Lake District Rivers
The complex physical landscape that we can see and study in the Lake District is a function of both the
underlying geology and the different physical processes that have shaped the rocks over many millions
of years. The Lake District contains examples of all the main rock groups – sedimentary, igneous and
metamorphic rocks. The modern day Cumbrian Mountains are remnants of much larger mountains
formed around 400 million years ago (during the Caledonian Orogeny) when plate movements
squeezed the rocks upwards (forming folds and faults) and intruding magma heated and changed the
existing rocks. A huge granite batholith now underlies most of the Lake District (another similar
example lies beneath Dartmoor in SW England). This igneous intrusion is surrounded by metamorphic
rocks such as slates. Over millions of years the high mountains were worn down and eventually
disappeared beneath tropical seas where deposits of limestone and sandstone were added as a layer of
sedimentary rocks. A further period of mountain building around 300 million years ago (during the
Variscan Orogeny) resulted in more uplift and then continued erosion. The rivers which drained this
geologic dome radiated outwards like the spokes of a wheel and carved deep valleys which removed
most of the sedimentary rocks from the area – remnants are now found only around the edges of the
Lake District. As the rivers continued to erode downwards, they cut into the ancient igneous and
metamorphic rocks leaving a radial drainage pattern that is at odds with the geology beneath. This is a
classic example of a discordant drainage pattern that has resulted from the superimposition of an
earlier drainage pattern on the overlying rocks.
During the Quaternary period, ice gradually covered the Lake District and valley glaciers flowed down
the pre-existing river valleys, deepening, widening and straightening them to form classic glacial Ushaped valleys. Tributary valleys were left as hanging valleys. The sequence of glacials and warmer
interglacials severely modified the original river valleys but the basic radial pattern has remained. When
the last glacial period ended around 10,000 years ago, the rivers returned as the main physical process
shaping the landscape. Their impact, however, has been minimal thus far and in many places rivers
remain as misfits (tiny streams/rivers in huge valleys). Large glacial lakes now fill many of the overdeepened valleys and form an important element of the drainage system.
When studying present-day rivers in a former glacial environment such as the Lake District, it is
important to think about how the rivers you and your students investigate will be different to the classic
textbook situation.
1. Both the long profile and the cross-profile of rivers at different points along the course will be
radically different in the Lake District. In what ways will they be different?
2. In a former glaciated environment, streams and rivers will rework glacial deposits (glacial moraine
and fluvioglacial material) as they erode the landscape. What effect will this have on the nature of the
material being transported and the availability of load? How does this link to the greater frequency of
braided streams in the Lake District?
3. The sources of many Lake District streams are typical marshy hollows but many are also corrie lakes
(tarns). How might this impact on flow regimes in the upper reaches?
4. How might the many hundreds of hanging valleys affect the long profile, landform frequency (e.g.
waterfalls), transportation and deposition of load?
5. Almost every major river in the Lake District has to pass through a large lake (mostly glacial in origin
but including some man-made reservoirs). These lakes have two main impacts – on river velocity and
the transportation of load. What will happen to water velocity as the river enters the lake? What will
be different about the volume of suspended load as the river enters and leaves the lake? What
eventually happens to most of these lakes?
The Lake District Rivers
Map showing the radial drainage
pattern in the Lake District. The
pattern of streams and rivers is not
controlled by present-day surface
geology but by a previous cover of
ancient sedimentary rocks.
The River Derwent is the longest river in the Lake District at 30 km. It is joined by two major tributaries –
the River Greta (17 km long) and the River Cocker (10 km long).
The source of the River Derwent is at Styhead Tarn underneath Scafell Pike and it flows in a northerly
direction through the valley of Borrowdale, before continuing through Derwentwater, giving the lake its
name. The Derwent then continues into Bassenthwaite Lake, picking up the waters of the River Greta
just outside Keswick. Beyond Bassenthwaite Lake the river flows westwards through the Isel Valley,
before leaving the Lake District National Park just before reaching Cockermouth. The River Cocker has
its confluence with the River Derwent at Cockermouth. The River Derwent flows into the Irish Sea at
Workington. [The River Greta passes close by to our residential base at Blencathra.]
The drainage basin of the River Derwent covers 675 km2. The area has an annual average rainfall of
1800 mm. The underlying solid geology is mainly impermeable igneous and metamorphic rocks. There
appears to be little or no geological control on stream network with a similar stream network density
displayed down the catchment. Without the lakes along its length, the catchment would have an even
more flashy response. Thus the lakes, and the position in the catchment relative to the lakes, have a
significant impact on hydrology, and sediment transfer. Land use in the catchment is primarily stockgrazing on the high fells and grass and silage on the lower lands.
The river valleys contain both glacial and contemporary fluvial deposits. Glacial deposits are major
controls on the supply of both coarse and fine sediments to the channel systems. These and the more
recent alluvial sediments form the majority of the channel margins and are being continually reworked
throughout the catchment.
Flooding and Flood Management
The streams and rivers in the Lake District can be quite ‘flashy’ – they react quickly to rainfall events. In
times of relative drought (rare in the Lakes) discharge can be low but after heavy storms, the
impermeable surfaces, thin soils and steep slopes result in water quickly entering the river system and
causing a dramatic rise in discharge and river levels. Bankful discharge can be reached within hours
giving very little warning of potential flooding.
Although population density is relatively low across the Lake District, flooding is a problem in several of
the urban areas such as Keswick and Cockermouth, and a few of the small villages, particularly those
close to river confluences. The danger comes from the high discharges which damage buildings, bridges
and other infrastructure, and the high velocities which increase the risk to humans.
Most of the rivers lie within the Lake District National Park boundary and it is difficult, therefore, to
manage river flow and discharge in order to avoid flooding. The aim is always to find a balance between
human safety and keeping the landscape as natural as possible.
On the 18th and 19th November 2009, exceptionally prolonged and heavy rainfall led to severe flooding
across parts of the Lake District. To put this in context, London and the south-east receives about
600mm of rainfall per year. Seathwaite in Cumbria recorded 316mm of rainfall in 24 hours! This was a
new UK record. Statistically, this figure is unlikely to be repeated for another 200 years (the return
period). Normally, the many lakes along the courses of the main rivers would act as ‘storage tanks’ but
in this instance, these huge lakes simply filled up and overflowed. Some were over a metre higher than
previous record levels.
The worst-hit areas were affected by flooding from the River Derwent, draining an area of the southern
fells and flowing through Borrowdale via Derwentwater and Bassenthwaite Lake to the coast at
Workington. In Workington, a police officer died after the A596 road bridge collapsed beneath him, and
the town was effectively cut in half as the remaining road bridge in the town was also severely damaged
by floodwaters. Cockermouth was also badly affected by flooding; with the town centre shops and
homes under two metres or more of floodwater and several hundred other properties were also
affected by flooding. There was widespread disruption across the region. However, new flood defences
in Carlisle built after the January 2005 floods held firm. Estimates of the insurance costs were put at
around £100 million.
The River Derwent catchment is divided into sub areas within the Catchment Flood Management Plan
(Environment Agency 2009). The area around the towns of Cockermouth and Keswick is identified as
requiring further action to reduce flood risk through investment in maintaining and improving the flood
defence infrastructure. In Keswick defences are mainly raised defence walls and Cockermouth benefits from
flood defences consisting of riverside walls, stop logs, floodgates and minor earthworks.
River Greta showing flood
defence walls at Keswick.
River Cocker showing
floodgate.
In contrast, the preferred policy for the rural upper catchments of the Upper Derwent and River Cocker
is to manage flood risk by working with natural processes (so-called ‘soft’ management rather than
‘hard’ engineering). The principal aim is to reconnect the streams to their floodplain through the
creation of wetland habitats (including wet/floodplain woodland), thereby reducing flood flows and
sediment loads.
The Environment Agency works with local authority planning departments to carry out flood risk
mapping and to advise on the location of new housing developments on or close to floodplains. They
also provide floodline and flood warning services alongside flood awareness campaigns. Current
planning now incorporates a greater awareness of the significance of climate change. Factors being
considered include:

more frequent and intense storms plus overall wetter winters

a gradual rise in sea level.
These new scenarios predict that the number of people and properties at risk is likely to double by
2100.
The emphasis now is on sustainable solutions within each sub-area. The EA has come up with six policy
options and the Flood Management Plan has considered how social, economic and environmental
objectives are affected by flood risk management activities under each policy option. In those areas at
greatest risk, it is recognised that taking further action to reduce risk will require additional appraisal to
assess whether there are socially and environmentally sustainable, technically viable and economically
justified options. Nothing happens quickly….
What has been done? In Cockermouth, it has been decided that engineering work should go ahead to
improve bank defence works and that gravel extraction should be used to increase channel discharge
capacity. In January 2010, 12,000 tonnes of gravel were extracted from the River Derwent. Vegetation
has also been removed from gravel shoals to allow more natural movement of bedload and reduce the
risk of permanent islands forming in the channel. Households in areas of greatest risk have been advised
to make their homes more flood proof.
In Feb. 2014 another £2 million of government funding was awarded to enhance defences at
Workington and elsewhere.
Links:
https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/289419/Derwent_Cat
chment_Flood_Management_Plan.pdf
The River Derwent in its
upper course. Although
there is some evidence of
higher discharges and
bedload movement, the
largest boulders in the
bedload have been there
some considerable time.
Much of this material
may be here because of
glacial erosion rather
than river erosion.
The River Derwent at
Cockermouth – note the
vegetated islands which restrict
flow and reduce channel
capacity at times of high
discharge. The bridge in the
distance also restricts flow and
debris can become jammed
under the arches. This can cause
water to back up and overflow
its banks or the bridge itself to
be damaged.
The River Derwent entering
Derwent Water Lake. As the
river reaches the lake, velocity is
reduced and the deposition of
load has led to the formation of
a small delta. Eventually, the
lake will be filled in.
The confluence of the River
Cocker and the River Derwent
at Cockermouth. Discharge
increases significantly beyond
this point.
The River Derwent at
Cockermouth fills the
floodplain and
overwhelms the town
centre.
Collapsed bridge at Cockermouth
after the 2009 floods. The town
was cut in half with residents
having to make a 21 mile detour!
Cockermouth town centre during the 2009
floods.
Hydrograph plot for the River Derwent at
Camerton recording station (between
Cockermouth and Workington) ‐ showing the
mean annual maximum flood hydrograph in
black and the November 2009 event in red.
The hydrographs of other observed annual
maximum flood events are shown in grey. The
units on the x‐axis represent the number of 15
min time steps.
The maximum discharge (measured in cumecs
or m3/sec) during the 2009 flood event is
about seven times greater than the mean
annual peak flow and over double any
previous flood event.