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Requirements for the Protection of Fisheries Habitat during Construction and Development Works at River Sites

These Guidelines were written by Mr. Donal F. Murphy, BE FIEI MIFM,
with the assistance of staff of the Eastern Regional Fisheries Board
15A Main Street, Blackrock, Co. Dublin.


The Fisheries Board is charged under the Fisheries Acts with the responsibility to protect and conserve all freshwater fisheries within its area of jurisdiction. Every river, stream, canal, lake, pond and reservoir within this area must be regarded as constituting and/or supporting a Fishery under the meaning of the Acts unless otherwise regarded by the Boards. The fisheries resource is also protected under national and EU legislation. Some notes on the legal protection given to fishery habitats are contained in Appendix I. While general and specifc requirements for the conservation and protection of the fisheries habitat may be set out in the planning conditions under which a project is approved, many issues regarding the timing, management, organisation, and methods of execution of the works inevitably arise during the construction phase. These Guidance Notes are aimed to identify the likely impact on fisheries habitat in the course of construction and development work, and to outline practical measures for the avoidance and mitigation of damage. These guidelines should not be regarded as all-embracing. Each project must be assessed on a case by case basis. It is, therefore, essential to consult with the Board. It may also be necessary to seek professional expert advice. All information contained in these guidelines were up to date at time of print.


Comprehensive use of guidelines resulted in fisheries requirements included in the design. This watercourse supports a healthy population of plants, inverts and fish as a result.

Fish and their Requirements

Fish need unpolluted water and abundant food in a habitat that provides spawning areas, shelter and freedom of movement. The bed and soil of a natural river and the associated aquatic and riparian vegetation combine to provide the food chain on which fish depend. A natural river channel is characterised by the morphological features which are vital for the life cycle of fish: gravel shoals or reed beds for spawning, pools and riffles where fish rest and feed, and turbulent reaches which enhance oxygenation.

Fig. 1. Overview of River System

All elements of this natural environment must be protected. These guidance notes outline:

Potential Impacts on Fish and Fish Habitat from Roads and Watercourse Crossings

Barriers to fish passage
  • Blockages in watercourses - physical or hydraulic.
Water pollution
  • Sedimentation - impacts include smothering fish eggs
    and causing mortalities in fish of all ages, reducing
    abundance of food and impeding movement of fish.
  • Cement, grout and concrete - toxic to fish.
  • Oil and fuels - direct impacts on fish, fish food and fish
Removal of bed material
  • Causes loss of instream vegetation and food. May
    destroy spawning or nursery habitats.
Disturbance of riparian vegetation
  • Loss of shelter and cover, loss of food (plant debris and
    vegetation invertebrates).

Design Stage

Permanent River Crossings

1. Bridges
Clear span bridging is the preferable option, causing no changes to bed and banks and no impact on fish migration. If piers are required keep them slim-line to minimise changes to the channel. Bed and bank work should be executed in natural materials. Adequate clearance should be allowed under bridges for angler access and mammal passage, if required, particularly in the case of a motorway project.

2. Culverts
Culverts are likely to obstruct or delay upstream fish passage unless the depths and velocities of flow in them are within the swimming capabilities of the species to be catered for. Entry and exit conditions are also critical for ease of fish passage.

Design Principles

1. Culvert should be as short as possible

2. Where the topography allows, they should be laid so as to remain backwatered in drought flow to a depth of not less than 500mm at the upstream invert, thereby providing a fishway over their full length.

3. In all cases, provisions must be made to ensure that the velocity of flow will be less than the swimming speed which can be comfortably maintained by the weakest upstream migrants.

4. Transition pools should be formed at each end to allow upstream migrants to enter and exit without stress or delay.

5. Culverts should be daylit over their full length: if necessary, light-ports should be provided at suitable intervals.

6. The use of trash screens should be avoided.

FIG. 2 Oversized Box Culvert Permanently Watered

Design Options

1. To conform to the principles set out above, culverts always need to be oversized and, generally, laid below the river-bed grade level by about 500 mm.

2. Where the bed gradient is too steep for full backwatering, the best option for achieving low velocity and adequate fishway is to provide a fish-pass at the
downstream end, as shown in Figure 3.

FIG.3 Fish Pass and Transition Pool at the Downstream End of the Culvert

3. Alternatively, the downstream water-level may be raised by providing one or more ponding weirs below the outfall. Such weirs should have fish notches to facilitate upstream movement. The pools formed by them should provide adequate resting and take-off conditions for fish.

4. In some cases it may be acceptable to use notched baffles to control the velocity and provide fishway in the culvert. As already recommended the culverts should be oversized to compensate for flood conditions.

5. More rarely, shaping and roughening of the invert may serve to provide flow conditions suitable for fish passage, especially during low flow. The objective is to create a low flow channel along the centre of the culvert.


Permanent River Diversions and/or Realignments

While permanent diversions are not encouraged, in limited circumstances they will be permitted. The new channel should display hydraulic and morphological characteristics fulflling the requirements of fisheries habitats. Bed and bank work should be executed in natural materials.

Fig. 4. Example of realignment design

Road run-off

All surface water collected from the road drainage should be treated in a sustainable manner to minimize the impact on water quality and prevent habitat degradation. Treatment should be designed with adequate storage capacity and in a manner to facilitate maintenance.

Construction Stage

Minimising impact: Site Layout and Organisation

The following measures are critical for preserving water quality and aquatic habitats.

1. Fuels, oils, greases and hydraulic .uids must be stored in bunded compounds well away from the watercourse. Refuelling of machinery, etc., should be carried out in bunded areas.

2. Run off from machine service and concrete mixing areas must not enter the watercourse.

3. Stockpile areas for sands and gravel should be kept to minimum size, well away from the watercourse.

4. Run off from the above should only be routed to the watercourse via suitably designed and sited settlement ponds/filter channels.

5. Settlement ponds should be inspected daily and maintained regularly.

6. Temporary crossings should be designed to the criteria laid down for permanent works.

7. Watercourse banks should be left intact if possible. If they have to be disturbed, all practicable measures should be taken to prevent soils from entering the watercourse.


Instream Works

1. Instream works may only be carried out in accordance with the Board's general requirements set out below.

2. Preparatory works - such as constructing temporary crossings, forming cofferdams, creating diversions, - must be carried out in accordance with an approved Method Statement and under supervision by the Board's officers. Similar requirements apply during removal and reinstatement.

3. Instream machine works should be minimised, and any machines working in the watercourse must be protected against leakage or spillage of fuels, oils, greases and hydraulic fuels.

4. Instream earthworks must be executed so as to minimise the suspension of solids.

5. Construction works, especially ones involving the pouring of concrete, must be conducted in the dry.

6. When cofferdams are being kept dry by pumping, the discharge must be routed to an approved settlement facility before return to the river.

7. Every care must be taken to insure against spillage of concrete or leakage of cement grout within cofferdams.

8. Temporary diversions may be used to facilitate working in the dry, subject to permission by the Board. Advance notice must be given and a Method Statement must be furnished and approved. Such approval will be subject to the Board's officers being satisfied that the diversion channel can be so designed as to accommodate fish migration.

9. The diversion channel should be formed in the dry, and arrangements should be made for authorised personnel to remove all fish from the natural channel before the flow is diverted.

Summary of the Board's General Requirements

January Instream Works Not Permitted
  • Some late spawning
  • Incubation of eggs continues
  • Kelts descending
February Instream Works Not Permitted
  • Incubation of eggs continues
  • Kelts descending
  • Spring Salmon runs
March Instream Works Not Permitted
  • Incubation of eggs continues and swim-up ofyoung salmonids begins
  • Spring Salmon runs
  • Coarse fish spawning
April Instream Works Not Permitted
  • Incubation ending
  • Swim-up on-going
  • Young salmonids dispersing
  • Smolts migrating to sea
  • Coarsefish spawning
May Instream Works Permitted
  • Young salmonids migrating downstream into nursery areas
  • Smolts migrating to sea
  • Coarse fish spawning and fry dispersing
June Instream Works Permitted
  • Young salmonids in nursery areas
  • Adult Sea Trout returning to rivers
  • Coarse fish spawning and fry feeding
July Instream Works Permitted
  • Grilse and Sea Trout moving upstream
August Instream Works Permitted
  • Low river flows
  • Sea Trout run tailing off
Sept Instream Works Permitted
  • Low River flows
October Instream Works Not Permitted
  • Spawning run commences as flows increase
November Instream Works Not Permitted
  • Spawning and incubation of eggs underway
December Instream Works Not Permitted
  • Spawning and incubation of eggs continues

Appendix 1

Some notes on Legal Protection given to Fisheries Habitat in Legislation

Summary of Relevant Legislation

Note: Full text of the above legislation can be accessed at

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