Water/Wastewater
Migratory fish were referred to specifically in the requirements of the Act mentioned above, so the barrage was constructed to incorporate a fish pass to allow migratory salmon and sea trout to return to the rivers Taff and Ely to spawn. In addition, young salmon have been released into the rivers, firstly as part of an impact monitoring programme, and latterly as a mitigation measure. The bay now supports healthy populations of freshwater fish such as barbel, chub, dace, gudgeon, roach and rudd, and Peter Gough reports an improving salmon, trout and grayling population in the two main rivers and their tributaries. He says, "The fish pass incorporates a counter so we have been able to measure the success of the joint activities with the CHA. The focus on migratory fish has proved to be an elegant way to protect and report water quality because most people understand that if salmon can live in a river, the water quality must be good."
A further stipulation of the Act related to potential effects on local properties from changing groundwater levels. Groundwater surveys were therefore undertaken before the construction of the barrage and have continued ever since.
Invasive species represent a threat to the ecology of the bay and zebra mussels are currently the most significant. Capable of rapidly colonising any structure within a water body, zebra mussels can become a significant problem as they adhere to the surfaces of boats, jetties, anchors, chains, pipes etc. As filter feeders, each zebra mussel typically filters up to 2 litres/day and David Hall from CHA believes that the biomass is so large that the entire volume of the bay could pass though a zebra mussel every two weeks. As a result of this filtration, the water is very clear and David says "This means that cormorants find it easier to prey on fish that swim near the surface, so the balance of fish species has moved in favour of bottom feeders."
data which transformed their ability to respond quickly to low DO. However, the radio systems had to contend with interference and line of sight issues, so in 2008, the buoys were connected to YSI's EcoNet system, which automatically publishes live data to a dedicated website.
A map showing the location of the YSI buoys is shown on the home page of
www.ysihydrodata.com and provides any web user with access to live water quality data. This data is collected at 15 minute intervals from the buoys via GSM and stored on a secure server that hosts the web data.
Two of the buoys are fitted with water quality monitoring sondes at both 1m below the surface level and also at 1m above the floor of the bay. The remaining seven buoys have one sonde monitoring at 1m below the surface.
YSI sondes are compact, rugged battery powered instruments capable of logging data from a broad selection of sensors that have been designed specifically to withstand the most harsh aquatic environments. The sondes in Cardiff Bay are fitted with sensors for DO, pH, conductivity, salinity, temperature and turbidity, but many other sensor options are possible.
Commenting on the reliability of the sondes, Steve Ellery says: "We have been delighted with the performance of the YSI 6- series sondes because they have enabled us to demonstrate extremely high levels of compliance with the DO requirement. The initial sondes were replaced after about six/seven years and we now run eight spare sondes so that when recalibration is due we can simply swap sondes without incurring any downtime in data collection.
The ability of the monitoring network to deliver live data means that we are able to respond to low DO levels very quickly and accurately, and as a result, over the last five years our compliance performance with the 5 mg/l DO has been over 99.9% every year."
Users of the YSI EcoNet system do not always opt for live web data display but Steve Ellery has never regretted the decision to do so. He says, "If the sondes were less reliable we would not wish to display inaccurate data, but since their performance has been so good, it has been great to be able to provide the data to anybody with an interest."
In addition to the buoy based monitoring network, CHA also takes monthly water samples from six locations for the laboratory analysis of a wide variety of parameters including phosphate, nitrate, ammonia, BOD and bacteria.
Water quality is continually assessed by David Hall and Steve Ellery Water Quality
Salmon are unable to survive in low DO water and this was undoubtedly a factor in choosing DO as the main indicator of water quality. However a wide range of other water quality parameters are also monitored.
DO levels are affected by a number of different factors. For example, windy weather helps to aerate the water and cold water is able to 'hold' higher levels of DO than warm. As a result, warm windless summer days pose the greatest threat. However, pollution discharges such as combined sewer overflows can also reduce DO levels. Algae have the potential to lower DO levels following death and eutrophication, but David Hall believes that algae in Cardiff Bay, on balance, have a positive effect on DO as a result of photosynthesis.
CHA employs two methods with which to combat low DO levels. An aeration system extends across the floor of the bay and provides an opportunity to circulate and aerate the water. This system is fed by air compressors which feed over 600 diffusers through a network of 20km of pipes. However, in extremely low DO conditions, CHA is able to deploy an oxygen barge which feeds pure oxygen directly into the worst affected water.
YSI multiparameter water quality monitoring sondes have been deployed in Cardiff Bay since the beginning of barrage construction. Initially, these were strategically placed logging instruments from which data was collected manually at regular intervals, but as CHA's Steve Ellery explains: "This was labour intensive and only provided a historical view of water quality, which meant that our ability to respond to poor water quality was limited and often delayed. We therefore installed 6 YSI buoys in 2000 and began to collect data via radio."
The radio telemetry provided CHA staff with access to live The Cardiff Bay EcoNet system publishes data to the web IET November / December 2011
www.envirotech-online.com Summary
Looking back over the changes that have taken place in water quality in recent decades, Peter Gough believes that the Taff may be the only capital city river in Europe with salmon spawning within the city and says, "This is testament to what
YSI Water Quality Monitoring Buoy Construction of the Cardiff Bay barrage was completed in 2000 has been achieved in a relatively short period of time."
The YSI water quality monitoring network has enabled the CHA to provide live data to the public and to ensure the protection of water quality in the bay. This has ensured that the area has become an attractive environment for all forms of life including human beings.
David Hall has lived in Cardiff for the whole of his life and believes that the protection of water quality has been key to the success that the city has enjoyed in recent years. He says, "If you include the housing, pubs, restaurants, sports facilities etc., the development of the Cardiff Bay area represents a total investment of about £2 Billion.
"The overwhelming success of this area hinges on the aesthetic quality of the bay; the water is clean, wildlife is thriving and many thousands of people enjoy a wide variety of leisure activities. Prosperity has once more returned to Cardiff, and this time, it's not coal we have to thank… its water.”
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