Out of all the work I carry out, my favourite has to be carrying out habitat enhancement in and on rivers and river banks. Fortunately, I was contracted recently by Chiltern Rangers to carry out just that on (what could be) a lovely little chalk stream on the edge of the Chilterns in High Wycombe, Buckinghamshire.
I knew the site well, having previously been there in an advisory capacity when Chiltern Rangers were planning some enhancements to be made to the wildlife pond which is also on the site. The stream in question is actually man made and eventually joins the River Wye (the chalkstream), but unfortunately during the construction of the artificial channel, the chalk substrate was more or less completely removed, leaving a silt / clay substrate, and the channel was widened in order to cultivate Watercress in previous decades. Immediately downstream of the site is a small brick culvert which restricts the flow, meaning that the water velocity is sluggish and a large amount of deposition has occurred. This deposition has completely covered what chalk and gravel there was left in the stream, and has completely destroyed any potential for trout to spawn in the stream – so we decided to put some back in and also relocate some of the silt into the margins to narrow the channel and create some shallow marginal reedbed habitat.
This isn’t the easiest site to work at, access for the machine is only possible on the right hand bank (looking downstream), which is approximately 12ft above the water level. This meant that I was somewhat restricted with where I was able to access the channel with the 13t 360 tracked excavator. It also meant that creating marginal berms with the silt was a lot harder than anticipated as I was effectively working blind from the excavator cab due to the height of the bank! Fortunately, I had an ex-Sparsholt College work placement chap with me for the project, who was very helpful in pointing out the bits I had missed!
Chiltern Rangers had arranged for 15 cubic metres of mixed stone (40mm to 100mm) to be delivered in cubic metre bags to the site which was unloaded with the telehandler. Unfortunately the combination of the 7 ton telehandler, the Land Rover, a 13t 260 excavator and two days of continual rain made the access track impassable to anything except the excavator (including my trusty Land Rover, as I found out to my cost when I went to leave the site!)
The majority of the work I was asked to carry out was:
- reprofiling the existing silty channel,
- relocating some of the silt to the margins to create a more natural channel margin,
- introducing the gravel and stone to the areas where woody debris items had been installed by myself, volunteers and Chiltern Rangers previously,
- removing one or two trees and undergrowth to allow some more natural light into the stream and encourage marginal weed growth.
I spent most of the first morning with a wide grading bucket on the 13t excavator, squeezing it in between some of the trees, clearing undergrowth and attempting to reach as much of the channel as possible – which isn’t as easy as it sounds! With the banks being predominantly clay, they were very slippery and sloped towards the channel, meaning that I also had to make sure there wasn’t a chance of the excavator sliding into the channel.
A few hours on the chainsaw in the rain was enough to clear fell most of the smaller trees which had grown up through the bramble and open up access to the channel. My ever-helpful work placement chap donned his chesties and was providing my eyes in the channel when my view from the excavator was blocked by undergrowth or the high, steep banks – ensuring I didn’t start ‘dredging’ rather than just removing the silt. Unfortunately, within the silt (and unfortunately typical of an urban watercourse) were all manner of nasties – broken glass, metalwork, tin cans and used hypodermic needles / syringes! The silt was also a great deal deeper than we realised when myself and John of Chiltern Rangers had carried out some preliminary tests a few months before.
For this reason, I decided it wasn’t possible to deposit most of the silt on the bank as planned, and opted instead to merely scrape it into the edge of the channel to create the margins. This also meant that run-off back into the stream would be reduced from the removed spoil due to the torrential rain!
The next job was to introduce the new gravel to the channel. As the aggregate company had been kind enough to bag each size separately, it was fairly easy to install a layer of the 70mm – 100mm stone around the woody debris, and then dress it with the smaller (40mm – 70mm) gravel on top. This required some nifty footwork and balance on the behalf of my work placement chap, as essentially, I have to lift each cubic metre bag on a lifting strap with the excavator and suspend it above the water whilst he uses a long handled slasher / billhook to cut through the bottom of the bag. He then has to move safely out of the way before I can move the dipper and arm around to spread the stone equally! Fortunately, this was old hat to him and within three hours, we had all the bags of the larger stone introduced in the three locations specified on the plans.
It didn’t take much longer to install the smaller gravel on top, and three new riffles were created in areas where the channel was slightly narrower and had increased velocity anyway in conjunction with some woody debris features.
Due to the weather (it rained solidly the entire weekend) and the fact that the site is predominantly clay on top of chalk, it turned into a bog! The only access to the area had also been nicely churned up by the telehandler delivering the gravel – as I found out when leaving the site as I had to bodily drag my Land Rover out backwards with the excavator to prevent it sliding into the pond, before tracking back in and repairing the damage as I tracked the excavator out!
Chiltern Rangers are hoping to revisit the site in kinder weather, and continue with their good work in improving it as an educational facility (it already has a nature-like dipping platform on both the pond and the stream), as well as improving the habitat within the stream channel and the site. My apologies for the lousy quality of the photos in this blog – the weather and damp was playing havoc with the camera!
All The Best,