Representation by Wessex Chalk Stream and Rivers Trust (Wessex Chalk Stream and Rivers Trust)
- Date submitted
- 11 January 2019
- Submitted by
- Members of the public/businesses
The Hampshire Avon Catchment Partnership (HACP) The HACP brings together local communities and organisations to plan and deliver positive actions that will improve the water environment of the Hampshire Avon. Hampshire Avon SAC, SSSI and the Scheme The river Avon and its tributaries – including the river Till – are protected under national and international law with qualifying features including brook lamprey, bullhead and Atlantic salmon, but also support other (protected) species such as water vole and otter. The river Avon is not in favourable condition, and water quality is not up to standard. Historic interventions such as dredging, channel realignment, construction of hatches and weirs significantly altered the state of the river system. More recent pressures include unsustainable groundwater abstraction, pollution from agricultural and urban sources as well as the multifaceted impacts of climate change. There is a legal and moral obligation to improve the conditions of the chalk stream and create resilient ecosystems for wildlife and people. We would like to promote a more ambitious programme of interventions with a focus on the rivers Avon and Till in and around the scheme area. Therefore, the HACP can only support the proposed scheme if changes are made to the proposal which ensure increased investments in the water environment. River Till crossing The crossing of the river Till is proposed as a 200m long, relatively high span viaduct. Although we appreciate the impact this has on landscape views and aesthetics, we support this approach in principal, as it will mean continuity for the river Till corridor through the scheme. Any work undertaken in the area should be done with utmost care to prevent disturbing the local water vole population (as identified in the reported survey results) and other protected species. We feel that an opportunity is missed through the decision to reinstate (current) agricultural use to the floodplain directly underneath and adjacent to the viaduct following completion of the scheme. From a landscape connectivity point of view this should be altered to river accompanying wetland area.
River Avon crossing In the proposed scheme, there is no mention to upgrade or even improve the crossing of the Avon east of Countess roundabout. This crossing is low, dark and constricted, and does not support a continuous river corridor for wildlife. The highly civil engineered structure impedes a natural river morphology and significantly impacts the river upstream. During the construction of the A303 in the 20th century, the river was moved and an artificial channel was dug. We would advocate to include restoration of the river to its original position approximately 100m westwards and increase the height and length of a (new) bridge, allowing a more spacious crossing, whilst remediating the impacts of the work undertaken when the A303 was first constructed in this area. These works should be aligned with restoration interventions in the area as part of the River Avon Restoration Plan, delivered by a partnership of local public, private and non-profit organisations. The first phase of this partnership work was bestowed with the UK National River Prize for its achievements in 2017.
Groundwater impacts Chalk streams are fully dependent on the chalk geology. The chalk aquifers provide a steady source of high quality, buffered groundwater. These characteristics provide the abiotic conditions that support the unique and biodiverse chalk streams. As part of the scheme proposals an in-depth (numerical modelling) study has been undertaken to investigate the impact of the construction of the stream on groundwater flows, directly influencing the rivers Avon and Till (6.3 Environmental Statement Appendix 11.4 Annex 1 Numerical Model Report). This modelling study is an approximation and generalisation of the real world and based on many assumptions, especially surrounding aquifer (permeability) characteristics. The single most coined mitigation measure in the environmental assessment to prevent any (negative) impacts on groundwater flows and thereby river flows is ‘design of scheme to avoid significant flow interference by minimising tunnel intersection with preferential flow zone between 69 and 73 m AOD’. This is based on rather limited evidence on the composition of the (local) aquifer - there might be more local horizontal flow zones present that have not been identified. The representation of the proposed tunnel in the model is rather ‘one-dimensional’ and does not cover potential impacts of tunnel boring on the wider permeability of the aquifer (i.e. creation of additional fissures and cracks). We feel that all-in-all the modelling approach does not produce all the answers necessary to conclude that the environmental impacts will be ‘negligible’.