6 minute read
The importance of multidisciplinary design
Steve Wilson
I have spent the last 20 years explaining to civil engineers that with SuDS, surface water drainage is no longer a purely engineering discipline. However, that does not mean that civil engineers do not have a very important and integral role to play in the design of SuDS alongside landscape architects. Suggestions that engineers only have a minor, if any, role to play in SuDS design should not be taken seriously. Every landscape architect that is involved in SuDS design should be engaging with and working collaboratively with civil engineers and vice versa. It truly is multidisciplinary work and everyone should recognise the value provided by the other professions.
One of the greatest arguments for multidisciplinary working is business risk management. No one can be an expert in everything and it is incumbent on the landscape architect and engineers to be aware of the limits of their professional knowledge. This is covered in the Pathway to Chartership syllabus for both professions. If someone does not seek advice on specialist areas of work and gives bad advice, they can be sued by the client. Professional indemnity insurance may also be invalidated.
SuDS design should begin at the earliest stages of planning a development when integration of SuDS into the layout allows the easier use of surface features that are integrated into the landscape. This requires input not only from planners and landscape architects to integrate the SuDS, but also from engineers to complete preliminary hydraulic models and comment on the likely engineering issues that may arise (e.g. is it possible to infiltrate close to buildings, will infiltration affect slope stability)?
Landscape architects should design the specific form and profile of any SuDS features. It is easy to spot a feature that has been designed by engineers without any real input from landscape professionals by the uniform slopes, lack of smooth transitions, generally deep and overly steep slopes and ugly concrete headwalls. A simple but very important example is shown in the photos overleaf where it is demonstrated the concrete headwall can be replaced by a much more visually pleasing solution that is just as effective from a hydraulic perspective.
Retrofit basin with 1 in 5 side slopes
Often landscape maintenance requirements will drive the maximum side slopes and planting in a SuDS feature. The retrofit basin on page 17 was designed with 1 in 5 side slopes to allow easy mowing but this gives a much more visually pleasing solution. The planting is designed so that overall maintenance costs are no greater than the plain grass area it replaced.
Combined pond to replace a proposed underground tank
In the example on page 19 it was recognised by the engineer that a landscape solution would provide a much better environment and space than a buried plastic tank. This was again achieved through a multidisciplinary approach. The landscape architect has made the pond into an attractive feature in its own right and the engineer has ensured it works hydraulically.
It is vital that engineers are employed to ensure a scheme will work hydraulically and also make sure it is cost effective, for example by minimising storage volumes using appropriate hydraulic models. During detailed design, qualified and experienced engineers will be needed to provide advice on a range of issues that may include:
– Design of permeable pavements to support traffic loads
– Checking infiltration designs to ensure that the infiltration rates are appropriate to the soil types and wider ground model
– Assessing stability of slopes or retaining walls that may be affected by SuDS
– Confirming if shallow infiltration close to buildings (ie <5m from the building) is possible. Although it is possible in many cases there are specific ground conditions that would preclude this (e.g., where gypsum dissolution could be an issue).
Even during construction, collaboration is essential because SuDS often require landscape construction methods to be used earlier in the programme than normal, for example to allow vegetation in swales to become established.
A prime example of where multidisciplinary working is required for what might, at first consideration, appear to be purely a landscape issue is the specification of filter media for rain gardens, especially larger ones that drain highways. The nature of filter media affects their drainage, pollution treatment and plant growth performance. All three are of equal importance. However, some refer to the filter media as a growing media, which gives the wrong impression and implies that only the plant growth considerations are important. The correct term is filter media. Input into the specification of the media is required from landscape, horticultural, soil science and engineering perspectives. It is not the exclusive domain of one professional field. This is especially true if the permeability of the media is being used to control discharge to a pipe (i.e. using it as a flow control). The filter material should not be compacted and needs to be protected from excessive silt accumulation during construction activities. It also needs to be of a suitable grading to ensure compatibility with either underlying soil transition layers or geotextile filters, using well-established filter criteria.
Education
The importance of multidisciplinary working between civil engineers and landscape architects in stormwater management should be encouraged from the start of their professional careers. Universities could share water-related modules between each discipline. This would break down the silos from early in the career formation. CIRIA (and the Landscape Institute) already run training course on SuDS with a trainer from each discipline wherever possible.
In conclusion, the best SuDS schemes are those where landscape architects and engineers collaborate to provide attractive and functional features that can be easily maintained and last for a lifetime and beyond.
Steve Wilson is a Chartered Civil Engineer and Technical Director of The Environmental Protection Group (EPG), which is part of the STRI Group.
Steve Wilson and Sue Illman were recently both awarded the CIRIA Lifetime Award for ‘Outstanding services to SuDS’.
