Backwater or Eddy Basins
by Brad Lancaster © 2016
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.
Key Elevation Relationships for Backwater or Eddy 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)(fig. 1).
If the upper edge of this downstream section of the basin (A) is lower than the inlet (B), the basin will act as a flow-through basin, not a backwater basin, as water will overflow at the downstream end (taking mulch with it) and, in this context, erode the earthen walkway. Thus, steeper streets will have shorter eddy basins (parallel with the street), while more-gradually sloping streets can have longer eddy basins.
For the most-complete additional information and examples… buy, read, and share these award-winning books (from which this information was sourced—especially chapter 8 of Volume 2):
For info on curb cuts and curb cores that enable street runoff to enter the basin, visit this section.
For more info on needed slope at curb-cut inlet, plus elevation relationships within the basin, see here.