The Great Stour Project - River Pollution

Introduction

Pollution has been described as:

“a resource in the wrong place”

Consider some of the useful substances listed below. List 1 contains elements or compounds essential for life, but, in high concentrations in a river, they become a nuisance or a danger.

List 2 contains heavy metals and other elements or compounds, valuable in the right place and at the right time, but dissolved in river water, undesirable, toxic or even carcinogenic.

It is the task of the Environment Agency (EA) to monitor our rivers and identify these polluting substances.

The EA is the watchdog maintaining a close eye on anything in the river catchment that could endanger the health of the river.  Water quality is continually monitored, and any random incidents of accidental spillage or deliberate pollution are rapidly detected and acted on;  successful court prosecutions against illegal polluters are brought by the EA.

How successful is the EA in keeping our local river, the Great Stour, pollution-free?

Of the total river length (255km), this study focuses on the middle section, a short but significant 12 km stretch between Chartham and Westbere.  It is here that the Great Stour passes through Canterbury. How clean is the river?  We are fortunate that the Environment Agency has monitored it in detail at 5 points here, both above and below the city. We shall be using EA data later in this investigation to analyse the river’s quality in detail. These then are some of the research questions we shall be exploring:

What effect does a large urban area like Canterbury have on water quality in the river?

What are the potential water pollution risks in and around Canterbury?

How much damage does a sewage treatment  works do to a river?

Our starting point is to look at the course of the river as it journeys north-eastwards from Chartham, via Canterbury, to Westbere, Grove Ferry, and beyond.  Below Ashford, in this middle section, the river cuts through the Chalk of the North Downs.  Freshwater springs recharge the river, giving it typical chalk stream characteristics - cool, clear water, with seasonal baseflow discharge, rising and falling steadily with the Chalk aquifer water table.

In this short journey through Canterbury, the river passes through first a rural landscape of grazing marsh, arable farmland and fruit farms, then on to the more heavily urbanised land use of Canterbury itself, collecting treated sewage effluent from four sewage works.  Both heavy and light industry are present here, and the river passes close to waste disposal and older brownfield sites (some of which are redeveloped).  Below Fordwich, unspoilt parts of the grazing marsh and reedbeds are under legal protection status (SPA, NNR, SSSI and Ramsar Convention). At Grove Ferry, more treated sewage effluent arrives via pipeline from Herne Bay.  Further downstream at Pluck’s Gutter, river water is abstracted by Southern Water.

Population growth in East Kent is currently running at 0.5% per year; this is putting increasing pressure on the river, both in terms of water demand and effluent disposal.  The Canterbury STW (Sewage Treatment Works) handles waste for about 40,000 people;  the May Street STW handles waste for 48,000 people in the Herne Bay area.  Both these STWs return treated waste water to the River Stour.  It is vital that the river maintains minimum flows of around 145 million litres per day (about 1.68 cumecs) to ensure dilution capacity, to conserve wildlife and to guarantee sufficient water for abstraction at Pluck’s Gutter. Here river water is withdrawn and chemically treated again, to be fed into the public water supply.  Can the public be confident that they are getting safe water to drink from this source?  Let us consider the potential sources of river pollution.

Continue on to Clickable map of potential pollution sources