Introduction

Scotland has an extensive network of rivers and streams. They have substantial biodiversity, conservation and economic value, and it is one of SEPA’s aims to protect and where appropriate improve their quality. In order that progress is made in this task, SEPA has built up an extensive monitoring network designed to represent the quality of all significant waters. Thus river lengths are assigned the quality of a downstream monitoring point. For the purposes of river length measurement, the smallest streams with catchments <10 km2 have been excluded, except where they are the main source of a larger river, or they are substantially polluted. This is in accordance with European conventions, and avoids having to monitor small streams which may seasonally dry up. The total length of rivers with a catchment area of 10 km2 or more is 24,404km and SEPA’s efforts are focused here. In 2003, about 800km of these rivers were considered to be of poor quality or seriously polluted, with a further 2,400km of only ‘fair’ quality.

In 1974 a river quality classification scheme was developed to monitor the quality of all rivers in Scotland. Since the formation of SEPA in 1996 the scheme was has been enhanced to incorporate developments in technology and science. The scheme is based on a five point scale (Table 1) and includes all rivers with a catchment area of 10 km2 or more and specific smaller rivers where known pollution problems exist. This is called the “classification network”.

The classification network and results are now available on SEPA’s map based webpage


The classification network

The classification network is divided into river stretches at confluences and pollution pressures. Every stretch is assigned a monitoring point where chemical and/ecological surveys are taken and the aesthetic appearance recorded. The quality or “class” of a length of river is calculated from the monitoring point results. The stretch lengths in each class are added together.

The classification scheme provides SEPA with a means to set improvement targets. In 1996 SEPA set itself water quality improvement targets to be achieved by 2000 (River classification results 1996-2000) which SEPA met by reducing 263.4km of poor or seriously polluted rivers. In 2000, based on the 1999 results, SEPA set new goals in to be achieved by 2006. This target took account of SEPA’s planned activities and Scottish Water’s planned investment programme to upgrade unsatisfactory sewage treatment works, and sewage collection systems. The 2006 goal is to decrease the length of rivers classed as poor or seriously polluted by a further 351km. More information about SEPA’s environmental targets can be seen in our latest corporate plan.


Digitised Rivers Network

In conjunction with the new targets in 1999, an improved system for describing river water quality was also introduced. The classification criteria remain unchanged but are now expressed on a Digitised Rivers Network (DRN), which can be displayed using Geographical Information Systems (GIS). This technology gives SEPA the ability to accurately measure river lengths, automate the classification procedure and allows electronic reporting.

The new DRN coupled with the new system has introduced some consistency issues but SEPA considers this necessary in order to provide a more objective, accurate and rigorous reflection of the quality of Scotland’s rivers. For instance, the total river lengths covered by the DRN is less than in the 1996-2000 classification system because the DRN does not include thousands of minor and generally remote headwater tributaries which have never been monitored. Also with the DRN, waters which are not directly monitored are described and reported as being unclassified, rather than being assumed to be of good quality, which was the former practice.


How is the quality of a river determined?

Every stretch is assigned a monitoring point where chemical and/or ecological surveys are taken and the aesthetic appearance recorded (For details see Annex 1). Chemistry results are used where a minimum of 12 samples is available from the preceding three year period, except in a very few cases where a significant change in quality occurs in a year (e.g. closure of a significant discharge). In this case, a minimum of 12 samples within a single year since the change are required. The standard chemical quality sampling frequency is 6 or 12 samples per year, dependent on the type of site. The ecological assessment is based on data collected from at least two surveys of invertebrate fauna each year. In some areas where water quality is “Excellent” ecology data is collected once in every three years unless a problem in water quality is detected. If any problem is detected in normally clean rivers, this results in immediate investigation and improvement action and restoration of more frequent ecology sampling, until water quality is shown to have been restored.

Aesthetic conditions are based on 1 year’s data from a minimum of 3 observations of the extent of litter and solid waste impact in the river assessed and recorded during ecological and/or chemical sampling visits

The final allocation of the quality class is based on the lowest class determined from the chemistry, ecology, aesthetic and toxicity assessments for the associated monitoring point. No attempt is made to assign zones of intermediate quality between stretches differing by more than one class.

The samples on which classification is based are those from the SEPA’s planned routine monitoring programme, whether they are of normal quality or impacted by a short-term event. Data resulting from any additional investigative sampling in response to pollution incidents or complaints are not used.

• Annex 1 (24k pdf)