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.