Surface Water Abstraction: Methods and Best Practices
A comprehensive guide to abstracting water from rivers, streams, lakes, and reservoirs in England and Wales, covering intake design, screening, and seasonal considerations.
Overview
Surface water abstraction involves taking water directly from rivers, streams, lakes, canals, or reservoirs. It is the most common form of abstraction in England and Wales and is regulated by the Environment Agency (EA) in England and Natural Resources Wales (NRW) in Wales.
Types of Surface Water Sources
Rivers and Streams
Rivers are the most widely used surface water source. Key considerations include:
- Flow variability: River flows vary seasonally and in response to rainfall. Abstraction licences typically include hands-off flow conditions — minimum flows below which abstraction must cease.
- Water quality: River water quality varies with land use, season, and weather. Treatment is almost always required.
- Flood risk: Intake structures must be designed to withstand flood flows.
Lakes and Reservoirs
Lakes and reservoirs offer more stable water levels and quality than rivers:
- Stratification: Deep reservoirs stratify thermally in summer, affecting water quality at different depths.
- Algal blooms: Nutrient-rich waters can develop algal blooms, particularly cyanobacteria, which can produce toxins.
- Drawdown: Significant drawdown of reservoir levels can affect ecology and amenity.
Canals
Canal abstraction is less common but occurs in some areas:
- Canals are managed by the Canal & River Trust, and abstraction may require their consent in addition to an EA licence.
- Water levels in canals are carefully managed for navigation.
Intake Design
Location
- Site intakes away from areas of poor water quality (e.g., downstream of sewage discharges, agricultural runoff).
- Avoid locations prone to siltation or debris accumulation.
- Consider access for maintenance.
Screening
Fish screens are required at most surface water intakes to prevent fish and other aquatic organisms from being drawn into the abstraction works. The EA's fish screening guidance specifies:
- Drum screens: Rotating cylindrical screens, typically 1mm mesh for salmonid waters.
- Band screens: Moving belt screens, suitable for higher flow rates.
- Passive intake screens: Fixed screens with low approach velocity (typically <0.1 m/s for sensitive fisheries).
Pump Selection
- Submersible pumps: Installed below water level, suitable for boreholes and some surface water intakes.
- Centrifugal pumps: Widely used for surface water abstraction.
- Variable speed drives: Allow abstraction rate to be varied in response to river flow conditions.
Seasonal Considerations
Surface water availability in England and Wales is highly seasonal:
- Winter: Higher flows, better availability, but higher turbidity and flood risk.
- Summer: Lower flows, hands-off flow conditions more likely to be triggered, higher water temperatures.
- Drought: Drought Orders can suspend or modify licence conditions.
Monitoring and Compliance
Licence holders must:
- Install and maintain approved flow meters.
- Submit annual abstraction returns to the EA or NRW.
- Monitor river flows at specified gauging stations to comply with hands-off flow conditions.
- Keep records of all abstraction.
Environmental Considerations
Surface water abstraction can affect:
- Low flows: Reducing river flows below minimum ecological requirements.
- Aquatic ecology: Affecting fish, invertebrates, and riparian vegetation.
- Wetlands: Reducing water levels in floodplain wetlands connected to the river.
- Downstream users: Reducing water available to other abstractors downstream.