What's going on here then?

[cuthound]

Looking through some old holiday photo's to while away a cold Sunday afternoon, I came across these taken at Buckby Bottom Lock (next to Whilton Marine).

 

They were taken in August 2013.

 

In the first picture, we entered the lock to go down with another boat. The lock had almost emptied, when water began flooding in over the top gates. Both boats had to move forwards to avoid being flooded (thank the diety of your choice we were not in a full length boat),

 

The lock began to refill, even though both bottom paddles were open and refilled to about 3/4 full. Then the water stopped coming over the top gates, and the lock emptied normally and we opened the gates and left.

 

 

The second photo was taken the next day, and shows a hire boat entering the same lock. Again, as he entered the lock it began to fill rapidly even though the top gates were open, so much so that the water overflowed the bottom gates!

After a few minutes the excess water ceased to flow and the lock could be operated normally.

 

 

So can anyone explain what was happening?

 

I don't think someone mis-operating a lock above could cause such a flow for so long, and the only other possibility I can think of would be a fault with the back-pumping system.

 

I have been through Buckby locks many times and never seen anything like this before.

 

 

 

 

[ukdiggerboy]

i would have thought the weir gates to the side were not open enough to take away excess water in upper pound ?

[RLWP]

You see this often in the Atherstone flight, and when you know about it it's quite common and makes opening gates easier

 

The water in the pound above the lock is surging backwards and forwards, like you used to get the water to do in the bath as a kid just before it sloshed onto the floor. The surges are caused by using the locks

 

Sometimes you'll start to open a gate, and then find you can't because the level in the end of the pound has risen. Wait for a few moments and it will drop again pulling the gate with it

 

Richard

[DeanS]

sloshing pounds...first I've heard of that.....

 

the lock 92 on the Rochdale 9 top gates wont move unless there's an overflow.......I've seen boats sitting there for 40mins trying to open the gates....it's caught me a few times.

[carlt]

This is the little known "Grand Union aegir" which is far rarer an event than the more famous Severn and Trent tidal bores.

[beardshave]

It's certainly happened to me on the Buckby flight and not just on the bottom locks.

There's a lot of water coming down that flight.

[alan_fincher]

It is usually to do with the back pumps being run far more and far longer than is actually necessary, and the chances are that CRT were using lots of electricity to pump water back up from the bottom into pounds that had no space for it to go into.

 

I seem to recall an explanation at Buckby something along these lines, and although the precise detail may not be spot on, I think I'm fairly close....

 

1) One back pump handles (I think) bottom 5 locks that are relatively close together.

2) Second back pump handles (I think) just the top two, which have longer pounds below them.

3) In order to avoid the pound below the second lock down going low, (because of the back pump at the top extracting from it), the bottom back pumps pump at a deliberately faster rate than the top one.

4) That results in an excess in that pound, if back pumps simply left running when there is already enough water

5) Water cascades over gates of bottom 5 locks in the manner you have pictured.

 

But don't complain too much, because often they have the back pumps turned off, and this can then result in trying to go through pounds towards the bottom of the flight that are a foot down or more.

i would have thought the weir gates to the side were not open enough to take away excess water in upper pound ?

 

By design there were no bye-washes on Grand Union locks of this type - they were specifically designed that excess water passes through the ground paddle culverts at the top end, but over the gates at the bottom.

Admittedly some locks have had subsequent modifications to provide a bye-wash through former side ponds, (Marsworth is like this), but I don't think Buckby bottom has any provision, hence it all goes over the gates.

It's certainly happened to me on the Buckby flight and not just on the bottom locks.

There's a lot of water coming down that flight.

 

Stoke Bruerne often has similar issues if the back pumping is run excessively, although I'm not sure the explanation is exactly the same, as I don't know how many pumps they have there, and which pounds the pump from and into. I have always understood that Buckby is made worse by two pumps working at a different rate.

[ukdiggerboy]

well ive learnt something today thanks alan

[cuthound]

Thank guys,

 

Alan's explanation seems the most plausible.

 

Not sure about Richards theory that it is caused by operating locks or someone having a bath in the pound

[Leo No2]

I believe Stoke Bruerne and Buckby are similar. They have what CRT call 'letter box' weirs which can, in Stoke Bruerne, cause flooding of the Navigation pub (perish the thought) but more importantly the pound between locks 19 and 20 which also tends to wash the roadway away and can flood the cottages to the east. They allow water into the lock but generally not out again unless a paddle is up, there's a leak in the lower gates (as is the case with Stoke Bruerne top at the moment) or they overflow the bottom gates. In Stoke Bruerne the pumping is initiated from the pump house at the bottom of the flight (on the east side below the bottom lock) and has outlets into the long pound and the Stow Hill pound right outside the four cottages. I assume the same principal applies at Buckby with the 'letter box' weirs. The excess water is only apparent if/when there is excess water in the Stowe Hill or long pounds in the case of Stoke Bruerne.

[RLWP]

Thank guys,

Alan's explanation seems the most plausible.

Not sure about Richards theory that it is caused by operating locks or someone having a bath in the pound

If you have a mooring by a lock, you'll see it. As I said, the pound at Atherstone above the lock with the side pond is a great place to see this in action.

 

It happens in all pounds, the water doesn't stop flowing instantly the paddles are shut

 

Richard

[matty40s]

I came down there late evening in Spring, and another 7 boats came along doing the same thing. The back pumps were on, and we were taking good all the water down.

2nd from bottom, I had to run ahead to open the bottom lock paddles as the towpath was underwater and the overflow reaching the houses.

It took us over 30 minutes to get through the bottom lock as the water coming from behind was filling faster than the lock was emptying.

[NickF]

sloshing pounds...first I've heard of that.....

 

the lock 92 on the Rochdale 9 top gates wont move unless there's an overflow.......I've seen boats sitting there for 40mins trying to open the gates....it's caught me a few times.

I have stood and watched it below the first pair in at the top of Frankton Locks, when the lower lock of the staircase is emptied you can watch the water slosh back and forth in the pound below.