Mountaintop Removal Mining and Catchment Hydrology

Abstract

Mountaintop mining and valley fill (MTM/VF) coal extraction, practiced in the Central Appalachian region, represents a dramatic landscape-scale disturbance. MTM operations remove as much as 300 m of rock, soil, and vegetation from ridge tops to access deep coal seams and much of this material is placed in adjacent headwater streams altering landcover, drainage network, and topography. In spite of its scale, extent, and potential for continued use, the effects MTM/VF on catchment hydrology is poorly understood. Previous reviews focus on water quality and ecosystem health impacts, but little is known about how MTM/VF affects hydrology, particularly the movement and storage of water, hence the hydrologic processes that ultimately control flood generation, water chemistry, and biology. This paper aggregates the existing knowledge about the hydrologic impacts of MTM/VF to identify areas where further scientific investigation is needed. While contemporary surface mining generally increases peak and total runoff, the limited MTM/VF studies reveal significant variability in hydrologic response. Significant knowledge gaps relate to limited understanding of hydrologic processes in these systems. Until the hydrologic impact of this practice is better understood, efforts to reduce water quantity and quality problems and ecosystem degradation will be difficult to achieve.

Landscape-Scale Disturbance: Insights into the Complexity of Catchment Hydrology in the Mountaintop Removal Mining Region of the Eastern United States

“…The effects of valley fills on storm flows are less well understood; both larger and smaller peak flows have been observed downstream of valley fills [12,23,28]. Differential responses of streamflow to surface mining are primarily due to different mining and reclamation practices, different scales of disturbance [2] and, to an uncertain extent, different disturbance histories.…”

“…Unlike traditional surface mining practices, such as contour, high wall and strip mining that impact a few hundred hectares, MTM disturbs thousands of hectares [2,15], with the largest MTM occupying ∼4000 hectares (∼40 km 2 ) [16]. MTM removes as much as 200 m of overburden from ridge tops [17] generating large volumes of waste rock that precludes replacing the material back on the ridge.…”

“…Runoff tends to be dominated by infiltration-excess overland flow [26,27], and some studies have found that streamflow downstream of surface mines tends to be flashy with large peak flows and storm flow volumes (e.g., [14,28,29]). However, MTM results in a two-part system with contradictory controls on hydrology [2]. Valley fills act like headwater aquifers that temporarily store and release water overtime [30], increasing catchment storage and potentially offsetting runoff increases from impervious surfaces.…”

“…MTM is a special form of surface mining adapted to mountain landscapes that removes forests, soils and overlying bedrock to gain access to underground coal seams. This practice leads to likely permanent and wholesale changes to catchment organization, structure, soils and vegetation that have important implications for catchment hydrology, geochemistry and ecosystem health [2][3][4]. The hydrological impacts of this practice are under increasing scrutiny following several devastating floods (e.g., [5]) and well-established patterns of biological impairment downstream of MTM [4,6,7] that implicate disturbance-driven changes in hydrology.…”

“…Despite the scale and extent of its disturbance, impacts from MTM on catchment hydrology are poorly understood. Knowledge gaps are vast and stem primarily from a paucity of pre-vs. post-impact studies due to limited access to private property [6] and the lack of consistent, long-term, scale-appropriate gauged watersheds [2]. The challenges of conducting research in heavily-disturbed and ever-changing environments [11] often prevents process-based and long-term studies, and the challenges of isolating the hydrological impacts of one disturbance within the context of multiple, overlapping disturbances [1] precludes better understanding of the hydrological changes that result from MTM.…”