Compiled by Butch Clark from information provided by the Colorado Mined Land Reclamation Board
As more people arrive in Colorado, there is a need for more gravel for use as aggregate. Gravel mining happens where the gravel deposits are — often in streams and in riparian areas. Gravel mining, particularly in these places, is a concern in many Colorado communities. The Colorado Division of Minerals and Geology (CDMG) is completing a guidance document for use by gravel mine operators who conduct in-stream aggregate extraction. Its purpose is to minimize environmental effects to stream channels, riparian zones, wetlands, aquatic life, and the in-stream ecosystem of the mined land and adjacent areas. Below are portions of the document. The CDMG would appreciate reviews and comments during the next year.
There are approximately 75 in-stream gravel mining operations in Colorado. These operations have potential upstream and downstream impacts and affect adjacent property owners and structures. The guideline is intended to provide a range of acceptable methods for the extraction of aggregate by in-stream gravel mining operations. Topics are extraction, structures to minimize impacts to hydrologic balance and effects upstream and downstream to fluvial systems, cost-conscious monitoring, and reclamation to ensure channel stability when mining is completed.
The CDMG’s guideline is not intended to be a rule or regulation. It is intended to assist operators, technical consultants, the CDMG staff, other regulatory authorities, and the concerned public to plan gravel mining projects and evaluate applications for the necessary permits.
The guideline has four sections. The first is a discussion of stream classification, based on geomorphology, for steams and rivers across Colorado. The second offers an overview of typical aggregate extraction methods and monitoring for potential effects when aggregate extraction occurs within stream channels. In the third section there is an overview of reclamation practices and mitigation measures. The fourth section outlines information for evaluating and permitting gravel mining operations. This section also provides suggested sources for obtaining this needed information.
A major focus in the guideline is on bedload sediment transport within stream systems. This process provides the material to be mined. In the summary of the guidelines is the general recommendation that the extraction rate for an in-stream operation should be equal to the bedload transport rate. This can minimize harmful channel effects such as headcutting, channel incision, bank erosion, and harm to stream-side structures. However, not all adverse effects can be avoided. For example, because water flowing downstream has become free of bedload, the stream will pick up bedload sediment to replace what has been removed. Potential consequences of gravel extraction, such as scouring of bed gravels, exposure of underlying substrates not suitable for desired aquatic habitat, destruction of pool and riffle structures, and other ecological effects require evaluation to minimize adverse effects from in-stream gravel mining operations.
Copies of the guideline will be available from the CDMG at 1313 Sherman Street, Room 215, Denver, CO 80203 (phone 303-866-3567 ). Contacts are Loretta Pineda and Bruce Humphries.