Mossy Creek-North River Environmental Bank
The geomorphic, hydrologic, hydraulic, and biologic parameters assessed indicate that restoration is necessary for Mossy Creek to become a stream capable of supporting historic and potential ecological functions. The scale and scope of any ecological intervention must be evaluated for the current condition and functioning versus the potential ecological functions capable of being supported within a resource. Existing conditions, including the lack of riparian buffers and cattle impacts, have contributed to a reduction of hyporheic exchange, fine sediment aggradation, excessive channel erosion, eliminated or degraded refugia and epifaunal substrate, limited shade and temperature regulation, and decreased or eliminated supply of organic matter for food and habitat. The agricultural impacts to the project reach have adversely affected the hydraulics and geometry of the stream channel. Sediment deposition within the channel has likely occurred from bank erosion and changes to flow regimes brought about by channel modifications and widening.
A variety of methods and data were used to formulate the design plan. Hydraulic analysis and channel morphology were measured in the field, modeled, and assessed at the reference reaches to aid in the creation of a design plan that will optimize functional improvement within project constraints. The design will rely on the Natural Channel Design (NCD) approach and methods tailored to a spring-fed stream. For the preliminary design, regional curve data for Ridge and Valley were analyzed and used for morphological characteristics. Regional curve data were obtained from published sources and verified with field observation.
The restoration will involve in-channel manipulation and rerouting of the channel. Design implementation will restore a more natural channel planform, which will enhance other geomorphic and hydrologic processes, including reduced erosion, increased floodplain connectivity, and decreased sediment aggregation. Throughout the reach, planform will be manipulated to more closely align with the NCD parameters. The channel itself will be narrowed to facilitate increased flow speeds that will be able to transport accumulated sediments within the channel. The sinuosity – the ratio of the stream length to the valley length – will be increased, which will form a more meandering planform and one more appropriate for the given slope of the valley. Site assessment and data analysis indicated that sediment transport is one of the major problems within this reach. The aggregation of fine sediments is visually displayed by islands that have formed within the channel and validated by cross sectional measurements. These findings indicate a sediment capacity issue that will be addressed by designing channel geometry to produce a shear stress value that will move sediment of the existing size.
Ecosystem Services is working with the landowner to develop the project as part of a stream mitigation bank.
- Provide mitigation for unavoidable impacts to aquatic resources
- Restore and protect critical trout habitat
- Improve floodplain connectivity
- Improve sediment transport capacity