Long-term hydraulic mining sediment budgets: Connectivity as a management tool.

Area of Science:

• Geomorphology
• Environmental Science
• Hydrology

Background:

• Late 19th-century hydraulic gold mining in California's Sierra Nevada generated substantial sediment.
• Upper Steephollow Creek is a severely impacted catchment by this historical mining activity.

Purpose of the Study:

• To map and model the distributed sediment budget of upper Steephollow Creek.
• To quantify historical and modern sediment storage and delivery from hydraulic mining.

Main Methods:

• Utilized modern geospatial methods and 2014 airborne LiDAR data.
• Developed digital elevation models (DEMs) for pre-mining, maximum aggradation, and modern surfaces.
• Calculated sediment volumes and sediment delivery ratios (SDRs) using geomorphometry.

Main Results:

• Approximately 23.5 × 10^6 m^3 of hydraulic mining sediment (HMS) was produced in the 54.6 km^2 catchment.
• Modern (2014) HMS storage is 3.75 × 10^6 m^3, representing 16% of production (SDR of 84%).
• Maximum aggradation (ca. 1884) storage was 7.15 × 10^6 m^3 (30% of production, SDR of 70%).

Conclusions:

• The study highlights a high sediment delivery ratio from the impacted catchment, exceeding typical agricultural basins.
• Strong longitudinal sediment connectivity exists in the region, with significant sediment transport over 130 years.
• Sediment connectivity dynamics show strong scale dependencies in space and time.