Trebarwith Strand is on the north coast of Cornwall. It is a fairly remote, sandy
bay, approximately 800 metres wide, sheltered by high rocky cliffs with many caves
and rock pools. There is a stream that flows across the beach into the sea.
There is an emergency/storm overflow from the Trebarwith Road pumping station, that
discharges to the Trebarwith Stream 70m from the Environment Agency monitoring point.
The operation of the overflow can lead to a temporary drop in water quality in the
Trebarwith Stream and Trebarwith Strand bathing water.
The South West Water sewage treatment scheme for Treknow, which provides secondary
treatment and UV disinfection, was completed in early 2007. Improvements to the storm
overflow from Treknow sewage treatment works (STW) were also completed at that time.
Storm overflow event duration monitoring (EDM) was installed at Treknow STW by December
2011.
Environment Agency investigations have shown that the impact on the Trebarwith Stream
and the bathing water from Treknow sewage treatment works has been largely resolved
by the addition of ultraviolet (UV) disinfection of the effluent. However, during
periods of heavy rainfall the stream can still be contaminated.
For the four year (2015-2018) assessment period where data is available, seaweed (macroalgae)
was not assessed as being sufficient to be objectionable, but was observed as being
present on 42% of visits. The bathing water can become covered with large amounts
of seaweed, depending on tides and the weather. This bathing water does not have a
history of large amounts of seaweed, but rocks, platforms or other fixed objects may
develop a covering of seaweed which can be slippery.
For the four year (2015-2018) assessment period where data is available, phytoplankton
(microscopic algae) was not noted at this site. Phytoplankton (microscopic algae)
naturally increase in number at certain times of the year. This process is known as
a phytoplankton bloom. This bathing water does not have a history of phytoplankton
blooms.
The risks to human health from contact, ingestion or inhalation with marine algae
that currently occur in UK coastal waters are considered to be low. However, some
individuals may be more sensitive and display some reactions.
A common marine algae found in UK coastal waters is Phaeocystis, which is often mistaken
for sewage as it forms foam and a brown scum, but it is non-toxic.
Streams and rivers are typically affected by human sewage, animal slurry and runoff
from roads. The Trebarwith Stream flows across this beach. The Environment Agency
have monitored the stream since 1990 and found that water quality is temporarily worse
after heavy rainfall.
The outfall from Treknow STW discharges to the Trebarwith Stream approximately 600m
upstream of this bathing water. This discharge is disinfected and designed to protect
bathing water quality.
Environment Agency samplers make observations of litter present on the beach at every
visit, this includes assessments of sewage debris, litter and tar. At Trebarwith Strand
for the four year (2015-2018) assessment period where data is available, sewage debris
was not noted at this site. Litter was not assessed as being sufficient to be objectionable,
but was observed as being present on 24% of visits. Tarry residue was not noted at
this site.
There are five farms in the catchment, which are mostly dairy and beef. During and
after periods of heavy rainfall, runoff to the Trebarwith Stream from agricultural
land is greatly increased, and the quality of the bathing water can be reduced.
The catchment surrounding Trebarwith Strand is approximately 650 hectares. The Trebarwith
Stream is approximately 4.3 kilometres (km) (seven kilometres long including tributaries).
It flows from west to east through farmland, quarry land, and a steep wooded valley
before entering the sea at Trebarwith Strand. The steep catchment means rain runs
off rapidly into the stream. The coastal cliffs are about 100m high and are some of
the tallest in Cornwall.
Land use is agricultural, with five farms. The agricultural land is mostly improved
grassland with some smaller arable areas. Mixed woodland areas can be found mostly
in the valleys. The coastal section is designated as both a Site of Special Scientific
Interest (SSSI) and Special Area of Conservation (SAC). The catchment is within the
Cornwall Area of Outstanding Natural Beauty (AONB).
Seaweed (macroalgae) and phytoplankton (microscopic algae) are a natural part of the
marine and freshwater environment. Below we note whether these have been recorded
in quantities sufficient to be a nuisance.
The majority of sewers in England are “combined sewers” and carry both sewage and
surface water from roofs and drains. A storm overflow operates during heavy rainfall
when the sewerage system becomes overwhelmed by the amount of surface water. The overflow
prevents sewage from backing up pipes and flooding properties and gardens. An emergency
overflow will only operate infrequently, for example due to pump failure or blockage
in the sewerage system.
Heavy rain falling on pavements and roads often flows into surface water drains or
highway drains, ending up in local rivers and ultimately the sea. The quality of bathing
water may be adversely affected as a result of such events.
It is the Environment Agency role to drive improvement of water quality at bathing
waters that are at risk of failing higher standards. It is natural for water to run
off the land to the sea. Water quality at a bathing water is dependent upon the type
and area of land (the catchment) draining to the water and the activities undertaken
in that catchment.
