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Water
Quality
The
bathing season starts 15 May and ends 30 September. During that
time the Environment Agency (EA) monitors bathing water
quality all along our coast on a weekly basis; the Partnership has an interest, of course,
in the quality of the bathing water at Bournemouth Pier, as well as in
the stream itself as EA results will indicate whether our projects are
having an effect at the coast.
Click
on thumbnail (right) for a map showing
the 14 sampling points
During
2003 stream water quality
was also tested weekly, at 14 different
points, with the EA and BSP Project
Officer working together on sampling, and partner Sembcorp Bournemouth
Water (then known as Bournemouth and West
Hampshire Water) undertaking analysis.
Comparisons can be drawn with
future years' results to demonstrate the success (or not) of the
various SUDS created, and other source control measures undertaken
this year and in the future.
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28
August 2003 |
The
summer of 2003 was exceptionally dry and hot, with an average
monthly rainfall (May-September) of just 34.6mm, compared with
70.3mm in 2002 and 40mm in 2001.
Subsequently,
the downpour on 28th August (12.5mm of rain) brought large
quantities of road run-off - a major source of diffuse pollution -
to the stream via surface water drains and overland.
We have
data to demonstrate the performance of the SUDS at Alderney on
that day, and other graphs that compare the quality with the week
before the rain - you can find them here.
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Overall
water quality 2003 |
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The
EA have developed a General
Quality Assessment (GQA) scheme for rivers and for the
classification of estuaries (below).
On
the basis of the standards set for chemical quality, allowing that
the overall grade will be the lowest of the three measurements,
the Bourne Stream in 2003 can be judged as Grade D 'fair'.
For
level of nutrients (nitrate) the stream is classified Grade 3
'moderately low'.
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Tested for
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Percentile
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Bourne Stream
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Grade
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DO (%)
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10-percentile
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56.0
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D – fair
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BOD (mg/l)
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90-percentile
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3.7
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A – very good
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Ammonia
(mgN/l)
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90-percentile
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0.7
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C – fairly good
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Nitrate (NO3)
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n/a
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15
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3 – moderately low
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DO
= dissolved oxygen
BOD
= biochemical oxygen demand
The
table above is an informal grading by the Partnership from mean data analysis of
water samples collected between May and September 2003, and based
on the EA's GQA standards (see below).
Tables
courtesy of: www.environment-agency.gov.uk |
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Notes:
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Acceptable
European standards
for bathing water (in terms of total
coliforms and faecal coliforms) are shown in the
EC
Bathing Water Directive)
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The
Bourne Stream is not defined as a bathing water, but because of the number
of children that like to play in it in Bournemouth's Lower Gardens, and
elsewhere, during
summer, the Partnership bear these standards in mind when considering
water quality issues and targets.
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