River Health:
What is it and how is it measured?

• River Avon
• What is river health?

River Avon

The Bristol Avon spans 75 miles through the south-west of England. The catchment has a population of approximately 1.5 million people. The river rises in South Gloucestershire on the southern edge of the Cotswold hills, flowing east through Wiltshire and draining through the West of England into the Severn Estuary at Avonmouth.

The Bristol Avon passes through many notable Wiltshire towns, including Malmesbury, Chippenham, Melksham, Trowbridge and Bradford-on-Avon before the river passes through Bath, Keynsham and Bristol in the lower reaches.

Rivers in the Bristol Avon catchment

What is river health?

River health is a complex topic and encompasses a variety of factors. The UK assesses river health using the EU's Water Framework Directive (WFD) classifications, where all waterbodies should achieve an overall classification of at least Good status. To obtain Good status, a river must meet good ecological and chemical status. There are a large number of water quality and other thresholds that a river water body needs to meet to be Good. These include elements such as:

Different factors that go into River Health classification

Factors that can affect the health and resilience of freshwater ecosystems include:

• Flow regime: How much and how fast water is flowing through the river? Is the variation appropriate for the time of year and the catchment? How long and frequent are high and low flows?
• Geomorphology: Is there enough physical habitat and variation in flows to create a dynamic and diverse river for various fish, macroinvertebrates, and other aquatic plants and wildlife to thrive?
• Barriers: Are there significant barriers throughout the river catchment e.g. weirs, which can prevent effective fish migration for spawning as well as change sediment, flow and energy fluxes across the catchment throughout the year?
• Water quality: What chemical and biological indicators are present within the water? How do these vary over time? Can the water quality conditions maintain aquatic life, e.g. dissolved oxygen levels appropriate for fish to survive? What are the inputs of any pollutants which could detrimentally affect water quality?