Works will include the design and construction of all platforms, gantries, access stairs, associated fixings and bracketry and the like needed to safely and effectively access the various aspects of the worksite.
The weir – which maintains the upstream river at a constant level, maintaining bank stability – is near the western end of Glasgow Green.
There are three gates which are raised or lowered depending on the tide and river conditions.
Initial underwater radar and dive surveys were carried out to assess the damage to the north gate, but it wasn’t until a dam had been constructed, to allow the George Leslie to start repair work, that a more in-depth investigation revealed “several defects”.
The report, by councillor Anna Richardson, city convener for sustainability and carbon reduction, states investigations “found additional damage and wear which had had not been identified previously”.
There is damage to the face plate, south roller carriage and guide rails, which allow the gate to be raised and lowered, as well as the bottom skirting and staunching rod, which help form a seal to prevent water loss.
Mechanical and electrical refurbishment works have also been commissioned to bring the weir up to “modern standards” and reduce risk of future failure, the report states.
This work includes new lifting chains and motors and a computer control system, which allows the gates to be monitored and operated remotely.
A contract for the work was awarded to George Leslie Ltd in March 2020, but didn’t start until August due to the pandemic. The project is expected to be complete by August 2021.
The two remaining gates remain operational, but surveys have found a need for “significant refurbishment”
“Significant wear and tear has become evident” on the middle and south gates, the report adds.
Cllr Richardson’s report states there is a reputational and financial risk to the council if repairs aren’t carried out and a “heightened risk of bank failures” could “hinder or affect future development of riverside sites”.
The rock bund will be constructed from the north embankment extending towards the north pier. The toe of the bund will not extend beyond the line of the north pier or onto the sill area of the north gate.
The rock bund will be used to provide access for plant and resources to construct the gabion basket retaining walls. Prefilled baskets will be lifted with a backhoe excavator located near the end of the bund. Divers will guide and position the baskets on the riverbed.
Drive sheet pile wall through the rock bund and into the riverbed. A proprietary sealant will be applied to the clutches of the piles before driving. The piles will be driven to the predetermined toe level with a soft start hydraulic vibrating hammer.
Underwater sounds and vibrations emanating from the pile driving operation will be greatly muffled when driven through the rock bund as opposed to open water.
The rock bund will then be closed off against the gabion baskets and the sheet pile walls. The void between the two rows of piles adjacent to the masonry will be filled with mass concrete to effectively seal the ends of the cut-off wall.