Tuesday, October 17, 2017

Building a Otter Holt

What to do on a Saturday if you have some kerb stones and limestone slabs and are fortunate enough to own 600m of river bank, build an otter holt!

Otters are frequently seen on our river. A small otter holt already is known to be used under an alder tree on the bank but it frequently floods so we wanted to make something bigger, dryer and easyer to monitor.

1. We dug a trench 4m back and 60cm wide into the bank, keeping a slight slope from back to front. Depth at the back was about 80cm.


2. We widened a chamber to the rear to a width of about 80cm (kerb stones are 1m long which dictated the width).
3. Lay stone flags on the floor of the chamber so it is raised of the ground and will stay dry.

4. Lay slabs on the edge of the trench to spread the load of the kerb stones used to bridge the trench and chamber.

5.Send a young child into the holt with a bucket of hay to spread into the chamber. (Should have been done before we put the top stones on but forgot. Fortunately his mum was not watching.)

6. Cover with a PVC sheet to stop water entering, install a pipe in the roof of the chamber at the highest point with a u-bend on the end to stop rain entering but allow hot, moist air to vent from under the PVC sheet otherwise it would condense and drip water back inside the holt. Also allows an infrared camera to be lowered into the top of the chamber and the site is within wifi range of the primary school so potential for a live feed to be sent to the school.
7. Cover with soil and rocks. Reduce the entrance to the holt down using a tree stump and rock to reduce light entering and make it a more natural looking entrance.
8. Collect spraint from the river bank adjacent and smear around edge of holt entrance.
9. Wait.......

Andrew on Hannah's blog

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