River Lea Site Visit

Last week the RRC team joined Diana Hammond and Jane Everett from Affinity Water, and Judy England from Environment Agency, for a site visit around Hertfordshire and Bedfordshire. Not too far from our office, the trip involved going along to see the Highly Commended Manor Park Road improvements on the River Lea in Luton.

We started off meeting at the Affinity Water offices in Hatfield, just a short 40minutes down the A1 from where RRC are based at Cranfield University. After a quick chat and looking over some maps to see where we would be visiting, we headed off to the first stop.

A short drive down the road from this site took us to the second stop of the day. This was the Tewin Water House Estate, just North of Haldens in Welwyn Garden City. Here, an 18^th century weir has been partially removed. Prior to removal, the grassland area directly adjacent to the stream was a waterlogged boggy area, and the weir created a Broadwater next to the property on the estate. Partially removing the structure has improved connectivity, lowered the water level and narrowed the channel significantly on this chalk stream.

The team walked along the approx. 150m stretch, looking at the clear waters with submerged starwort on the gravel-bed, and use of pre-vegetated coir rolls along almost the entire stretch at this site, to reshape the channel. This method appears to have worked very well, and banks have vegetated successfully since installation only 2 years ago. We discussed optimal positioning for coir rolls to ensure they vegetate successfully. The best water depth would ensure they are wet enough so they don’t dry out and die down, but also that they are not drowned out. The landowners on both sides of the river wanted the channel to be aesthetically pleasing as quickly as possible, and were happy with the coir rolls and vegetation establishment.

Pool and riffle features have also been created at this site, and berms developed post-restoration. The channel started to narrow through silt deposition straight after the weir was taken out, but since, has become more developed, highlighting the geomorphological benefits of this restoration. Naturally, when the coir rolls deteriorate over time, the channel will be able to find its own path and widen where it wants to. The wildlife has improved at this site, as we found the shell of a large egg, and saw a family of geese.

Navigating the banks at the most downstream end meant descending a small but steep bank to access the channel. Climbing back up, Martin decided to trust a low hanging branch to pull himself back up, and consequently went for a little dip in the very shallow flowing stream. Moreover, nobody was hurt, only a little wet!

We stopped off at a local bakery to pick up lunch, and purchase the largest pieces of chocolate-covered chocolate cake I have ever seen. Thank you to the Woodhall Park Estate for kindly letting us stop off for lunch at their facilities, before heading off to look at Phase 1 and Phase 2 of the restoration on the River Beane, on the estate.

Phase 1 of the Woodhall Park Estate restoration was to create a bypass channel around the Horseshoe Weir. This involved an approx. 600m channel being excavated through the field adjacent to the weir. A gravel ford was created to leave a shallow point across the channel for quad bike access on the estate. New bankside trees were planted and the entire channel was gravelled, creating elevated and depressed areas in the channel bed. The channel still looks engineered since its completion in December 2017, and needs more time to soften to its landscape.

The second phase of the work at this site is to construct a bypass channel around a Grade II listed weir which was originally built to create the Broadwater. On the day we visited, the contractors were busy building the walls of the new channel. The channel is lined with sheet piling, concrete shuttering, and reinforced with a wall made of engineering bricks to withstand extra water pressure. We walked upstream overlooking the Broadwater, and observed the earth bund which has been constructed to steal water from the Broadwater and feed this side channel. Due to very low flows, this channel was nearly empty, however the bankside features were clearly visible. A layer of coir rolls overlays rock rolls to support the banks of the newly constructed side channel. Once completed, the channel will carry on average 60% of the water flow, with 40% remaining in the main channel. At low flows, all the water will be in conveyed through the newly constructed bypass. Both phases of the work at this site have improved wildlife and habitat. We spotted a white egret, several herons and ducks.

The final site of the day was to the Manor Road Park site on the River Lea in Luton. This project was completed in June 2018, with several techniques implemented across the approx. 140m stretch. A children’s play park was redeveloped to move it approx. 10m further away from the channel running along the side of the recreation park. This created a floodplain area and allowed room for the small channel to be remeandered in this space. Concrete steps were deconstructed and the space was used to build up berms on the right hand bank. Soil which was produced by excavating the new channel was used to make the left hand bank berm. 6 riffles were also created and designed to make sure they stay in place and don’t move longitudinally along the stream.

Coir rolls were used at outfalls from the bordering concrete wall, to dissipate energy and filter fine particulate matter. The project also tries to encourage growth of wildflowers on the bed. From the road above on the left hand bank, over-hanging branches were shading the channel. These were cut back to let more light into the stream and encourage vegetation growth for biodiversity and to allow natural channel processes to improve geomorphology locally.

On the day we visited there was a lot of grey, smelly sewage fungus depositing on the gravels, possibly from nearby road runoff or upstream misconnections. However, the channel is usually ‘gin clear’ and you can see the gravel on the bed. This highlights a gap in communication with the local water company who needs to control sewage problems and misconnections within the catchment.

There were a few issues with designing the new channel to connect to the existing part of the channel downstream. The original channel was in a concrete box, and the downstream section remains this way as it is culverted for approx. 1km under the industrial estate towards the Vauxhall Headquarters downstream. However, the 140m section which has been restored provides a more aesthetically pleasing stretch at the edge of the park.

This small project cost approx. £360,000, with £50,000 of that solely for the movement of the playground. The restoration has connected the community to the river, improved insect diversity, and developed a vision to have a riverside walk all the way to the train station. A student from Cranfield University is currently working on the site as part of their Masters project, to give the project more backing. This site is a great project to springboard other projects in the area, and demonstrate the benefits of urban river restoration.

Thank you to Di and Jane for organising and facilitating this visit for us. We all enjoyed getting out of the office and getting to see a site so close to where we are located! The variability of these projects shows the range of restoration techniques which are available, as well as the site specific considerations which need to be taken into account for any restoration project.

Luton River Restoration Project recognised at top awards - Affinity Water article

Manor Road Park River Restoration Project recognised at top awards - Luton Borough council article

More project information      -    RiverWiki      -       Photos

Nicola

"We had a great day at the River Lea on the RRC Team day out. It was lovely to see Di, Jane and Judy. I particularly enjoyed seeing the contrast between the different site locations within the catchment. The rural private houses and School had very different challenges and opportunities to the park in Luton city centre. In Luton, it was great to see so many people out in the local community enjoying the parkland and the previously inaccessible river."

Jackie

"As I am office based, I really enjoyed having the opportunity to see the results of river restoration, as well as getting an idea of some of the challenges that need to be overcome and the different perspectives of involved parties."

Martin

"It was fascinating to see the rate of change at all of the sites. This highlighted the influence vegetation has on recovery in these small chalk systems and how an existing marginal or riparian edge very quickly transforms the restored stream, which was critical in these locations working with estate managers and town councils. A great day and the sun was shining - which always helps when you have just put your feet in the water!"

Josh

"It was great to see so many sites in one day! Thank you to Di and Jane for showing us round. I particularly enjoyed seeing the crystal clear waters and starwort at the Tewin Water House Estate."