Rainfall and canals

HAVING survived the wettest summer in a 100 years I think it's fair to say two things I take note of on a daily basis are the expected rainfall and the water level in the Cut, writes Ralph Freeman.

Boaters that are based on rivers or near river sections are especially vigilant and with good cause.

Shortened Caldon cruise

My trip down the Caldon in early July was curtailed by 'Wet Friday' which caused the Churnet to flood, big time. Very early on Friday morning (6am) I put the locks at Cheddleton between me and the flood meadows by Oakmeadowford Lock.

Being well above the level of the river and it's flood meadows is definitely a good thing at times like that! The 'lake' in the photo is in fact the Churnet in flood near Hazelhurst Junction. Scary eh? The message therefore is never underestimate the ability of a small river or stream to flood during/after a heavy downpour.

A more recent example

More recently I was doing a 'pit stop' in Aston Marina, which coincided with the heavy rainfall which led to the breach at Dutton. The water level in the marina rose overnight Tuesday, detectable even before I got up on Wednesday by a list to port!

The water continued to rise rapidly throughout Wednesday morning with it becoming cloudy with sediment. Not a good sign! By now the water level was above the bottom of the pontoons, a rise of some seven inches. Fortunately the rain stopped and the levels began to fall overnight, but what would have happened had the rain continued?

To raise an area the size of Aston Marina, plus the two and a half mile pound, by that amount takes a considerable volume of water, presumably run-off; so where had all this extra water come from? Thursday morning, as I cruised down to Bridge 86 to moor in the sticks, it was obvious the adjacent Trent was very much in flood and only the towpath separated it from the canal for long stretches between bridges 88 and 86. However the towpath along this section had been repaired recently and all looked well.

Source of the extra water?

I suspect the water had come into the Trent & Mersey Canal from a small stream which runs down from the nearby hillsides, under the canal just south of the marina and into the Trent. Looking at the flattened vegetation by the culvert it was clear water had come over the top of the culvert and into the canal.

Now whether that culvert was partially blocked or the level of the Trent had 'blocked' it anyway is not really the point. The point is large amounts of water entered the canal from an unexpected source.

Where does it go?

The question then is where does this excess water go to? Normally it would go down the bywash at Sandon Lock into the pound below. In flood conditions it's doubtful whether the bywash could cope and transferring the water to the next pound in these circumstances is really not that helpful.

There is a small overflow spill as shown in the photo not far from Bridge 84. However, it is weed infested and obviously could not cope, otherwise the rise in level would not have been so great. Most pounds have at least one ground paddle buried in the hedge on the towpath side, usually near the point where a stream runs close to or under the canal. This is to enable the pound to be drained for maintenance purposes, but I believe it has another (vital?) function.

Local lengthsman

After, or even during, a period of heavy rain, in days gone by, the local lengthsman would raise this paddle to dump some of the excess water out of the canal into a nearby water course. Now this person, over a period of time would have built up a knowledge of how 'his patch' behaved during periods of heavy rain. It was quite usual for these employees and lock keepers for that matter, to turn out at all hours to tend their 'patch' so to speak.

On the pound in question the position of such a ground paddle is about a 100 yards north of Bridge 86. However, no paddle gear is visible, having been removed at some time in the past? So is this emergency sluice still available under the heavy metal plates on the towpath or has it been removed? If so why?

Modern level monitoring

Some canals have SCADA 'black boxes' monitoring levels, but are staff brought in during rainy spells to monitor the output of these systems 24 hours a day and has CART enough staff left to respond in the case of widespread rainfall as happened recently?

Many stretches have no SCADA. Therefore, as far as I can tell, these pounds have no real time monitoring of water levels other than that provided by boaters and their mobile phones?

Who monitors canal levels?

So the real question is who monitors canal levels 24/7? Waiting until the rain stops and assessing the damage seems to be somewhat inadequate policy when the cost of a breach, we are now told, is in the region of £1.5m.

Now here's a thought: If it took two lengthsmen to cover a 16 mile pound that would cost say 50k in wages per year.

Dividing 50k into 1.5m = 30

So if the lengthsmen prevented just one breach in 30 years they will have paid for themselves ! That's ignoring costs due to disruption etc.
Makes you think?

The photo shows a 'neglected' ground paddle in the hedge bottom on the Trent & Mersey near Stone. Note the lack of grease and lubrication. Would it work if needed? Has it been tested recently?

Not Brindley's fault

I dispute the statement implying the canals were not designed for heavy rain. If that were the case how come they have survived for over 200 years? All the equipment is (was?) there to control water levels in the majority of pounds, installed by the canal builders like James Brindley. It's easy to blame him for the Dutton Breach; after all he is long dead, and not therefore able to sue for libel or defamation!

What is clear though is the canals are not being operated in a manner to survive heavy rainfall. Controlling the rise in water levels in the canals is critical if extensive damage is to be prevented Events over the last few years, I would suggest have proven this point.