Effects of Land Use Changes on Stormflow Dynamics

Caption:  Locations of George's Creek, Savage River, and smaller order gaged watersheds.  Click for a larger view.

In the Appalachians, many local communities are plagued by two water resources problems that represent a legacy of environmental degradation from both underground and surface mining activities: poor water quality resulting from acid mine drainage and economic losses and personal hardship from persistent flooding.

In association with the ROCA Project, we conducted a comparative, multi-scale hydrological analysis of stormflow generation in the region in order to assess the effects of surface mining and mined land reclamation practices on flooding. We examined forested and reclaimed small, gaged zero order watersheds as well as two larger (< 200 sq. km) river basins in the region.

Caption:  Flooding in George's Creek in 1996.

Caption:  Flooding in the town of Lonaconing in 1996.

Zero Order Watersheds

Caption:  Two-hour unitgraphs computed for MAT1 and NEF1.

Results suggest that the peak discharge response of surface-mined/reclaimed lands can be as much as 1.5-10 times greater than that of forested lands in the basin.

Two-hour unitgraphs were derived from data collected during a summer 2000 rainstorm event (shown at right). The shapes of the resulting unitgraphs are virtually identical (i.e., comparable lags and peak rates of direct runoff), suggesting that the two watersheds differ principally with respect to the amount of precipitation "abstracted" during rainstorms.

We also found that surface soil organic matter may be the best predictor of both infiltration capacity and the stormflow response of the watersheds. Deforestation, surface mining, and reclamation appear to dramatically reduce the organic matter present in the soil, especially at the surface where infiltration takes place. The replacement of an organic rich forest floor with a tightly-compacted mineral soil apparently reduces infiltration capacities and increases both effective rainfall and direct runoff.

Results suggest that surface mining and conventional reclamation of previously forested lands on the Appalachian Plateau can dramatically affect the runoff response of small “zero-order” watersheds to precipitation, potentially contributing to the magnitude of downstream flooding of steep, V-shaped valleys that are characteristic of this region.

River Basins

Caption:  Unit hydrographs for George's Creek and Savage River basins.

Using an adjusted direct runoff hydrograph, a six-hour unitgraph was derived for Georges Creek (shown at right). The derived Georges Creek hydrograph is substantially more peaked, with a peak discharge value that is nearly 50% greater than the value for Savage River. The less-attenuated unitgraph is consistent with our working hypothesis that land use/land cover changes due to surface mining, reclamation, and urbanization may be exacerbating flooding in this basin.

Future Work

For a second phase of the research, Maryland Bureau of Mines (MBOM) has provided funding to make comparable field measurements on other mined watersheds in the Georges Creek basin to examine the variability in stormflow responses. We are also interested in understanding and predicting the cumulative hydrologic impacts of widespread surface mining in larger river basins, as well as in testing whether alternative reclamation practices might be useful in helping restore "normal" hydrologic responsiveness of mine-lands.