I am currently involved with a staged subdivision that proposes to treat road runoff through numerous pods. Are there any WSUD references guiding the removal of coarse sediment for such small systems? No space has been allowed to incorporate a grassed buffer. Any opinions/experiences or recommended reading would be helpful. Cheers
Coarse sediment removal - bioretention pods
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Bioretention pods should incorpate a designated sump for collection of coarse sediment (coarse sediment forebay). This is essentially a zone at or directly adjacent to the "kerb cutout" where coarse sediment can collect and be easily removed. The calculation method the TDG for WSUD will assist with defining the volume. The minimum size of the forebay should be 500mm by 500mm to allow easy maintenance. The forebay can be formed through flat rock, pavers or concrete (a surface which allows easy removal of sediment by machine or hand). Care need to be taken to ensure levels from the kerb through the forebay to the filter media surface do not result in sediment accumulating within the kerb. Some guidance is provided in the WSUD standard drawings in this regard (to be released in the next week or so). If a coarse sediment forebay is not included, coarse sediment will still accumulate at the entry to the bioretention pod. But removal of the coarse sediment may be more difficult and might result in removal of the some of the plants as well (in order to remove sediment).
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