The Swansea barrage (or the Tawe barrage) is a structure near the mouth of the

River Tawe The River Tawe (; ) is a long river in South Wales. Its headwaters flow initially east from its source below Llyn y Fan Fawr south of Glasfynydd Forest, Moel Feity in the Black Mountain (range), Black Mountains, the westernmost range of the ...

Swansea Swansea ( ; ) is a coastal City status in the United Kingdom, city and the List of urban areas in the United Kingdom, second-largest city of Wales. It forms a Principal areas of Wales, principal area, officially known as the City and County of ...

, Wales. It was completed in 1992, creating a

marina A marina (from Spanish , Portuguese and Italian : "related to the sea") is a dock or basin with moorings and supplies for yachts and small boats. A marina differs from a port in that a marina does not handle large passenger ships or cargo ...

which extended the leisure boat facilities already being offered by the former South Dock. The barrage structure includes a boat

lock Lock(s) or Locked may refer to: Common meanings *Lock and key, a mechanical device used to secure items of importance *Lock (water navigation), a device for boats to transit between different levels of water, as in a canal Arts and entertainme ...

spillway A spillway is a structure used to provide the controlled release of water downstream from a dam or levee, typically into the riverbed of the dammed river itself. In the United Kingdom, they may be known as overflow channels. Spillways ensure tha ...

fish pass A fish ladder, also known as a fishway, fish pass, fish steps, or fish cannon, is a structure on or around artificial and natural barriers (such as dams, locks and waterfalls) to facilitate diadromous fishes' natural migration as well as mov ...

and generator

turbine A turbine ( or ) (from the Greek , ''tyrbē'', or Latin ''turbo'', meaning vortex) is a rotary mechanical device that extracts energy from a fluid flow and converts it into useful work. The work produced can be used for generating electrical ...

. The turbine serves a dual use: acting as a power generator for the National Grid as well as being used to pump water back into the Tawe river system. The barrage has an installed generating capacity of 200kW. The barrage scheme gave rise to a number of environmental concerns. Fish navigation up the river and

dissolved oxygen Oxygen saturation (symbol SO2) is a relative measure of the concentration of oxygen that is dissolved or carried in a given medium as a proportion of the maximal concentration that can be dissolved in that medium at the given temperature. It can ...

levels were problems that arose after completion.

Salt water Saline water (more commonly known as salt water) is water that contains a high concentration of dissolved salts (mainly sodium chloride). On the United States Geological Survey (USGS) salinity scale, saline water is saltier than brackish wate ...

that came in at high spring tides sank to the bottom and stayed there, reducing oxygen levels. The Environmental Advice Centre was commissioned to undertake an

aeration Aeration (also called aerification or aeriation) is the process by which air is circulated through, mixed with or dissolved in a liquid or other substances that act as a fluid (such as soil). Aeration processes create additional surface area in t ...

scheme trial in the Tawe in the summer of 1998. The system was based on a diffuser design and propeller mixer, which proved highly effective at exporting the salt water from the deep area of the trial site and raising dissolved oxygen concentrations at the bed. Following the success of the trial system, a more extensive system was designed for installation in 1999–2000. The installation was conducted using a diving team to ensure optimal location of the diffusers within the river channel. The installation was expected to treat all the problem areas over a long reach of river and ameliorate the poor

water quality Water quality refers to the chemical, physical, and biological characteristics of water based on the standards of its usage. It is most frequently used by reference to a set of standards against which compliance, generally achieved through tr ...

present in these areas. Monitoring results from the system installed to date have indicated that aeration has effectively raised the oxygen concentration and assisted in the export of saline water from the system. Following the success of the River Tawe aeration scheme, the city of

Cardiff Cardiff (; ) is the capital city, capital and List of urban areas in the United Kingdom, largest city of Wales. Cardiff had a population of in and forms a Principal areas of Wales, principal area officially known as the City and County of Ca ...

used the same method to improve the quality of the water in its newly created bay. Other fears that arose with the building of the barrage such as the raising of the

water table The water table is the upper surface of the phreatic zone or zone of saturation. The zone of saturation is where the pores and fractures of the ground are saturated with groundwater, which may be fresh, saline, or brackish, depending on the loc ...

causing ground

subsidence Subsidence is a general term for downward vertical movement of the Earth's surface, which can be caused by both natural processes and human activities. Subsidence involves little or no horizontal movement, which distinguishes it from slope mov ...

problems in the low-lying areas around the River Tawe did not materialize.

Notes

{{Energy in Wales Dams completed in 1992 Energy infrastructure completed in 1992 Buildings and structures in Swansea Dams in Wales Tidal barrages Swansea Bay Hydroelectric power stations in Wales Pumped-storage hydroelectric power stations in the United Kingdom