Placer-Mine Site Reclamation Evaluation in Alaska

Currently applied stream channel reclamation techniques utilized by placer-gold miners in Interior Alaska are frequently not successful in meeting reclamation goals required by various land management agencies. Upper basin channels with a gradient of one percent or greater are particularly at risk of failure after reclamation. Surveys were conducted on thirteen previously reclaimed streams in order to analyze each site's hydraulic capacity and fluvial stability. Morphological parameters were compared to established values which are generally considered to represent stable channels, using the Rosgen stream type classification system. Additionally, surveyed channel width and depths were compared with dimensions derived from relationships in the literature for hydraulically stable, gravel-bed streams. The Corps of Engineers HEC-RAS program and field data were used to model flood events and estimate velocities and shear stresses in the channels and overbanks. Analyses indicated that most stream channels were constructed with, or quickly developed. excessively large width-depth ratios, steep energy gradients, and low sinuosities. These factors, combined with low rates of natural revegetation common to subarctic climates, resulted in failure (continued erosion and bank instability) for most of the thirteen sites.