The whole of the Grand Junction ( another Jessop cut?) works this way, although some side ponds have been converted to by-weirs to accommodate the extra flows from Tring Sewage works. It is however important to have the bottom gates slightly TALLER than the top gates or when there's too much water about it becomes impossible to open the top gates.
BW have replaced a couple of top gates on the Aylesbury arm with over-tall ones. The arm receives the overflow from the Tring reservoirs below lock 9 and when the reservoirs are overflowing these top gates are extremely difficult to open , because the water is the at a higher level above the top gate than in the lock, to an extent which depends on the water flow, the difference in gate levels and the amount the bottom leaks. Regards N ----- Original Message ----- From: "Brian Dominic" <[EMAIL PROTECTED]> To: <[email protected]> Sent: Wednesday, May 16, 2007 7:02 PM Subject: Re: [canals-list] Re: Re: Summer Trip > [Default] On Wed, 16 May 2007 10:54:16 +0100, > [EMAIL PROTECTED] finished tucking into their plate of fish, > chips and mushy peas. Wiping their mouth, they swiggged the last of > their cup of tea, paid the bill and wrote:: > > >>But it does tend to support my belief that the Rochdale locks originally >>(ie in the case of the ones on the trans-Pennine length, until the 1990s) >>lacked conventional bywashes, instead relying on the system involving >>slots in the upper gate recess walls. These allow water to overflow into >>the chamber via the upper ground paddle culverts (possibly supplemented by >>water coming over the top gates when there is too much for the slots - >>which are relatively short compared to conventional bywash weirs - to cope >>with), and bottom gates which are (or should be) designed with the tops of >>the gates at exactly the same level as these slots, so that if the lock is >>full the water will overflow over the bottom gates. The same system was >>used elsewhere (GU, K&A, Basingstoke that I know of) and does seem to have >>been favoured by Jessop. >> > I'm fairly certain the locks on the Cromford didn't have bywashes and > it would be our intention not to install them when we restore - we'd > use the method used on the Erewash, where the bottom gates are > slightly shorter than the top ones, so water can flow through the lock > when the level in the upper pound is high. > > Brian L Dominic > > Web Sites: > > Canals: http://www.brianscanalpages.co.uk > > Friends of the Cromford Canal: http://www.cromfordcanal.org.uk > > (Waterways World Site of the Month, November 2005) > > > > Yahoo! Groups Links > > > >
