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The report on flooding in Chipping Campden, 20/21 July 2007

(From the Chipping Campden Bulletin. Reproduced with kind permission of Jeremy Green)

Report by D J Atkinson

Preamble

Chipping Campden is peculiarly susceptible to flooding when prolonged heavy rain or sudden thaws occur in an already sodden catchment area. To a large extent this is due to the size and peculiar character of the catchment area, most of which drains into the river upstream of the Care Home and Guild site and Sheep Street It is also due to the confinement of The Cam's channel and choke points through the town.

In the recent past, serious floods occurred in the wake of long periods of bad weather affecting the region usually in winter, 1947 and others, but also in July 1968. Park Road has suffered from lesser floods periodically, especially in the 50s and 60s, the last in spring 1993. Obviously drainage has become a much more concerning problem for the town over the last century and particularly over the last 50 years with much new building (spreading and infilling), property improvement, the raising of road levels and much more hard standing. The situation has also worsened due to changes in land use, farming methods and land drainage in the area.

Much attention was given to clearing the channel of The Cam after bad experiences in the 50s and the bed was deepened in some places. In the 70s the Landgate drain was added to help the stream from Westington and alleviate the risk in Sheep Street.

Much more was done after freak flash floods in 1982 when local storms, first in June and then more dramatically in July, caused monsoon-like downpours on hard-baked land around the town. On the 14th July, about 3 inches of rain fell in 2 hours. All gutters and drain courses were soon overwhelmed as floodwater cascaded off the Hoo and on all hard surfaces. The Leysboume end suffered particularly badly. Over 140 properties were flooded in all. After that, major improvements were made to the main piped town drains taking the Scuttlebrook (Aston Road and Leysboume) under Bedfont House, the streams from Back Ends/Hoo Lane/Littleworth under Park Road, and those from Westington and Catbrook/The Green side to the Landgate drain. Much beneficial clearance of the channel of The Cam was also done.

Meantime, the community has not taken enough care of the channel of The Cam and there has been mounting public concern about lack of response to blocked drains and inadequate care, clearance and maintenance of all drains and watercourses. Then came the flooding on 20th July 2007 - the worst inundation in living memory.

Purpose of the report

This report aims to record how the flood developed in the town on 20th July 2007 and identify the needs for action revealed by these experiences. It is intended to inform townspeople and help the local authorities to consider action to improve watercourse and drain clearance/maintenance, and to prioritise works to increase the storm capacity of the Cam's channel. It should also aid review of plans for warning, emergency action and management of flood crises by the town and district councils.

This report does not address the damage caused to property or the impact of this flooding on the wider area downstream where there was much devastation of crops and farmland from Station Road out to Pudlicott Mill and to Paxford.

Assessment

Building development, particularly over the last fifty years, from Westington Mill to the water meadows beyond Campden Mill, has greatly increased the vulnerability to flooding along this constricted reach of the Cam.

Without the drain improvements made in the 1980s the flooding on the 20th July would have been much worse. Drainage at the Leysbourne end took the floodwaters quite impressively. At the other end of town, however, where the run-off from a wider catchment area and from a more built-up sector of the town was far greater, the drainage was overwhelmed. The Cam's constricted and hemmed in channel simply could not carry the waters away to the water meadows and widespread flooding was caused by excess surface waters that could not get into the Cam, and river overflows caused by backing up at the several bottlenecks. It must be stressed that there was no backing up from the water meadows downstream of Campden Mill as these are well below the problematic reach of the river through the town and they did not flood. The main reasons seem to be fairly obvious:

The dire state of the west reach of the Cam from Westington Mill to the twin culverts under the Silk Mill. This is due to the narrow culvert under Blind Lane and limiting surface water drainage in that area, and the poorly maintained river channel.

The age-old inherent limitations of the twin culverts through the Silk Mill Site. In really bad weather conditions, the river has always backed up here. Increased run-off upstream, now also including the Care Home, exacerbates the core backing-up problem at this critical stage in the channel. A bypass facility is essential here.

The town drain from Littleworth. This discharges under Park Road, at about 75 degrees into the river channel at low level and backs up alarmingly. This drain alone threatens flooding, in extreme conditions, in Park Road.

The Care Home. This is part of the added building problem but it has not affected the Cam's channel and it has surface water attenuation in the form of a large holding tank beneath the courtyard, the purpose of which is "to reduce the risk of creating or exacerbating a flooding problem": the tank and its size was requested by the authorities as part of the planning permission. The rare and extreme 20th July conditions, not anticipated in this process, did cause the Care Home to flood badly and there was some excess of surface run-off.

The inadequacy of drainage in Sheep Street and Cutts Yard. In extreme conditions the surface water and incoming floodwaters from upstream cannot easily get into the river and get away. Accumulation here must be relieved.

The dire state of the Landgate drain, its junction with the Cam, and the river channel itself down to and past Campden Mill. Both channels are choked and a much wider, deeper and clear-sided channel is needed all the way to the water meadows - at least to the full capacity of the culvert under George Lane. If all that is not enough, another large town drain needs to be driven from Cutts Yard down Coldicott Close, along Calf Lane and into the water meadows in order to relieve the Cam.

Nobody, therefore, should be under the illusion that the town's drainage situation has been made satisfactory. Properties lying low and close to the river are at serious risk of flooding if and when conditions similar to those on 20th July occur again. This is the second such flood in forty years and given current global warming and weather trends, the probability of recurrence in the next few years must be high. The town, however, can be glad that the Cotswold district council (CDC) already acknowledges the exceptionally "at risk" situation in the town. This is expressed in its current policy statement on flood defence as follows: "3.6. We have agreed with the Environment Agency that within the council's area there is 1.5 km of 'critical ordinary watercourses; ie watercourses which are not classified as 'main river' but which the council has agreed with the Environment Agency to be critical because they have the potential to put at risk from flooding large numbers of people and property. The watercourses concerned are the Cam, Chipping Campden at Sheep Street and the Silk Mill and a tributary, where culverted, beneath Bedfont House, High Street".

This should surely extend to the whole watercourse through the town from Westington Mill to the water meadows and include the tributary from Hoo Lane that is piped and culverted under Littleworth and Park Road.

The call for action

The basic need is to achieve and maintain a good cleared state of the drains and both sectors of the river channel. Flooding of property should then only threaten in extremes of weather conditions following reasonable warning and with relief work in operation. Even so, drain heads and covers at low level must be expected to back up in these conditions.

Complete protection against the worst of ground and weather conditions is not a realistic expectation. However, there is much that needs to be done to improve the situation and reduce the risk and extent of flooding in the worst of situations.

First, cease adding to the risk of flooding. To achieve this action is needed:

  • By the Cotswold district council (CDC) to curtail development in all the area that drains into the Cam west of the bridge in George Lane. Much of the land is not for development anyway and infilling has peaked. There should be no new building development on the brown field sites from Cutts Yard across to the petrol station site until main drainage concerns have been resolved,
  • By the town council to form a volunteer river warden team to inspect main channels regularly and organise clearance of obstacles/rubbish. The same team could have important duties, alongside the fire brigade and helpful local farmers, when flooding threatens/happens.
  • By CDC/Sevem Trent/County Highways to achieve a much higher level of clearance and maintenance of culverts, ditches and drains in Campden.

Second, resolve evident flood resilience problems and make improvements. There may be a possibility of increasing floodwater retention in the valley below Campden House. The practicality of improving retention around the old swimming lake may be worthy of investigation. The dam here, where a sluice gate used to operate, could be extended effectively - but at what cost?

The greatest concern is the achievement of real improvements to drainage along the whole channel of the Cam through the town. The need, put simply, is to clear the way for high volumes of floodwater to get through the town safely and accumulate, where they must have done in the past, on the flood meadows below Old Campden House. Their release from there could be controlled if necessary.

Third, improve local readiness and emergency action when flooding threatens. The town council should review preparedness to respond in the event of a serious flood warning. This should include calling on a voluntary river/drains warden team to carry out pre-arranged emergency checks and clearance. Householders of properties in the "at risk" areas should consider flood boards and readiness to fend off floodwaters but riparian dwellers should seek advice before altering features on the banks of the river. Everyone concerned needs to be vigilant to prevent builders waste and garden and other rubbish being tipped into the channel or being left around and vulnerable to being swept into the channel by floodwaters.

Fourth, make appropriate arrangements for relief work. Thankfully, a great deal of praiseworthy work was done by local firemen and other volunteers, not least from local farms, and by called in fire and rescue services. The effectiveness of all this is not addressed in this report No doubt this will all be assessed and reviewed by the town and district councils.

About seventy-five percent of all the drain off from the wider catchment area, together with a good slice of the now much more built up town, has to get into the Cam upstream of the new Care Home and old Guild/Silk Mill site. These flows are then joined by run-off from the Westington side and the middle of the town all before the river passes George Lane.

The channel of the Cam through the town is unevenly canalised varying from concrete walls to ordinary field and garden banks, and from as little as one metre in width to about three metres. It is not deep and it tends to be silted-up and hampered by rubbish as well as by encroaching owner- built features and field/garden overgrowth; in fact its passage is quite tortuous. There has not been enough control of this waterway for years and carelessness within the community has not helped.

The capacity of the Cam - is inescapably limited by the old twin, sixty metre long culverts under the Guild/Silk Mill. Properly cleared, these provide a total drain access of about 1.8 square metres: unless and until an active bypass channel can be created, floodwaters will always back up here when the river is in spate, spreading on to the surface of the land and invading properties. The other striking features are as follows:

  • The generally much higher banks on the south side of the river except around the Care Home and Sheep Street. These shape the flow and retention of floodwaters spilling from the Cam.
  • The critical under-capacity of the river culvert under Blind Lane that causes back-up as soon as the river is high. The long high stone wall over the culvert at Westington Mill then diverts floodwater away from the river.
  • The inadequate bridge culvert at Sheep Street that seems to have even less capacity than the twin culverts under the Guild/Silk Mill. This is due to the lower inner arch span and an exposed pipe across the channel.
  • The extensive barrier, to the passage of floodwaters, caused by the wall along the west side of the new care home at the Guild/Silk Mill and another extensive barrier caused by the buildings and connecting walls along the whole east side of Cutts. In these two places there are no by-pass channels for the Cam - where there is most need. A by-pass in a pipe should be driven from the river, under the Craves Field behind the care home, along the south side of the home and under Sheep St to join the Landgate Brook and so back into the Cam well beyond Sheep St: this will greatly reduce the volume of water forcing its way through the Guild/Silk Mill culvert and the Sheep St culvert. A second pipe should be sent from the river, just past Sheep St, and through Cutts yard, Coldicot Close, Calf Lane and on to the water meadows.

Recommendation

It is recommended that the town council should adopt this report and together with their observations/ comments, forward it to the district council for their action. It should form part of what is to be presented by the district council to the Environment Agency, the water authorities and Gloucestershire county council for their consideration of priority flood resilience planning,

D J Atkinson.

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