Specialist geotechnical contractor Bam Ritchies has completed a six week ground investigation as part of work to safeguard Hampstead Heath’s “beautiful and much-loved ponds”.
Ritchies undertook the work for parent company and main contractor Bam Nuttall for the City of London Corporation to establish the risks of failure on the earth embankment dams which retain the 30 ponds on the heath.
The ground investigation included trial pits, windowless samples, dynamic probing, restricted access cable percussive boreholes and overwater boreholes at 140 locations with exploratory holes ranging in depth from 3 to 15m deep.
A lightweight modular pontoon was used to carry out the overwater boreholes on the model boating pond using a cable percussive rig, which remained on the pontoon for a week.
City of London Corporation has been consulting on the works needed to prevent the dams that form the ponds from failing in extreme rainfall and major storms on the advice of its supervising engineer to minimise the risk downstream.
A brief storm in 2010 resulted in the stock pond overtopping with earth scoured away from the top of the dam, which combined with three of the largest ponds being classieifed as large raised reservoirs under the Reservoir Act 1975.
Despite hydrological analysis which showed that both chains of pond dams could fail in an extreme storm, putting at risk, lives property and infrastructure in North London, local opposition had been vocal.
The City Corporation has been consulting on the Ponds Project since July 2012 and finished a period of more formal public consultation in February 2014. This consultation was focusing on design options and the results will influence the final chosen design. There will be a further consultation when a detailed planning application is submitted.
The results of the ground investigation will be used to design the £15M Hampstead Heath Ponds flood prevention dams project, which is expected to take 18 months to complete.