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Backwater or eddy basins are largely self-maintaining, thus they are typically my favorite—especially for do-it-yourselfers. As an eddy basin fills with water, the water gradually and calmly backs up to the basin’s inflow point, and surplus water continues flowing down the pavement-stabilized street-curb gutter. When done right there are no erosion problems.These basins are ideal for mulched bottoms—do not put rock in an eddy basin’s level bottom as it will impede the rapid infiltration you desire. Mulch may float in basins, but for the most part will not leave; instead more will be gained—especially if inlets are at upstream side of basins. Incoming water transports leaf drop from the street into basins.

 

Figure 1. Eddy or backwater basins. The upper edge of the farthest-downstream section of the basin (A) must be higher (ideally at least 4 inches [10 cm] higher) than the basin’s curb-cut, or curb-core, inlet (B) to ensure pooling water calmly backs up to the inlet. Arrow denotes water flow.

Figure 1. Eddy or backwater basins. The upper edge of the farthest-downstream section of the basin (A) must be higher (ideally at least 4 inches [10 cm] higher) than the basin’s curb-cut, or curb-core, inlet (B) to ensure pooling water calmly backs up to the inlet. Arrow denotes water flow.

Regenerate mulch as needed with leaf drop and cut-up prunings from the plants growing in the basin. The rate of decomposition of the biomass in the basins will be quicker than non-basin areas due to the increased water inputs, which leads to a nice balance. I’ve found that by the time plants are ready for another pruning, the basins are ready for another application of mulch from cut-up prunings.

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Simple good engineering of these basins will make the all the difference in their performance; get off on the right foot with some overview tips in the full Eddy Basin blog entry on my website, along with a photo of eddy basins implemented in Clarkdale, Arizona, by Eden on Earth Landscaping.

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