"Steve Haywood" <[EMAIL PROTECTED]> wrote: >I would conjecture that the reason by-weirs weren't built on >canals was simply a matter of cost. Building overflows wells, channels and >culverts would have been a far pricier business than simply ensuring lock >gates were set at different levels. In other words, you could argue that as >a more sophisticated solution to a problem (and one that ensures safer and >easier boating), replacing by-weirs is simply doing what the original >engineers would have done if they'd been given free rein.
One of the main users of this design (the inventor?) was Jessop, who is not known for skimping, so it may not have been for cost saving even though any good engineer will try and avoid spending needlessly. It has the major advantage of saving water, by spilling surplus water into the lock. IIUC, the top of the top gates is usually only slightly above the normal upper pound level. Excess water first goes down the paddle weirs, but if these can't deal with the volume the upper pound will rise and excess will eventually start weiring over the top gates. I think that the distance between the normal upper pound level and the top of the top gates is such that even if the top gates are weiring it is still possible for a normal human to open these gates when the lock is full (by which time water will be weiring over the bottom gates, of course). So boating isn't that difficult with this design. Although I admit I'm not sure what counter-measure there is for opening the bottom gates when the top gates are weiring. Whereas the bywash system has disadvantages. For example, the draw from water entering the bywash can pull a boat of course, and the flow when this water exits can do the same by pushing if the exit is badly laid out. The latter is a very annoying problem on some French canals, which are cleverly designed with the bywash outflows at right angles to the waterway right in the lock mouth, and down which there is often a considerable flow. >Certainly I wouldn't have any concerns about the loss of heritage if BW built >new >by-weirs on the Rochdale 9, any more than I did when they put baffles over >the gates of some locks on the Calder and Hebble to make them safer. Do you *really* want to be known as a person who is happy with paddle baffles? Adrian Adrian Stott 07956-299966
