Trent River Authority Gunthorpe Flood defences

Trent River Authority
Flood Defence Report
Gunthorpe 1981/2
The village of Gunthorpe lying in the Trent
floodplain to the north of the river and east of
the A6097 is subject to infrequent flooding.
The properties requiring protection are spread
over a large area making schemes for
alleviation costly in relation to the benefits
Extensive mining subsidence and the
consequent flood protection works upstream of
Gunthorpe will result in somewhat less
frequent flooding in the village, which will not
be itself affected by subsidence. The TRA
Radcliffe to Gunthorpe hydraulic model
predictions of probable flood levels and
frequencies under post-subsidence conditions
were used to assess benefits and for design
The properties to be defended fall conveniently
into four distinct areas, three separated by
corridors of washland which must be
maintained if flooding upstream is not to be
worsened. Only one of these areas can be
protected at an economic cost, but it is
regarded as an environmentally sensitive area
where the perceived disadvantages of a flood
protection scheme to amenity will probably
outweigh the expected alleviation of flooding.
Gunthorpe village lies in the northern
floodplain of the non-tidal River Trent some
eight miles east-north-east of Nottingham. The
majority of the development, Main Street, is
immediately north of the river and east of the
A6097 main road. The historic and predicted
pattern of flooding of this area suggests that it
may be sub-divided into two areas viz. Main
Street (north) and Main Street (south). Also
there are two other areas where there is a
history of flooding and which may be
considered as separate problems, namely “The
Park” lying along the eastern edge of the A6097
and north of Main Street; and further north
and to the west of the A6097 Cottage Pasture
The intervening corridors of land, in addition
to separating these areas geographically,
contain washland flows which must be
maintained if flooding upstream is not to be
aggrevated. Relatively little washland flow
occurs to the south of the river where the
floodplain rises steeply and the A6097 is
carried across it on a high embankment to
Gunthorpe Bridge.
Mining subsidence will occur extensively in the
next few years to the west of the A6097
requiring remedial works to protect
agricultural areas between Radcliffe and
Gunthorpe. It is understood that, owing to
geological difficulties, the A6097 and the area
to the east will not be undermined.
Cocker Beck joins the Trent on the north bank
just upstream of Gunthorpe Bridge and runs
parallel to the A6097; however its contribution
to flooding is considered negligible compared
with the Trent.
During periods of high discharge in the River
Trent, mainly residential properties are
affected by floodwaters in the areas of Main
Street (north and south), The Park and Cottage
Pasture Lane. Other isolated properties are
also affected eg. Grange Farm and The Cedars
to the west of the A6097, opposite The Park.
The A6097 is also severed at times of severe
of sluices at Gunthorpe weir there would be an
flooding, but in view of the importance of the
unacceptable rise in water levels. Sluices,
floodways to levels upstream it would be
probably similar to those at Colwick, would
impossible to raise the general level of the road
prove exorbitantly expensive.
without providing flood arches, a measure
which would prove far too costly in relation to
Design Proposals
the benefits achieved.
The need to maintain floodways limits the
range of possible solutions to local
TRA Hydraulic Model
floodbanking at vulnerable points. Larger scale
In the late 1960s a physical model of the River
works to divert flows from the northern
Trent from Radcliffe railway viaduct to
floodplain would require substantially greater
Gunthorpe was constructed at the then
benefits than those at Gunthorpe alone. Since
Authority’s Trentside laboratory. Its purpose
proposals for remedial works upstream of
was to examine the effects on flood flows of
Gunthorpe have already been made, it can be
likely future subsidence and the possible
assumed that any benefits available in those
consequent remedial works.
areas will have been accounted for.
The major conclusions to be drawn from the
results of the tests in relation to flooding at
The suggested works for each area are
Gunthorpe are as follows:-
summarised below:-
[a] With the maximum expected degree
Cottage Pasture Lane
of subsidence and the remedial works
proposed in the model report
The works envisaged comprise a floodbank
constructed, the general flood levels in
along the southern edge of Cottage Pasture
Gunthorpe village will be reduced by up
Lane tying into the Cocker Beck floodbank at
to approximately 150mm. This is based
the western end and turning northwards along
on the National Coal Board’s prediction
the western verge of the A6097 for some 80M.
that no mining will take place under the
The top level of the defence would be 18.90M
village itself.
AOD and the total length 230M.
[b] The level of the A6097 north of the
Cottage Pasture Lane itself would have to be
river is an important factor in
diverted for a length of 70M at its eastern end
determining flood levels upstream
to take it over the proposed floodbank. Access
especially in the Shelford and Burton
ramps to 7no. properties along Lowdham Road
Joyce areas. The existing low areas
would be provided.
must be maintained, or alternatively, if
the road is raised in these areas flood
There are several service manholes, lamp-
arches will have to be provided.
standards etc. along the verge of Lowdham
Road which would require repositioning or
The possibility of diverting flows through
arches to the south of the bridge was examined,
but it was concluded that without the provision
The Park
Main Street (South)
As the majority of the affected properties
A floodbank, top level 18.30M AOD would be
lie along the eastern verge of the A6097 it is not
required running west to east between the river
possible to construct a floodbank on the side of
and Main Street. At the western extremity the
the road. A floodbank on the western verge
bank would be tied to the embankment of the
would require ramps across the road to
slip road from the A6097. It would then run
maintain the height of the defence and these
along the river’s edge to the south of the
would be unacceptable on such a busy road. It
Unicorn Hotel and water-ski club carparks
is concluded that the only physically feasible
before turning northwards across Main Street
scheme would involve raising the road itself as
at the eastern boundary of ‘Holme Port’ to tie
a defence over a length of some 600M to a
into high ground to the rear of that property.
height of 18.90M AOD immediately opposite
The length of the proposed embankment would
the properties. This would not affect the
be approximately 350M.
floodways to the north and south of The Park.
In order to maintain access to the water-ski
To complete the ring defence a further 1000M
club’s launching ramp a pait of steel flood gates
of floodbanking would be constructed along the
is proposed, of overall width 4.5M and height
northern, eastern and southern boundaries of
1.6M. Main Street would have to be raised
the area tying in at the ends of the raised
locally to carry it over the floodbank adjacent to
section of the road.
‘Holme Port’.
Main Street (North)
The works required at this site would consist of
a floodbank to the rear (east) of properties east
of Main Street, tying in to high ground at the
caravan site in the north and Davids Lane to
the south. The top level of the bank would be
similar to those of the other sites and the
length would be about 400M.
Two lengths of road raising would be required
on Main Street (120M) and Peck Lane (40M).
The former would be raised by a minimum of
0.5M, the latter by up to 0.9M. Peck Lane is an
(Edited extract September 2001)
unmade road at this point.
Note: A number of detail points have changed
since the report was written – primarily the
To the west of Main Street a 240M length of
building of properties on the flood defence line
floodbanking would be constructed to the rear
in Thorpe Lea. The Trentside barrier height
of properties between The Paddock and
appears too low at 18.30mAOD on modern
Brooklands Close.