RESOURCES ON SOIL VOLUME
Al Key: Green Infrastructure for Your Community, January 2014
Excerpt: Vines, hedges, and palms all require high quality soil in appropriate volumes, but there is a paucity of research to guide designers on how much soil to provide. If no one has any data, how can you determine what the proper sizing of woodies and large monocots? Are there any empirical calculations we can make?
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James Urban, FASLA: Paper presented at Designing with Nature: The Art of Balance - American Society of Landscape Architects Annual Meeting, October 2007
Abstract: Compacted soils to support pavements and infrastructure increase the run off rate of rainwater. Only a small percentage of each rain event, even if the pavement is porous, can infiltrate compacted soil for aquifer regeneration and vegetation hydration. Soil compaction also stunts the growth of trees by restricting root penetration. Absorbing soils that are not compacted, placed under pavement can be a significant tool for rainwater management and improvement of the urban forest.
By using the BMP methods discussed below, paved city plazas, streetscapes, and town centers can become areas for rainwater mitigation. They can transform the urban forest into a rainwater mitigation asset. The strategies discussed will support roadways, parking lots and sidewalks while providing un-compacted soil volumes to absorb large amounts of water and enable large tree growth. These methods can contribute to sustainable designs in varying effectiveness for increases in water management with no loss of the paving's structural integrity.
Using trees and their required soil for rainwater management has additional advantages over other rainwater management strategies. The large healthy tree canopies created by large volumes of absorbing soil provide other benefits. The tree's canopy cools the air and paving which helps reduce urban heat island impacts and cools run off water temperature. A large canopy absorbs the initial 1/10th of an inch of the rain event and evapo-transpires large amounts of water increasing the effectiveness of the system. Healthy, long-lived trees also contribute to the social and economic health of urban communities.
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