Location and Basic Geography
The River Mersey
originates at the confluence of the River Tame
and the River Goyt
in the town centre of Stockport, Northwest England.
It flows west, towards Liverpool, passing through South Manchester towards Warrington, where the river becomes tidal at Howley Weir and the Upper Estuary starts. It widens to form the Inner Estuary at Runcorn. Here is the confluence with the navigable River Weaver.
The Mersey Estuary continues through the ‘Narrows’ a straight narrow channel with depths of up to 30 m driven by a change in geology. It forms the Outer Estuary, a large area of inter-tidal sand and mud banks as it flows into Liverpool Bay on the Irish Sea. The Mersey is a tidal river with the second highest tidal range in the UK of about 10 m. These strong tides have created deep channels and sandbanks throughout the Mersey Estuary, which can make navigation difficult.
Water Quality of the River Mersey
With the opening of Liverpool’s first dock back in 1715, the Mersey catchment became a prime location for industrial expansion. It was the advent of mechanised spinning and weaving which induced the siting of new mills along watercourses within the region. Associated with the textile industry was an increase in the bleaching, dying, finishing trades as well as chemical works. Allied to the growth of these was the growth of the paper, heavy chemical and glass industries, which are still in production to this day. All of these industries used the waterways as a means for the disposal of industrial waste. This has resulted in a legacy of pollutants within the River Mersey of particularly noxious substances such as mercury; pesticides such as DDT; and persistent organic contaminants, such as polychlorinated biphenyls (PCBs) and pentachlorophenol (PCP).
As industry grew, so too did the human population. Nearly 5 million inhabit the Mersey catchment. Historically the domestic waste produced by this population has been disposed directly into the waterways resulting in gross pollution. Progressively a situation was reached where the environment did not have the capacity to degrade, dilute and disperse all of the material put into it.
Time for a Change
In 1985, at the inception of the Mersey Basin Campaign, set up as a consequence of this, the Mersey Estuary was the most polluted estuary in the UK, receiving up to 60% of the mainland pollution generated by industry and a population of over 5 million inhabitants. Water quality has improved in recent years as a result of initiatives such as the Mersey Basin Campaign and more stringent EU requirements, and also by technological changes and advances in scientific understanding.
In an effort to rid the Mersey Estuary of its unenviable title of the most polluted estuary in Europe, North West Water embarked, in 1981, upon a clean-up scheme designed to counteract the years of misuse and neglect. From an examination of the main problems, it was seen that levels of oxygen within the main river systems and Mersey Estuary, driven by the high levels of sewage discharged into the waterways, was a major stumbling block to improved water quality.
One of the first steps was to tackle to direct discharges of crude sewage into the regions waterways. For example, new primary sewage works at Sandon Dock replaced 28 crude sewage discharges directly into the Mersey Estuary through the MEPAS scheme (Mersey Estuary Pollution Alleviation Scheme), diverting wastewater to a new treatment works. This is just one programme initiated as a direct result of massive investment by North West Water (and now United Utilities) in sewage treatment and its associated network.
The MEPAS scheme on the River Mersey.
Further improvements to the treatment of wastewater now include tertiary treatment for the removal of ammonia from wastewater. Exposure to short periods of ammonia may kill salmonid fish species. For example, at Davyhulme wastewater treatment works in Greater Manchester, a natural purification process using a biological aerated flooded filter process removes ammonia, reducing discharges into the Manchester Ship Canal.
Extract from the Mersey Basin Campaign. http://www.merseybasin.org.uk/information.asp?page=1&pagesize=5&confirmed=1&id=0&docid=57