--- In [email protected], [EMAIL PROTECTED] wrote: > > > As I understand it, that's correct. The hirers' notes that a local boat hire company used to put in their boats included a Q&A section explained the overflow arrangements and contained something memorable along the following lines... > > Q: But that's not a very clever way to design a lock, is it? > A: The system was devised by William Jessop, the finest engineer who has ever graced our waterways, or ever will. > > Splended though this rejoinder is, I feel that it doesn't move us very far forward in terms of whether or how we should adapt good 18th century working designs to be more suited to modern pleasure boat use... > > 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. > > Martin L
Thanks for that Martin. Interestingly the process was taken a stage further on the Marple flight(and possibly elsewhere). There are recess overflows round the bottom gates as well which was only made possible because there were ground paddles at the lock tail as well as the head. I do not recall any of these recess overflows round the head gates on the "Rochdale Nine" however but it is sometime since me and those empty forebays were in close contact ! Regards Pete
