How to Rewild

Rivers and Streams

Habitat Management Plan

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Rivers and Streams
Habitat Guide

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Britain has some of the world’s most biodiverse watercourses, in part because our nation is home to more than 80% of global chalk streams. These aquifer-fed waterways have, in good condition, crystal clear, cool waters which are perfect habitat for breeding fish, specialist invertebrates and flowering aquatic plants. Yet many of our streams have been degraded by pollution, channelisation, water abstraction and climate change.

Chalk streams aren’t the only habitats of value here – the blue veins which weave through our countryside connect up fragmented patches of habitat, allowing the dispersal of animals and plants in the water and along the banks. These waterways provide us with important resources, while also carrying nutrients and sediment from one ecosystem to another. In fact, nutrients flow not just down but up healthy rivers, from the sea to the highest headwaters, in the body of migrating fish.

Sub Habitats

A watercourse identified by UKHab as priority habitat, based on its water quality, biodiversity or potential habitat quality (more info at UKHab website).

All running watercourses which are not identified as a priority habitat (not including ditches – see Aquatic Marginal Vegetation).

Value

Our streams and rivers are not just aquatic habitats, but linear features that join up ecosystems across the wider landscape. They enable the flow of nutrients both down (with gravity) and up (with fish migration) the river system, boosting the productivity of habitats in and around headwaters, floodplains, estuaries and coastlines. The cyclical patterns of intense winter flows and summer lows create diversity in the landscape, enriching floodplain soils and refilling our reservoirs.

These habitats have been channelised to drain agricultural land and canalised to allow for the passage of boats. They have been shaped by human settlements, and shape human settlements, providing aesthetic beauty and recreation, drinking and bathing water, sewage dilution, industrial and agricultural water, generating fine aggregates for construction, and cooling the heart of cities and towns during summer heatwaves.

Their biodiversity value is hard to understate, yet many of these systems are highly degraded, with pollution in many forms – nutrients, sediment, pharmaceuticals, microplastics, pesticides and hot water all flow in from sewage ‘treatment’ plants, urban areas, farms and industrial works along the riverbank. Many rivers and streams are a shadow of their former winding form, with much of their path now hemmed in by high banks, concrete walls, routed through pipes and culverts, or dried up due to land drainage and water abstraction.

There are some remaining healthier river systems, which have been awarded the Priority Habitat status – but even here, biodiversity is knocked back by human impacts. Rivers have high potential for biodiversity, supporting threatened mammals like Water Vole, all manner of invertebrates, birds and amphibians, alongside the occasional Grass Snake. With a range of different flow rates, a jungle of submerged plants thrive in the slower-flowing lentic zones – backwaters and eddies, while algae and a thriving biofilm support diverse fish and invertebrate species in faster flowing rapids and riffles – the lotic zones.

Wild river
Buffer zones between pasture/arable and river edge can greatly reduce the nutrient and sediment runoff spilling into the water.

Protect

While pollution is an issue for biodiversity in river systems, it tends to be more of a problem in the immediate zone around a sewage outflow. Low levels of nutrient pollution throughout the system are also likely to be an issue, but are hard to resolve on a single site without substantial investment in river or stream diversion work (see Restore). Creating buffer strips, fencing-off intensively grazed fields and widening existing buffer zones along the edge of a watercourse will reduce the nutrients and other pollutants flowing into the system – this is the easiest course of action for tackling local nutrient pollution.

As both linear and aquatic features which join up our landscape, rivers and streams are doubly susceptible to invasive species. These can spread rapidly through the connected, flowing system, whether through seeds, by swimming or being transported in or on the body of other organisms. Invasive plants which are of particular concern include Himalayan Balsam, Floating Pennywort, Giant Hogweed, Crassula, and Water Fern. Animals include Signal Crayfish, American Mink, Killer and Demon Shrimp, and Zebra Mussels. Many of these organisms dominate their ecosystem, outcompeting native equivalents and/or predating native species. Tackling them requires specialist knowledge (with too much detail to go into here), but identifying them and getting experts involved is half the battle.

Rivers and streams are fed by smaller watercourses like drainage channels, which may contain standing water for some of the year. While these sources aren’t necessarily flowing, and may not be river or stream habitat, working to improve them will have beneficial impacts downstream. Treatment wetlands can be installed inline in drainage ditches (i.e. shallow ponds containing a reedbed) – these pre-filter nutrients and sediment from your land, while also creating new habitat. Leaky dams can slow the flow of floodwater through drainage channels, causing sediment to drop into the channel, rather than flowing downstream (this can create local flooding around the dam). Funding is available for the creation of leaky dams in some areas.

Working further back from the water, stream and river protection extends to land management in most habitats. Water flows through every ecosystem – as a rule, river health can be improved downstream by slowing its flow and treating or mitigating pollutants like pesticides, fuel, fertilisers, sewage and urban runoff. Trees intercept rainwater with their leaves, and hold soil together with their roots, so planting trees or encouraging natural regeneration on slopes is an ideal way to improve water quality downhill.

Abstraction of water from wells can reduce the supply left to fill smaller streams, to the extent that many of these streams dry up sooner in summer than they would under natural conditions. Reducing the use of well water to only what is needed, and minimising irrigation of crops at times when evaporation rates are high can not only reduce the impact on the aquifer, but also improve soil health. Digging ponds on your land can help to recharge the aquifer over time, even if they dry up in summer months.

Logjam or natural leaky dam
A natural logjam in a river, which is replicated by the creation of leaky dams, which slow down the water and create refuges for biodiversity.

Restore

Any work you plan on doing which will affect the supply, bank or course of a river or stream is subject to legislation in the UK. You will need to ask a professional company for flood modelling, (which can cost £5-10K) before applying for your flood risk activity permit (FRAP). Drainage channels like rhynes/reens may also be covered by similar legislation, and at the very least, it is worth contacting the internal drainage board to find out more information. For work directly on a river or stream, you must speak to the Environment Agency – the local permitting person will be able to assist you with this. Design, permits and planning alone can cost upwards of £75K for river restoration, though this is for a medium-sized project.

You may have hidden streams and rivers that run below the surface of your land in culverts or pipes. In recent years, ‘daylighting culverts’ has become common practice – excavating these hidden waterways and restoring their natural form. This allows light to reach the riverbed, encouraging the growth of plants, which boosts biodiversity in the stretch, while creating meanders that can slow the flow and slightly reduce flooding downstream. Regardless of the biodiversity benefits, there is also an aesthetic appeal of running water, which adds interest to the ecosystem in every season.

Many of our rivers and streams have been straightened and channelised, even if they don’t run through pipes. Rivers were straightened to fit them into our formal landscape, and carry flood water away rapidly, but this just increased the peak height of floods in narrower sections like towns and cities. This straightening also scoured the riverbed clean, destroying aquatic vegetation and biodiversity, while carrying sediment away. Efforts are now underway in many river systems to reverse the work – ‘rewiggling’ watercourses everywhere from the Scottish Highlands to the Somerset Levels.

As many watercourses have been dredged or scoured over time, deepening them into unnatural v-shaped channels, rewiggling also involves raising the water table. This is typically achieved by blocking up the current river and routing the flow across the former floodplain. The new course can be further improved by adding wetland pools which join the channel via small tributaries. These will flood during high river flows and settle pollutants and sediment out of the system, preventing them from travelling downstream. However, the tributaries must join at exactly the right angle, to prevent these side channels silting up or diverting the river entirely. This is the kind of nuanced technical issue which leads to the high cost of design work in these restoration projects.

Beavers are the ultimate ecosystem engineers, restoring health in a landscape with flowing water, and anything we do is just a feeble attempt to recreate their behaviour. But if you have a highly degraded stream, or barely-flowing ditch, it may be possible to turn this into a biodiverse ‘beaver’ wetland without any help from the creatures themselves. We can use logs embedded in the channel walls to back flow up into the area behind the dam. This can be excavated to create a pond, with shallow sloping sides suitable for marginal plants. Rock dams can also be used in place of ‘leaky’ log dams, and these are less likely to break down over time. As with any intervention that keeps water on the land for longer, this work can help to recharge the underlying aquifer.

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