The initial application was for 376 units across two new blocks on the car park adjacent to the existing Pearson House in Harlow. The site was in Flood Zones 2 and 3, at risk of flooding from the River Stort. Around 25% of the site was shown to be in Flood Zone 3b, which meant that no vulnerable uses could be located there.
The existing Environment Agency (EA) hydraulic model of the River Lee was obtained and re-run for the 1 in 100 year (+35%CC) and 1 in 100 year (+70%CC) to confirm the critical flood levels.
Site-specific topographic survey data was used to re-run the 1 in 20 year event and more accurately delineate Flood Zone 3b. This demonstrated that the site was not in Flood Zone 3b. Floodplain compensation was carried out to quantify the volume of displaced floodwater in a 1 in 100 year (+35%CC) event and provide a solution.
Mitigation measures included the preparation of a Flood Warning Plan to be provided to all residents to ensure they were aware of the risk to the site. This detailed the actions to be taken upon receipt of a flood warning, and the most suitable evacuation route offsite.
The proposed drainage strategy included sustainable drainage features in the form of lined permeable paving and green roofs. The drainage strategy attenuated the runoff onsite with a limited discharge rate to the ditch, providing a 50% reduction compared to the existing rate. This provided a significant improvement, both to the site and the local area. The scheme was granted planning permission in 2019.
Preparation of a Flood Risk Assessment, Drainage Strategy, Negotiation with the Environment Agency, Hydraulic modelling study and preparation of a Flood Warning Plan.
Land adjacent to Pearson House, Edinburgh Way, Harlow, Essex