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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

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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

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

(EREP 5%/annum)

Environmental River Enhancement Programme (EREP)

  • Walkover / Planning surveys

  • Capital Works strand

  • Enhanced Maintenance strand

  • Auditing of crews for implementation of environmental guidance notes

  • Monitoring Programme at selected sites

Capital Works

‘Design & build’ appropriate ‘structures’

Import materials

Instal fencing

Enhanced Mtnce

Use machine on-site to achieve ‘added-value’

Habitat retention

Modify the long- and cross-section where channel bed permits

EREP: 100 km of river works annually

Fundamental Question:

  • What am I trying to do here?


  • What am I catering for?

Capital Works

Pre-requisites include:

  • Water quality

  • Channel gradient

  • No conveyance issues

Capital Works delivery

  • OPW and IFI agree site

  • IFI design and supervise

  • OPW arrange land access

  • OPW order in materials

  • OPW undertake the ‘construction’ work instream and any fencing

  • IFI undertake any pre- and post- monitoring

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

Excavated thalweg

through bedrock with large

exposed boulders.

Centrally excavated pool.

Lateral scour pool.



Anglers walkway

Lateral scour


Paired stone


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.






Gravel Shoals

These will need to be

circa 300mm. beneath

the height of the deflectors.

Page 4 of 10

Enhanced Maintenance

  • NO pre-requisites

  • Conveyance improvement essential

  • Implementation of 10-point environmental guidance notes, as relevant

  • Chance for value-added work in maintenance

Enhanced Maintenance

Managing conveyance

Enhanced Maintenance

Managing conveyance

10. New Excavations in the channel:

  • 10.1 Excavate bed to form deeper pool areas and shallow riffles

  • 10.2 Overdeepen the channel along one side and place spoil on opposite side – particularly on curves and bends

  • 10.3 Use existing spoil to form SIMPLE low-level structures

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


10.2 Overdig in low gradient channels – not a lost cause!!!

Place spoil

this side

Standard Trapezoidal form


this side

Major issues for design and delivery of EREP

  • Engineering imprimatur on any plan developed (peace of mind for all)

Major issues for design and delivery of EREP

  • Landowner permissions for any access and import of materials

Major issues for design and delivery

  • Clear plan as to “who-does-what-and-when”

Major issues for design and delivery

  • Channel bed – gradient – water quality as issues


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