Articles of interest: 
Siltation Monitoring Trap
(by kind permission of
Nethan-Valley AA)
To enable the above named association to monitor siltation levels
throughout the River Nethan catchment area. The association designed a silt trap
which is inserted 150 mm deep into the existing substrate in the river bed, the
traps will be placed in areas of flow type's shallow and deep glide.
Method: Excavate a hollow in the river bed to accommodate
the outer sleeve = 150mm deep, place sleeve in centre of excavation then back
fill. Ensure that the top of the sleeve is level with existing substrate before
inserting measuring trap.
The measuring trap should be filled with clean water before it is inserted into
sleeve, it should then be lowered slowly into sleeve allowing existing water to
displace gently. Great care should be taken when working close to the trap and
by positioning yourself downstream of the trap will prevent any false
siltation readings through accidental disturbance while placing the equipment in
situ.
pictorial construction
Trap construction
These traps are inexpensive and very easy to make, the materials required
are as follows:
1 x 150mm length of 100mm diameter PVC pipe (Marley drainage pipe.)
1 x 100mm diameter end cap.
1 x 2 litre clear plastic lemonade bottle.
1 x 150mm plastic ruler.
Araldite Rapid Epoxy Resin
1 x 3Kg bag, white waterproof tile grout.
Plasticine
2 Part epoxy resin from car accessory shops (Optional if end caps are not
available.)
Method:
Insert 100mm dia. end cap in to end of 100mm dia. drainage pipe.
Cut clear lemonade bottle 150mm from bottom, (Carefully cutting square to
axis.)
Make up sufficient wall tile grout (watery mix) to fill convex section at
bottom of bottle e.g. approx. 20mm.
Stand bottle on a level surface in work area then carefully pour in the
mixture up to line above convex section
at bottom of bottle. Allow 24 hrs for setting.
We have added a piece of wire (optional) to the centre which allows us to
remove the gauge from the sleeve easily.
If a wire is to be added it must be when the grout is still soft.
Cut 150mm clear plastic ruler to 140mm.
Mix up sufficient Araldite to stick ruler vertically to inside of bottle
just above grout line.
The two part epoxy resin can be used to form end caps but it is messy to
work with and requires a well ventilated work area.
To form end cap cut a section of 100mm pipe approx. 20mm thick, it must be
cut square. Place the section of pipe on to a piece of waxed ceramic tile or
flat plastic such as a margarine tub lid.
Seal around pipe bottom with Plasticine, place on a level surface.
Following the manufacturers instructions mix up enough epoxy resin to fill
10mm of the 100mmpipe.
Leave to cure, and then remove from pipe. The plug can then be glued into
the 100mm tube to form end cap with Araldite Rapid.
Important:-
These traps should only be placed after consulting with the riparian owner
and SEPA and should be placed at a time when
juvenile fish have left the redds. We recommend
that between the end of May and the end of September to be the ideal time
frame. Low water flow conditions are excellent for carrying out the
installation of the gauge.
Disclaimer: The Nethan-Valley Angling
Association accept no responsibility for the actions of, or injuries to
anyone who chooses to construct and use the silt monitoring gauge.
