Constructed weirs and pools for safe, non-erosive conveyance of stormwater runoff: An example of regenerative design

Stormwater conveyance practices are grounded in industrial design that neglects integration with system processes, economics, and aesthetics.  As a result, the greater volume of runoff from impervious surfaces, coupled with smooth and hardened conveyance systems (e.g., pipes and trapezoidal concrete channels), magnifies and transfers energies to the discharge or outfall.  These outfalls cause erosion, conveyance structures fail, stream channels are degraded, in-stream sedimentation increases the influence of localized erosion upstream and downstream of the outfall, and an increasing spiral of degradation results.  Conventional stormwater conveyance practices lower local shallow groundwater, destabilize soils, result in excess removal of native vegetation, increase the potential for introduction of invasive plants, degrade water quality, and cause stream channel destabilization.  Local governments are forced to spend scare public funds on remediation measures and local residents remain disconnected from their watershed.  Alternatively, the technique of using step pools, wiers, and sand berms minimizes the width of vegetation disturbance and opportunities for invasive plant establishment, minimizes soil destabilization, optimizes the conversion of stormwater to groundwater, reduces erosive energies and the adverse effects on the receiving water, and results in an increase in natural capital.  This approach is truly a regenerative design since the use of these elements result in a system of physical features, chemical processes, and biological mechanisms that can have dramatic positive spiraling effects on the ecology of a drainage area.  This model results in increases in vernal pool wetland area, improved water quality treatment, contributes to local micro-habitat diversity, and provides a significant aesthetic value.  These projects are generally a win-win-win arrangement, as conventional construction practices and materials are more expensive, conventional conveyance provides no environmental benefits and are more difficult to permit, and people generally enjoy the aesthetics associated with a well vegetated channel form when compared to the conventional conveyance alternative.