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I spent a fascinating couple of hours with Micro Drainage in their Newbury offices recently, discussing the weather (as you do) and learned that, thanks to current hydrological requirements, most development sites can now be defined as 'water treatment plants'!

I arrived with the common perception that developing solutions to handle clean and waste water is rather like trying to stem the tide, as the country is being hit with a double whammy - the need to build houses in fewer locations with a large percentage of these being sited in flood plains, and the seeming impact of global warming, which appears to be increasing the pluvial element of the weather - i.e. the amount and frequency of heavy downpours causing localised flooding. You may agree or not agree with the scientific assessment of global warming, but it is incontrovertible that we are witnessing more frequent and more violent water events.

Consequently, following the Pitt Report after the 2007 floods, unitary authorities have now been designated as LLFAs (Lead Local Flood Authorities) with responsibility for local surface water flood risk under the Flood and Water Management Act 2010. Looking ahead to next year, Schedule 3 of the Act will also clarify their responsibility for the adoption and maintenance of SUDS (Sustainable Urban Drainage Systems) as an SAB (SUDS Approving Body). This requires them to make critical decisions about water issues and flood assessments in their local area, ensuring that developments are able to cope with the Environment Agency's 'fluvial' flood risk assessments, carried out at a 'catchment scale' for the rivers and coast.

The most interesting fact was that after identifying how water behaves on a particular section of terrain earmarked for a construction project, the task of the drainage engineers is to create a drainage system that replicates the natural flow characteristics, taking into account any landscape remodelling, construction or roadworks, so that no more and no less is either introduced to, or removed from the site - a zero sum game that blends any development into the terrain seamlessly.

How water behaves on any particular bit of terrain is quite complex, but can be straightforward to model and analyse with the latest technology available. Provide a terrain map, using ground surveys or LIDAR data, import the GIS data into Micro Drainage's WinDes application and triangulate the data to provide a digital terrain model, which provides a height map. A TIN analysis is used to show flow paths, ridge lines and sink points, identifying the line of steepest slope for each triangle, and adds colour-coded arrows on a range of gradients.

As recent extreme flooding events have been caused by rainfall (pluvial), rather than river (fluvial) inundation, the deluge is digitally represented, applying a depth of water to the ground, and analysing how it drains away over a given time - showing 'blue' corridors and identifying the depth, direction and velocity of overland flood flow routes. Well, the concept is simple to understand - and so are the charts and graphs that the software produces, as the results have to be shown to authorities, developers and clients, each with their own agendas and requirements.

MICRO DRAINAGE
It's not just about SUDS, though. Every element of water on the site has to be included in the calculations, from predicted rainfall to flooding risks, the quality of water from rain water harvesting, water treatment plants, green roofs, and other natural sources. Did you know, for instance, that a sudden downpour of just a few minutes after a dry spell is the most seriously polluting pluvial event, as roads, carparks, petrol stations and service stations have been accumulating rubber from tyres, oil and other hydrocarbons, and these are washed into culverts and the water system relatively undiluted?

Did you also know that the downpipes that are a prominent feature of our houses are an impediment to natural water flows and that thousands of houses in Portland, Oregon, have done away with them in the interests of creating more sustainable structures? Have you also heard of blue/green corridors, which are designed to allow water to flow near the surface at a more natural rate than covering an area with concrete which diverts all water through a single escape route? These corridors encourage biodiversity, can improve ecosystems, provide amenity value and a healthier environment for future generations - as well as improving the quality and controlling the quantity of the surface water flow.

It is this level of detail that is being addressed in modern water drainage systems, and Micro Drainage, an XP Solutions company, is the principal developer of the software needed to handle the problem. The company supplies a number of core modules for sanitary and storm water pipe design, creating drainage layouts, simulation of models to test for extreme rainfall events, and controlling water sources and quality by looking at storage and filtration requirements, 2D analysis and calculation of flood flow paths.

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