Grand opening of Acacia

by Sam Hughes

The Central Park/ Acacia Hall River Restoration Project took a massive step forward at the end of March, writes Sam Hughes.

On Thursday 25th March 2021, after months of delay because of the pandemic, the (rather ugly but essential) cofferdams were removed from the upstream and downstream ends of the project area, and flow was returned to the restored western channel of the Darent that runs through Central Park then past the redeveloped Acacia Hall.

I can’t tell you how excited the SERT team is about this, after more than three years of hard and very muddy work!

Before…

This is now a very different stretch of river compared to the one SERT found more than three years ago. This section of the Darent had been subject to heavy modification in the past.  When I took over the management of the project in 2018, I found an over-widened, dark and hidden backwater, choked with silt and vegetation, heavily shaded by dense stands of self-seeded sycamore, littered and cut off from receiving any significant life-giving flow.

The weir at the downstream end of the site formed a major obstacle to fish passage. All of these impacts had gradually impeded flow down the western channel, resulting in the eastern channel – modified for flood relief – becoming the main watercourse.

Choked river at Acacia Hall before restoration

Developing and delivering in partnership

We immediately recognised that this stretch of river desperately needed help to bring it back to health. We have worked in partnership with Dartford Borough Council, the Environment Agency and collaborated with CBEC to design and deliver a showcase restoration project that reintroduces chalk stream river form and function on the Darent.

This was done by removing the Acacia Hall weir and delivering nature based measures using natural materials to recreate the type of natural variation in channel width and depth found in less disturbed river systems. These measures “kick-start” more natural, variable flow patterns, creating a greater variety of habitats that attract and support wildlife. All of these measures had to be at worst flood risk neutral, which meant a lot of measuring and modelling to make sure there was no increase in flood risk caused by any restoration measures. The modelling results actually showed a slight decrease in flood risk. Win!

Nick, a Senior Project Officer at SERT and Site Manager for the Acacia Hall Project, wrote about the delivery phase which took place over the wet and muddy winter of 2020-2021 and the measures put into place.

The Acacia Hall weir in spring 2018. Impeding flow and fish migration, silted up and choked with vegetation

Channel Opening Day

We arrived early, everyone buzzing with anticipation and prepared for a busy day and a big event, a lot to do on a blowy, showery and distinctly cool spring day.

Perhaps most of all, we were all itching to see the river flow again once the cofferdams were removed. Clear water gliding over clean gravel down a restored reach of a bubbling chalk stream. A place for people and wildlife to enjoy, a valuable move forward in the push for restoration in the Darent catchment.

Martin Moore led the fish rescue from the western channel, working with experienced SERT and EA staff to minimise handling and stress. This was because the water level in this channel would fall which might have resulted in fish becoming trapped as the restored channel was opened up again.

Opening day after Acacia Hall weir removal and restoration © South East Rivers Trust

In the meantime other team members cleared litter and pulled the ubiquitous shopping trolley [we wonder if part of the shopping trolley life cycle is, in fact, aquatic] from the channel. Others walked the channel to complete maintenance checks to make sure that all of the restoration structures built back in the winter of 2020 and early 2021 were in good shape, before the upstream cofferdam was removed.

By late lunchtime the upstream cofferdam was out and after many years, water started to flow back down the restored western channel. For me, it was a really moving moment.

Right, the team put fish back into the channel

Fish released as part of Acacia Hall restoration © South East Rivers Trust

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