Swales are widely used Sustainable Urban Drainage Systems (SuDS) that can reduce peak flow, collect and retain water and improve groundwater recharge. Most previous research has focused on the unsaturated infiltration rates of swales without considering the variation in infiltration rates under extreme climate events, such as multiple stormwater events after a long drought period. Therefore, fieldwork was carried out to collect hydraulic data of three swales under drought conditions followed by high precipitation. For this simulation, a new full-scale infiltration method was used to simulate five rainfall events filling up the total storage volume of the swales under drought conditions. The results were then compared to earlier research under regular circumstances. The results of this study show that three swales situated in the same street show a variation in initial infiltration capacity of 1.6 to 11.9 m/d and show higher infiltration rates under drought conditions. The saturated infiltration rate is up to a factor 4 lower than the initial unsaturated rate with a minimal rate of 0.5 m/d, close to the minimum required infiltration rate. Significant spatial and time variable infiltration rates are also found at similar research locations with multiple green infrastructures in close range. If the unsaturated infiltration capacity is used as the design input for computer models, the infiltration capacity may be significantly overestimated. The innovative method and the results of this study should help stormwater managers to test, model, plan and schedule maintenance requirements with more confidence, so that they will continue to perform satisfactorily over their intended design lifespan.
Permeable pavements are specifically designed to promote the infiltration of stormwater through the paving surface in order to reduce run-off volumes and to improve water quality by removing sediment and other pollutants. However, research has shown that permeable pavements can become clogged over time and this reduces their infiltration capacity. In order to assess the infiltration of permeable pavements, a variety of infiltration test procedures have been utilised in the past. However, the results have generally been inconsistent, and have shown a large variation in the range of infiltration rates measured. This paper evaluates the performance of two new experimental test methods developed in the Netherlands to more accurately determine the surface infiltration rate of existing permeable pavement installations. The two methods were the falling head full-scale method and the constant head full-scale method. Both of the new methods involved inundating a large area of the pavement in order to determine the infiltration rate through the pavement surface. Double ring infiltrometer tests were also performed to enable a comparison of the results. The study found that the new falling head full-scale testing method produced the most accurate results.
Although permeable pavements have been used all over the world in recent years to infiltrate and treat stormwater, only limited research has been undertaken to investigate and compare the long-term performance of these sustainable urban drainage system devices. This paper presents the results of an extensive international review of research on the reduction of infiltration capacity of permeable pavements over time. The results of these studies, coupled with specific knowledge of the key environmental factors on the individual research locations and infiltration testing methods used, enables the maintenance of these SUDS to be strategically planned in order to meet specific European and international infiltration capacity guidelines.
