CAMBRIDGE AS GEOGRAPHY - CASE STUDY: RIVER HARBOURNE.

1. RIVER FLOOD EVENT
HARBOURNE
EXAM CASE STUDY
AS GEOGRAPHY - HYDROLOGY

3. INTRODUCTION
This case study follows precisely the Cambridge AS 2019 syllabus requests
for the “Hydrology and Fluvial Geomorphology” case study.
Candidates must study a recent river flood event showing the causes of the
flood, impacts on both people and the environment, and evaluate attempts
to reduce the impact of the flood.

4. 21 FLOODINGS IN 60 YEARS
As far back as 1938, the rural Devon
village of Harbertonford has recorded
regular flooding. In the past 60 years
the village has been flooded 21
times.
The River Harbourne flood defence
scheme was constructed in 2002 to
combat regular flooding of properties
and access roads to the village.
It is not a large scale construction but
it is one of the best examples of
sustainable river management in
Southwest England.

5. THE NATURE OF FLOODINGS
The flashy nature of the
catchment means there
is little warning for the
residents of the village
to prepare for the
flooding and the misery
it may cause.
One elderly resident of
the village had resorted
to living solely on the
upper floor of her
house.

6. WHY DOES THE RIVER
FLOOD?
The River Harbourne is a small
river tributary of the River
Dart, in Devon.
There are a number of
reasons for flooding.

7. PHYSICAL FACTORS
There has been an increased frequency in the number of intense
rainfall events.
The river starts 350m above sea level on the impermeable granite
bedrock of Dartmoor.
Dartmoor receives 2020mm of rainfall annually, twice as much rain
as lower surrounding coastal areas.
The river cuts through steep narrow valleys on to slate bedrock
descending 300m in 12 km.
For the size of catchment the river has a high drainage density.
The village of Harbertonford lies at the confluence of 3 rivers – the
River Harbourne, the Harberton Stream and the Yeolands Stream.

8. HUMAN FACTORS
Many properties are built on the
low-lying floodplain in the
central area of the village.
The A381 road has been
widened over the years to cope
with traffic pressures, increasing
the amount of runoff flowing
directly to the river.

9. MANAGING THE RIVER
Harbertonford is designated
as a Conservation Area and
several listed structures,
including the village bridge,
are contained within it.
Atlantic salmon, bullhead, sea
trout and brown trout occur in
the river and protected species
are also present within the
catchment, including otters.
Because of that, it is important
that any flood management
work should be sensitive to
the environment.

10. HARD AND SOFT ENGINEERING
The river is managed using a variety of hard and soft engineering techniques.
The aim of the scheme was to provide a range of flood defence measures
and to enhance the local environment.
As a result it was decided that the scheme should use natural local materials
where possible in keeping with the surroundings with minimum need for
maintenance.
The scheme has two main features – an upstream flood storage reservoir,
and flood defence works through the village.
This option has reduced the risk of flooding from one in three years to a
minimum of once in 40 years.

11. UPSTREAM MANAGEMENT
Wetland area and flood storage area
1km upstream from the village of Harbertonford a
wildlife area was created containing flood-resistant trees
and shrubs.
The area directly upstream from the dam will become a
41,000 sqm water storage area in times of flood.
Local schoolchildren will monitor the afforested area as
part of an ongoing partnership.

12. UPSTREAM MANAGEMENT
The Palmer Dam
Built to control the flow of the river, this mound
was constructed using locally excavated materials.
The dam gates can be controlled to restrict river
flow in times of flood.
A culvert was created to allow the free movement
of fish up and downstream of the dam, whatever
the flood conditions.

13. THROUGH THE VILLAGE MANAGEMENT
Bed-lowering
To keep the aesthetic quality of the central village
green, the riverbed was lowered to increase the
river’s carrying capacity without the need for flood
walls.
Channellisation
Throughout the lower sections of the village, along
Bow Road, a 200m wall has been created to protect
the residential area from overtopping. The river is
now twice as wide. The wall on the bend of the river
is reinforced to reduce erosion.

14. THROUGH THE VILLAGE MANAGEMENT
Storm drains
Storm drains have been added to reduce the impact of flood
water entering the main channel from Harberton Stream.
Riffles and pools
Due to the extensive work a system of riffles and pools were
created to maintain the river’s natural flow while providing a
habitat for fauna.
New culvert
A new culvert to allow water to flow under the main road
was installed to relieve pressure on the existing drainage
network.

15. FLOOD HAZARD MAP
Flood hazard mapping is used to identify areas that are
susceptible to flooding when the discharge of a stream exceeds
the bankfull stage.
Using historical data on river stages and the discharge of previous
floods, along with topographic data, maps can be constructed to
show areas expected to be covered with floodwater for various
discharges or stages.
They can also be used to highlight properties and infrastructure
at risk, which allows planners and insurance companies to
produce cost benefits analysis.