Evaluating sediment production from native and fluvial geomorphic-reclamation watersheds at La Plata Mine

Abstract

San Juan Coal Company reclaimed 743 ha at its La Plata Mine using the GeoFluv™ fluvial geomorphic reclamation design method from 1999 through 2008 to achieve long-term stability against erosion (no major slope blowouts and rill and gully formation), reduced maintenance, and increased biodiversity as compared to traditional reclamation methods (e.g. terrace, berm, and downdrain designs). Qualitative inspections of the completed reclamation confirmed the fluvial geomorphic reclamation method benefits. In the fall of 2011, the company began implementing a research study to quantify the sediment production rate from these geomorphic landforms and surrounding undisturbed native lands.Data were acquired from subwatersheds differentiated as native (undisturbed by mining), fluvial geomorphic design with topdressing and poorly established vegetation, and fluvial geomorphic design with topdressing and significant vegetation establishment. The three subwatersheds were selected to ensure similar size, aspect, and slope and were located close together to minimize storm variation effects. Temporary check-dam-type sediment control structures designed to impound runoff from a 2-yr, 1-h storm were installed at each subwatershed outlet. Erosion pins in the impounded area facilitated sediment deposition measurement. Precipitation was recorded by the La Plata Mine Meteorological Station and supplemental site-specific precipitation gauges.Precipitation sufficient to cause sediment transport provided data for the end of the 2012, all of the 2013, and the beginning of the 2014 water years. The site data provided direct relationships between sediment production and precipitation. The sediment yield from the undisturbed native site was 9.53 t ha−1 yr−1, while the fluvial geomorphic design with topdressing and poorly established vegetation site averaged 13% lower than the native site, and the fluvial geomorphic design with topdressing and significant vegetation establishment averaging 41% lower sediment yield than the native site. Land-disturbing activities that can accelerate erosion and sediment yield will accompany global population growth. The results of this study indicate that use of this land reclamation method can mitigate erosion and sediment yield increases associated with that growth.