Stormwater bioretention filtration system with overflow/bypass capability

A stormwater treatment system comprising a substantially water impermeable treatment container having an enclosed side wall, a bottom wall, and at least a partially open top to define a container interior, an underdrain pipe located substantially horizontally in proximity to said bottom wall and exiting said container through an outflow pipe opening in one of said side and bottom walls, said underdrain pipe including a plurality of perforations to receive treated stormwater, a stormwater inlet pipe communicating through an inlet pipe opening in said side wall at a location closer to said top than to said bottom wall, and an interior overflow/bypass outlet pipe communicating with said outflow pipe opening, said overflow/bypass outlet pipe receiving at least partially untreated stormwater that flows through said inlet pipe at rates in excess of that capable of treatment within said container, said inlet pipe opening and said outflow pipe opening closer to a side wall in plan view than to a center of the container, a substantially horizontally oriented dissipation plate within said container and located below the position of said inlet pipe opening to receive stormwater flowing through said inlet pipe opening and dissipating the stormwater before it falls into the treatment container interior located below said dissipation plate, wherein said treatment container is positionable below ground level with said partially open top in communication with the atmosphere, said container interior including a filter media that fills the container to a level no higher than the level of the dissipation plate, said filter media comprising a layer of mulch overlying a soil mixture of non-organic and organic material and live plant material growing in the filter media, said plant material capable of growing out through the top of the container above ground level, and wherein said dissipation plate extends from a side wall a distance toward the center of the container to lie below the entire inlet pipe opening and having a free edge, said filter media within the container interior extending up no higher than said free edge, and wherein said overflow/bypass pipe extends from said inlet pipe opening and communicates with said outflow pipe opening, said interior overflow/bypass pipe including a plurality of downwardly directed openings oriented above and spaced from said dissipation plate to enable stormwater through said interior overflow/bypass pipe to fall through said downwardly directed openings onto said dissipation plate and into the container interior, and to enable high stormwater flow through said stormwater inlet pipe into said interior overflow/bypass pipe to bypass the filter media and exit directly through said outflow pipe opening, said dissipation plate extending substantially horizontally and closer to a side wall in plan view than to a center of the container.