Monday, 20 January 2014

Erode is long!

One of the regular volunteers with Friends of Henllys LNR recently mentioned that one of the footpaths off the LNR was in a dreadful state due to prolonged torrential rainfall. Upon a closer inspection the stone footpath had been washed away in places 50cm wide and 35 cm deep.

55 cm wide and 30 cm deep
Water flowing along the footpath from 2 stream breaches
The cause of this appeared to be from 2 places where the stream, which is elevated to the footpath, broke its banks in 2 places. Some of this is due to silting up and blockages from fallen branches snagging and building up dams forcing the stream along different paths. We decided to take action on Friday, before it became even worse and just in case it gets repaired and the underlying cause was not investigated or treated.

Water pooling around LNR access gate
We decided that we could build a couple of fascines from brash collected on the Reserve from trees felled as part of the management plan with TCBC and volunteers. The woodsman’s grip mark II worked a treat...
Woodsman's grip II improved with a surplus electrical cable
...and the two bundles were tied up with wire and transported across the muddy reserve by wheelbarrow.
Could do with an ox
They were then put in place after several different orientations to best limit the flow onto the footpath.

Fascines in place note the water still running down the breach
We built on or fascine experiences on the Local Nature Reserve over the last 4 years and knew that these would silt up in time and would stabilise the banks, however, we needed to do a fix now, to stop further erosion. We decided to use some of the silt that had accumulated nearby to the fascines (probably adding to the problems) and backfilled behind and on top/through the fascine nearest to the bank. After a good load of this, the breach did appear to be blocked.
Backfilled with silt, breach appears repaired
A little further downstream and by standing in the stream, the second breach appeared to be caused by blockages in the normal route of the stream including branches and a carpet flytipped from the houses above in Llys Gwyrdd. These were unblocked by hand and 2 defences built up near the breach to try and halt the flow of water onto the footpath.
No more water flowing over breach 2
At the end of the footpath where the pooling was most prominent, we dug two drainage channels back towards the stream, but the flow away didn’t look fantastic considering the channel was over 30cm deep in places.
On the Saturday night, there was another yellow weather warning, more blocked drains and again more water cascading down the roads and into this stream. Sunday heralded a lovely day and we were fearful that these defences would not have held. However, it is nice to be surprised occasionally and the path near to the gate was immediately drier.
Much drier due to drainage channel
Moreover, the eroded channel was much drier with water in just the deepest sections.

(Sun) This was full of water on Friday and with heavy rainfall on Saturday evening drained away really well
Walking upstream, we were pleased to see that both the breaches had successfully held, which was brilliant news for us. A great result for a couple of volunteers.

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