- 20th May 2019
- Posted by: Joanne Woodhouse
- Category: Blog
We will be attending the 9th Institute of Fisheries Management specialist conference on Fish, Flows and Climate Resilience this week so we thought it was timely for, Dr David Mould, our Fish Pass Hydraulic Design Lead to reflect on his visit to the recently commissioned Shotley Grove fish pass:
The Shotley Grove Fish Pass
The Shotley Grove fish pass was designed by us for the Tyne Rivers Trust who were working in partnership with the EA, with the works funded by the European Maritime Fisheries Fund (EMFF).
Shotley Grove weir was the last barrier on the Derwent for migrating sea trout, with the river upstream providing valuable spawning habitat. The solution is a rock pool pass with 6 traverses, each with a head difference of 0.3m. Notches within each of the traverses provide a swim-through route upstream for fish. Also, the outer (right-hand wall) acts as a baulk as it cuts diagonally across the face of the weir water gathers provides a further route upstream. A key lesson learnt was that the size of the boulders led to differences between the design velocities and the measured velocities following construction.
Access to the site was down a long and bumpy track and therefore the use of concrete within the design was minimised. The pass was constructed using natural materials and the stones which provided the traverses were sized so as to be stable during large flood events. This meant the boulders used were approximately 1m by 1m by 1m. The hydraulic design of the traverses and notches was undertaken before the structural design started and the size of the boulders known. The velocities through the notches were calculated assuming that the notch acted as a weir, with the velocities in the notch calculated using the upstream water level.
This would have been a reasonable assumption if the notches would have had a relatively short length, but in this case, due to the size of the boulders, velocities at the downstream end of the notch were higher due to the lower downstream water levels. This led to velocities being marginally higher than designed by around 0.1 to 0.2m/s.
The velocities remain within suitable swimming speeds for the length of sea trout expected at the site, however, if the size of the stones would have been incorporated into the hydraulic design at an earlier stage, this difference could have been avoided.
As an industry leader with a multi-disciplinary team of specialists we are presenting on the following topics throughout the conference:
- Jon Whitmore, Technical Director and JBA’s Lead in Hydroecology, will be co-presenting with Gavin Coe, Contracts Manager at the River Stewardship Company, on CDM compliance in fish pass design.
- Rachelle Ngai will be presenting on the outputs from our work for the Committee on Climate Change looking at how taking a long-term approach to considering risks from climate change, and anticipating land use changes to manage these risks, could deliver benefits in terms of resilience to climate change
- Katie Burnham will be presenting on our Natural Flood Management (NFM) work for the National Trust on the importance of carefully considering site characteristics to ensure measures appropriately deliver required design outcomes.