As the season for instream rehabilitation work in rivers closed on Sunday last (30th September), MulkearLIFE is delighted to announce that major planned instream works on the Newport River have now been completed. These works, implemented by the Office of Public Works, have been completed despite one of the worst summers in 20 years with high levels of rainfall, which resulted in extremely elevated water levels in local rivers throughout the Mulkear Catchment.
Dedicated OPW Crew on the Newport River (Image: Glen Wightman)
The Newport River is a major tributary to the Mulkear River and has suffered significantly due to past drainage schemes. One of the most significant problems is the lack of instream cover and an absence of complex habitat. Much of this beneficial habitat and complexity was removed during the installation of the drainage scheme. Instream cover is important from an ecological protective in that it provides protection for a wide range of species and helps to create habitat complexity and thus promotes higher biodiversity.
Plaque detailing Mulkear Drainage Scheme 1874 (Image: Ruairí Ó Conchúir)
Much of MulkearLIFE’s work programme involves the implementation of a variety of habitat enhancement measure to improve the instream complexity of the river environment for Atlantic salmon and other species. For almost 140 years, much of the Mulkear catchment has been subjected to extensive drainage works. This has resulted in the easement of flooding but as a consequence has led to a degradation of habitat which has resulted in a decline in the salmon population. The enhancement measures under the EU funded LIFE project are designed to mimic natural conditions and have been proven to increase salmon numbers with consequential, wider and additional biodiversity benefits.
The OPW crew in action on the Newport River (Image: Glen Wightman)
The river restoration plan for the Newport River was developed by MulkearLIFE in conjunction with the Office of Public Works and was focused in the area from Bunkey Bridge downstream to Annagh Bridge. The plan revolved around the installation of large boulders (termed random boulders) within the river channel. Such large boulders are a natural physical feature of salmonid rivers and the concept behind the river restoration plan was that the ‘strategic’ placement of such random boulders would mimic naturally occurring boulders.
Transporting boulders (Image: Glen Wightman)
The real beauty of the work is that it does not restrict or impede the flow of water no does it create a risk of flooding by impacting negatively on flow or diverting flow. Rather the instream works greatly enhance the complexity of biodiversity in the river and along the river bank.
OPW conducting river enhancement work (Image: Glen Wightman)
The strategic placement of random boulders provides a number of key functions. They help to dissipate the energy of a stream in flood flow thereby limiting bank erosion. They also provide back eddies, or resting places, for fish during flood events). They provide a niche for a whole range of macroinvertebrates. In the absence of boulders many of these species would not be present. Larger trout and salmon hold or rest in the slack water created behind boulders and can quickly move out into the current to catch drifting food items. Salmon and trout are territorial animals. They settle for a smaller territory in circumstances where they cannot see each other. The placement of boulders therefore breaks up the habitat, increases the number of territories and thus increases fish numbers. Boulders will add scouring (i.e. depth) around there position. Sediment will deposit immediately downstream of boulders creating ideal lamprey ammocoete habitat. Boulders that are exposed during low flow periods provide resting locations for, dipper, grey wagtail, heron and kingfisher. In addition they are used as sprainting spots for otter. Finally, the boulders provide hiding places and cover when the fish are threatened by predators.
Dipper utilising a newly placed random boulder (Image: Ruairí Ó Conchúir)
Preparation work started in August with the placement of boulders along OPW’s access path that runs parallel with the Newport River. In excess of 240 boulders, many weighing in excess of 2 tonne, were placed into position. With the boulders in position in early September the actual placement of the boulders into the river channel commenced.
One of over 240 random boulders strategically placed (Image: Glen Wightman)
Using a hydraulic excavator the highly skilled OPW crews then place the boulders precisely where they will best perform in the river, mimicking naturally occurring features. This precise placement is required in order to eliminate the impact on patches of aquatic vegetation, like Water Crowfoot, present in the river. The machine operators took great care to avoid damaging the riparian zone when placing the boulders under the direction of MulkearLIFE staff.
Close-up of River-water Crowfoot, Rannunclus (Image: Ruairí Ó Conchúir)
As the season closes out, 2012 was a highly successful year for the Office of Public Works in terms of the instream works completed on the Newport River. Approximately 675 tons of rock was used to enhance 3.2kms of river through the strategic placement of over 240 boulders. The works were carried out precisely to plan which is evidence of the hard work, skill and professionalism of OPW team. MulkearLIFE is fortunate to have such a dedicated partner in the Office of Public Works. Their commitment and enthusiasm to rehabilitate the Mulkear catchment is greatly appreciated.
Random boulders below Bunkey Bridge (Image: Glen Wightman)
A full technical on these works will be available in due course.