Private Client, Hampshire

MJ Abbott Limited were successful in winning the tender for both Phase One and Phase Two works at an exclusive new private residence near Alresford in Hampshire. The extensive landscaping scheme was conceptualised and designed by landscape architect Jantiene T Klein Roseboom of Imagination Design Ltd.

The site in question is of great importance in terms of ecology, a site of special scientific interest (SSSI) and also prime chalk downland which gradually falls to the River Arle. With a great emphasis on close collaboration with the Environment Agency, Natural England and many other agencies, the landscape architect had a clear vision of how the site was to be developed with a completely sensitive approach.

Imagination Design had been working and developing the site for several years prior to MJ Abbott's involvement, which had seen the creation of new flower meadows and the complete overhaul of the existing two lakes and stream network.

Phase One of the project comprised the installation of the site wide utilities to provide the infrastructure for the future development of the site. This included the drilling of three new boreholes (geothermal, potable water supply & observation boreholes). The geothermal borehole is in preparation for the heating system for the proposed new build house, and the observation borehole houses the data loggers which record water temperature and groundwater level. A new concrete reservoir was installed at the top of the site to receive water from the potable water supply borehole to provide a gravity-fed water supply to the site.

As well as installing new water mains around the site to the newly constructed timber fishing lodge, various water troughs for livestock and take-off points for irrigation, large SWA cables were also installed which would provide the eventual electricity supply to the development, once three-phase electricity is brought to the site.

Three geothermal recharge trenches were constructed along with the necessary pipework which would allow the recovery of the water used within the geothermal heating system for the house.

The existing dwelling at the site was a modest brick built cottage which required demolition by David Horton Contractors Ltd, demolition specialists. The existing sewage infrastructure which served the cottage and the neighbouring property was outdated and required a complete overhaul to meet current regulations.

A new state-of-the-art waste water system was installed which replaced the existing system for both the neighbouring property and the proposed new dwelling. 2 no. 2.8m diameter x 3.0m deep concrete balance and reactor tanks were installed using trench support equipment, and then fitted with Advanced Aeration (Bio Bubble) technology ensuring that all sewage entering the system will be treated to the highest standard before being discharged to the main river.

A second smaller sewage system was installed at the fishing lodge using 1500mm diameter concrete ring sections prior to being fitted out and commissioned by Advanced Aeration (Bio Bubble).

The Phase Two works had a large emphasis on the landscaping of the site to create the landscape architect's vision. The landscape had to be cut to create a flowing and gentle sloping plateau from the proposed house site down to the lakes.

This incorporated a large earthworks “cut and shape” with flowing curves which were met with sharper embankments to reveal the streams and lakes of the site from the proposed house location. This area was to be turfed with high quality turfs and sown with specific meadow grass seeds.

The existing chalk carrier stream which fed the lakes, and was home to many rare native crayfish, had to be moved as part of the architect’s vision. The existing carrier stream was dammed using a temporary inflatable water dam and a diversion was made back to the River Arle under the watchful eye of The Environment Agency and Natural England. As the carrier stream drained, a team from Natural England were on hand to find, remove and re-locate the native crayfish (over 30 large crayfish were found).

When the new carrier stream was excavated, over 200m in length, the new stream was lacking any chalk throughout the excavation. This new stream, all in subsoils and flints, would have rapidly suffered from wash-out and erosion, so a radical approach was decided between contractor and landscape architect.

Various methods of constructing the new stream were considered, including butyl liner and concrete lining, however none of these were environmentally sensitive or in keeping with the chalk downland site. MJ Abbott's Project Manager, Adrian Riggs, suggested that chalk be used as a liner. With very little historical reference and no real evidence of chalk being used as a liner for running water it was not without risk, however wishing to keep the site completely in touch with its surroundings, chalk worked for dew ponds so could it work for a stream?

Over 360m³ of fresh, white chalk was excavated and borrowed from the top of the site and hauled to the newly excavated stream. The stream was over-dug throughout the base by approximately 400mm (now only 50-100mm above the existing water table), and this over-dig was replaced with the newly borrowed chalk, saturated with sprinklers and compacted in layers using a Rammax (sheep's-foot) roller. This same process was repeated along the full length of both sides, before the stream was reshaped.

Due to the River Arle being so close to the site (within 15 metres), groundwater was always an issue and disturbing virgin chalk in wet ground is never advisable, however new silt traps were necessary to ensure silt would not become a catalyst for weed growth in the nurtured lakes. A new silt trap was formed using large concrete "lego" blocks to avoid major cast in-situ concrete silt traps. A similar process was used to create to create a new footbridge across the stream.

To finalise the works for Phase Two, over 600m of high voltage overhead cables had to be lowered and buried below ground. Working closely with SSE & BT, all the overhead cables were buried, enabling the site to provided with a new three phase power supply. GRP control kiosks were installed as the main housing for the meters and electrical distribution was installed in accordance with NICEIC regulations.

MJ Abbott's clients said: "We were so thrilled by our visit to site last week. The landscape looks truly fabulous. The forms and shapes are really great, very natural-looking but very usable. It is a triumph. Thank you so much for all your work on it. Now we just need a house....!"