Sociable

Friday, 31 August 2012

The Third Dam breached again.


Yesterday morning the dam I call the Third Dam was still there, but by the evening it had been breached. The thunder storms of the afternoon with their heavy rain were too much for it after all the rain of the past days, and once again powerful forces took it away. This is the dam that caved in to the rains in July 2011. This time it took with it at least two other smaller dams downstream. 

Dynamism is the watchword when dealing with beavers and their work in the landscape, but false pride always insists that 'my' beavers' dams are permanent. Here are the photographs that give this idea of permanence the lie: and just in time for any migratory fish you may think. Just so!




Once again it was just the wedge of the dam that blocked the line of the old ditch that gave way: the rest has survived.


The drop in the water level revealed a good deal of the coarse woody debris that has been accumulating in the pool.

Some of the fish will have been washed downstream and may have been held in the pool, where the dam survived, some two or three hundred metres downstream. This dam lies in a stretch of the burn where it is becoming more natural (i.e. less straight).

I thought I should go and find my trail camera, opposite a lodge beside the Big Ponds, but when I reached the place I left it, it had gone: stolen, I think. Nearby was a plastic shopping bag, full of empty beer cans and knotted to keep them in - a thoughtful gesture, if it was left by the same people who had taken the camera with its Joby Gorillapod. I have now had three trail cameras stolen. Each time I buy another I think I will put it somewhere safe out of the way of raiders but inevitably, it seems, they fall prey to sticky fingers. I shall have to buy an armoured container and heavy chain to secure my next trail camera.

Thursday, 30 August 2012

Beavers and a Timber Operation







These two photographs show the landscape by the Bamff drive as it was a year ago.

Things were to change because we wanted to fell the Whitehills plantation. Overflow from the dam in the picture shown above was running down the drive. This worried the contractor, Ken Barclay. He thought the drive would not stand up to the heavy lorries with water running down it.


This photo shows the water running down the drive.

The dam was breached, but rebuilt by the beavers. Then, another attempt was made to cut a notch in the dam, but it collapsed, causing a flood down the drive. I was furious. With hindsight and the acquired skills of Lewis Smith and Mark Blair, we should have installed a pipe and cage levelling device, but that was to come.



Over the weeks that followed the beavers rebuilt the dam, as in the clip of video above.





The plantation was felled with astonishing speed and the timber stacked by the side of the drive.
The drive, once an elegant carriage drive and admired by archaeologists, received rough treatment at the hands of the heavy machinery. The wet year and the mud made things worse.

The reason that the drive was used for the extraction of timber and as a loading area was that Perth and Kinross Council would not grant a licence for the use of the nearby public road for this purpose. In the past this was customary, but is no longer permitted.

Unfortunately, some of the timber blocked the culvert that led the under the drive. The overflowing water ran down the west side of the drive, dammed from time to time by the beavers, until the slope of the ground made it flow across it. Despite this, the beavers continued their damming to stop the water flowing down the drive. Well done, beavers!




This photo shows the ditch west of the stacked timber along the drive. A dam is in course of being rebuilt.




At last all the timber was driven away and it was possible to unblock the culvert. Fortunately, it turned out not to be seriously blocked under the drive, but choked by sediments and the weight of timber that had been lying against its entrance.




Stewart Crabb, who did the excavation, thought he might need a pump to lower the water level upstream of the drive so that he could see what he was doing. In fact this turned out to be unnecessary.





Here is the flooded drive downstream of the blocked culvert. Humans have added a dam to the one begun by the beaver to prevent a heavy flow reaching the Lodge.






This is the drive, looking south after the culvert had been cleared, but before the addition of a 450mm pipe to the inflow.





Here is the dam that the beavers have built to replace the dam that was destroyed in February this year (or was it March)?





And here is the entrance to the culvert with the pipe in place.



  • Knowing what I know now what would I do differently? 

  1. The dam that was breached should have been fitted with a pipe and cage levelling device. That would have taken the water off the drive and Ken Barclay would have had fewer worries about its status.
  2. Between us we should have avoided stacking timber where it would interfere with the entrance to the culvert. The beavers never troubled it because it flowed gently and there were no sounds of rushing water to interest them.
  • What do I need to do now? I think it will be necessary to 
  1. fix up a flow device to protect the entrance to the culvert and
  2.  to install another such at the top dam that was breached last February. 


All useful experience, I think.




Sunday, 19 August 2012

MITIGATION

The other day Tina Ng-A-Man told me that I had not explained why it was necessary to instal a pond leveller, or similar installation in a body of water. When I looked back at the post I saw that she was right. The purpose of a leveller, or flow device (call it what you will) is to prevent beavers from raising the water level unacceptably (for humans).

As this query coincided with closeness to the deadline for my contribution to the September number of 'The Alyth Voice', I thought I should write a piece that dealt a little bit with flow devices, levellers or whatever you care to call them.

Here it is:



The swifts have flown, an early sign of the shifting of the seasons. I realised they had left Bamff one morning recently. I was taking a short cut across some fields to look at the flow device, which we have had installed to lower the water level in a stretch of ditch, when the thought came to me that the swifts must be on their way. There were no swifts around: they had flown. 

The beavers first built a dam to raise the level of the ditch upstream of a bridge some years ago. From time to time it would be dismantled, but the beavers would rebuild the dam. The raised water level that resulted from this damming has caused some minor flooding in the neighbouring fields, particularly at the gateways. This brings a problem in that cattle and sheep poach the grass there and turn the ground to a sea of mud in a wet season (and which season has not been wet for the last how many years?). The mud and dung can lead to polluted runoff into ditches and burns, so it is important to reduce these concentrations of dirty ground. A recent visitor from the English Environment Agency pointed this out to us as Louise and I took him for a walk to see round our Beaver World. 


The wet patch in question is just beyond the makeshift gate.


Rather than dismantle a dam and have it rebuilt by the beavers it is better to deceive the beavers. Various devices have been developed to do this. The installation we took our visitor to see consisted of a 20 foot (6.096m) length of polyethylene drainage pipe of 200 mm (8 inches) diameter, a round cage made of concrete reinforcing mesh, some old iron fence posts to hold the pipe in place and wires to tie the pipe to these old iron fence posts. Steel rebars are the usual thing, but anything similar will do. First, a notch is cut in the dam to take the pipe. The water gushes through and the level drops. The greater part of the pipe is laid upstream and pinned down (but kept clear of the bottom of the ditch by some 6 to 8 inches (150-200 mm). The cage of steel mesh is installed. The diameter has to be big enough to keep beavers far enough away from the inlet of the pipe inside the cage for them not to notice the flow of water into it. The distance upstream of the dam where the upstream end of the pipe is placed is important because beavers react to the sound of running water near their dams. If a pipe can be laid far enough upstream of the dam for the beavers not to want to go and look there, and silent so as not to attract their attention, the water level can be regulated to fit in with human wishes rather than those of the beavers. Thus the installed pipe will carry away water that humans judge to be surplus and a conflict of interest between beavers and humans will be avoided. The Martinez Beavers web site has some excellent links.(www.martinezbeavers.org)

I drove on after looking at the levelling device. At the road end I found Danielle Muir, the P&K Council countryside ranger. She was cleaning a sign for the Cateran Trail. Danielle told me that she has to check the rain water gulleys at the Steffort Corner on the Alyth Road from time to time to release the toads, frogs and newts that fall into them. The problem is caused by the kerb stones that have been installed there. The amphibians walk along the line of the kerbstones and fall into the drain and eventually die unless they are rescued. I understand that Perth and Kinross Council are fitting kerbstones that have a notch cut in them that enables amphibians to walk past gulleys. 

Mitigation is about enabling us to live with wildlife and wildlife to cope with us.


The water level has risen since the photographs I took just after the installation of the flow device, but is still well below former levels and, above all, below the level of the field behind. You can see water lying in the gateway behind the new post and rail fence.




The far ground of this photograph shows a new riparian strip, planted and fenced last spring.




The bridge over the ditch with the dam.



Tuesday, 7 August 2012

A Flexpipe Water Leveller at Bamff

At last a pipe and cage water leveller has been installed at Bamff. Delay seemed interminable owing to the need to fix the gaps in one of the boars' enclosures that resulted from the recent clear fell of some timber. Bad weather played its part too. However, the fencing has been achieved and today Messrs L.Smith and Mark Blair installed a pipe and cage.






Here are some photos I took this morning. Unfortunately, I have no recent fully 'before' picture to start the series, but you should see from the muddy bank where the water level used to be. These first photos, however, give and idea of the immediate landscape before the pipe and cage take effect.



You can see here that the dam has been breached to allow the laying of the pipe.



In this photo, Mark Blair (on the left) and Lewis Smith ('Lush' to one and all) are working on the laying and fixing of the pipe. 






You can see the cage in the distance. The idea is that the beavers will want to find the leak in the dam and not suspect that the water may be going through a pipe set some metres upstream inside a cage. 




This gateway just south of the dammed ditch has been waterlogged for some time now. Two years of very wet summers and a wet winter have made for  a deeply muddy gate way.




This is the manual that guided Lush and Mark. It comes from Snohomish County, Washington, USA and is posted on the Martinez Beavers brilliant web site:




Beaver paw marks.



A stone is placed over the pipe where it passes through the dam.



With the pipe installed the dam can be repaired and the whole system left for the beavers to consider.