Stand with your back to the river, and look around. What you see will have a huge impact on the river.
Muddy fields, poached and gullied by livestock or arable fields left bare in winter, mean that heavy rain will cause more erosion, often guttering along farm tracks and into nearby watercourses. This is diffuse pollution, both as fine sediment and nutrients, with obvious negative implications for aquatic life.
Belts of native trees and herbaceous vegetation cover protected from livestock grazing (and trampling), natural drainage through well-structured soil, areas retained as wetland — all of these will help to intercept rainfall and aid absorption into the ground from where it will be released more slowly into rivers. As a result, flows are ‘buffered’; peaks are lower during floods, and retained at a higher level during droughts. Soil and nutrients are better retained in the catchment. The result is a much healthier river and with lower flood risk too.
A catchment based approach that tackles land use issues is vital to maintain healthy rivers, and is essential when considering rehabilitation projects.
Case study: The River Axe in Devon
The video below describes the issues caused by dairy farming in the catchment of the River Axe in Devon, which suffers from excessive levels of nutrients and sediment and very ‘flashy’ flows, impacting the whole river ecology including the precious sea trout.
The causes of these issues, their solutions and the associated farming regulations are well summarised in this short video and apply to a greater or lesser degree to many farmed catchments in the UK.
WTT has carried out an Advisory Visit on the River Axe, and the EA published a report in 2019 which, we understand, led to greater focus on farming practices in the catchment.
Urban catchments
In more urbanised environments, the proliferation of hard, impermeable surfaces means that rainfall cannot seep into the soil and slowly be released, but will flow directly over land or via drains into rivers, resulting in a ‘flashy’ river that rises and falls quickly.
There is also no mechanism to intercept and/or adsorb pollutants such as fuel.
Sustainable drainage systems (SuDS) aim to reduce surface water flooding, improve water quality and enhance the amenity and biodiversity value of the environment by mimicking natural drainage regimes.
Our roads, roofs and pavements are all tributaries of the rivers that first spawned the cities This video about the River Don explains that Sheffield (as all our cities) is actually One Big River: