South East Rivers Trust (& the Wandle Trust)

Hogsmill River Restoration at Kingston University

Phase 1: Tree Pinning (24-25th February)

I have let my blogging duties slide recently due to being flat out with work so I need to kick this entry off with a catch up. The Trust has been working up a partnership project with Kingston University to improve habitat and flow characteristics as the Hogsmill flows past the Knights Park Campus in Kingston. The river, as with most urban rivers, has been significantly modified by human intervention and subsequently is now artificially straight and wide with a uniform bed, laminar flows and lacking habitat within the river and on the banks. The fact that one bank is formed by a sheer wall certainly does not help with this.

The uniform and straight stretch before the work
The uniform, straight and featureless stretch before the work

Nature needed a bit of help to kick start this stretch back into life, however, after months of planning, it was nature that was jeopardising the project with the continual rain that raised river levels to unworkable conditions. With a couple of weeks to go to the start of the first phase of works, we did the only thing left to do, start sun dancing to disperse the clouds and beckon the sun. And who would have guessed it, it only went and worked. Plenty of hurrahs and rejoicing later, on Monday 24th February under beautiful clear skies, a willing team of volunteers gathered at the University. The first phase, which took place over two consecutive days, involved securing five tree trunks, which were being felled as part of the Council’s routine maintenance schedule, onto the bed of the river.

The purpose of pinning the trees into the river has multiple benefits. Under moderate to high levels as water flows over the structure, on the downstream side a scour hole is created helping to break up the uniform shallow bed and provide deeper pools for fish to lurk in. This scouring process then throws ups gravels, producing a loosely compacted gravel shoal perfect for invertebrates to take up residence and fish to spawn in. The trees provide cover, refuge and habitat, all of which are currently noticeably lacking in this stretch. Under lower flow conditions, the trees help to back the water up a little to provide a greater depth and act to narrow the river helping with fish passage.

A tree being maneuvered into position
A tree being maneuvered into position

Once felled the tree trunks were tidied up as to remove any branches that would potentially catch debris.  En-masse with the aid of lifting straps and plenty of dogged determination and hard graft, the trees were moved into the desired positions. These were pointing upstream as to focus the scour into the centre of the channel. If moving the trees wasn’t hard enough, then armed with post knockers, chestnut stakes were driven into the bed on opposite sides of the trunks and limbs.

Who needs a gym with a work out like this. (Photo by Ollie Lacfi)
Who needs a gym or a shower with a work out like this (Photo by Ollie Lacfi)
Another tree gets moved into position. (Photo by Ollie Lacfi).
Another tree gets moved into position (Photo by Ollie Lacfi)

Fencing wire was then looped between the stakes before being driven all the way home to secure the trees in place. As a fail safe, a six tonne breaking strain wire rope secured the trees to land anchors to prevent floating downstream in the unlikely event that they were to break free.

The fail safe anchor system in place
The fail safe anchor system in place

In addition to the five trees, one large log which has been washed up on the side of the river was also used. The effect of the work was immediately apparent . As the water forced its way under, over and around the trees, the compacted gravels were getting kicked up as holes started to be formed. As the water flows over the trees, a meandering sequence was also being seen.

The river adjusting to the new structres
The river adjusting to the new structures

We had an impressive response to this project, mustering 17 and 13 volunteers on Monday and Tuesday respectively, from a pool of University staff, students, local residents, and interest groups such as the Thames Anglers’ Conservancy.

A big thanks to all that took part (Photo by Ollie Lacfi)

A huge thank you to all involved over the two days: Tanya, Samantha, Tara, John, Andrew, Simon, Glyn, Jean, Mark, Helen, Bill, Reenal, Lawrence, Graham, James, Adam, Paul, Elliot, Sarah, Ollie and Rachel Burgess at Kingston University.

Phase two which involved creating a 73 metre long wetland berm with brash and gravel was completed over the weekend. The blog will be going up shortly.