Low Flow Trials –

learnings involving

innovative designs

Paul Wainwright

• Eleven trial sites established in

2015-16

• Marne, EMLR and WMLR

catchments

• Install and test a range of

different devices in different

settings

• Learn about construction and

management challenges

• Monitor hydrological

performance

Objectives

Criteria for selecting sites

• Landowner amenable/enthusiastic

• Accessibility for construction

• Accessibility for demonstration

• Variable landscape/infrastructure settings

• Where dams could be treated in a series

• Proximate to existing hydro/eco monitoring sites

Bugle Ranges

• 40ML dam on dairy farm

• TFR 0.7 L/s

• Concrete mechanical bypass

installed

Marne Catchment - Pipe Bypass – TFR 2L/s

Bypass weir

Low flow

release point

Controller, battery,

3G antenna, air pump

Dam wall

Water level

Inflows

Electric actuated fail

open vent valve

Electric actuated valve

and flow release outlet

0.1% accuracy

hydrostatic sensor

Inlet foot

valveFlow

meter

Macclesfield Trial Site –TFR 4.5L/s

• Today is the first step in the process of

implementing the Securing Low Flows

project

BYPASS DEVICES

• Non electronic

• Relatively cheap

• Robust

• Gravity based - requires minimum 2 degrees of fall

between weir and release point

• Tricky to install in wet/peaty watercourses

• Require maintenance to ensure they don’t block

Pro’s and Con’s of the different devices

RELEASE DEVICES

• Electronic

• Instrumentation can be expensive

• Reliability

• Quick to install/ can be partly off-site

• Can be installed in wet/adverse conditions

• Maintenance tends to be complicated

• Generally need protection from stock etc.

Pro’s and Con’s of the different devices

• Landholders generally supportive

• Understand the need to test concepts

• Open to sharing the idea with others

• Interested in the monitoring outputs

The community experience

1. Is the low flow device doing what it is supposed to do?

• Measure total inflow to dam/arriving at dam• Device what is delivered through the low flow device

Hydrometric monitoring for the low flow

trial sites

2. Reliability of supply for landholder

• Change in storage in dam• Bathymetric survey + water level• Compare low flow and non-low flow scenario