Celebrating 25 Years of the Chilterns Chalk Streams Project

River Chess Smarter Water
Catchment
The River Chess is currently
benefiting from £3 million of
funding from Thames Water’s
Smarter Water Catchments
programme (2020-2025).
The Chess was chosen as one
of three catchments in which to
pilot this partnership approach
to developing and delivering a
catchment management plan.
Thames Water’s aspiration is that
multiple benefits will spring from
an holistic approach to catchment
management. The project is split
into five themes: managing flows,
improving water quality, controlling
non-native invasive species,
improving wildlife corridors,
involving people and working
together.
Steph Horn, catchment coordinator
explains ‘Year 1 saw the
development and delivery of
‘The State of the River Chess’,
a baseline report to enable the
partnership and wider public to
understand how things are today
on the Chess. In Year 2 we have
trained over 40 Citizen Scientists to
monitor habitat and water quality
from the headwaters of the Chess
to the confluence with the Colne.
Together we will address data gaps
highlighted by the baseline, as well
as provide crucial monitoring of
our different mitigation actions in
the River Chess. Looking ahead, we
hope to engage further with local
landowners, using seed funding
in the form of grants to enable
farmers and landowners to deliver
projects with multiple benefits
for the River Chess and the wider
catchment landscape.’
River Chess Pressures
The River Chess fails to meet
‘Good Ecological Status’ due
to a combination of nutrient
enrichment from treated
sewage effluent, low flows and
modifications to the river channel.
In its upper reaches, the River
Chess flows through the town of
Chesham, where there are multiple
connections between the road
network and the river. In this area,
fine sediment is transported from
valley sides via the road to the river
channel during heavy rain. Treated
effluent from Chesham Wastewater
Treatment Works contributes
between 40 and 80% of flow to the
river depending on groundwater
levels in the catchment.
The sewage network around
Chesham is infiltrated by
groundwater when levels are
high, overwhelming the treatment
capacity at the Wastewater
Treatment Works. As a result,
the storm tanks at the Works
discharged untreated effluent to
the River Chess for prolonged
periods during 2020 and 2021.
Untreated effluent causes dissolved
oxygen levels in the river to decline,
threatening the health of fish and
Proportion of Phosphorus in River Chess
from different sources
2020-2025 Predicted 2025+
1% 2% 1% 2% 1% 1%
96%
WWTW 96%
Agri-arable 1%
Urban 2%
Industry 1%
Agri-livestock 0%
Septic tanks 0%
Intermittent 0%
invertebrates. Thames Water have
embarked on a programme of
works to minimize groundwater
infiltration into the sewer network
during future periods of high
groundwater levels.
It is estimated that 96% of the
phosphorus in the river is currently
sourced from sewage, and the river
is classified as ‘Poor Status’ with
regard to this nutrient.
The Environment Agency has
introduced a new permit
4%
14%
3%
75%
WWTW 75%
Agri-arable 4%
Urban 14%
Industry 3%
Agri-livestock 2%
Septic tanks 1%
Intermittent 1%
requirement for final treated
effluent from Chesham Wastewater
Treatment Works to contain no
greater than 0.25 mg/L phosphorus
by 2024. Modelling by the
Environment Agency predicts
that this should enable the River
Chess to reach ‘Moderate Status’
for phosphorus (< 0.191 mg P/L)
and that Chesham Wastewater
Treatment Works will then
contribute c. 75% of the total
phosphorus load in the river.
Contains Environment Agency data © Crown Copyright 2022
CURRENT STATE
RIVER CHESS | 35