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This study investigates the processes and characteristics of solids removal in two types of permeable pavement: UNI Eco-Stone and porous asphalt. The mechanisms and processes behind solids removal within permeable pavement structures was studied for these two types of permeable pavements using both field installations and laboratory experiments. Results from the study showed that both pavement types are capable of excellent total suspended solids removal, in the range of 90 to 96% removal of solids from influent. Particle size distribution analysis of accumulated sediment within the pavement structure and in the influent and effluent showed that the particles in the effluent of the pavements are substantially finer than that in the influent. Laboratory results involving no crust formation indicated that, although solids removal occurs throughout the entire structure, the "sieving action" occurs primarily at the geotextile interface.

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[1] The forest floor in many ecosystems consists of a partially decomposed organic layer (duff), which together with the litter layer comprises the boundary between the atmosphere and the mineral soil. Processes controlling the duff water budget during dry periods (which occur during most of the summer) were investigated using field monitoring, field flow exclusion manipulations, and coupled, multiphasic water and heat budget modeling. The objective of this paper is to model the significant processes that govern the dynamics of the duff water budget during drying. During dry periods the moisture content of the duff's F layer cycles diurnally with minimal moisture movement between the duff and mineral soil. Field exclusion of dew, lateral flow, and mineral soil flow suggests that diurnal drying cycles during the dry period are driven by diurnal atmospheric energy fluxes leading to coupled heat and mass fluxes within the duff. The fine root system and lateral flow do not typically influence drying. TOUGH2 was used to develop a one-dimensional, multiphasic (both liquid and vapor) coupled water and heat budget model which confirmed that the vertical moisture fluxes lead to diurnal cycles.

Abstract:The partially decomposed organic layer (duff: F and H layers) of the forest floor is an important boundary between the soil and atmospheric processes. Here we use both empirical data and a three-dimensional coupled heat and water budget model to explain the duff hydrological hillslope shift between very brief wet periods when lateral flow in the duff and infiltration into the mineral soil occur and dry periods when evaporative flow dominates and both lateral and mineral soil flow are not important. The duff moisture transitions from wet to dry periods were the result of low lateral flow which moves liquid and water vapour only centimetres to metres, very rapidly and mostly in the H layer immediately after precipitation. During wet periods, the net lateral fluxes were negative on divergent areas and positive on convergent areas of the hillslope, leading to a net moisture loss in divergent areas and a net gain in convergent areas. The response to lateral flow in the H layer was more rapid than in the F layer. The transition from the lateral downwards flow to mineral soil to evaporative control was within approximately 48 h of precipitation. Canopy species and aspect were important with lodgepole pine, southwest aspect and 4-cm deep duff controlled by evaporative processes while Engelmann spruce, northeast aspect and 30-cm duff were more controlled by hillslope redistribution processes.

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