Tidal Weir

tidalweir

The River Clyde near Glasgow green in the city has a tidal weir. It was constructed in 1901, then rebuilt in 1949 after serious flood damage and has since been renovated.

There have been other forms of tidal weirs going back hundreds of years protecting various bridges and structure. The main function is to protect the banks and buildings in the lower parts of the city up stream of the weir from collapsing by balancing the water levels in the surrounding land of the river Clyde upstream.

Downstream flows and river heights are monitored along with tidal heights, moon phases and atmospheric pressures to control water levels and make adjustments on operating weir gates.

The weir gates open by being raised with chains and this allows water flow beneath the gates.

At Mid Clyde Angling Association, we became concerned about reports from various sources of seal predation and salmon mortalities in the area of the weir when low flows of water were present.

Kemp Meikle, a retired civil engineer and member of Mid Clyde Angling Association decided to research this further and studied historic flow and tidal influences of the weir and surrounding river, as well as present predictions. He felt that the weir was not being operated to its full potential and openings were possibly not fulfilling minimal requirements for salmon to migrate safely past the weir, some minor adjustments could allow better gate openings and flows to allow migration of salmon, under the gates and also allow the weir to do the job its was designed and built to do more efficiently, to no extra cost.

A meeting was organised and various clubs local authorities, the river biologist and sepa were invited to attend. Unfortunately for reasons unknown some people did not attend.

Sepa were very interested in Kemp’s findings and studies and said that they had problems below the weir with low oxygen levels and combined sewage outflows (cso’s),which in low summer levels caused de oxygenated water levels, causing stress to fish and various aquatic invertebrates. Sepa representative’s asked Kemp to revisit and study his findings and they would look at things more closely, as they felt this could be of great benefit to the aquatic environment below the weir at minimal operational cost. When Kemp’s further research and rechecking of his findings are complete, a new meeting will be organised to see how this can be taken further and possible implementation of findings.

Here is a link for more on weir.

Discussions between the RCFMT and GCC have agreed the following which will afford increased opportunity for fish to ascend.

1.Single gate operation whenever flow conditions and tide level permit (providing shelter and increased gate opening).

2.Testing of a “WINDOW” of 300mm gate opening during periods of low flow and neap tides (ascertaining the time taken for the retained water level of 4.17 m to be re-established).

3.This “WINDOW” could be likened to a Borland fish pass – providing opportunity to ascend at a fixed time (testing conditions which may principally influence spring and summer runs but can occur at any time).