Brown’s Beck Brook, Upper Slaney, Donard, Co. Wicklow, Ireland

Introduction

Brown’s Beck Brook (also known as Donard stream) is a second order tributary of the Carrigower River, Co. Wicklow (Fig. 1), which in turn joins the River Slaney, one of the main river systems in south-east Ireland.  According to the most recent Environment Protection Agency (EPA) WFD report (2013-2018), the status of the impacted reach near the village of Donard is ‘good’, but the status drops to ‘poor’ immediately upstream.  In addition, this reach has undergone localised channelization involving major realignment and re-sectioning of the channel, and subsequent construction of a concrete ford crossing in the 1960s (Lat. 53° 0′ 58.4, Long. -6° 37′ 23.2) (see Fig. 2). The ford, while being degraded and leaky was c. 1.5 m high and continued to represent a barrier for fish, including Atlantic salmon (Salmo salar). The structure was therefore designated for modification/removal by the Inland Fisheries Ireland (IFI), in consultation with the landowner, and was included as a case-study under the UCD Reconnect project (www.ucd.ie/reconnect/). Baseline characterisation and ongoing hydromorphological, habitat and ecological monitoring have been carried out at the site since spring 2017. The results from this impact study will be updated here once the Reconnect project has been completed.

Fig. 1 Current imagery of the Ford on Brown’s Beck Brook (Left) and on the OSi 6’ map before channelization (1838). The X-sections and monitoring stations shown left refer to work carried out under the EPA-funded Reconnect project (2015-W-LS-8).

Fig. 2 The Brown’s Beck Brook ford looking upstream prior to removal, with individual for scale.

Mitigation

River continuity has been restored by replacing the ford structure with an open box culvert that effectively acts as a single span bridge (Fig. 3).  The restoration was carried out in three phases over two summers as follows: first, the stream channel was temporarily diverted around the ford structure to allow access for removal (October 2018); second, the ford was demolished and removed (July 2019); and third, the new single span bridge was installed with the base buried below the channel bed, the original position of the channel was reinstated and the temporary diversion channel was cut-off and back-filled (August 2019).  An energy dissipation structure in the form of a low-level, transverse rock weir was used to prevent bed incision and the creation of a knickpoint immediately downstream of the new crossing. All restoration works were carried out by a hired contractor, under the direction of the IFI.  The total cost of the restoration works was c. €50,000, which was covered by the Salmon Conservation Fund (now renamed the Salmon and Sea Trout Rehabilitation, Conservation and Protection Fund to reflect the broader focus on sea trout as well as salmon). While these costs are high, it is worth noting that the Brown’s Beck Brook restoration works were exempt from planning permission and any associated appropriate assessments that can significantly increase the total cost of restoration projects in Ireland.

Fig. 3  Restoration phases on the Brown’s Beck Stream: (a) and (b) creation of a diversion channel (October 2018); (c) and (d) removal of the concrete ford structure (July 2019); (e) and (f) installation of the road passage (August 2019).

Post-removal and future work

Since the removal, the river has undergone some morphological adjustment, including localised bank erosion in the vicinity of the original structure (especially upstream) and natural bed regrading (Fig. 4). The magnitude of these hydromorphological changes is currently being assessed by the Reconnect project team, in the context of longer-term channel response to channelization. Future work is planned for summer/autumn 2020, including electro-fishing upstream and downstream of the original structure, to establish any changes in fish communities. The removal of the barrier has opened up access to spawning habitat upstream, but this area has yet to be calculated.  Water quality status is not expected to change following the modification.

Fig. 4. Bank erosion upstream (left) and view downstream (right) of the culvert, following installation. These morphological adjustments are being monitored as part of the EPA-funded Reconnect project. The wooden box structure (left) houses instrumentation for the upstream monitoring station for the collection of water level, turbidity and suspended sediment samples.

Reconnect is funded under the EPA Research Programme 2014-2020. The EPA Research Programme is a Government of Ireland initiative funded by the Department of the Environment, Climate and Communications. It is administered by the Environmental Protection Agency, which has the statutory function of coordinating and promoting environmental research.  The Reconnect project was set up to assess the extent and impacts of barriers on Irish rivers and is developing a methodology for prioritising their modification or removal to improve hydromorphology and connectivity in Irish rivers.  The project is due to be completed in March 2021.

Selected publications from the Reconnect project

Atkinson, Siobhan & E.L. Carlsson, J., Ball, B., Kelly-Quinn, M. & Carlsson, J. (2019). Field application of an eDNA assay for the threatened white-clawed crayfish Austropotamobius pallipes. Freshwater Science 38(3) DOI: 10.1101/562710.

Atkinson, S., Bruen, M., O’Sullivan, J.J., Turner, J.N., Ball, B., Carlsson, J., Bullock, C., Casserly, C.M. & Kelly-Quinn, M. (2020) An inspection-based assessment of obstacles to salmon, trout, eel and lamprey migration and river channel connectivity in Ireland. Science of the Total Environment, 719: https://doi.org/10.1016/j.scitotenv.2020.137215 [open access].

Casserly, C.M., Turner, J.N., O’Sullivan, J.J., Bruen, M., Bullock, C., Atkinson, S. & Kelly-Quinn, M., (2020). Impact of low-head dams on bedload transport rates in coarse-bedded streams. Science of the Total Environment,  716:   https://doi.org/10.1016/j.scitotenv.2020.136908 [open access].

Casserly, C.M., Turner, J.N., O’Sullivan, J.J., Bruen, M., Bullock, C., Atkinson, S. & Kelly-Quinn, M., (2021). Effect of low-head dams on reach-scale suspended sediment dynamics in coarse-bedded streams, Journal of Environmental Management 277: https://doi.org/10.1016/j.jenvman.2020.111452  [open access].

Case study and photos were provided by Reconnect. Thank you!