Environmental River Enhancement Programme (EREP). An approach to addressing WFD hydromorphology issues in arterially drained channels in Ireland James J. King, Inland Fisheries Ireland. RRC meeting – Best Practise River Restoration Design and Construction, Lyndhurst, England
An approach to addressing WFD hydromorphology issues in arterially drained channels in Ireland
James J. King, Inland Fisheries Ireland
RRC meeting – Best Practise River Restoration Design and Construction,
13 – 14.7.2011
OPW channels make up 20% of channels in Ireland
11,504 km of Channel
(90% <3m base width
2000km of channel maintained annually
‘Design & build’ appropriate ‘structures’
Use machine on-site to achieve ‘added-value’
Modify the long- and cross-section where channel bed permits
Construct 2 alternating stone deflectors
Introduce a gravel spawning
shoal which will be one channel
width in terms of length.
Excavate a thalweg associated with the
deflectors and place a single layer of broken stone
or cobble on the bed of the thalweg.The thalweg
should be 1/3 channel base width.
Page 4 of 7
through bedrock with large
Centrally excavated pool.
Lateral scour pool.
Page 5 of 6
Page 7 of 34
A specification for particle size in introduced gravel shoals (for salmon) is available on page 113 of Channels and Challenges. The smallest particles (4mm – 8mm) are the least important in the mix.
New paired stone deflector with associated pool and gravel shoal (see page 9 for specification).
Remove this structure and reuse stone material in new paired deflector.
Excavate a thalweg along this line which is circa 1/3 basewidth with a max depth of 0.5m
Construct a deflector which is 1/3 basewidth
Please note that from here d/s to location on page 31 some rock breaking may be required at intervals to achieve the objectives outlined.
Construct a series of alternating deflectors d/s to the first road bridge. These should be spaced ,at intervals, to keep the flow moving through the thalweg.
Vary their spacing to accommodate local changes in bed gradient. See the appendix for deflector design ( page x of ).
Excavate a thalweg circa 1/3 channel base width which will be
0.7m. in depth at low flows. Punctuate the thalweg with one
pool between each pair of deflectors as illustrated. Individual
pools should be centrally placed, be ½ channel base width in
width , 3.5m. in length and have a maximum depth of 1.3m..
Place one boulder in the centre of each pool. Place a gravel
spawning shoal at the tail of each pool and recommence the
excavation of the thalweg towards the tail of each gravel shoal
to “lead” the flow into the next pool. Gravel shoals should extend
from the face of the deflector to the opposite bank. Ensure a
depth of 40cm. In gravel shoals – see appendix for gravel size mix.
Repeat this sequence downstream to the first bridge.See plan drawing of this proposal on the next page ( page4 of x).
Page 3 of 10
Schematic Plan of the works outlined on Page 3 of x.
These will need to be
circa 300mm. beneath
the height of the deflectors.
Page 4 of 10
undertakelarge-scale new diggings in an agreed plan and only if channel bed is of suitable material
7.7.2011: C6/7/1 Overdig the bed – narrower, deeper inset channel
7.7.2011: C6/7/1 bedrock – use spoil to form low berms – narrower, deeper inset
Standard Trapezoidal form