Effects of Placer Mining on Hydrologic Systems in Alaska: Status of Knowledge

Nearly all significant information about effects of placer mining on hydrologic systems in Alaska is referenced in available reports. Addition of sediment in quantities and sizes that cause significant changes in normal relationships among stream discharge and sediment size and concentration (and indirect changes generated) appears to be the primary impact of placer mining on Alaskan hydrologic systems. Other potential water-quality effects to be considered are: increases in organic loading and minor element content; potential for acid drainage; and impacts on aquatic biota. Existing information , adequately defines parameters that may be affected by placer mining but cannot quantify hydrologic changes resulting from individual operations or predict magnitude or duration of impacts in unmined areas. Studies that would improve current knowledge include: Short term assessments, using aerial photography, satellite imagery, and existing hydrologic records, to document historical changes and active placer-mining features; short-term studies involving minimum data-collection efforts and using empirical sediment-transport formulas to estimate effects of mining activities; and river-quality assessments of selected basins affected by placer mining. These studies will not provide the quantitative information that could be gained from long-term detailed study of specific placer-mining activities, but will provide qualitative information for management decisions needed in the near future.