In collaboration with the National Trust at Mottisfont, we recently wrapped up a river restoration project on the River Test. This project was brought about following the National Trust’s decision to change their approach to fishing on the estate with a focus solely on creating a fantastic habitat that will support a robust population of wild trout. Of course, these habitat improvements won’t only be enjoyed by trout, but by all chalk stream fish, invertebrates, birds and mammals.
One 50m stretch of the riverbank was made almost entirely of concrete sandbags, covered with a thin layer of soil. This meant the marginal fringe was limited to terrestrial plant species. We removed the concrete sandbags and replaced them with a gently sloping margin made from locally dug floodplain gravel. This offers a diverse array of emergent plants the opportunity to colonise the margins, creating an ideal habitat for aquatic insects and juvenile fish to take cover in.
Sloping margins are also great for drought resilience. During the summer when flows are at their lowest, marginal plants grow down the marginal slope concentrating the flow, before dying back and peeling away with the arrival of higher winter flows. Marginal turfs and topsoil from just upstream were then used to cover over the gravels and will have greened up by spring.
At the upstream end of this stretch, there was a rock weir that needed to go. Removal of the lumps of concrete that formed this weir has allowed the river upstream to flow more naturally - making conditions far more favourable for beneficial chalk stream plants. An existing bankside willow was pushed over to provide low, overhead cover and the surrounding banks were graded to provide more lovely gently sloping margins.
Elsewhere, up and downstream, large numbers of bankside trees were either felled or hinged into the river. In areas where there were no trees present, we transported them to the river from nearby woodland. In channel woody features like these create a diversity of flow, scour the gravel clean and also provide lots of cover for juvenile and adult fish alike. It doesn't take resident fish long to take advantage of these new habitat features.This good-sized wild trout showed up within 24 hours of us placing this new woody feature on site (image above).
By the time we had finished, around 600m of the river had been improved. We can’t wait to see it all greening up come spring and look forward to continuing to work with the National Trust on more of their stretches of river at Mottisfont over the coming years.