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Evaluation of Surface and Subsurface Processes in Permeable Pavement Infiltration Trenches
Citation:
Brown, R. AND Mike Borst. Evaluation of Surface and Subsurface Processes in Permeable Pavement Infiltration Trenches. Journal of Hydrologic Engineering . American Society of Civil Engineers (ASCE), Reston, VA, 20(2):04014041, (2015).
Impact/Purpose:
The hydrologic performance of permeable pavement systems can be affected by clogging of the pavement surface and/or clogging at the interface where the subsurface storage layer meets the underlying soil. As infiltration and exfiltration are the primary functional mechanisms for green infrastructure (GI) stormwater control measures (SCMs), the objective of this study was to evaluate placement of pressure transducers in 2.47-m (8.1-ft) wide permeable pavement strips and develop data analysis techniques to determine when there is a significant change in hydrologic performance to signal a need for maintenance or replacement.
Description:
The hydrologic performance of permeable pavement systems can be affected by clogging of the pavement surface and/or clogging at the interface where the subsurface storage layer meets the underlying soil. As infiltration and exfiltration are the primary functional mechanisms for green infrastructure (GI) stormwater control measures (SCMs), the objective of this study was to evaluate placement of pressure transducers in 2.47-m (8.1-ft) wide permeable pavement strips and develop data analysis techniques to determine when there is a significant change in hydrologic performance to signal a need for maintenance or replacement. Pressure transducers installed in piezometers were placed at roughly the one-third and two-third points along the length of two permeable paver strips to measure the rise and fall of water in the subsurface storage layer, and level measurements have been collected for approximately 13 months. When the working surface area was not clogged and rainfall intensity was sufficient, infiltrating runoff was localized near the upgradient edge. This created a positive and measureable subsurface gradient between piezometers as water was accumulating in the trench from infiltrating runoff. As surface clogging progressed and the location of the infiltrating water approached or passed the location of the downgradient piezometer, the water level gradient between piezometers from infiltrating runoff reversed. In measuring the water drawdown after each event, the exfiltration rate to the surrounding in situ soil decreased drastically following the first three events after construction of the system. The primary source of the initial exfiltration rate decline was attributed to infiltrating runoff rinsing the fine solids attached to the washed stone and depositing them at the bottom of the trench. About 1.7–1.8% of the mass of the stone consisted of silt and clay sized particles (particle size smaller than 75 um). This significant source of fine-grained particles from construction materials can be eliminated if cleaner stone is used. A continued and significant decrease in exfiltration rate with age was measured during the first year of use. In order to optimize the design of these systems, a life-cycle analysis that incorporates exfiltration rate decline with age should be included. Another item to consider during the design process is the variability of urban soils. Installation should be targeted in soils with larger hydraulic conductivities to improve hydrologic performance, so more preconstruction soil borings and soil tests are necessary to characterize the in situ soils.
