By Juliet Merrifield HKD & Fred Maillardet HCO
Are you thinking of paving your driveway or front garden? Did you know that rainwater running off your driveway or paved front garden may contribute to flooding in Hassocks?
Global warming is now recognised to be leading to more erratic weather patterns with more extremes of heat and rainfall expected in the UK. Hassocks has suffered from surface water flooding in recent years, the cause being twofold:
1. Heavy rain swells the flow in the chalk stream tributaries entering the village from the South Downs, and this can overflow the banks when it becomes excessive, particularly just above Spitalford Bridge.
2. Surface water draining from any hard surface will settle in the lowest adjacent area if not conducted away via the local underground drains. But remember that drains in Hassocks were built many years ago and were not designed to cope with increased rainfall.
The first of these can be substantially reduced if not eliminated by natural flood management techniques like the ‘leaky dams’ on the two main tributaries which are slowing the flow of water into the village. However, the second would appear to be increasing in frequency and severity due to the growing number of areas being paved over with non-permeable surfaces, particularly to accommodate parked vehicles outside houses. Such areas are liable to collect pollution including oil, petrol and brake dust which may then be washed off into drains which usually feed into the nearest stream.
Since 2008, planning permission is needed to construct or replace a driveway or patio of more than five square metres unless the materials are permeable. Permeable paving needs no planning permission, the recommended approaches being:
• The use of gravel or a mainly green grassed area with paved or reinforced tracks to accommodate the wheels.
• Directing water off an impermeable surface to a border, rain garden or soakaway.
• Using permeable block paving, porous asphalt or porous concrete constructed over a permeable subbase which could still be hardcore if sufficiently large stones are used to enable some water to be stored as well as passing through to the ground beneath.
The Environmental Agency’s Guidance on permeable surfacing contains much useful information on the options available, and how to accommodate driveway slopes, different underlying soils and maintenance requirements. https://bit.ly/3OHD8lm