(Reproduced from Department of the Environment
(1980) Water Data 1978.)
River Measuring authority Temp. (°C) pH EC (µS cm−1) SS (mg 1−1) DO (mg 1−1O) BOD (mg 1−10) NH3 (mg 1−1N) Nitrate (mg 1−1N) Chloride (mg 1−1Cl) Tees Northumbrian 8.4 7.8 355 19.8 11.19 2.4 0.198 3.73 33.3 Trent Severn-Trent 11.3 7.8 1062 24.9 10.85 4.2 0.254 8.72 133.5 Don Yorkshire 21.1 7.5 1433 35.4 8.28 4.6 4.771 7.15 218.8 Bedford Ouse Anglian 11.0 8.1 845 20.8 9.77 3.1 0.151 10.04 63.5 Thames Thames 11.2 8.0 553 22.1 9.47 — 0.376 7.37 40.3 Exe South-West 10.9 7.3 167 8.6 11.00 1.9 0.056 2.53 18.1but increasing attention is being paid to the continuous measurement of water quality in the rivers.
Some of the water quality sampling stations on the main rivers have now many years of records. The number of measured variables has increased as further details are required. In the UK before 1989 these records were sent to a central authority, the Water Data Unit (Department of the Environment). Some of the data were published regularly and a sample is given in Table 8.1. The 1978 records of a selection of water quality measurements are shown from stations on six main rivers. The choice of rivers ranges from the Tees, rising in the highest parts of the Pennine moors in north-east England, through the industrially affected Trent and Don, the Bedford Ouse and Thames representative of Lowland Britain, to the Exe, rising on Exmoor in the extreme south- west of the country. The values of the water quality variables are annual averages computed from sample measurements, or continuous records where such recording instruments are installed. The variables are those of greatest importance in the assessment of river water quality and most commonly measured by the Authorities. The poor quality of the Don stands out, with high conductivity and the highest concentrations of suspended solids (SS), BOD, NH3 and chlorides. The River Exe flows through a truly rural area and
its waters are of the highest quality, needing little treatment before supplying the City of Exeter. The Bedford Ouse and Thames also drain predominantly rural countryside, but
their velocities are lower and they receive the effluents of large cities and towns as well as the water from intensively fertilized arable lands.
In the interests of river quality on a nationwide scale, central government has instigated overall surveys from time to time. A report for England and Wales was published for the year 1980 by the National Water Council (NWC, 1981). It recorded steady increase in the length of unpolluted water courses since a similar survey in 1958. Of the 39 880 km of rivers and canals surveyed in 1980 in England and Wales, 69% were described as of Good quality according to the NWC river classification and only 2% of Bad quality, i.e. waters grossly polluted and likely to cause nuisance. The latest survey in 1990 by the National Rivers Authority (NRA, 19910) showed that of the 39960 km of rivers, 89% of total river length was of Good or Fair quality, 10% was Poor and 2% Bad. The improvements in water quality are attributed to increased investment in new and upgraded sewage treatment works and trunk sewers. Another reason for the improvements has been the increased waste water treatment by industry, and in some areas, the decline in industrial production has resulted in less pollution reaching the rivers.
Both of these surveys were carried out using the NWC water quality classification which had no statutory basis although there was some obligation to the European Community (EC) Directives. Application of this classification was varied among the several authorities and thus it was difficult to make nationwide comparisons.
The Water Act 1989 made it a statutory requirement, for the first time in the UK, to have a system of water quality objectives. The National Rivers Authority for England and Wales immediately instigated research into the complex problem of defining a new classification which could also incorporate EC Directives. A set of Statutory Water Quality Objectives (SWQO) are proposed to maintain and improve the quality of controlled waters, to be set for defined individual stretches. Controlled waters include rivers and canals, lakes, reservoirs, groundwater and estuaries with the first three miles out to sea (NRA, 1991b).
The foundation for determining SWQOs is the definition of use-related classes for the controlled waters. The following uses have been identified
• abstraction for potable water supply • water contact activity
• salmonid fishery—game fish • cyprimid fishery—coarse fish • migratory fishery
• commercial harvesting of shellfish • commercial harvesting of marine fish • abstraction for industry and agriculture
• general and special ecosystems—safeguarding aquatic life • basic amenity which would include navigation.
Each of these user classes has specific requirements for physical, chemical and biological standard values. An example of water quality guidelines in international practice is given for potable water supply in Section 8.4.
The EC Directives are also detailed in their definition of concentrations allowed of quality standards especially with regard to toxic substances.
A method of application of SWQOs to a sample reach of a river is suggested as follows:
Name of river Name of stretch Length of stretch, km
NRA class current target (TC) Use-related class (URC)—uses listed Components of SWQO EC classes—specific directives TC URC Compliance with component ECC
It is recommended that overall compliance would require compliance with all individual components.
A new general classification is also proposed to attempt to eliminate subjective interpretation and to be applied with a consistent approach throughout England and Wales. This would be based on three chemical criteria to which will be added a biological quality of the river. The standards proposed for the chemical variables are shown in Table 8.2 and the classification determined by the chemistry would be modified by a ‘biological over-ride’ using a method such as an ecological quality index or an improved technique yet to be determined.