Trevaunance Cove is on the north coast of Cornwall. It is a sand and rock beach resort,
approximately 250 metres wide, backed by cliffs. There is a small stream that disperses
over the sand.
There is an emergency/storm overflow from the Cove pumping station. The overflow discharges
to the Trevaunance Stream 70m from the beach. There is an emergency/storm overflow
from the Peterville pumping station that discharges to the Trevaunance Stream 750m
from the beach.
The operation of the overflows can lead to a temporary drop in water quality in the
Trevaunance Stream and Trevaunance Cove bathing water.
This bathing water is included in the Surfers Against Sewage “Safer Seas Service”.
This service can alert you to Combined Storm Sewer Overflow discharges via a phone
App and in addition, it includes the Environment Agency Pollution Risk Forecast warnings
where they are available. Further details of the service can be found at - http://www.sas.org.uk/safer-seas-service/
In the past untreated effluent was discharged off Trevaunance Point very close to
the bathing water. The sewage treatment scheme for St Agnes which provides Chemically
Assisted Sedimentation, was completed by South West Water in 1996. The scheme also
included a new relocated outfall, some resewerage and improvements to combined sewer
overflows. The treatment at St Agnes STW was upgraded with ultraviolet (UV) disinfection
and an advanced membrane filtration process in 2004.
Storm overflow event duration monitoring (EDM) was installed at St Agnes STW, and
the Peterville and Cove pumping stations by May 2011.
Environment Agency investigations have shown that the St Agnes stream catchment can
be impacted by urban drainage as it flows through and under St Agnes. Investigations
are ongoing to pinpoint and resolve these impacts and reduce the risk to Trevaunance
Cove bathing water. In 2019 we undertook a misconnection survey on Trevaunance Stream
using CCTV. This identified a significant issue in the lower catchment area which
was quickly rectified.
In 2023 we have commissioned additional monitoring of the lower section of Trevaunance
Stream and will request microbial source tracking on samples to understand sources
of pollution. This will ocntinue into 2024 along with monitoring all freshwater inputs.
For the four year (2020-2023) assessment period where data is available, seaweed (macroalgae)
was assessed as being sufficient to be objectionable for 17% of visits, with 71% of
visits noting the presence of seaweed (macroalgae). This bathing water does not have
a history of large amounts of seaweed (macro algae).
Wrongly connected domestic waste water pipes can also affect the bathing water quality.
We have checked the local sewerage system for misconnections.
Modern sewerage systems have two separate systems, one takes foul sewage to sewage
treatment, the other takes rainwater runoff through surface water drains to rivers,
lakes and the sea. Misconnections occur when waste water pipes are plumbed into surface
water drains instead of the foul water sewerage system. This can give rise to pollution
when the waste water is discharged directly to the environment through the surface
water drain. For example, a washing machine or toilet may be incorrectly plumbed so
that it discharges to the surface drain rather than the foul sewage drain.
For the four year (2020-2023) 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.
There are no active pollution risk forecasts made at this bathing water. However any
bathing water has the potential to be affected by a pollution incident and if this
occurs a pollution risk warning with associated advice against bathing will be issued
on this website.
Streams and rivers are typically affected by human sewage, animal slurry and runoff
from roads. The Trevaunance Stream flows onto this beach. The Environment Agency have
monitored the stream since 1986 and found that water quality is temporarily worse
during and after heavy rainfall. Monitoring has also shown that on occasion the water
quality can be poorer during dry weather.
The outfall from St Agnes STW is discharged to the sea 640m west of bathing water.
The 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 Trevaunance
Cove for the four year (2020-2023) 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 19% of visits. Tarry residue
was not noted at this site.
There are two farms in the catchment. During and after periods of heavy rainfall,
runoff to the Trevaunance Stream from agricultural land is greatly increased, and
the quality of the bathing water can be reduced.
The catchment surrounding Trevaunance Cove is approximately 960 hectares, with two
streams entering the sea at the beach. The Trevaunance Stream is approximately 2.2
kilometres (km) long and flows through the village of St Agnes before entering the
sea at the bathing water. The Trevellas Stream is approximately four and a half kilometres
long and flows through a valley which has been modified by historical mining activities.
The stream enters the sea at the north eastern end of Trevaunace Cove approximately
500m from the Environment Agency monitoring point. St Agnes beacon is nearly 200m
in height and is located in the northwest of the catchment, the stream valleys are
generally steepest at or close to the coast.
The catchment is mostly agricultural with just one or two farms. Urban areas include
the village of St Agnes and there are at least three caravan sites, the rural areas
are a patchwork of improved grassland and arable land. Much of the coast is designated
as a Site of Special Scientific Interest (SSSI).
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.
