Trent River Authority Flood Defence Report Gunthorpe 1981/2 Introduction 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 accruing. 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 purposes. 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. General 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 Lane. 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. Problem 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 raising. 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. thinking.