Tidal flow in rivers

[Edwardo]

Am I right in supposing that the direction of tidal flow in a river will change after the respective top or bottom of the tide? If so is there a way to predict it. I will be sailing much in the Alde/Ore and notice that flow direction does not correspond to published times of heights/lows. The flow is strong so it would useful to know.

Thanks in advance

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[chas]

Depends where you are in the river but normally in an estuary the stream ebbs and flows with the tide. The ebb can be stronger than the flow as it also has the force of the river water in it. This can be accentiuated by heavy rainfall upstream. The speed of the tidal stream is more often affected by shape of the estuary - sand banks etc will concentrate it and produce some strong tial streams.

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[trev]

Its a gradual change along the tidal length, and the rate is much dependent on the area - gradient/downstream river flow/curvature etc. I would recommend a chat with a few local fishermen from your particular area.

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[Boathook]

My boat is moored on the River Avon in Dorset and the river is nearly always on the ebb. It does slow right down though as the tide comes in and speeds up on the ebb. The same could apply to your location. Another great effect is the amount of rain that feeds into the river.

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[vyv_cox]

Entirely dependent upon the characteristics of the river, rainfall, tidal range on the day and no doubt other factors. Compare the river mentioned by another poster that is "always on the ebb" with the Severn bore, a 6ft wall of flooding water, or the smaller one on the Dee.

Looking at tide tables may help, on longer rivers e.g. the Dee, high water at Chester is an hour later than at the estuary mouth. So by the time that big lump of water gets to the weir in the city centre the tide is into its second "twelfth" outside. Not surprisingly it then goes out faster than it came in. I would guess that this doesn't happen much on a river rather like the Alde, where the entrance is narrow and the river is not all that long. However, having a lake or larger body of water upstream makes a big difference, something the Dee doesn't have but the Alde and even more so the Blythe at Southwold, does.

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[Bergman]

Dunno about the Alde and Or - I guess most rivers are unique

Where I live on the Ouse, the flood runs for about 3 hours and the ebb about 9

Seems that further up you go longer the ebb and shorter the flood.

Here the flood can rise as much as 6 meters in a little over 3 hours so can be quite spectacular, no something to mess about with.

If the river is in flood, which is not uncommon, flood tide disappears almost totally, river only drops a foot or two on the ebb and flow on the flood is negligible, compared to up to 8 kts in normal conditions.

Best answer is to talk to the locals.

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[LadyInBed]

Same on the Frome.

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[alan43]

No, you can't assume that the direction of flow will change at times exactly corresponding to local high/low water. Depending on characteristics of the estuary, your particular location, the volume of river water on the day, the heights of high & low tide on the day, etc., you might well find that the ebb flow continues for some time after local low water, and the end of the flood flow might occur before or after local high water. In some places there might be an hour or more between the reversals of vertical and horizontal movements.
Local knowledge is good, as is building up your own by observation.

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[Mirelle]

Tidal flow on the Ore and Alde

You really should buy yourself a copy of the Yachting Monthly guide "East Coast Rivers".

You also need the guide leaflet to the Ore and Alde available from most local chandlers or from Small Craft Deliveries, Quay Street, Woodbridge, who will also sell you a chart and a copy of the book mentioned above.

Having said that, the ebb runs a lot longer and harder than the flood, and HW Snape is about an hour and a half after HW Orford Haven, subject to weather conditions of course.

Unless you are experienced and have a powerful engine, do not venture below Havergate Island on the ebb or you may find yourself over the bar unintentionally.

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