APEM has an unrivalled knowledge of the Manchester Ship Canal, having been monitoring its water quality and ecology since the 1980s.
Over the past 30 years APEM has been involved in an extensive programme of research and collaborative projects with United Utilities, the Environment Agency, Salford City Council, the Mersey Basin Campaign and Healthy Waterways Trust to investigate methods of improving the water quality in the historically polluted Manchester Ship Canal.
History of the Manchester Ship Canal
The Manchester Ship Canal was opened by Queen Victoria in 1894, allowing seaborne freight to be brought directly into the heart of industrial Manchester. It extends some 56 km (35 miles) from the Mersey Estuary to Manchester Docks.
The canal was built by canalising sections of the lower River Irwell and River Mersey. For the 20.5 km from its upstream limit in Manchester to Rixton near Warrington, where it splits from the Mersey, the canal is therefore a canalised river draining the River Irwell and the rivers that join it further downstream.
The remainder of the canal downstream of Latchworth Locks is completely artificial and in a new channel. Water within this section is saline and is topped up from the estuary during high tides. These two parts of the canal are to all intents and purposes separate.
There are five large locks and sluice complexes in the canal at Mode Wheel, Barton, Irlam, Latchford and Eastham, which allow shipping to travel between the Mersey Estuary and Salford Quays.
Decline and regeneration
Following a decline in shipping use, Manchester Docks eventually closed as a shipping port in 1984, leading to severe urban decline in the area. Subsequent regeneration of the Manchester Docks area, renamed Salford Quays, from 1987 onwards led to a thriving area of intense development.
The Quays now incorporates modern apartment buildings, office developments, art and cultural centres and Media City UK, including major facilities for the BBC and ITV. The shift from deprivation and decline in the Quays area to its current prosperity is inextricably linked to the history of water quality within the freshwater section of the Ship Canal.
Water quality within the Ship Canal
The Manchester Ship Canal has experienced poor water quality since its construction. The key causes of this are: first, the Mersey catchment from which it derives most of its water is heavily populated and generates huge amounts of waste; and second, the structure of the canal serves to retain sediments and promote stagnation of the water, reducing overlying oxygen concentrations.
Bottom water anoxia has historically been a common problem within the canal and has led to unpleasant floating rafts of sediment, bubbling of hydrogen sulphide and unpleasant odours.
The water quality issues have prevailed in the Ship Canal for many decades, and although the overall trend is one of improvement, most continue to the present day below Mode Wheel Locks.
However, above Mode Wheel locks – in the Turning Basin and at Salford Quays – significant changes to the way the water body is managed have resulted in dramatic improvement in water quality.
Following the closure of Manchester Docks in 1984 the site was left derelict but nonetheless ideal for regeneration, thanks to a combination of water frontage and a location at the heart of a large urban area, close to Manchester centre. However, poor water quality in the Manchester Ship Canal was a major stumbling block.
For this reason, initiatives to improve conditions in the canal began as part of an overall redevelopment plan that was supported financially in its early stages by the government. However, it was the visionary drive of Salford City Council, which owned a third of the freehold to the site, which really made the difference. The council championed an imaginative and far reaching environmental management strategy from the outset.
Salford City Council bought the land surrounding Salford Quays in the early 1980s. Three of the Salford Quays basins were isolated from the Ship Canal during 1987-89, creating what is known today as Salford Quays. The isolation prevented polluted water from the canal entering the quays, while the installation of a destratification system eventually created water quality suitable as a ‘blue flag’ bathing water.
Improvements at the Turning Basin
Alongside the success story of Salford Quays, impressive improvements have also been made to the adjacent Turning Basin area of the Ship Canal, upstream of Mode Wheel Locks.
The initial objective was to improve the aesthetic value of the upper reaches by resolving the problems of foul odours, gaseous bubbling and sediment mats, which occurred due to thermal stratification and low oxygen concentrations. Short term management measures were therefore focused on satisfying the oxygen demand of the sediments and the water column.
The River Irwell (top right) as it flows into the Turning Basin and upper reaches of the Manchester Ship Canal (in white) and Salford Quays. The Lowry arts centre, Imperial War Museum North and Media City UK can be seen in the bottom left.
Investigations in the 1980s identified that within the canal artificial means of elevating oxygen concentrations were required. Over the past 30 years several reviews of available aeration, destratification and oxygenation technology have therefore been undertaken, many equipment trials have been commissioned, and several different types of operational systems have been deployed. These have achieved successful long-term elevation of oxygen levels in the Turning Basin.
Following comprehensive field trials of suitable oxygenation technology, five oxygen injection units were installed into the Turning Basin in 2001. These were capable of injecting up to 15 tonnes of oxygen per day and the system performed well, maintaining the oxygen concentration required throughout the Turning Basin. It was operated throughout the months of May to September.
As well as being involved in the design of this system, throughout its subsequent operation APEM undertook surveys of the Turning Basin three times a week to inform its operation and utilise the minimum amount of liquid oxygen necessary.
From oxygenation to aeration
The oxygenation system came to the end of its design life in 2011. With improvements in the water quality of the canal it was identified that use of liquid oxygen was no longer necessary. Instead, some form of water column mixing was now feasible, allowing atmospheric gases to replace oxygen.
In 2010 and 2011 APEM was responsible for conducting field trials to identify the most cost-effective and sustainable replacement for the oxygenation system in the Turning Basin.
The initial stages of the project in 2010 involved an equipment review to identify manufacturers of mixing and destratification devices, capable of using atmospheric oxygen to elevate oxygen concentrations.
A shortlist of manufacturers was then invited to participate in field trials of their equipment in the enclosed basins at Salford Quays. The performance characteristics of the shortlisted equipment were then assessed using Rhodamine WT dye as a tracer to generate data relating to turnover time and mixing extent. Assessing the performance characteristics of the different types of equipment generated performance data which aided design and modelling for full-scale trials in the Turning Basin.
The performance of the existing Helixor system was used as a benchmark against which to assess the performance of the other mixing/destratification devices.
Using the performance data generated, a standardised performance assessment for each type of mixing system was undertaken. Data on energy usage were also determined to provide cost per unit volume data for mixing power generated. These data were then used to identify the most suitable systems to be taken forward to the next stage: the full-scale trails in the Turning Basin. Further trials were undertaken in 2011 of the new commercially available ‘air gun’ type devices.
Following this, in 2012, 30 mixers were successfully installed into the Turning Basin and APEM is responsible for the monitoring and management of their performance to maintain target oxygen concentration throughout the water column.
The freshwater canal
Initial investigations on the Manchester Ship Canal concentrated solely on the 3.5 km of the upper reaches around the Turning Basin and docks. But more recently attention has been focused on the 17 km of the freshwater Ship Canal down to Bollin Point.
The first large scale detailed water quality and biological investigations of the freshwater canal were undertaken by APEM in 2006 and 2007. The Ship Canal begins as a canalised section of the River Irwell and the surveys aimed to assess the impact that improvements at various wastewater treatment works within the river’s catchment would have on the water quality in the canal. This was carried out in the context of the canal’s designation as a coarse fishery by the Environment Agency under the Water Framework Directive.
As part of the extensive field study component of the project, water quality and hydroacoustic surveys were commissioned of the entire canal. Surveys were carried out throughout the year with a view to informing improved management options for the canal. Principally, this required an understanding of fish populations in terms of their behaviour, population structure, and the risks posed by key environmental and water quality parameters.
The subsequent analyses of recent and long-term APEM datasets then allowed the biological responses to various water quality and environmental scenarios to be linked, culminating in the production of a biological response model.
In 2014 APEM undertook a comprehensive review of all the data and information available from the past 30 years on the water quality and ecology of the full 33 km of the canal from the Irwell to Latchford Locks.
This included APEM’s extensive water quality monitoring data set from monitoring contracts with Salford City Council, United Utilities and other clients over the last 30 years. It also included Environment Agency monitoring data including that collected by continuous water quality monitoring sondes, as well as a number of previous academic and commercial reviews.
This information was used to create an almost continuous data set of water quality within the canal and inflowing rivers over the past 40+ years.
This was prepared for United Utilities as part of a wider investigation into the water quality of the canal. The review was specifically concerned with the changes in water quality over the preceding three decades, along with development of the ecological community in the system and the impact of future development.
In addition a high level estimate of source apportionment for factors influencing oxygen demand was undertaken. The review outlined a series of recommendations, including further study and steps towards an aeration system within the canal.
Following on from this work, APEM is currently involved in a large scale programme of works for United Utilities. This aims to design an aeration system to elevate and maintain oxygen concentrations within this section of the canal, in order to comply with the requirements of the Water Framework Directive.
To date (2016) this has included:
- Desktop study of the range of equipment and techniques available
- Water and sediment quality monitoring, assessment and modelling
- Bathymetric and topographical surveys to inform scheme design.
Further stages of the work will include:
- Pilot trials of selected technology and modelling of trial data
- Design and implementation of a system
- Design and implementation of a comprehensive monitoring regime to ensure effective management of the operational system and assessment of compliance with monitoring objectives.
We have also undertaken a range of water quality and ecological surveys of the canal over the past 30 years for other clients, including:
- Ongoing work to support the Carrington and Trafford power station developments.
- Work to support proposals for a water taxi service between central Manchester and Salford Quays.
- Assessment of the potential impacts of a thermal exchange system at the Media City development on water quality and ecology in the Ship Canal.
- Assessment of the potential impacts of a discharge into the Manchester Ship Canal at Stanlow, Ellesmere Port.
- Massive improvements in water quality in Salford Quays and the Turning Basin, paving the way for multi-million pound regeneration programmes.
- The area is now home to the Lowry arts centre, Imperial War Museum North, Media City including the BBC, Coronation Street and a shopping complex.
- Innovative oxygenation and aeration schemes successfully trialed, developed and implemented.