APPENDIX F

Option SL4 Supporting Information � Proposed in-channel works summary � Bank Repair Feasibility Sketch (SL4A) � In channel improvement works summary sketches (SL4B-E)

Location In-channel habitat improvements SL4 A – Bank stabilisation directly downstream of GSK outfall using ~100m of Gabion Walls

- Works to stabilise this bank that has been built oversteep in made-ground and now eroded and has been found failing in a number of places. - Works have been costed for a 100m length to take advantage of the construction works, as the failure of adjacent lengths of the bank may well occur in the future. - Gabion based solution will include seeded coir soil bags that will green-up the finished gabion wall. - Undermining of gabion wall and deepening (‘incision’) of the watercourse would be prevented by a Reno mattress, which would be buried under the existing riverbed - Maintenance programme required would be a trimming back of vegetation and removal of large saplings every 5 years. - Retaining structure would have a 100 year design life.

SL4 C – Teville Stream ‘backwater’ along Willowbrook Road

- Once works to realign the channel are completed upstream of the Deacon Way culvert, the flow from the culvert outlet will be confined to that from surface drainage entering the lower culvert - Proposed to leave the existing channel to adjust more naturally to changed flow through build up of reeds from natural seed bank (existing reeds are present) which over time will create a natural backwater and attenuate surface water runoff and reduce contamination - Maintenance programme required to be determined during detailed design, for costing assume: cutting annually; skim surface sediments every 5 years, total reedbed replacement every 25 years

SL4 D – Teville Stream adjacent to allotments

- Vegetation management – trim overgrowing trees/branches and scrub - Woody debris - use the trimmed branches etc to create small bundles of woody debris, to secure with twine and stakes at channel margins, to create variation in depths etc in over-deep/over-wide channel - Difficult access in this section for more formal works

SL4 E – Teville Stream through Brooklands Park

1 – Replace small step weir under access bridge with a cobble riffle to retain bed level control but improve local flow and potential fish and eel passage 2 – Improve marginal habitat along sections of bank with existing hard protection by using coir fibre rolls pre-planted with reeds and staked into bed with wooden poles and stakes (water depth will determine depth of fill and stake length requirements)

SL4 F - Brooklands Lake

- Create area of reedbed in North-West corner of lake where there is existing build-up of silt, indicating this is an area where silt is likely to drop out - Design of reedbed in terms of elevation and plant bedding structure would need to be determined at detailed design, assume need to purchase Phragmites sp (Common reeds) either as seed or pre-grown in pallets - Approximate area c. 10m x 50m (500m2) -Maintenance programme required to be determined during detailed design, for costing assume: cutting annually; skim silt surface every 5 years (leaving roots), total reedbed replacement every 25 years

Working with Form and Function – Which WFD mitigation measures are we proposing to deliver on Teville Stream?

• Remove obsolete structure – By diverting stream around Deacon Way culvert, however other structures remain in place that may control fish passage such as the sluice outfall from Brooklands Lake

• Removal of hard bank reinforcement / revetment, or replacement with soft engineering solution – We may be able to ‘green-up’ revetted/sheet piled banks downstream through Brooklands Park to the lake through placement of coir rolls to establish marginal vegetation

• Preserve and, where possible, restore historic aquatic habitats – We

hope to restore a more natural meandering channel habitat through the downstream part of the realignment around Deacon Way. We can also restore more marginal habitat through in-channel works

• Increase in-channel morphological diversity, e.g. install instream

features; 2 stage channels – We will include 2 stage channel form within the realigned cross-section, and create small in-stream features where possible in the channel

• Re-opening existing culverts & alteration of channel bed (within

culvert) – Diversion around Deacon Way culvert and de-silting of downstream culvert to improve flow and water quality, however other culverts remain and it will not be feasible to remove all at this stage

• Enable fish to access waters upstream and downstream of

impoundments – We are unlikely to directly and fully address this, but our works will not preclude future works to improve fish passage. Replacement of the small weir at Brooklands with a cobble riffle will provide a minor improvement in potential fish and eel passage

• Preserve and where possible enhance ecological value of marginal

aquatic habitat banks and riparian zone – This will be a key action to improve marginal habitat throughout the channel length in either the more open channel upstream of the railway or the more confined channel downstream

• Appropriate techniques to prevent transfer of invasive species – Giant

Hogweed Plan being produced • Appropriate techniques to align and attenuate flow to limit detrimental

effects of, pipes, inlets, outlets and off takes – We will identify suitable locations for reedbeds to trap sediment and provide some natural attenuation of pollutants. These are likely to require longer term management commitment