Promoting biodiversity and sustainability with natural channel systems
By Paul Kos
Restoring stream corridors to naturally functioning ecosystems is a way mining companies are demonstrating sustainable practices, enhancing biodiversity, and obtaining approval—regulatory and social. Stream restoration is intended to exceed typical reclamation practices by creating natural channel systems that provide habitat and passage for aquatic and terrestrial organisms rather than a linear, armored channel.
In the US, regulations governing mine closure have, in many cases ignored the geomorphic and stream power considerations of the streams, which have been a deterrent to stream restoration in past mine reclamation projects as no erosion was allowed; yet, erosion is a key component of natural stream ecosystems and a fundamental principle of stream flow and integral to stream restoration projects. _q_When I started reclaiming mine sites, I never thought I would design fish ladders, but I've been designing natural streams throughout the west for over 15 years now._q_ To comply with regulatory requirements, stream restorations at mine reclamation sites typically included riprap or other hard armoring that prevent erosion. Such armoring prevents the channel from acting in a natural manner. In recent years, however regulatory ideology has slowly changed to allow limited erosion in stream restoration projects, and this regulatory shift allows many more channels to be restored to match undisturbed channels around them and to restore a naturally functioning ecosystem.
A restored stream channel typically exceeds permit requirements as to flow capacity, ability to provide habitat, and provides passage for aquatic organisms. These benefits can be used for third-party review and certification of a project as beneficial to wildlife habitat. These independent project reviews and certifications allows the mine operator to demonstrate commitment to stream restoration goals and to use recognized best management practices which benefit all stakeholders.
Sounds great, but at what cost? Regardless of the channel type, water management systems are typically a small percentage of the total reclamation costs at a mining property, and the greatest costs are typically slope grading, topsoiling, and vegetation. Adjusting the channel construction costs from hard armor to a natural system has a negligible impact on the final cost. Also, by incorporating geomorphic concepts and data, stream restoration uses channel geometry and vegetation for erosion protection over rock armoring, and the additional excavation and vegetation costs may actually be less than rock procurement and placement costs. Maintenance expenses are also generally less because the restored stream behaves as a resilient ecosystem through a natural balance of erosion and sediment deposition. Flooding is safely conveyed using the vegetated floodplain rather than riprap armoring.
Stream restoration doesn’t require a significant effort beyond simple reclamation. The upland grading is the same for both projects, and the only difference is the few feet at the bottom where water can flow in the design storm. While a traditional channel only contains riprap armoring, a restored channel creates habitat and resiliency using:
- Low-flow channel: Seasonal low flows are concentrated in the low-flow channel to provide a continuous water path. The low-flow channel usually meanders across the floodplain to limit channel gradient.
- Riffle-pool sequences: Riffle-pool sequences create alternating aquatic habitats with riffles on straight segments and pools at bends. Both habitat types are necessary for fish and insect to propagate. These structures also provide gradient control and can be used on channel slopes up to 5%.
- Floodplain and Terrace: Flood flows occur on the floodplain, and higher flows may reach terraces. The greater flow area and vegetation on floodplain decrease flow velocities and limits erosion. _q_If you're already grading the site to construct a channel, why not go the extra step and create something that mimics a natural stream?_q_
- Boulder walls or vegetated soil lifts: High velocities at the channel banks or site topography may require localized armoring, and boulder walls or vegetated soil lifts can provide this armoring.
- Vegetation: Stream restoration requires a diverse seed and plant mixture that mimics a natural stream setting. Riparian species are required along channel banks and floodplains where water is typically present. These grasses and shrubs occur naturally on floodplains, tolerate high water tables, and provide erosion resistance. This vegetation also provides shading for aquatic habitat that controls stream temperatures, and promotes biodiversity in both land and aquatic animals and insects.
Choosing to restore stream channel segments as part of your mine reclamation project can make it easier to obtain current and future permits, and it will help demonstrate the mining industry’s commitment to sustainability to the global community.
About the Author
Paul Kos is a professional engineer with 22 years of experience in project management and engineering support to mining, water resources, and environmental projects throughout the western United States and Canada.