Changing Waters: Trends in Central Appalachian Streamflow in the Presence of Mountaintop Mining
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Mountaintop mining (MTM) became popular in the 1970s in Central Appalachia and today remains the dominant form of coal mining in the region (Ross et al., 2016). Approximately 6-7% of the Appalachian Coalfield Region in West Virginia, Kentucky, Virginia, and Tennessee is covered by mountaintop mining operations (Lindberg et. al, 2011). MTM involves stripping mountain surfaces by up to 300 vertical meters of rock material (“overburden”) to gain access to thin coal seams (Lindberg et al., 2011; Palmer et al., 2010). The overburden is then deposited in adjacent valleys as so-called “valley fills,” often burying headwater streams that originate in the mountains. These valley fills increase a watershed’s storage potential to an unknown degree.
Hydrologic processes play significant roles in species habitats, aquatic chemistry and ecology, and overall aquatic ecosystem health (e.g., Miller & Zégre, 2014). The impacts of human activities and climate variability may cause hydrologic regimes to change, threatening the processes by which streams support ecosystem and human health. MTM research, especially in Central Appalachia, has largely focused on the effects of MTM on water chemistry and aquatic ecosystem health (Bernhardt et al., 2012; Palmer et al., 2010; Bernhardt & Palmer, 2011; Lindberg et al., 2011). This study contributes a regional-scale examination of hydrologic alterations in the presence of changing climate and land cover conditions to the field of hydrology.
One of the possible effects of topographic change from MTMVF could be a change in flow duration curves. I expected to see increases in low flows due to increased storage in the new MTM systems; during a storm, the valley fills likely increase the storage potential of the area. Furthermore, I hypothesized that any possible effect of MTM on hydrology will increase with an increase in the watershed area affected by MTM.
For this study I performed both time series analysis on precipitation and streamflow data as well as spatial analysis of MTM extent. First, I compiled streamflow and precipitation data from twelve watersheds in West Virginia and tested for trends in hydrologic and precipitation indices for the full periods of record. Second, I compared the trends in the post-mining time period (post-1976) with the pre-mining record, to test for trends in streamflow related to MTM. Third, I used four snapshots over time of MTM coverage data to characterize each study watershed by the percent land area covered by MTM, and compared these coverages with the magnitude of hydrologic trends, where trends existed. Comparing streamflow and precipitation totals between pre- and post-mining time blocks produced a few significant results, indicating that only two of the watersheds violated the assumption of stationarity from pre- to post-mining. I found some significant trends when considering metrics other than annual totals of daily-resolution data; minima and runoff ratios demonstrated some presence of trend in some watersheds, though not across all watersheds. Minima were more sensitive to time series analysis than annual totals. Sites 10 and 6 had the highest and third-highest amount of MTM, respectively (Table 2), and both had increasing minima over all years of data. The trends in minima in these watersheds could be associated with the high amounts of MTM. Increasing minima support the hypothesis that MTM increases the amount of storage in the landscape and provides more steady inputs of baseflow from storage sources. Site 10 demonstrates some of the characteristics expected of a watered affected by MTMVF. The late summer streamflow, or the low flows, appear to be increasing at Site 10. Runoff ratios overall had more significant results than the other streamflow metrics. Runoff ratio provides information as to whether the relationship between streamflow and precipitation is changing. Based on runoff ratios in summer and winter months, I assessed whether trends were detectable in high flow and low flow periods. The only watershed with a detectable upward trend in annual summer runoff ratios over time was Site 10. These above results indicate that baseflow in the streams of the Sites 6 and 10 watersheds may be increasing over time. Based on the results of this study, I conclude that some aspects of regional streamflow regimes do not meet the assumption of stationarity in the face of MTM; the characteristics where trends are most detectable include streamflow minima and seasonal runoff ratios. Future research could increase the scale of hydrologic regime analysis to more watersheds throughout the coalfield region. Studies of this nature can support informed decision making and understanding of the trade-offs between the benefits of altering land cover for economic growth and the possible negative impacts of environmental degradation (Defries & Eshleman, 2004). Policy decisions regarding MTM will need to evaluate scientific data on the impacts of MTM in order to make the best choices to protect human, wildlife, and economic health.
Knowlton, Meagan (2016). Changing Waters: Trends in Central Appalachian Streamflow in the Presence of Mountaintop Mining. Master's project, Duke University. Retrieved from https://hdl.handle.net/10161/11936.
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