) All estuaries have this behaviour to a greater or lesser extent, depending on the area of water inside and the restriction at the entrance. The tidal height just inside the bar will lag the tidal height outside, and the flood will run inside the bar until the level outside has fallen to equal the level inside the bar, well after HW outside.
Johnah's very useful comments about when the ebb usually starts (HW+0h30) is based on historical experience. My question is whether anyone has noticed any difference this year. As I mentioned above, the levels at Tidemill seemed to be lower and later than the published tables; it certainly caught out several boats who left their berths at the expected time and had to wait 20mins by the entrance for the level to get up to what they ovbiously expected. Any Tidemill residents noticed this behaviour this year?

 

[MikeBz]

It’s not as mountainous as I recall it being in the late 2000s, when it seemed to tower above us when entering at half flood.

 

[PeterR]

When I passed the marina on the 9th it was exactly at the time of predicted local high water which was supposed to be 2.63m. The guage was showing a fraction under 2.5m and the flood was still going at about half a knot. That seems to be pretty standard in high pressure conditions, even if the tide at sea is much as predicted. The next day a friend of mine who was visiting the marina had his departure delayed when a large motor boat tried to get out out too soon and spent 20 minutes stranded on the cill. The cill guage is reputed to be very acurate so either the mobo misread the guage or tried to leave based on when it was predicted to be OK and didn't look at the guage at all.

I don't have that much experience of the Tidemill but futher still upstream at Larkmans the tide is even more subject to weather induced fluctuations both in terms of height and timing. On spring tides they will normally start trying to launch boats of around 1.8m an hour before HW at the Tidemill but frequently the tide seems to be later than predicted and its not uncommon to spend the first few metres after launching pushing your keel through the mud..