Environmental River Enhancement Programme (EREP)

An approach to addressing WFD hydromorphology issues in arterially

drained channels in IrelandJames 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

EREP: 100 km of river works annually

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

Fundamental Question:

• What am I trying to do here?

OR

• 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

Excavate a thalweg associated with thedeflectors and place a single layer of broken stoneor cobble on the bed of the thalweg.The thalweg should be 1/3 channel base width.

Flow

Introduce a gravel spawning shoal which will be one channelwidth in terms of length.

Page 4 of 7

Page 5 of 6

Anglers walkway

Lateral scour pool.

Paired stone deflector

Centrally excavated pool.

Stonedeflector

Excavated thalweg through bedrock with largeexposed boulders.

Lateral scourpool.

Page 7 of 34

Remove this structure and reuse stone material in new paired deflector.

New paired stone deflector with associated pool and gravel shoal (see page 9 for specification).

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.

Excavate a thalweg along this line which is circa 1/3 basewidth with a max depth of 0.5m

Flow

Construct a deflector which is 1/3 basewidth

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.

Page 3 of 10

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 inwidth , 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).

Thalweg

Pool

Gravelshoal

Flow

Flow

Schematic Plan of the works outlined on Page 3 of x.

Deflectors

Gravel ShoalsThese will need to becirca 300mm. beneath

the height of the deflectors.

Thalweg

Pools

Page 4 of 10

Boulders

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

undertake large-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 channel

Overdig this side

Place spoilthis side

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

Standard Trapezoidal form

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

Ends