'99 Update

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Water

Introduction

River quality has declined in recent years due to drought conditions. However, as rainfall returns to long term trends and groundwater recharges there may be an improvement in river quality in future years.

Indicator 1: Water Consumption

The average consumption of water in Hertfordshire is currently 169 litres per head per day (l/d) compared to 170 l/d the previous year. Leakage has been reduced from 148 million litres per day (Ml/d) in 1997/98 to 135 Ml/d in 1998/99, a reduction exceeding the Water Industry Regulator target.

The 1998/99 average peak week demand at 773 Ml/d was 22 Ml/d lower than the previous year peak demand. Demand is influenced by weather conditions and reductions in leakage.

Indicator 2: River Quality

The Environment Agency monitors the chemical and biological quality of our rivers using a system that classifies river quality from A to F: A = Very Good, B = Good, C = Fairly Good, D = Fair, E = Poor, F = Bad. The quality of 340km of rivers in Hertfordshire is shown on the map.

River Quality in Hertfordshire (1994-96 to 1996-98)

• 31% of the rivers in Hertfordshire were of Very Good or Good quality in 1996-98 compared to 35% in 1995-97, a decline of 4%;
• 11%, or 30km, of the rivers in Hertfordshire were of Poor quality (E) in 1996-98 compared to 9% in 1995-97, an increase of 2%.

25km more river has been incorporated into the classification this year. The decline in water quality is thought to be due to drought conditions in recent years, which have led to low flows and pooling of water. This has led to reductions in dissolved oxygen and reduced dilution of effluents. Underground water was not replenished, further lowering river levels. Rainfall, groundwater recharge and river flows returned closer to the long term average in 1998 and 1999, which may be reflected in better water quality in future years.

Indicator 3: River Quality Objectives

The river reaches that are monitored for their water quality also have River Quality Objectives (RQOs). The RQO scheme is based upon the recognised uses of a river. At present, objectives are only based on the River Ecosystem (RE). These address the chemical quality requirements of different types of aquatic ecosystems as outlined below:

Class RE1: Water of very good quality suitable for all fish species
Class RE2: Water of good quality suitable for all fish species
Class RE3: Water of fair quality suitable for all fish species
Class RE4: Water of fair quality suitable for coarse fish populations
Class RE5: Water of poor water quality which is likely to limit coarse fish populations

This graph shows the latest available information.

• 315km of river had a River Quality Objective.
• 51% of these passed their objective in 1995-97, compared to 100% passing in 1994-96.

This is thought to be due to drought conditions in recent years.

Water Resources in Hertfordshire

From January to March 1999 groundwater levels rose in most areas. Levels then started to recede but river flows remained average or above. May saw below average rainfall, but heavy thunderstorms in June kept flows in the runoff rivers above average. Groundwater levels continued to decline as is normal in summer. July was hot, with below average rainfall, but a wet first half of August produced above average flows in many rivers. The first half of September was hot and dry with the second half producing well above average rainfall. Below average rainfall for October and November delayed the onset of the winter recharge period. The Chilterns catchments have now saturated and recharge has started.