Celebrating 25 Years of the Chilterns Chalk Streams Project

The earliest river flow records from
the 1700s suggest that the source
of the Bulbourne was near Park Hill
on the outskirts of the Bulbourne
village, north of the current
location marked on Ordnance
Survey maps at Cow Roast.
Today, flows in the Bulbourne are
strongly modified by groundwater
abstraction, both for drinking
water supply and for the Grand
Union Canal. The current source
of the river migrates between
approximately 13 and
5 km from the confluence with the
Gade in response to variations in
groundwater levels.
In the urban reaches of the
Bulbourne, runoff from road
surfaces and verges contributes
sediment to the river channel.
This sediment builds up within the
over-widened river channel, and
the low flows lack the power to
move this sediment downstream.
This combination of sedimentation,
over-widened channels and no/
low flows contributes to the poor
ecological status of the river.
Berkhamsted Wastewater
Treatment Works contributes
treated effluent to the Grand Union
Canal and Bulbourne downstream
of Berkhamsted. In 2020 and 2021,
when groundwater levels in the
catchment were above normal,
storm tanks released untreated
effluent into the canal and river on
numerous occasions. Investigations
by Thames Water demonstrated
that groundwater infiltration into
the sewer network in Berkhamsted
was an issue during this period,
and a remediation plan is under
development.
Environment Agency modelling
suggests that 96% of phosphorus
in the Bulbourne currently arises
from wastewater treatment;
urban runoff being the second
largest contributor. During AMP7
(2020-2025), Thames Water are
introducing measures to reduce
the concentration of phosphorus
in final effluent entering the
Bulbourne.
Given the interplay between
different issues in the catchment,
improving the ecological status
of the Bulbourne will require
a partnership approach to
river management, with close
collaboration between the
organisations responsible for
the Grand Union Canal, water
companies and regulators,
authorities responsible for the road
network and local interest groups.
Ortho-Phosphate (mg/L)
0.4
Ortho−Phosphate (mg/L)
0.4
0.2
0.2
0.0
0.0
Ortho-phosphate concentration over time
BULBOURNE ABOVE G.U.C. AT LOCK 55, BERKH
2012 2014 2016 2018 2020 2022
2012 2014 2016 Year2018 2020 2022
Bulbourne upstream of
both Berkhamsted WWTW
and Grand Union Canal
Proportion of Phosphorus in River Bulbourne
from different sources
2020-2025 Predicted 2025+
1% 3%
96%
WWTW
5%
BULBOURNE ABOVE GADE
12%
83%
WWTW
Poor status
Moderate status
Good status
Bulbourne downstream of
both Berkhamsted WWTW
and Grand Union Canal
Contains Environment Agency data © Crown Copyright 2022
Contains Environment Agency data © Crown Copyright 2022
CURRENT STATE
RIVER BULBOURNE | 33