Nicholas Pearson Associates
Kentchurch weir
Kentchurch weirUpstream River Monnow

Projects /
Kentchurch Weir Removal, River Monnow

In 2009 Nicholas Pearson Associates coordinated the non statutory Environmental Impact Assessment (EIA) and undertook the initial ecological surveys for the removal of the Kentchurch weir on the River Monnow, a tributary of the Herefordshire Wye. The weir was considered to be large at approximately 2.6m high and 30m wide. It became redundant around the 1970’s and was proving to be a barrier to the migration of fish upstream to spawn. 
The Environmental Report proposed full removal as the most appropriate option on this dynamic river and in 2011 the weir was removed. A tracked excavator began by lowering a 3m wide section down to the river bed. Once breached the flow was directed through the breach allowing the impounded area to be dewatered. To reduce localised erosion, a small section of weir and the right bank revetment wall were left in situ.  
Most of the weir was removed within three days and the contractors were off site within two weeks. Cardiff University are continuing to monitor the changes in the rivers morphology. The level of sediment deposition immediately upstream was found to be significantly less than anticipated and the level of finer grained sediments was almost negligible. Analysis identified no hazardous substances within the sediments. 
Lowering the level of the river upstream has uncovered four ancestral weirs. The right bank was eroded by approximately 5 metres, due not only to the removal of the weir but also very high flows on the river, therefore stabilisation works were required. Works included bank regarding, toe protection with willow bundles and bankside tree planting. The river has been left to recolonise naturally and fish have since been recorded spawning upstream.

Client:  Natural Resources Wales (NRW)

Location: River Monnow, Kentchurch, Herefordshire

The removal of in stream barriers is an important step towards achieving Water Framework Directive (2000, WFD) targets to improve the status of inland and coastal waters to ‘good ecological status’ by 2015. The Environment Agency and Natural Resources Wales, have a duty to improve the quality of rivers and water bodies in line with WFD targets.

In 2009 Nicholas Pearson Associates coordinated the non statutory Environmental Impact Assessment (EIA) and undertook the initial ecological surveys for the removal of the Kentchurch weir on the River Monnow, a tributary of the Herefordshire Wye. The weir was considered to be large at approximately 2.6m high and 30m wide. It became redundant around the 1970’s and was proving to be a barrier to the migration of fish upstream to spawn. 

The Environmental Report proposed full removal as the most appropriate option on this dynamic river and in 2011 the weir was removed. A tracked excavator began by lowering a 3m wide section down to the river bed. Once breached the flow was directed through the breach allowing the impounded area to be dewatered. To reduce localised erosion, a small section of weir and the right bank revetment wall were left in situ.  

Most of the weir was removed within three days and the contractors were off site within two weeks. Cardiff University are continuing to monitor the changes in the rivers morphology. The level of sediment deposition immediately upstream was found to be significantly less than anticipated and the level of finer grained sediments was almost negligible. Analysis identified no hazardous substances within the sediments. 

Lowering the level of the river upstream has uncovered four ancestral weirs. The right bank was eroded by approximately 5 metres, due not only to the removal of the weir but also very high flows on the river, therefore stabilisation works were required. Works included bank regarding, toe protection with willow bundles and bankside tree planting. The river has been left to recolonise naturally and fish have since been recorded spawning upstream.