Case study:Upper River Nairn restoration project - Revision history

Alexrrc at 10:39, 25 March 2019

2019-03-25T10:39:14Z

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	{{Case study status		{{Case study status
	\|Approval status=~~Draft~~		\|Approval status=Approved
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Aberarder Estate at 13:55, 5 March 2019

2019-03-05T13:55:15Z

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	\|File name=AberarderUpperWetland.jpg		\|File name=AberarderUpperWetland.jpg
	\|Caption=Aberarder - Upper Wetland		\|Caption=Aberarder - Upper Wetland
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	~~{{Case study image~~
	~~\|File name=Aberarder.jpg~~
	~~\|Caption=Aberarder - Aerial View~~
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Aberarder Estate at 09:43, 27 February 2019

2019-02-27T09:43:36Z

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	\|File name=Aberarder.jpg		\|File name=Aberarder.jpg
	\|Caption=Aberarder - ~~Arial~~ View		\|Caption=Aberarder - Aerial View
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Aberarder Estate at 17:41, 22 February 2019

2019-02-22T17:41:02Z

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	\|File name=AberarderNewLowerChannel.jpg		\|File name=AberarderNewLowerChannel.jpg
	\|Caption=Aberarder New Lower Channel		\|Caption=Aberarder - New Lower Channel
	}}		}}
	{{Case study image		{{Case study image
	\|File name=AberarderUpperWetland.jpg		\|File name=AberarderUpperWetland.jpg
	\|Caption=Aberarder Upper Wetland		\|Caption=Aberarder - Upper Wetland
	}}		}}
	{{Case study image		{{Case study image
	\|File name=Aberarder.jpg		\|File name=Aberarder.jpg
	\|Caption=Aberarder		\|Caption=Aberarder - Arial View
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	{{Case study image		{{Case study image
	\|File name=Aberarderpostconstruction2.jpg		\|File name=Aberarderpostconstruction2.jpg
	\|Caption=Wood structure		\|Caption=Aberarder - Large Wood structure
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Aberarder Estate at 15:29, 22 February 2019

2019-02-22T15:29:54Z

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	{{Case study documents		{{Case study documents
	\|File name=Aberarder redd distributions 2017 and 2018.pdf		\|File name=Aberarder redd distributions 2017 and 2018.pdf
	\|Description=~~Aberarder redd distributions~~ 2017 and 2018		\|Description=Location of salmonid redds surveyed in 2017 and 2018 spawning seasons
	}}		}}
	{{Case study documents		{{Case study documents
	\|File name=Aberarder wetland enhancement.pdf		\|File name=Aberarder wetland enhancement.pdf
	\|Description=Aberarder wetland enhancement		\|Description=Aberarder wetland enhancement
			}}
			{{Case study documents
			\|File name=Aberarder study site & restoration overview.pdf
			\|Description=Aberarder study & restoration overview
			}}
			{{Case study documents
			\|File name=Aberarder redd counts.mp4
			\|Description=Location of salmonid redds
	}}		}}
	{{Additional Documents end}}		{{Additional Documents end}}

Aberarder Estate at 15:09, 22 February 2019

2019-02-22T15:09:45Z

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	Three different design strategies were proposed in discrete sections of the site. Due to practical site constraints, the design in the upstream sections of the site could only involve the localised reprofiling of the river corridor (mainly the removal/ re-grading of existing embankments) while, in the downstream section, channel realignment and the reinstatement of ‘online’ wetlands were implemented. Almost 1 km of channel length was realigned into a more sinuous course through a lower elevation area. Importantly, this connected a series of three online wetland areas before tying back into the existing channel course downstream. Furthermore, to mitigate the lack of large wood (LW) processes through the site, riparian planting was conducted in conjunction with the installation of ‘bar apex’ LW structures at appropriate locations through the realigned channel.		Three different design strategies were proposed in discrete sections of the site. Due to practical site constraints, the design in the upstream sections of the site could only involve the localised reprofiling of the river corridor (mainly the removal/ re-grading of existing embankments) while, in the downstream section, channel realignment and the reinstatement of ‘online’ wetlands were implemented. Almost 1 km of channel length was realigned into a more sinuous course through a lower elevation area. Importantly, this connected a series of three online wetland areas before tying back into the existing channel course downstream. Furthermore, to mitigate the lack of large wood (LW) processes through the site, riparian planting was conducted in conjunction with the installation of ‘bar apex’ LW structures at appropriate locations through the realigned channel.

	accumulation (and associated channel ‘perching’), flooding/ land drainage and reduced habitat quality, improving the WFD classification status of the River Nairn was also a key objective of the Project. Currently, the waterbody (River Farnack confluence to source in the River Nairn catchment, Waterbody 20306) has been classified by SEPA as being at poor status, primarily as a result of morphological and hydrogeomorpholocial pressures on the waterbody resulting from modifications to the bed and banks of the river. Through the River Basin Management Planning Strategy, SEPA has identified and prioritised water bodies where improvements are required to enable good ecological status to be met. As part of the second cycle of the River Basin Management Planning Process, SEPA has identified the River Nairn as a priority catchment and as part of a national strategic plan, the URNRP will help national objectives to be met.		Whilst the primary objectives of the restoration project were to address the issues of excess sediment accumulation (and associated channel ‘perching’), flooding/ land drainage and reduced habitat quality, improving the WFD classification status of the River Nairn was also a key objective of the Project. Currently, the waterbody (River Farnack confluence to source in the River Nairn catchment, Waterbody 20306) has been classified by SEPA as being at poor status, primarily as a result of morphological and hydrogeomorpholocial pressures on the waterbody resulting from modifications to the bed and banks of the river. Through the River Basin Management Planning Strategy, SEPA has identified and prioritised water bodies where improvements are required to enable good ecological status to be met. As part of the second cycle of the River Basin Management Planning Process, SEPA has identified the River Nairn as a priority catchment and as part of a national strategic plan, the URNRP will help national objectives to be met.
	\|Monitoring surveys and results=Post works monitoring is essential for evaluating the physical and ecological performance of the project. Given the near unique scale of application of the ‘process-based’ restoration approach, the project provided an invaluable opportunity to monitor how the river environment responds to the various components of the implemented works, providing valuable insight and guidance for the application of this type of approach in other areas.		\|Monitoring surveys and results=Post works monitoring is essential for evaluating the physical and ecological performance of the project. Given the near unique scale of application of the ‘process-based’ restoration approach, the project provided an invaluable opportunity to monitor how the river environment responds to the various components of the implemented works, providing valuable insight and guidance for the application of this type of approach in other areas.

Aberarder Estate at 15:08, 22 February 2019

2019-02-22T15:08:10Z

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Aberarder Estate at 14:59, 22 February 2019

2019-02-22T14:59:43Z

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	{{Motivations		{{Motivations
	\|Specific mitigation=~~River engineering relating to agriculture~~		\|Specific mitigation=Flood risk/ channelisation, embankments
			\|Hydromorphological quality elements=Realignment, large wood, wetland reinstatement
			\|Biological quality elements=Macroinvertebrates, fish
			\|Physico-chemical quality elements=Carbon storage, nutrient storage
	\|Other motivation=To restore a heavily modified section of the Upper River Nairn back to a more natural state whilst also reducing the risk of flooding to protect agricultural interests		\|Other motivation=To restore a heavily modified section of the Upper River Nairn back to a more natural state whilst also reducing the risk of flooding to protect agricultural interests
	}}		}}

Aberarder Estate at 14:57, 22 February 2019

2019-02-22T14:57:15Z

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	\|Planform / Channel pattern=Changing from a canalised straightened channel to a meandering/ wondering channel		\|Planform / Channel pattern=Changing from a canalised straightened channel to a meandering/ wondering channel
	\|Management interventions=Riparian tree planting, fencing		\|Management interventions=Riparian tree planting, fencing
	~~\|Social measures=Regulatory bodies (incl with SEPA and SNH)~~
	}}		}}
	{{Hydromorphological quality elements header}}		{{Hydromorphological quality elements header}}

Aberarder Estate at 14:55, 22 February 2019

2019-02-22T14:55:44Z

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	There are also more general Natural Flood Management (NFM) benefits of the project. With greater floodplain/ wetland connectivity, there is greater inundation of areas adjacent to the channel under certain flood magnitudes. The storage of water in such areas will provide an increased level of protection to downstream areas. Furthermore, the re-establishment of native woodland will also contribute to NFM, adding roughness to the floodplain (slowing flows and increasing water storage times) and increasing the interception of water (surface flow and rainfall) through slowing flows and water absorption. Through such processes, the works will provide greater resilience to the effects of climate change. This is also the case for drought conditions; the previously homogenous condition of the channel has been replaced with a much more diverse morphology (particularly considering the wetland areas) that provides far greater potential for biotic refugia.		There are also more general Natural Flood Management (NFM) benefits of the project. With greater floodplain/ wetland connectivity, there is greater inundation of areas adjacent to the channel under certain flood magnitudes. The storage of water in such areas will provide an increased level of protection to downstream areas. Furthermore, the re-establishment of native woodland will also contribute to NFM, adding roughness to the floodplain (slowing flows and increasing water storage times) and increasing the interception of water (surface flow and rainfall) through slowing flows and water absorption. Through such processes, the works will provide greater resilience to the effects of climate change. This is also the case for drought conditions; the previously homogenous condition of the channel has been replaced with a much more diverse morphology (particularly considering the wetland areas) that provides far greater potential for biotic refugia.
	The work has generally improved the understanding of the benefits of such projects and the appropriate methods of their delivery. This has been a key case study for this type of work for SEPA and, with monitoring ongoing, dissemination of information will provide an invaluable resource to the wider river restoration community.		The work has generally improved the understanding of the benefits of such projects and the appropriate methods of their delivery. This has been a key case study for this type of work for SEPA and, with monitoring ongoing, dissemination of information will provide an invaluable resource to the wider river restoration community.


	Given the explicit development of an integrated steering group and the associated project management approach, challenges during the project were minimised. Also, experience from previous construction projects by the design/ build team meant that many potential issues were avoided. There was careful planning of the construction phase of the project such that the most intrusive works (i.e. construction of the realigned channel and large wood implementation) were conducted ‘offline’, minimising the risk of high flow events impacting the works and fine sediment pollution. Such ‘assisted recovery’ designs explicitly require a degree of ‘field fitting’, allowing for unexpected issues encountered to be managed through appropriate short notice design variations. This was the case in the furthest downstream section of the site where, due to wet ground, it was not safe for construction machinery to excavate the initially proposed realigned channel in this area. It was therefore decided that the proposed design be modified such that the third (furthest downstream) wetland feature would be instated through this ~200 m long section, subsequently proving to be an appropriate revision. Such a short notice adjustment was only possible due to the close and established working relationship between the designer, regulator (i.e. SEPA) and contractor.		Given the explicit development of an integrated steering group and the associated project management approach, challenges during the project were minimised. Also, experience from previous construction projects by the design/ build team meant that many potential issues were avoided. There was careful planning of the construction phase of the project such that the most intrusive works (i.e. construction of the realigned channel and large wood implementation) were conducted ‘offline’, minimising the risk of high flow events impacting the works and fine sediment pollution. Such ‘assisted recovery’ designs explicitly require a degree of ‘field fitting’, allowing for unexpected issues encountered to be managed through appropriate short notice design variations. This was the case in the furthest downstream section of the site where, due to wet ground, it was not safe for construction machinery to excavate the initially proposed realigned channel in this area. It was therefore decided that the proposed design be modified such that the third (furthest downstream) wetland feature would be instated through this ~200 m long section, subsequently proving to be an appropriate revision. Such a short notice adjustment was only possible due to the close and established working relationship between the designer, regulator (i.e. SEPA) and contractor.