The Do Nothing Approach
After a trapezoidal channel is maintained it may go through a period of initial adjustment where banks vegetate and ultimately reach a stable state. In spite of being somewhat different than designed these channels may perform needed drainage functions, some level of ecological services and may even be more stable. The Do Nothing approach is simply leaving the system in its current state. This approach is the least expensive and may be the best solution if some ecosystem functions are already present in the system after a modification as a result of recovery, or the costs of enhancing the system outweigh the benefits. Generally, if the system is not causing a problem, the Do Nothing approach should be considered. The major challenge of this approach will be to estimate the true drainage benefits of the system in addition to the current and potential services performed by the system.
A trapezoidal channel that has just been maintained.
A trapezoidal channel with vegetated banks that are stable.
A channel originally constructed as a trapezoidal channel that has evolved to a two-stage system.
Passive enhancement means stopping activities that cause degradation or prevent recovery to allow natural processes to return to a channel system. Passive enhancement encompasses a range of options and might include changing land use in the watershed to prevent soil erosion and increase water infiltration; managing livestock to protect riparian vegetation and stream banks; planting native vegetation; keeping toxic chemicals out of the water; managing activities from construction sites, timber harvesting, and road building to prevent sedimentation; and choosing not to build, harvest, or graze in sensitive areas.
The Passive Enhancement approach may be selected to target a specific ecosystem function or when resources are limited. This approach provides little to no engineering input, can be relatively inexpensive, and can greatly enhance certain impaired ecosystem functions. In highly modified channel systems, passive enhancement might include livestock fencing, purchasing conservation easements, invasive species removal, native vegetation planting, and establishing no-mow zones. Although passive approaches may have positive effects, the approach may not be viable for channels that have been so degraded that recovery can take decades or longer, especially where accelerated erosion of high banks is severe. In agricultural settings, for example, providing grassed buffer strips along the top of ditches is an agricultural Best Management Practice that might be considered a Passive Enhancement approach for improving the ecological function of the channel system.