- 19th April 2018
- Posted by: Sophie Bunker
- Category: Blog
Under the Environment Agency Water Environment Management Framework, JBA Bentley was commissioned to design the replacement of four pairs of pointing doors that prevent tidal ingress into a freshwater system. Understanding of existing upstream fish passage opportunities into the catchment was required, along with the design of a solution to maximise and increase those opportunities.
The water management infrastructure at the site was complicated. Each pair of pointing doors sit downstream of a bottom-opening guillotine gate that maintains upstream (freshwater) levels for the purposes of navigation, abstraction and ecology. The guillotine gates are raised and lowered in response to changing water levels in the catchment.
Downstream tidal range of the pointing doors results in the freshwater system being tide-locked for an extended period of every tidal cycle. This arrangement gives rise to a wide-ranging head difference across the structure, as well as highly variable velocities between the pointing doors. These conditions meant that there was limited understanding of at what stage in the tidal cycle the pointing doors would close and prevent upstream passage.
JBA Bentley designed a novel, soft-closure damper system to delay closure of the pointing doors and maximise the window of passage opportunity. This system was deemed necessary as the size of the pointing doors, and resulting stresses associated with the turning moment prevented the deployment of any off the shelf system secured to the soffit of the door and the bridge abutment.
Furthermore, JBA Bentley deployed time-lapse cameras to record pointing door closure events on rising tides under various states of fluvial flow and tidal range. The time-lapse deployment revealed the duration of pointing door closure events varied between 20 seconds and approximately three minutes, and that the soft-closure mechanism deploys for approximately 20 to 30 seconds.
Fluvial and tidal water level data, along with the guillotine gate position has been provided by the client and JBA Bentley is in the process of calculating velocity through the guillotine gates. This will give us an understanding of the proportion of the tidal cycle that could be considered passable to fish wanting to migrate from the estuarine to freshwater environment, in both the pre-installation and post-installation situations.
The use of time-lapse cameras negated the deployment of staff to manually observe closure events and reduced risks associated with prolonged manual observation in an exposed and inhospitable situation.
Want to know more?
Are you attending the River Restoration Conference on 24-25 April? We’ll be showing you how our catchment and river restoration team deliver innovative and sustainable solutions to improve our rivers and catchments.
We are giving four presentations and have eight posters for you to see our project examples. Read the abstracts to find out more in our interactive guide below.