Hertford Union - First Pound and Middle Lock Report

Motivation:

I saw several recent reports on Facebook groups, mostly the London Boaters group, reporting low levels on the first pound of the Hertford Union Canal lock flight (the pound between the top No 1 lock and the middle No 2 lock.)

Various suggestions were made about the likely cause for the low water levels.

Suspicions:

The two most commonly suggested causes were:

• Boater behaviour: particularly not closing lock paddles or gates.
• Poor maintenance: particularly leaking lock gates losing water.

I personally added another suggestion:

• Poor design: the fall of the various locks contributing to this pound emptying.

Methodology:

I decided I would position myself on the Hertford Union Locks for a few days and observe and record boat movements and water levels in the four pounds of the canal. I combined this with my regular activity as a voluntary towpath ranger.

I was not interested in the details (names and registrations) of which boats were moving, although I did record the number of boats sharing a lock.

I also did not measure the exact levels of the pounds, sticking to three basic levels: 'okay' - full and fine for navigation, 'low water' - obviously depleted by more than 6 inches, and 'unnavigable' - when the pound was so shallow as to be able to see silt and debris at the edge of the channel.

I recorded my observations on first arriving at the locks in the morning, at each locking through, and occasionally during the day if there were no movements. To do this I used a simple online form system (JotForm) on my mobile phone. In the evenings I would collate these reports as a spreadsheet.

I also talked with Trust staff, other volunteers, boaters, residents and local businesses about the locks and water levels.

Observations:

Spreadsheet:

https://drive.google.com/file/d/0B0NrtZDJStXhV2NDLUhhVmFxb0E/view?usp=sharing

Day 1:

On the first day (Bank Holiday Monday), I found some paddles left up on arriving - tail paddles at the lower and middle lock. The locks were empty, but the pounds were okay. Additionally operatives were making safe a tail paddle at the top lock which had been broken the previous day (apparently dropped, causing the wooden support to split.) The towpath side paddle of the middle lock was also broken and unusable.

There were 8 lockings through while I was there (from 9am to 4pm), 10 boats moving in total.

The pound between the middle and top lock was reduced to 'low water' after the first five lockings, and after the next three. Each time I saw this I ran some extra water down from the top lock to refill the pound, which usually took about five minutes.

No boater behaviour was observed that could be criticised, all paddles were lowered and gates closed when necessary.

Day 2:

On the second day (Tuesday 2 May), there were no issues when I arrived, and all pounds were okay.

This day was a little busy with boaters returning from the IWA Cavalcade in Paddington.

There were 9 lockings through (between 9am and 4pm), 12 boats moving in total.

The pound between the middle and top lock was again reduced to 'low water' after the first five lockings, and once again I ran some water down from the top lock to bring this back up.

No boater behaviour was observed that could be criticised, all paddles were lowered and gates closed when necessary. Most boaters were extremely experienced with locks.

Day 3:

The third day (Wednesday 3 May) was very much quieter. A paddle had been left up at the top lock, draining that lock, but all pounds were full and okay.

There were no lockings through until 13:47 so I could observe the pound between the top and middle locks for about four hours without the level being disturbed by lockings. During this time the level did not observably fall at all. Any leak from the middle lock's gates was being made up for by such water as was leaking through the top lock's gates.

There were 2 lockings through (between 13:47 and 4pm), 3 boats moving in total.

The pound between the middle and top lock fell about four or five inches with these lockings, not enough for me to consider the pound being at 'low water'.

Again, no boater behaviour was observed that could be criticised, all paddles were lowered and gates closed when necessary. The boaters today were younger but no less adept at working the locks.

Lock gates:

From the lock side I examined the suspect tail gates of the middle lock for leaks and damage.

The tail gates are leaking, faster than leaks in the head gates can fill the lock. Left from full, the lock will empty in approximately 1 hour. When the lock is empty, the towpath-side tail gate is slightly unbalanced and will slowly swing open under its own weight. This makes it difficult for boaters to close after locking down.

The gate mitres have been recently replaced (2015) but have since suffered some damage (likely from collisions and scrapes from boats using the lock.) In particular the towpath side rubbing strip is hanging from a single point, which means that the mitre on that side is less well protected from damage than it should be.

Anecdotal Evidence:

A local resident recalled that on occasion the pound between the middle and top lock was often low, but had also been seen to overflow the lock gates and inundate the towpath.

Older boaters recalled that the last lock keeper of the flight would often adjust water levels to keep the pound full.

A Canal & River Trust operative described this pound as being 'a deep pound' - the depth compensating for the shortness of the pound.

Another Trust operative said that water was regularly let down by staff into this pound each morning, and blamed the losses on the Victorian design of the locks.

Research:

The Top Lock No.1 has a fall of 6' 3" (1.91m).
The Middle Lock No. 2 has a fall of 8' 11" (2.72m).
The Bottom Lock No. 3 has a fall of 3' 9" (1.14m).
(source canalplan.eu)

Conclusions based on observations:

I have no evidence to suggest that boater behaviour is causing problems with this flight. Some paddles were found to be left up on two of the mornings, but I did not observe any losses from the pounds as a result. My presence may have prompted better locking operations from some boaters, but I cannot draw any conclusion from this.

The pound between the middle and top lock was seen to fall several inches with each locking through. This is in line with the likely loss of water due to the difference in the fall of the top and middle lock.

The pound between the middle and top lock was not observed to change level over four and a half hours while the middle lock's head gates were shut, and there were no lockings through.

The middle lock's tail gates were observed to be leaking more than the same lock's head gates. Some damage was observed to these gates. The towpath side tail gate was seen to be unbalanced, swinging open under its own weight.

It's my conclusion that the losses to the pound between the middle and top lock are almost entirely caused by each locking through. Boater behaviour and poor maintenance are not regular causes of these losses.

Recommendations:

Water level control:

It would be helpful for Trust volunteers or staff with some training in water level control to monitor water levels in this pound at busy times when there are the most lockings through. According to local observers, this would be on Saturdays and Sundays. This will allow water to be let down safely when necessary, after about every five lockings through. The presence of staff/volunteers could also help prevent any accidental loss of water.

For Boaters:

Ideally, always empty the top lock after you have used it. This should help keep the water level in the pound below topped up.

Maintenance:

The middle lock's tail gates rubbing strip should be reinstated ASAP to avoid further damage to these gates.

The middle and top lock's broken paddles should also be repaired.

Invitation for comments:

This is not intended to be an engineers report - and my voluntary observations are far from exhaustive. I would have liked to observe these locks in use through a weekend as well, to gauge boat movements during their most busy time. I'd welcome comments with further observations, anecdotes and recommendations.