11 May 2011
Most SUDS systems will be expected to last a good many years. SUDS are intended to reduce flood risk, and to do that they need to operate effectively, and to do that continually they need to be maintained.
Under the Flood and Water Management Act 2010, lead local authorities will be the adopting authority for SUDS systems, and therefore the ease and cost of maintenance will an important issue for them when assessing SUDS applications.
Drainage has traditionally been the last thing considered on a development, but the locations of the SUDS elements within the site should be determined as part of the initial layout plan, and future maintenance requirements incorporated at this stage. It seems obvious, but access to all features must be adequate for maintenance vehicles. The classic problem is a watercourse running between back garden fences, but I have come across attenuation ponds which have been completely surrounded by fencing without gates and on one occasion located in an area only accessible by pedestrian bridges!
Throughout the design process, designers should be asking themselves, “How would I maintain that?” For example, swales, dry ponds and any other grassed areas should have side slopes no steeper than 1 in 3, and ideally 1 in 4, so they are suitable for sit-on mowers. If the design includes buried storage, even in grassed open space this should be strong enough to support maintenance vehicles. Watercourses and wet ponds need periodic de-silting, which is most easily done with a mechanical digger close to the bank, so fencing is a major impediment. The need to fence is is usually the result of steep banks being considered a safety hazard. But with a little more thought at design stage, the slopes could be reduced or shelved and together with the visual clues given by planting, the need for the fence removed completely.
Photo courtesy of Illman Young Landscape Design
These are the obvious examples, but the same consideration should be give to the whole SUDS design. After all, if maintenance is too difficult, it tends not to get done.
By putting the effort in at the beginning, designers reduce the effort required for decades to come.
Beryl Kemplen BSc (Eng) CEng MICE
AVDC Engineering Manager