You are here:
GEOPHYSICAL ANALYSIS OF PERMEABLE PAVEMENT INFILTRATION DURING SIMULATED RAINFALL EVENTS
Citation:
Trottier, B., R. Versteeg, D. Werkema, A. Meyal, G. Partridge, AND C. Johnson. GEOPHYSICAL ANALYSIS OF PERMEABLE PAVEMENT INFILTRATION DURING SIMULATED RAINFALL EVENTS. Symposium for the Application of Geophysics to Environmental and Engineering Problems (SAGEEP), Denver, CO, March 20 - 24, 2022.
Impact/Purpose:
This abstract presents research and development results from a project to measure and monitor recharge through permeable pavement green infrastructure engineering systems. We developed an in situ autonomous remote controlled subsurface water sensor, which uses the geophysical measurement of direct current resistivity to detect and monitor precipitation as it permeates the pavement and travels downward in the ground. Permeable pavements are designed to reduce storm water runoff by enhancing precipitation recharge into the ground. The success of these pavements depends on the flow of water through the pavement and into the ground. Over time the permeability of these pavements decreases due to clogging. This research demonstrates that in situ geophysical sensors can monitor and measure the recharge through the permeable pavements and verify their functionality and guide stakeholders to remotely monitor their effectiveness and adapt cleaning protocols to maintain their permeability and reduce storm water runoff.
Description:
As flooding events increase in frequency and intensity in response to climate change, permeable pavement may provide flood mitigation that can reduce surface runoff in developed areas as well as promote direct aquifer recharge. The reduction of surface runoff helps to limit erosion, pollution, demands on waste-water treatment, and potential hazards. In 2021, an infiltration test station was developed in Storrs, Connecticut to evaluate the relative efficacy of permeable pavement relative to natural soil during simulated rainfall events, and to demonstrate remote and autonomous geophysical methods to continuously monitor long-term infiltration. The test site consisted of four plots: two with permeable pavement pads, one natural soil, and one impermeable control plot. Each plot was approximately 2.5 meters squared and had electrical resistivity probes installed to depths of approximately 1 meter. To replicate precipitation, three watering wands were connected to a constant water source, secured to a fixed structure, and centered above each plot at a height of approximately 0.75 meter. Three of the plots were watered for a three-hour period while the covered control plot was not. Before each test, desired flow rates were calibrated by collecting a targeted volume of water over a set time interval from each wand. Predetermined flow rates were calculated to approximately span the range of local rainfall rates. A 0.5-inch/hour flow rate was used to emulate light rainfall, a 2-inch/hour flow rate for moderate rainfall, and a 4-inch/hour flow rate for torrential downpour. Relatively minimal ponding was observed on the porous pads during testing, but as simulated precipitation rates increased, so did surface runoff. Modifications were made to accommodate the higher test rates, reduce surface runoff, and ensure vertical flow through the pads. A challenge of assessing permeable pavement efficacy is understanding the recharge impact within the subsurface. To overcome this challenge, time-lapse electrical resistivity probes were installed below each plot. The data collected from these probes were automatically uploaded to Subsurface Insights for processing and visualization. During the test, the probes recorded sudden drops in apparent resistivity, which were interpreted as infiltration in direct response to the simulated rainfall. As these probes measured resistivity along the length of the probe itself, a 1-dimensional profile of infiltration over time was observed. As contact resistance varies between probes, data were plotted relative to a temporal datum to compare infiltration responses between pavement plots. The data exhibited a sharp decrease in resistivity within a few minutes after the artificial recharge events began, followed by a sudden rebound in resistivity at the conclusion of each test, which lasted several hours, and then a gradual attenuation to pre-test values within approximately 1-1.5 days. The rapid response times indicate that both concrete pads have high permeability and similar attenuation rates to the natural soil, which demonstrates the permeable pavements have a comparable rate of infiltration and do not retain water for a longer period than the natural soil. These results suggest that infiltration through permeable pavements reasonably simulates infiltration through natural soils and may have promising applications as an alternative to impermeable pavements and structures as the demand for flood mitigation technology increases with the increase in flooding events. Additionally, these results demonstrate the successful application of remote autonomous resistivity probes to monitor recharge beneath permeable pavements. Such monitoring technology is important for municipalities and stakeholders to evaluate permeable pavement effectiveness and inform maintenance cycles.