Chalk streams
The chalk streams in England
are estimated to account for 85% of the world’s chalk stream habitats and, of
these, a majority are in Hertfordshire.
A healthy water body has
thriving populations of fish, plants, diatoms (microscopic algae) and
invertebrates (animals that do not have backbones including flatworms, leeches,
snails and other molluscs, and insects such as mayflies, stoneflies and caddis
flies). They depend upon a healthy flow of water and a variety of natural
habitats. All of these are affected by the levels of pollution and nutrients in
the water, and the shape and structure of the water body.
Groundwater
Most of Hertfordshire’s
water comes from sources deep below ground level called aquifers (an underground
area that holds water), from which water is extracted through boreholes.
Groundwater levels vary throughout the year as a result of the amount of
rainfall penetrating through to the aquifer to “recharge” it. It can take as
long as 6 months for rainwater to filter through to the aquifer but this is
dependant on the location and the amount of rain received. Most recharge is made in the
autumn and winter months, during this period less rainfall runs off into
rivers, is lost from evaporation or used for plant growth.
This gives rise to the highest
groundwater levels around April, and lowest levels usually in October.
River health
Within the UK, the health of
the water environment is assessed using the Water Framework Directive. Under
this Directive, the aim is for all rivers, lakes, reservoirs, streams, canals,
estuaries, coastal and groundwater (known as water bodies) to be in good
ecological health by 2027.
Every year the Environment
Agency analyses the data collected and compares it to a standard. The standard
used is a water body that is of a similar type, but is in a natural, or almost
natural, condition. That is to say, it has not been greatly affected by
pollution or other human activities, and is considered to be in good ecological
health.
The assessment measure is
then given a classification that depends on how it compares to the standard.
When the health of a water body is worse than the target of Good Ecological
Status or Good Ecological Potential, we say that it is failing, and the reasons
why are investigated.
In 2009 the status of each
water body was classified in a River Basin Management Plan. Hertfordshire also
collects data each year which indicates the health of water bodies based on
current best evidence and the River Basin Management Plan will be formally
updated in 2015.
There are 41 water bodies
within Hertfordshire. In 2012, based on current best evidence, their health has
been assessed as follows:
14.5% were classified as good; these include
Tykeswater near Radlett and the Upper Ash.
39% were classified as moderate; these include
the Upper Rib and the Ver.
34% were classified as poor; these include the
River Quin and the Lee at Hertford.
2.5% were classified as bad; this is the Stort
Navigation through Bishops Stortford.
10% of the water bodies have not yet been fully
assessed.