Post-SMCRA Reclaimed Minesoils: Slope and Cover Effects On Runoff Under Natural Conditions.

In West Virginia, surface coal mining disturbs a large area of mountain landscapes.  A special type of soils called “reclaimed minesoils” or simply “minesoils” is established through the mining reclamation process.  West Virginia has placed special emphasis into the planning and executing of effective reclamation work, however the task has been proven to be challenging.  During the reclamation processes, surface grading for stability requirements often causes high surface compaction and consequently high bulk density and low porosity, which are properties that will affect soil hydrologic behavior.  Minesoils are considered to restrict water movement and to be poorly drained with low infiltration rate and high runoff potential, therefore, they are at greater risk for runoff and erosion; based on this consideration and due to environmental regulations, mine companies are required to install expensive drainage structures to control surface runoff.  Additional external factors affecting water infiltration are slope gradient, and vegetation or soil cover; in recent years, an important effort has been placed in studying the best vegetative cover for minesoil reclamation practices.  Since minesoils have been known to be highly variable, on-site observations and research should be conducted on individual mine sites with the goal of  characterizing variable soil properties, which will guide the implementation of appropriate land use management and practices. The objective of this study was to measure the effect of slope and vegetative cover on runoff and infiltration in reclaimed minesoils under natural rainfall.  Twelve research runoff/infiltration plots were be placed on a 20 ha reclaimed mine surface in Cowen, WV.  A completely randomized 2x2 factorial experiment with 3 replications was designed for the study.  The two factors considered were soil cover (vegetation) and slope.  Selected slope levels were 3-5% and 10-15%, and soil cover was either grass only or a combination of grass and forest.
ANOVA results indicated statistically significant differences in runoff and sediment production between collection dates and slopes; no interactions between slope and cover were observed.  There were no significant differences for sediment and runoff amount for forested plots regardless of slope, however for the grass-covered plots, higher slopes did increase significantly the sediments and runoff produced with respect to the lower sloping plots.  Collection times have been grouped into two periods: period 1 (P1) March through May and period 2 (P2) May through June.  Differences in hydrologic behavior were observed between periods.  In the first period, forested plots and higher slopes showed increase runoff and increase in total sediment production, however, no statistically difference with lower slopes and grass cover plots were observed.  Interesting to observe is that the “concentration” of sediments in runoff water was significantly affected by changes in cover, grass cover decreased the concentration of sediments; slope did not affect sediment concentration.  In the second period, forested plots and higher slopes also showed increase in runoff and increase in “concentration” of sediments in runoff water, however no statistically difference between lower slopes and grass plots were observed.  Higher slopes produced more sediment independently of cover.  In average, the grass-covered plots showed higher infiltration and less sediments production than the forested plots.  Based on the data collected between March and July 2009, stability analysis indicates that runoff amount is not a good estimator for sediment production in our minesoils runoff plots.  High variability in percentage of infiltration/runoff, sediment production and sediment concentration in runoff water between plots, indicated the inconvenience of classifying all the minesoils in the same hydrologic class group without on-site examination.