horndeanmatters

A short while ago Land East Of Horndean (LEOH) was given Outline Planning Permission. This is not full permission for a developer to go ahead and build, but only approves the principal of the number of houses, the housing density and the access points with a lot more information to be provided.

One of the areas that is of significant importance on the development that will need a lot more robust survey and analysis is the concerns from Portsmouth Water to ensure the development can be safely designed and built without affecting the public water supply.

The outline planning permission has a number of conditions attached to it, several of which require very significant works by the developer to satisfy Portsmouth Water, the EA and EHDC that the works can be carried out, and very simply if they can not, then detailed approval will not be given.

To find out more about the issues and how they might be resolved I contacted Portsmouth Water and spoke to Tracey Viney, the Environment and Biodiversity Specialist, who very kindly agreed to set aside some time to discuss this in more detail and explain the issues.

Why were Portsmouth Water concerned about the development of LEOH?

Essentially there are three reasons:

• Bechsteins Bats
• Footpaths and Access
• Water Supply.

Bechsteins Bat.

This is an endangered species and Wikipedia advises that there are thought to be about 1,000 in the UK. Surveys undertaken by a number of developers in the area have confirmed that Bechsteins bats are present in a number of woodlands around Horndean and Rowlands Castle, including at the LEOH site. The bats are protected by European law and any developer needs to demonstrate that the development will not impact the population. If not, the development cannot be permitted.

There is a strategic issue here. Portsmouth Water have plans for the Havant Thicket Reservoir which is a long term and very important future water supply site which could also support the needs of adjacent water companies like Southern Water (who are currently considering desalination plants as an option). As Portsmouth Water have considered the plans for the reservoir over the last years this has included their own significant research and study into Bechsteins bats and other ecology.

At the moment there is no evidence of a maternity bat roost on the site planned for the reservoir, but they do use the site, and the risk is the displacement of the bats due to construction work, moving them onto the planned reservoir location, potentially affecting Portsmouth Waters plans.

The LEOH development removes very few trees, and none of these affect known Bechsteins bat roosts but the detailed application will need to show more information on where the bats roosts are, their feeding / commuting areas, and that sufficient open space has been set aside to protect these areas so their habitat remains sustainable. This also includes conditions such as no flood lighting which might deter the bats. The good news is that the result of this is more public open space (about 21 Hectares or 50 acres on the site in all).

You may recall the LEOH application was delayed while further studies were carried out. This gave time for a specialist consultant to capture bats, fit a radio transmitter on the bat with a glue (that drops off after a few days) and track where the bat travels. This identifies the roosts, feeding areas and flight paths. Essentially this data was then used to design in zones of no development to be left around the remaining woodland. The final report that is submitted with the detailed applications needs to show this has been fully designed in and works as a overall strategic approach to the area to ensure that Bechsteins bats are not displaced.

Footpaths

The Havant Thicket Project is not just a water resource, it will provide a community recreational facility with access for clubs to undertake sail and canoe training, fishing, bird watching hides, cycle paths, footpaths and public parking with an information centre.

To optimise the green infrastructure opportunity the reservoir development could provide there must be good public access to Horndean. Therefore the opportunity to provide improved linkage from the existing woodland and excellent path network at Havant Thicket / Staunton Country Park via LEOH should not be missed.

Over the next 12 to 24 months the final layout of the housing and roads will develop and this will introduce opportunities to plan in a network of public accesses which will join up with Horndean, the SDNP and also tie in with the existing bridge over the motorway which will connect LEOH with Cowplain.

Water Supply

This is the important one and to explain the concerns we need to understand a little about the geology of the area, how water travels through the ground and is collected by Portsmouth Water, and the control measures that would be required.

Part of the land at LEOH is clay and part is chalk. The clay is pretty impermeable and where it is thick enough caps the aquifer very well. The chalk can act as an exceptionally good filter for water as it makes its way through the ground and water from Buster Hill that fell as rain tens of years ago is only now arriving at the Havant Springs. This is a natural resource area where good, clean water literally flows up out of the ground and is collected, treated and then made available to us all.

The drawing shows the Geological Plan where we are and the section runs through Butser Hill, Horndean and Havant Springs. You can see the area of Reading and London Clay meeting the chalk where we are in Horndean. Click on the image to enlarge.

It would be very simple to assess the risk if the geology was uniform but it is not. The layers of chalk and clay, were folded and then in part scraped away by glaciers and erosion over millions of years and this has created below ground paths (like pipeways) that allow water to flow very quickly from parts of Horndean to the springs at Havant & Bedhampton. Testing with tracing dye has shown that this can be very fast (54 hours). Vertical ‘Solution Features’ (we have heard the term Sink Holes used extensively) provide a number of vertical shafts to some of these pipeways. These fractures and fissures in the ground are relatively small in diameter, perhaps typically 4 to 8 inches in diameter. Where they appear at the surface the ground can be unstable.

These solution features could allow contaminants to enter the ground and get to the public water supply springs very quickly. Portsmouth Water have had experience of oil spills at Lovedean & Worlds End which have lead to the need to stop using the works. Nitrate and pesticides used in farming can also pose a risk to the public water supply.

There has been survey work on LEOH over a number of years associated with different development proposals and this has identified perhaps 30 ‘Solution Features’. Portsmouth Water are looking for these to be surrounded by a 10m diameter exclusion zone. For example, they could be designed in to form small areas of green space, locations for play equipment, grazing areas or left to grow wild.

As the plans evolve more robust survey will be required to ensure that the ground conditions are more fully understood and all solution features have been identified.

The drawing shows the location of the known ‘Solution Features’ (the coloured dots) and these will need to be properly surveyed and coordinated into the detailed plans. The area of clay and chalk can be seen on the plans.

The construction phase is also a key issue. How the foundations are built is of significant interest to Portsmouth Water, as piling operations could have an impact. It does not take a pollution incident in this sensitive area to close the springs. The simple action of drilling boreholes or piling for foundations in to the ground can cause particles to be released in to the groundwater causing turbidity. These particles can interfere with the water treatment process, slowing down the filtration process and reducing the effectiveness of disinfection. Previous drilling operations at Horndean close to junction 2 of the A3(M) have resulted in turbidity problems at the Havant & Bedhampton Springs. (Photo)

Some of the control measures will be to prohibit piling on Hazleton Farm. Parts of Pyle Farm or North of Rowlands Castle Road which are over clay are less affected by this, especially where the clay is deeper, provided the piles do not penetrate the clay in to the chalk.

The risks need to be considered not only in the construction phase (which would hopefully be well controlled) but also once occupied. The drainage for the local roads will need to go into separate pipes (storm water drainage) and pass through petrol interceptors before going into balancing ponds.

The next steps then are for the developer to agree with Postsmouth Water the additional survey work, then carry it out and then submit clear construction methodology plans which address every concern in full. If this is satisfactorily achieved then this would address the conditions for detailed planning to be granted. The main control measures for this are a presumption against building in vulnerable areas, for example within 10m of a sinkhole and a presumption against piling or any form of ground improvement (vibropiling) to prevent the water supply becoming turpid.

The detailed applications will also give further opportunity for Portsmouth Water to consider the control measures to be included as planning conditions.

The outline permission has a large number of conditions which were put forward by Portsmouth Water and the Environment Agency and which have been incorporated into the approval which must all be addressed prior to any detailed permission being given. If they are not, then EHDC will not be overruling the Water Company and the developer will need to work on their plans again to submit robust schemes which will address the risk.

Looking further forward, the proposals for the Havant Thicket Reservoir would provide a colossal water supply that would give Portsmouth Water a buffer they do not currently have and a resource that can be shared with adjacent water companies who are stretched, as well as an excellent community facility for us to use. A blog on this will be published later this week.