DougTheMac
New member
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?
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?
