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INTRODUCTION
The River Bulbourne is one of our several chalk stream rivers, which are fed by groundwater stored
in the chalk aquifer, and flow SE from the Chiltern hills, which stretch from Bedfordshire at the
N. Eastern end to Oxfordshire and the River Thames at the S.Western end.
The fully flowing Bulbourne is about 7 miles in length, and downstream it finally joins with the
River Gade at Two Waters, Hemel Hempstead.
Along its course, it has suffered many diversions over time, including being culverted in places
entering Berkhamsted, and then ignominiously being forced to weave in and out of the canal, both in,
and downstream from, Berkhamsted.
The river’s headwaters, and even down to Northchurch, are known as a winterbourne river, whereby
it is expected to dry out at some period during the summer.
THE UPPER BULBOURNE REACHES
The headwaters of the river have suffered even more dramatically over the last 200 or more years.
The present source of the river is at Dudswell, on the South side of the canal, about 300 metres
downstream from Cowroast, where there is a pumping station and lock.
Bulbourne source, January 2001.
Photographer Jean de Selincourt.
Bulbourne approx. a quarter of a mile from source, view from
side of canal. June 2001.
Photographer David Simmons.
However, there is clear evidence that this source has migrated downstream from higher reaches
overtime. In 1700 the source was quoted to be at Parkhill Farm, near Pendley, being 2 ½ miles
above it’s present source. What are the reasons for these changes?
In the later half of the 18th Century came the excavation of the Grand Junction Canal, which opened
in 1799. Canal systems require a lot of water to function. Cowroast lock is the beginning
of what is known as the Tring summit, which stretches on for 3 miles, all being the highest
level of the canal here. From either end, in use, the locks empty downhill, and every time
a lock is opened about 50,000 gallons of water is lost. The 4 Tring reservoirs were constructed
in the early half of the 19th Century to supply this need. And the Bulbourne head springs,
then via a pond, already flowed into the summit.
But still more water was needed, resulting in boreholes at Cowroast, first in 1848, and later
at Northchurch, first used in 1942, all for pumping water directly from the aquifer. There is
a mountain of evidence to show that these pumps have had, and still have, great implications for
the health of the Bulbourne.
Also, at Newground, 1 mile NW of Cowroast, a borehole was sunk in the late 1800’s,
which for many years has been supplementing the Aylesbury Vale’s public water supply;
again more depletion of the Bulbourne’s local aquifer. However of recent years, changes
have been made to decrease the amount of daily pumping, with provision of an alternative
source to supply the Vale, and pumping at Cowroast was due to finally cease recently,
during December 2009.
RECORDING THE WATER TABLE DEPTH.
The Rivers and Wetlands Conservation Group of the Chiltern Society have been recording the water
table levels monthly for the past 16 years, via measurements taken in boreholes sunk for this purpose,
one being in Dudswell and two in Northchurch. The Environment Agency does the same, and
they receive our figures. We alternate fortnightly.
The figure clearly shows how the depth to the water table varies in the winterbourne section.
Note the seasonal changes with highest levels in Spring and minima towards the end of each year.
The wide variations from one year to the next are mostly related to variation in the amount of
rainfall penetrating to the aquifer but also to the amount of groundwater abstraction from New
Ground and Cowroast. The blue bars at the top denote periods when there was surface flow at
Dudswell; just 49 months out of 170, or about 29% of the time.
REPORT REFERRING TO R.BULBOURNE’S UPPER REACHES, FROM OCT,’06
By the end of October ‘06, following several dry summers, the water table depth lay
at approx. 4¾ metre down below the river bed, which was the lowest depth reached
since 9 years (Oct.’97). Fortunately we were now getting a wet winter and there was
a rapid rise in the ground water to reach the river bed at Dudswell by late January
‘07 and by March ‘07 was flowing from the ‘head’. This was the first time to see
the upper reaches flow for 4 years; the river finally dried in Dudswell at the end
of August, which was unusually late in time. The thirsty aquifer had been filled.
By November ‘07, the water table reached its lowest at a mere ¾ metre down, and by 12th
January ’08 the river was flowing from it’s ‘head’. The public water supply was guaranteed,
no restrictions, for the year. And again the river dried at Dudswell, unusually late, at
the end of August.
By November ’08, the water table was at its lowest just 1/3 metre down. And in ’09
flow from the ‘head’ and in Dudswell ceased at the end of May; this was much earlier
than in the last two years.
By November ’09 the lowest autumn borehole reading was recorded at almost 2 metres,
considerably deeper than at the same time last year, and as routinely soon began to
rise again. The most recent reading, taken on 17th January showed the water table
to be just 1/10th metre down; on 22nd January we had a day of rain, and since then
the ‘ditch’ bed holds standing water, for a stretch, but there is still no flow.
Let’s hope we have some useful February rain.
Authors: Beryl Buckingham and John Norris
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