Presentation on theme: "Environmental River Enhancement Programme (EREP) An approach to addressing WFD hydromorphology issues in arterially drained channels in Ireland James J."— Presentation transcript:
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
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 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. Flow Introduce a gravel spawning shoal which will be one channel width in terms of length. Page 4 of 7
Page 5 of 6 Anglers walkway Lateral scour pool. Paired stone deflector Centrally excavated pool. Stone deflector Excavated thalweg through bedrock with large exposed boulders. Lateral scour pool.
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 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). Thalweg Pool Gravel shoal Flow
Schematic Plan of the works outlined on Page 3 of x. Deflectors Gravel Shoals These will need to be circa 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
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 spoil this 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