The role of surface water drainage schemes in flood prevention
The role of surface water drainage schemes in flood prevention.
With the mounting demands for building more homes and associated infrastructure, open land is being paved over at an ever increasing rate. Many planning authorities have recognised the problem has reached a critical stage; an area the size of a hundred football pitches is being built over every day in England alone. Couple this with more frequent torrential downpours, recently experienced by many parts of the United Kingdom, water run-off has cascaded down
from surrounding higher ground, over-filling streams and rivers and causing flooding on a huge scale to agricultural land and many UK towns and cities.
Triple FASERFIX® SUPER 500 channel runs installed across road in St. Ives, Cornwall Some metrological scientists are suggesting the recent wet weather is caused by global warming, if this is so then we may expect more regular down pours and subsequent flooding events in future years.
Central and Local Government, Planning Authorities and Engineers are urgently looking into ways of slowing and controlling water run-off from higher ground, including; bolstering river defences, dredging, building dams upstream to create higher water catchment areas, upland
tree planting schemes, proper management of flood plains and investing in larger Sustainable Urban Drainage Systems (SUDS). There has even been a suggestion that beavers are reintroduced into the UK to control water flow in upper reaches of some rivers!
Surface water drainage channels are primarily designed to rapidly drain rain water from manmade hard surfaces such as concreted and asphalt roads, car parks, cycle-ways and paths, paved concourses and the like. The idea is for the rain water run-off to be directed into SUDS where hopefully, it will drain slowly away via streams and rivers or seep down through the sub-soil, there to replenish the natural aquifers.
Flood prevention installation to protect rail line. Channels installed as part of SUDS flood prevention SUDS and associated surface water drainage channel runs do pose their own problems – they
will not solve the problem of devastating floods on their own, they must be carefully engineered and sized to ensure proper control of expected surface water run-off. Any drainage scheme must be integrated into an overall flood prevention plan otherwise
uncontrolled local flooding may still occur.
To help specifiers optimise their surface water drainage schemes, a Dunstable based company Hauraton Limited provides a free hydraulics design service and technical support for their surface water drainage products which include drainage systems that store and then slowly
release water into the sub-soil and large, high capacity channels that have been found useful in combating local flooding in susceptible areas within Europe.
Larger capacity channels offered by Hauraton include; FASERFIX® SUPER 500 with a drainage cross-section of 2141cm2, FASERFIX® BIG BL 300 with a drainage cross-section of 812 cm2 and large FASERFIX® EL special channels made with a drainage cross-section of up to 10,000cm2.
Also available are RECYFIX® NC 300 with a drainage cross-section of 863 cm2 and RECYFIX® HICAP® 680 with a drainage cross-section of 4430cm2 and a retention volume of 443.0 per l/m.
FASERFIX® channels are made from the company’s Fibre Reinforced concrete, whilst RECYFIX® channels are made from 100% recycled polypropylene. All channels are available with ductile iron gratings/inlets and have a loading category of up to Class F900.
FASERFIX® EL channel component RECYFIX® HICAP® 680 FASERFIX® SUPER 500 installed in a major drainage scheme in Scotland
Case Study - Control of local flooding, St Ives Cornwall.
With its picturesque setting, beaches, art galleries and shopping facilities, St Ives Cornwall, is a popular place to work, live and spend holidays. In recent years this has increased the requirement for homes and a support infrastructure designed to welcome the thousands of visitors. The town now extends way up the surrounding hillsides and along the approach roads, particularly the A3074 and B3311. With so much development, a large area of the surrounding countryside has been built on and paved over with buildings, associated access roads and car parks.
Installation of RECYFIX® HICAP® 680 channel run Double FASERFIX® SUPER 500 channel runs installed across road in St. Ives, Cornwall St. Ives Town Council became very concerned about the risk of flooding in the lower town.
Weather fronts racing in from the Atlantic bring heavy rain fall, particularly during the winter months. This has resulted in rainwater cascading down the steep roads and into the lower town’s narrow streets and passages. The memory of the devastating floods in neighbouring towns and the need to protect valuable real-estate gave extra urgency to the plans for a new road drainage scheme.
Hydraulics experts advised the Council that existing road drainage could be compromised during extreme rainfall events; a new drainage scheme with a very large capacity had become essential. Slotted channels were considered but rejected as it was feared the narrow slots could be easily blocked by debris and in any case the small inlet area could not cope with the predicted large quantities of water that accumulated on the town’s steeply inclined approach roads. Instead, civil engineers were looking for a drainage system with large inlet apertures. In addition, the application called for a particularly robust channel that could take the large volumes of traffic and the many delivery vehicles entering the town.
The Local Authority invited tenders for the FASERFIX® SUPER 500 channel made from fibre reinforced concrete because it met all the design criteria: an extremely robust and rugged channel having a large drainage cross section, matched with heavy-duty ductile iron gratings to class E 600 for heavy load applications.
The grating specification chosen featured three parallel rows of slots, each 20mm wide. Careful calculations were undertaken to ensure the installed system could easily cope with the very large quantity of water expected.
The building contractor, Carillion Construction, installed a total of 186 meters of FASERFIX® SUPER 500 channels across various roads leading down to the lower town in order to ensure effective flood prevention. Single, double or triple channel runs were installed across the carriageways depending on the volume of run-off water to be diverted.
The project was supported by Hauraton’s project managers, Andy Beirne and Steve Wiseman who provided hydraulic calculations and engineering advice during the design and installation phases. The local Building Control department, planners and the building contractor were impressed with the design support received from Hauraton and full of praise for the company’s excellent cooperation and flexible service. Happily, now the new scheme is operational, even when there is heavy rainfall, all the run-off is safely diverted.
For Case Studies go to www.drainage-projects.co.uk
For details of all Hauraton products go to www.hauraton.co.uk