Flow Resilient River Habitat

Mike Blackmore

 The River Test is world famous; considered the cradle of English fly fishing and epitomising the chalk stream experience. Just the mention of its name conjures images of gin-clear water, bright, clean gravel, lazily waving Water crowfoot (more commonly known by its Latin name, Ranunculus), and sturdy, speckled, almost-golden chalk stream Brown trout.

There are of course, sections of the river that fully live up to this reputation; exhibiting truly archetypal chalk stream characteristics. Beautiful reaches that provide both vigorously healthy habitat and, for those that seek it, an unmatched angling experience.

However, the unfortunate truth is that for vast lengths of the Test, this iconic image has passed from reality, to legend, to myth. Riverbeds of bright flint gravel have been lost under dark silt, strewn with nodules of ‘tufa’ (calcium carbonate precipitant). Ranunculus has been unceremoniously usurped by ribbon weed and other species that favour sluggish, silty conditions. Even that most fundamental of chalk stream characteristics, thirst-inducing, gin-clear water, can be scuppered by slightest bed disturbance upstream. Riverfly abundance appears to be dwindling and water quality issues are far from solved.

Many of the woes that beset the Test can be (and often are) manageable. Good management can keep the bed clean, the banks rich and diverse, the weed growing and the fish rising. This management is hard, physical work, undertaken by committed and passionate people. People endeavouring to balance the ecology of the river with the economics of (sometimes highly commercial) fisheries. As summarised by a keeper I know, it’s a job of “doing the best you can, with the water you’ve got”.

And that is the crux of it. The health of any river, especially a chalk stream, is intrinsically bound to its flow. Strong flows dilute pollutants, scour away excess silt, promote weed growth and keep the river cool, oxygenated and full of living things. A well-flowing river is forgiving. It will accept a bit of gardening, a bit of angling pressure, even the odd mill, gauging weir or other more intractable impoundment. Flow papers over the cracks, glosses over the stains, props up the wobbly table. We need it more, yet have it less, than ever before.

Being aquifer-fed, chalk streams are inherently stable systems. Water levels take a long time to rise and fall. In an age before large-scale aquifer abstraction, even drier winters may have sufficiently charged aquifers to provide steady flows through the summer. Before modern urbanisation and intensive agriculture, winter runoff would probably have less of an impact on flooding. Channels cut to receive average flows would be more likely to hold up through both summer and winter.

This does not mean that flows did not previously vary (far from it). Indeed, water would be harnessed, diverted, backed-up, flushed through and near-constantly adjusted by an army of millers, ‘drowners’ (water meadow managers) and estate workers. These people’s livelihoods depended on knowing the annual fluctuations of the river and timing the adjustments of their control structures accordingly.