Witnessing instant improvements
It was fantastic for volunteers to be able to see instant rewards for their efforts.
For example, at Bassetts Mead, in Hook, water was instantly flowing quicker over freshly made gravel riffles after volunteers put in huge efforts to add a massive 30 tonnes of gravel into this section of the River Whitewater. This took place with the help of a Hampshire & Isle of Wildlife Trust tractor. The work was funded by Hook Parish Council. Adding to last year’s efforts, a total of 60 tonnes of gravel has been added to a 160 metre section of the river. It was hard work! We offer huge thanks to volunteers – and the fish and invertebrates are very grateful, too!
Why is the work necessary and important? In a healthy river environment, some fine sediment is normal. It gets there from decaying plant matter and run-off from the surrounding land and provides habitats for mayflies, eel and lamprey.
However, because of modern urbanisation and land management practices, fine sediment supply to our rivers can be much higher than would occur naturally. This can be a problem, clogging riverbed habitats and preventing life-giving oxygenated water from flowing through the riverbed.
Fine sediment is transported by the river where flows are high and the sediment is kept in suspension, until it is deposited in lower flow areas, like along the margins. But when flows are too slow and sediment levels are high, it will deposit in areas it shouldn’t and can smother riverbeds, ruining habitat for fish and invertebrates.
To counter this, adding fresh clean gravels is a simple way to improve spawning habitats for fish and invertebrates by creating a coarse riverbed that water can flow through, as well as over. This allows invertebrates to live in the riverbed. Fish can bury their eggs where they incubate over the winter.
Adding gravels also increases habitat diversity as the river will move it in higher flows to create a more varied range of deep pools and shallow riffles.