Guildford Borough Council's Land and Surface Water

GUILDFORD BOROUGH COUNCIL’S LAND AND SURFACE WATER DRAINAGE REPORT

FEBRUARY 2007

1. HISTORY. Areas of Pirbright are low lying and susceptible to localised flooding. During 1968 a summer storm caused wide spread flooding in the area, particularly at the junction of Mill Lane and Guildford Road. The banks to Hodge Brook were raised to prevent water discharging onto the road and flooding houses. During 2000 there were floods on large areas of agricultural land and in localised areas where watercourses were unable to cope with the severe conditions. The rising ground water levels created problems behind Gole Road, Church Lane, The Gardens, Mill Lane and Vapery Lane. The ponds also began to overflow

2. RESPONSIBILITIES. Guildford Borough Council, as the Land Drainage Authority for the area, maintain a large number of open and piped watercourses in Pirbright. This is as the landowner and in the public interest using powers under the 1991 Land Drainage Act. These maintenance duties have been taken on to ensure that critical watercourses are maintained to a high standard. These watercourses remain the responsibility of the owners. Other sections of watercourses, including agricultural ditches, culverts, pipes and ponds are the responsibility of the riparian owners. There is a duty on each owner under the 1991 Land Drainage Act to maintain this infrastructure, accept the water and pass it on. Other organisations that have ownership and duties in this area are the Highway Authority, Surrey County Council Highways, Thames Water responsible for the foul and surface water sewers, the Ministry of Defence as large landowners in the area, Network Rail and the Basingstoke Canal Authority. The Basingstoke Canal Authority has a duty to manage the sluices on the canal in such a way that the discharges do not surcharge the local watercourses. The Environment Agency is responsible for Main River including both the Rivers Wey and Backwater.

3. STORM OF 13TH AUGUST 2006 This storm deposited 85mm of rain on an area centred on Surrey Heath in two hours. This included Pirbright who received both the rainfall and the drainage from watercourses that drain a large part of the storm area and the run from a huge catchment area. This was a one in hundred year event. These storms are unpredictable, where they occur, their intensity and their frequency. Surface water systems cannot be built for storms of this intensity. All that can be done is to ensure that all systems are maintained to a standard that will limit damage. With climate change it is likely that there will be an increase in this type of storm in the future.

4. GUILDFORD ROAD, PIRBRIGHT. Extensive flooding was caused to properties on the section between Hodge Brook and Aldershot Road, (residential and commercial properties). Investigations have shown that large volume of water accessed Mill Lane from the adjacent watercourses, arable land and culverts and flood water ran down Mill Lane and flooded Guildford Road. The highway drainage was unable to cope with the volume of water. This lead to the flooding of the area. The highway at the junction of Mill Lane with Guildford Road flooded and was unable to escape as the road drainage that discharges into the Hodge Brook at this point was blocked. To improve the drainage in this area Guildford Borough Council had the 450mm diameter culvert that discharges from Guildford Road to behind Ganavan and into the ditch across Law Meadows pressure jetted and cleaned. The owner of Law Meadows has had the ditch cleaned and desilted. The 225mm pipe from Colleens Field connecting into this system has also been cleaned. Surrey County Council will be raising the road crossovers in weak areas to help prevent water running off the highway into properties. They have also cleaned all the road gullies and pipes. Guildford Borough Council have met some owners and farmers in the area and worked with them to have watercourses cleaned, trees removed and desilted. This will substantially increase the capacity. At present only approximately one third of the catchment area has been cleaned in this way. The benefit of this is to control the watercourse flows and prevent water leaving the channels and flooding roads and properties. Consideration is being given to further small flood defences when funds are available. Surrey County Council Highways are considering the installation of a road drainage system in Mill Lane. This will be composed of road gullies connected to larger pipes that will discharge into the Hodge Brook. This will permit the reinstatement of the bank The bridges and culverts crossing the road will have ‘flood sluices’ fitted to allow water on the highway to escape into the watercourses. Consideration is also being given to re-engineering some footpaths to raise them and prevent water flooding into properties. The residents of the service roads should ensure that their highway crossovers are improved and surface water drainage upgraded to prevent further flooding problems. It is considered that if maintenance of drainage systems is increased, all watercourses are reinstated and the items of improvement to flood defences are installed, the risk of flooding during normal storm conditions will be reduced. Guildford Borough Council has made a stock of sand bags that is available locally.

5. GUILDFORD ROAD TO CHURCH LANE This is mainly agricultural land. This tributary of the Hodge Brook had become restricted b y neglect over a number of years (trees and silt). A section was piped in past years. The local Farmer, Land Owners and Council have worked together to restore this area and improve capacity. This is a critical area for inspection and maintenance. The watercourse flowing from Pirbright Common past Thompsons Close via a culvert down Church Lane to discharge adjacent the Church, has presented a number of problems in recent years. The watercourse was diverted and piped down Church Lane after past problems with flooding. This pipe continuously blocks with silt and causes severe flooding to the highway. There is a problem with rubbish and garden refuse being thrown into the watercourse. A and a section that was recently piped and now requires re-engineering. Guildford Borough Council own some of the common land in this area and carries out some maintenance. There have been no reports of flooding to property in this area. During the summer when weather conditions permit Guildford Borough Council will carry out a small catchment study of this area followed with small works to improve the flood defences. It is considered that the small flood improvements with regular maintenance, the cooperation of local owners and residents that the recent instances of flooding can be substantially reduced.

6. THE MANOR TO PIRBRIGHT COMMON. The Hodge Brook runs through this area and has several tributary watercourses. Guildford Borough Council maintain the main channel up to the access road from Apple Tree Cottage despite not knowing the riparian owner. From The Manor and parallel with the main channel there is a secondary channel running parallel to the Hodge Brook. This takes drainage from the local agricultural land and acts as a bypass channel when the Hodge Brook is surcharged or blocked. This channel has been cleaned and desilted by the Land Owner, which will improve capacity and act to balance flows. There is no connection to the secondary channel from Manor Farm at the junction with the access road from Apple Tree Cottage. At this point the secondary channel stops. Over the access road the Hodge Brook splits again. One section runs towards West Hall Farm and the other to two channels that flow towards Pirbright Common via Vine Farm. There is a very large flood meadow on the twin channel Vine Farm section. This has a large stand of trees. The sides of the watercourses have been raised, probably by depositing arising during desilting. This needs attention. Historic drawings show a pond located on Pirbright Common behind Vine farm. This is owned by the M.O.D. The pond is completely silted with self seeded willow grown and fallen. If this pond were reinstated it would balance water flowing from the common and at the same time collect the large amount of silt that is passing into the watercourses down stream. The M.O.D. and English Nature have been contacted for help and advice on restoring the pond. Two properties have flooded on this section. The Council considers that cleaning; desilting and restoring the system together with some small engineering works will reduce the incidence of flooding in the future.

7. MILL LANE During the August floodwater ran down Mill Lane and caused flooding in the village. The source of this water was part surcharging of watercourses and part discharges from agricultural land and unmade private roads. There are discharges onto the highway, particularly from the M.O.D. unmade roads leading to Pirbright Common i.e. Admirals Walk, Vine Farm. There are also farm access and residential drives that also discharge onto the road. The water travels down the road gaining volume and speed until it reaches the section adjacent Guildford Road where the road drainage cannot cope with the volume causing flooding to the highway. Remedial works include action to prevent discharges onto the high, more positive highway drainage and sluices at the culvert crossings to return water to the main channels. Surrey County Highways are proposing to re – engineer the drainage adjacent Guildford Road and restore the bund. The Council considers that, in normal circumstances, with all the water courses reinstated together with small engineering works will reduce the incidence of flooding on Mill Lane, and thus the Village.

8. VAPERY LANE AND WEST HEATH. The drainage in this lane has been a problem for a considerable time although damage is restricted to highway flooding. The local farmer has cleaned the ditches and the Council has jetted the pipes and culverts. There is still work to be done to improve the drainage in this area.

9. THE GARDENS/VILLAGE POND The Councils maintenance and repairs have reduced flooding in this area. There has been no further flooding since 2000.

10. HODGE BROOK, GUILDFORD ROAD TO FOX CORNER. One property at Fox Corner and a stable area flooded in August. There was considerable disruption at Mill House. Guildford Borough Council cleans and desilts the Hodge Brook but some side channels and watercourses were severely silted and caused flooding to agricultural land and out buildings. The owners have been advised how to protect their land and premises and the watercourses have been desilted. Managing the weir and running channel at the Mill is an important factor in this area. The Council will advise the owner who flooded on works to protect his property in the future. The Bullswater Bridge channels will be desilted in 2007.

11. NATIONAL SHOOTING CENTRE – BISLEY. Two properties flooded. Found to be uncontrolled runoff from the Centre and inadequate and blocked drainage. A scheme has been designed by the Council at no cost and now awaits the owner’s proposals. M.O.D. have been informed of the flooding from local watercourse and have advised G.B.C. that it will be cleaned shortly.