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1 Possible Submission about Water and Flooding (See maps 3a and 3b) From Mole Valley Local Development Framework: Strategic Flood Risk Assessment Update 2012 ( and associated maps for Bookham referred to below found here: Some Points from the MVDC Flood Risk Assessment and Maps Bookham Fields (BK 05a, 05b, 05c) and Commonside Area (FT 10) are in a Groundwater Source Protection Zone 3 Bookham Equestrian Centre (BK04) is mostly in a Groundwater Source Protection Zone 2 Groundwater Source Protection Zones indicate areas of known high ground water levels (so are susceptible to ground water flooding) as well as indicating areas that can recharge a water abstraction point (in this case, in Leatherhead). According to the MVDC report Strategic Flood Risk Assessment 2012 Update the conclusion was that the risk of groundwater flooding on these sites was low, but recent heavy rainfall has shown that this conclusion was misguided. Development should not be considered on any of these sites due to the risk to property from groundwater flooding combined with a moderate to high probability of it occurring. Ground water flooding is flooding that occurs as a result of high ground water levels, typically in winter. It can be very slow to clear, as ground water levels fall very slowly and can take weeks or even months to clear. It is not the same as surface water flooding which can be caused by blocked drains and culverts and by springs flowing onto a road; so ground water and surface water flooding occur together. This appears to be quite common in Bookham. This quote is taken from section 6.21 of the MVDC report which discusses the likelihood of groundwater flooding..there are areas at risk in Mole Valley, especially to the north of the North Downs where the chalk meets the clay, sand and silt of the Lambeth Group and Thames Group (London Clay). This is exactly what is happening in the area of the A246 to Lower Road, and beyond. Consequently none of the sites in this area should be considered to be suitable for development as ground water flooding would be a considerable risk to property and would be combined with a moderate to high probability of it occurring. Note that Lower Road is the approximate location of the edge of the unconfined chalk, so this is roughly where chalk meets less permeable strata, giving rise to the numerous springs. As the layer of chalk thins, there are likely to be pocket deposits of other strata, so that this area is geologically very complex. This creates localised issues, such as the emergence of springs, which can result in surface flooding but the source of the flood is ground water.

2 Suitability of Sites for Building When there is development on areas that are above chalk, there are four negative factors to consider The development footprint - dwellings, footpaths, roads, garages, etc prevents rain from being absorbed by soil and then chalk. Chalk is very permeable and so can absorb and hold large volumes of water, with subsurface water moving slowly. Instead, rain creates run-off, which if collected by a surface drainage system will either go into a combined drain and sewer line, or possibly into what is called a Sustainable Urban Drainage System. The design of these SUDS varies and they may enable collected run off to be absorbed into the chalk via some form of soak away. However, without maintenance, drains become blocked and surface flooding can result. In addition, SUDS systems are designed to a limit, but in very heavy rainfall they can become overwhelmed and again this can cause surface flooding. Gatwick Airport has large systems to reduce the impact of floods but these were overwhelmed twice in 2013 problems in the South Terminal in October and North Terminal on Christmas Eve were due to flooding. Gatwick has now committed to spend approximately 15 million on expanding water collection and storage systems. Several sites, BK04, BK05a, BK05b, BK05c are on groundwater protection zones. These have a role to play in recharging the aquifer that Leatherhead sources its fresh water from, as shown on Bookham map 3a. Building on chalk that has a role in recharging this aquifer will reduce the recharge rate - and the larger the scale of development the greater the impact. MVDC is in an area of water stress, that is, it is difficult to increase water supply. Under these conditions it is folly to build on any areas that help to recharge aquifers that are being used for water abstraction. During the last month 18 sink holes opened, and the British Geological Society have predicted more will occur in coming months, due to weakened underground layers of rock that may collapse. According to Dr Tony Cooper of the Royal Geological Society, chalk is especially vulnerable to this, as it dissolves more easily. Consequently, building on chalk makes little sense. Building on other sites may not make much sense either. Villages were originally built along the spring line that stretches across Surrey East and West Clandon, East and West Horsley, Effingham, Little Bookham, Great Bookham, etc because water was available. This is the line where permeable chalk meets less permeable layers a thin ribbon of sand, another ribbon of silt and then the large area of London Clay. Clay is much less permeable than chalk and so as ground water flow is from south to north (and the land falls from the Surrey Hills to Bookham Commons) ground water emerges where chalk meets the less permeable clay the spring line. Building in this area can also create problems, as springs can emerge anywhere. One house in Little Bookham Street had a spring emerge in their lounge. Surface water flooding has been fed by springs, along Lower Road at the recreation ground and at the junction with Manorhouse Lane. Springs emerging on Manorhouse Lane have caused considerable damage to the road so building on the spring line could create problems. The approximate line where chalk meets clay is just south of Lower Road, so the spring line is in the vicinity of BK 05d, BK 18, BK 22, and BK 12. The underlying geology is just not suitable for development on these sites.

3 Preston Cross Farm (BK 12) Recent floods have shown that the Bookham flood risk maps (3a and 3b) created as part of the MVDV flood risk study are inaccurate, for example, many springs have emerged along the length of Little Bookham Street, and in one case, in one of the homes in Little Bookham Street. Yet no risk from flooding is shown on map 3b. Perhaps even more surprising is that flooding that the council should be aware of (at the junction of Manorhouse Lane and Lower Road) is not on the map. The source of ground water varies as it can travel large distances, but ground water from Preston Cross Farm probably contributes to flooding on Little Bookham Street. Consequently, Preston Cross Farm should not be considered suitable for development due to ground water flooding risks and the increased risk of flooding along Little Bookham Street if this site were developed. Localised changes in geological strata such as drift deposits of clay in the chalk formation probably occur along Little Bookham Street and on the Preston Cross Farm site. Changes such as this would contribute to the flooding observed there. The general direction of ground water flow is to the north, but this is influenced by the topography of the site the lie of the land. No contour lines were given in the maps of proposed sites provided by MVDC making an assessment of the topography difficult. Both topography and local geology are important in determining the propensity of a site to flood. Two profiles of the site are given below, using a commercial mapping tool to produce the profiles. In the MVDC site description it was claimed that The land slopes down from all boundaries towards the ponds in the centre. These profiles show that this statement is incorrect; the land slopes down south to north with a fall of about 8 metres and also falls away, east to west, towards Little Bookham Street, with a fall of over 6 metres. This elevation profile is south to north across Preston Cross Farm from Lower Road to Fox Lane, showing a fall of about 9 metres. Ground water flow is also south to north and this combined with changes in the permeability of sub strata and the fall in elevation will cause ground water flooding along the northern part of the site. At the southern edge of the site (Lower Road) the sub strata is chalk which is very permeable, changing to less permeable strata (such as impermeable London clay or Lambeth group) somewhere before the northern boundary (Fox Lane).

4 This figure is the elevation profile across Preston Cross Farm, west to east; from the public footpath north of Water Lane to Little Bookham Street. Again, the combination of geological changes and the fall is likely to give rise to ground water flooding in the eastern part of the site, and photographs taken by residents show that this is the case. Ground water flooding in this area has not been confined to this year and has occurred on a regular basis in previous years. Thus the risk of flooding damaging properties on this site is high, and the probability of it occurring is also high. This should eliminate this site from consideration for development. Land to the rear of 261 Lower Road (BK18) The Oast House Flooding has occurred regularly along Manorhouse Lane, at the junction with Lower Road, with water constantly emerging from the school playing field part of the Berkeley Homes proposal. This has flooded the junction completely, across both roads and footpaths, making the journey to school by pupils from Bookham walking to the Howard of Effingham very hazardous, as they walk down the centre of Lower Road, where the water depth is lowest. This is very dangerous as this road is very busy with school traffic. It should be noted that flooding at this junction is not restricted to this year, it occurs on a regular basis, showing the school playing field site is unsuitable for development. The field on the other side of Manorhouse Lane (BK18, opposite the school playing field) has also been flooded on a regular basis, and again this is unsuitable for development due to the ground water flood risk. Water also flows from this field onto Lower Road. Drains in Lower Road at the junction with Manorhouse Lane have been blocked, presumably to prevent water from entering the overloaded combined drain and sewage system. This can lead to severe flooding (due to the combined drain and sewer overflowing) which could result in flooding with raw sewage. This system must be operating well beyond its design capacity and is probably symptomatic of overloaded drains and sewerage systems throughout the area. Repeated flooding on this site should eliminate it from consideration for development. Surface flooding from spring water has also occurred in other locations though these are illustrated on Map 3b, such as at the bottom of Little Bookham Street, on Lower Road opposite the Recreation Ground, at the footpath to the Howard and at Fox Lane. Flooding in these areas occurs on a regular basis, not just this winter.

5 Land to the west of Attwood (BK14) Flood maps show that Bookham Brook, which flows close to the perimeter of Land to the west of Attwood (BK14) has been assessed as a Flood Risk Zone 3. Given that there are errors in the map, this site should not be considered suitable for development for several reasons Development in this area would increase the likelihood of debris accumulating in Bookham Brook, and greatly increase the severity of flooding alongside this site. The lower Mole (below Leatherhead) is known for its specimen fish, supporting predatory fish such as chubb, pike, perch and eels, together with some very large barbel, carp and bream Water quality in this section of the Mole is good, the large size of fish are indicative of no major pollution incidences. Increased pollution of Bookham Brook from surface run off from housing close to (and above the level of Bookham Brook) would be inevitable and would jeopardise the fish population and health of this section of the Mole. This risk, taken together with the risk from bordering a flood risk zone 3 should exclude this site from being considered for development. The topography of the land in this area favours using it as a part of a Mole River flood defence scheme, as it could form a temporary reservoir in times of severe flooding on the Mole. This would be easy to achieve with the installation of a sluice gate at the Bookham Brook culvert under the railway line. Partial closure of the sluice gate would permit the area to flood - to a maximum depth of about 2 metres, with the flood reservoir boundary approximately following the 40 meter contour line. Some reinforcement to the railway embankment would be needed, but this would be a low cost approach, providing storage for a considerable volume of water, helping to protect Cobham from future floods. This should be included in the Bookham flood defence feasibility study which has just been announced by the Environment Agency. Due to the risk of flooding and the potential for water pollution from site development this site should not be considered further for development.

6 Bookham Fields (BK05a, BK05b, BK05c, Bk05d) Flooding occurs regularly on the recreation ground, on Lower Road and the pavements just to the north of Bookham Fields. This is almost certainly due to ground water flowing across Bookham Fields,( flowing north from Godstone Farm and beyond that, Polesden Lacey) emerging from the ground where the permeability of the underlying strata changes. Foundations for buildings and roads anywhere on Bookham Fields would interrupt ground water flow when ground water levels are high, would most likely cause flooding. As a large part of the site is in a ground water protection source zone (Zone 3) it is known to be prone to ground water flooding, so there is a high probability of the site having high ground water during wet spells. Combined with the moderate to high risk of flooding (the flooding that already occurs is an indication of this risk) this site is not suitable for development and should not be considered further. Figure taken from the Environment Agency publication, the Mole Catchment Abstraction Management Strategy, published June 2007 (page 29) showing the extent

7 INFRASTRUCTURE Fresh Water Supply An important element of infrastructure is fresh water supply is it available? Each person uses about 160 litres of fresh water a day. Adding new housing developments across Mole Valley will result in a higher population and higher fresh water consumption, and Mole Valley is in a water stressed region. This means fresh water supply is limited. Given that in 2012 we had a drought order in place across much of the south east for about 6 months, it is reasonable to ask where the water will come from. The simple answer is not from the treatment plant in Leatherhead, which is the source for much of the area s fresh water. Sutton and East Surrey supply most of the region and their water is mostly from boreholes into the chalk aquifer. In 2012, the water level in the aquifer was very low, hence the imposition of drought orders. Since then it has been relatively wet, so water supply is not a current issue, but is a long term concern. Given that in the space of two years Mole Valley has experienced both extended drought and severe flooding it would seem that MVDC should plan for drought but prepare for floods. Planning for drought would mean making sure there is an adequate source of fresh water and that existing residents will not suffer more frequent drought restrictions due to an increased population. The Environment Agency report The Mole Catchment Abstraction Management Strategy discussed this in some detail. The water source for Leatherhead s water treatment plant is unconfined chalk, and abstraction impacts on the water flow in the Mole near Leatherhead. The resource availability for Unconfined Chalk is over licensed, so no additional abstraction will be permitted. Shortfalls in supply were predicted by this report, and so there must be a clear and transparent guarantee of supply before any large housing developments are approved in any part of Mole Valley. This must not be by increasing pressures on existing consumers, so that drought orders become commonplace; there must be new, adequate sources of supply. Currently, Sutton and East Surrey have plans to increase water treatment capacity at Bough Beech, but if this reservoir cannot be filled due to low winter water flow its treatment capacity will be irrelevant.