Filling the Berm

Biochar is well suited to Environmental Site Design (ESD) for stormwater management applications. Its ability to absorb up to six times its weight in water and its long drying time can be used in slowing down runoff to maintain discharge timing while increasing infiltration and evapotranspiration.

Many ESD standard practices include a gravel underlayment to promote drainage. Some of those same ESD practices do not contribute sufficiently to meeting the Channel Protection Volume (Cpv) requirement, i.e. the amount of water that is allowed to run off from a 24-hour one year storm (that is, the average of the largest 24-hour storms historically occurring in an area each year). Since Cpv is sometimes difficult to meet with ESD alone, traditional structural practices must sometimes augment the more distributed ESD practices.

One of the practices that does not contribute to Cpv is infiltration berms. These are long mounds
built orthogonally to the flow of runoff. They consist of 6" of topsoil over an aggregate core. If, like the Stockholm tree planters, we were to load the gaps in the aggregate with biochar, that much more channel protection volume could be earned based on the additional water holding capacity of the biochar.

Of the other practices that already contribute to the channel protection volume, a thick layer of unground biochar between the soil and the aggregate or gravel underneath would help prevent clay particles from blocking the drain, contributing thereby to a more sustainable solution.

Since these two modifications deviate from the specifications in the Maryland Stormwater Design Manual, special review and approval of the innovations would be required at the county and/or state level. MARVALUS Engineering may be the one to request approval of these innovative practices and then earn royalties on their application. Developers and owners probably wouldn't mind paying a small fee along with the price of using biochar if it saves them the expense and real estate of added structural devices or maintenance of the aggregate layer.

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