All the flooding around the Bonner Mall got me thinking about porous asphalt and permeable pavers. With all of the precipitation we get there’s got to be a better way to manage stormwater and the pollution carried in rainwater runoff (air pollution particles, spilled oil, detergents, solvents, de-icing salts during freezing conditions , dead leaves, pesticides, fertilizer, and bacteria from pet waste, just to name a few).
Although Bonner County does not have a Building Department or building inspectors it does have extensive land use regulations, including impervious surface regulations for shoreline properties. All waterfront properties greater than one acre may have no more than 15% impervious surface. Smaller parcels, depending on size, may have 25% or 35%. If all structures on a property are no closer than 75 feet from the shoreline, these ratios can be increase by 50%, but what waterfront property doesn’t have a waterfront deck or dock? According to Bonner County Code impervious surfaces include “… rooftops, walkways, patios, driveways, parking lots, concrete or asphalt paving, gravel roads, packed earthen materials and oiled, macadam or other surfaces which impede the natural infiltration of stormwater.”
A project we did in Cocolalla got us researching porous asphalt and permeable pavement and pavers. The general idea is to use the natural filtration of water through soil to control contaminants before they reach our waterways. There are so many options and materials for driveways, parking area, walkways, decks and patios. Below is an easy to read summary that I found, much clearer than one I could create.
Porous Asphalt: A great advantage to porous asphalt is that the same mixing and application equipment is used as for impervious asphalt. Only the formula for the paving material changes with porous bituminous pavement. Bituminous permeable paving is appropriate for pedestrian-only areas and for very low-volume, low-speed areas such as overflow parking areas, residential driveways, alleys, and parking stalls.Permeable paving is not ideal for high traffic/high speed areas because it has lower load-bearing capacity than conventional pavement.
Porous Concrete: Again, the same equipment may be used as for standard concrete. Larger pea gravel and a lower water-to-cement ratio is used to achieve a pebbled, open surface that is roller compacted.
Plastic Grid Systems: High strength plastic grids (often made from recycled materials) are placed in roadway areas. Some are designed to be filled with gravel on top of an engineered aggregate material, while others are filled with a sand/soil mixture on top of an aggregate/topsoil mix that allow grass to be planted on the surface. The grids provide a support structure for heavy vehicles, and prevent erosion. After heavy rains, the grids act as mini holding-ponds, and allow water to gradually absorb into the soil below.
Block Pavers: This material can be used to create a porous surface with the aesthetic appeal of brick, stone, or other interlocking paving materials. They are most often used for driveways, entryways, walkways, or terraces to achieve a more traditional, formal appearance.
