Abstract
Sustainable drainage systems (SuDS; or best management practices) are increasingly being used as ecological engineering techniques to prevent the contamination of receiving watercourses and groundwater. Permeable paving is a SuDS technique, which is commonplace in car parks, driveways and minor roads where one of their functions is to improve the quality of urban runoff. However, little is known about the water quality benefits of incorporating an upper geotextile within the paving structure. The review focuses on five different categories of pollutants: organic matter, nutrients, heavy metals, motor oils, suspended solids originating from street dust, and chloride. The paper critically assesses results from previous international tests and draws conclusions on the scientific rigour and significance of the data. Findings indicate that only very few studies have been undertaken to address the role of geotextiles directly. All indications are that the presence of a geotextile leads only to minor water quality improvements. For example, suspended solids are being held back by the geotextile and these solids sometimes contain organic matter, nutrients and heavy metals. However, most studies were inconclusive and data were often unsuitable for further statistical analysis. Further long-term research on industry-relevant, and statistically and scientifically sound, experimental set-ups is recommended.
Highlights
The management of storm water with Sustainable drainage systems (SuDS) such as permeable pavements, ponds and swales can have a positive effect in reducing these pollutants and delaying the volume of water discharging to the sewer or receiving water body
The review of permeable pavement system literature indicates that there are very few studies that directly research the impact of geotextiles within permeable pavement systems on improving the water quality
There is an indication that the presence of a suitable geotextile within a permeable pavement system reduces the breakthrough of suspended solids
Summary
The runoff from urban areas carries various pollutants including organic matter, nutrients, heavy metals, oils and suspended solids, which have previously been deposited onto impermeable surfaces. The change from permeable to impermeable land (e.g., roofs, roads and pavements) reduces groundwater recharge and creates a large volume of runoff and a higher peak flow rate in the drainage system This can often lead to urban flooding, during heavy rainfall and when sewers operate at their full capacity [1,2]. For situations such as commercial and retail sites, SEPA considers that two levels of treatment are required and as such a washed stone-filled sub-base below a proprietary paving system and in conjunction with a geotextile, preventing fines from entering the sub-base, would provide two levels of treatment Such an arrangement would deliver the requirement for “reasonable steps” [4] to be taken to protect the water environment. Very few ecological engineering research studies on permeable pavement systems produce directly comparable water quality results for paving constructions with and without an upper geotextile layer.
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