Filling the Niches
While our structural practices have barriers to innovation inherited from earlier versions of the Maryland Stormwater Design Manual that would impede adoption of Stockholm's approach to planting trees, the newer Environmental Site Design (ESD) practices appear to be more flexible. In Calvert County, additional flexibility is written into the stormwater ordinance that allows alternative treatment methods to be approved and used, as long as they meet the performance criteria of the Manual.
Among the ESD practices that lend themselves to inclusion of biochar in their construction are green roofs, reinforced turf, micro-bioretention, rain gardens, landscape infiltration and infiltration berms. The specifications for these practices not only offer biochar niches, but call for the added performance that biochar so uniquely provides.
|Photo by Donghee Bae (CC BY-NC-SA 2.0)|
- Green Roofs: the planting media spec calls for "a soil-like mixture," the base gravel layer could also be mixed with biochar, allowing longer roots and even more drought tolerance.
- Reinforced Turf: the spec requires that the turfgrass inside the permeable interlocking concrete pavers be grown on sand or sandy loam, which doesn't exclude the use of biochar to make the grass more resilient against drought and vehicle traffic.
- Micro-bioretention, rain gardens, landscape infiltration and infiltration berms: the spec allows for amendments to the loamy sand or sandy loam to bring pH to within 5.5 to 7.0. Acidic soils in the Coastal Plain could use biochar to raise the pH. The spec also discusses breaking up compaction from construction at the bottom of the bioretention basin. This refracturing step would be a good time to mix biochar into that 12" zone.
These aren't the only ESD practices that offer niche opportunities for biochar. One that might use great quantities of char in gravel niches is Submerged Gravel Wetlands. We just need to identify and quantify the costs and benefits of using that much char.