General discussion about anything even only vaguely club or rowing related
|Tide Tables on the BBC by jmg - Wed 25th May 2005, 10:09am|
|In addition to the controversial new TV forecasts, the BBC seem to have made some quite positive changes to their weather website, including tide tables. Not being a regular on the tideway, I don't know whether this is well known and understood, but I wonder if anyone can explain reasonably simply why the shape of the curve changes so dramatically as you work your way downstream from 'Richmond' Lock to Kew, Hammersmith etc etc etc etc? Also, what effect if any does this have on the stream, particularly where on the curve would you expect the strongest stream?|
|by dw229 - Thu 26th May 2005, 12:45am|
|From my understanding, it's all about width Jon...|
|by Simon - Thu 26th May 2005, 8:29pm|
|This is something I've never really understood either, but is it not that the weight of the land water coming down the river has progressivly less and less effect as you move downriver? This weight delays the turn of the tide from running out to running in, so you get a longer gap between High and Low than between Low and High. The effect of tis is less at Tilbury than at Richmond because by the time you get to Tilbury you're dealing primarily with sea water.|
Apologies for typos, been v busy today and am falling asleep already...
|by Martin - Fri 27th May 2005, 9:28am|
|Have been trying to work out this, Simon, if it could be effect of freshwater flow meeting tidal flow. Like you I think I've convinced myself it would do the right sort of thing. But I'm not sure that the freshwater flow is big enough to have that much of an effect. Maybe it is some combination of the two.|
|by jmg - Fri 27th May 2005, 10:10am|
|I was thinking of the stream initially too, but like Martin I'm not sure it would have enough effect - on the Richmond graph it's twice as long between high and low than between low and high tide. Also, looking at the graphs, the low tide point is three hours later at Richmond than at London Bridge, while high tide is only an hour later.|
I think the width idea sounds plausible, with the flow driven by the height changes out to sea and the gradually narrowing channel forcing the level to rise faster than you would expect, then ebbing more slowly as well....?