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Submitted to: Hydrological Sciences Journal
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 10/13/2004 Publication Date: 1/3/2005 Citation: Bonta, J.V. 2005. Changes in concentration-discharge regression parameters due to coal mining and reclamation activities. Hydrological Science Journal. 50(1):155-173. Interpretive Summary: Assessment of the impacts of mining and reclamation, and development of best-management practices and total maximum daily load estimates, require knowledge of changing watershed runoff conditions and of changing sources of chemicals into stream waters. Often there is a relation between surface water chemical concentrations (C) and instantaneous discharge (Q). However, little is known regarding the watershed-scale effects of mining and reclaiming watersheds on changes to these relations. The effects of surface mining for coal and reclamation on C-Q relations were comprehensively assessed on three small experimental watersheds in Ohio (C06, M09, and J11). Comparisons were made of mathematical parameter changes between the natural/undisturbed conditions (Phase 1), land disturbances caused by mining and reclamation activities (subphases of Phase 2), incomplete reclamation (subphases of Phase 3), and the final condition of the reclaimed watersheds (Phase 3F). A total of 5047 laboratory analyses of 36 chemical constituents were used. Of 429 possible relations tested, 153 (36%) were statistically significant, and there were no correlations between C and Q for the others. Surface runoff diversions that guided water to a rock chute left in place during Phase 3F at C06 caused many significant differences between Phase 1 and 3F C-Q relations. The return of relations from Phase 3F to premine conditions at M09 is attributed to reclamation consisting of crimping straw into the land surface and no runoff diversions. The haul-back method of mining at J11 contributed to the observed C-Q relation changes due to the diverse surface disturbances of ongoing concurrent mining and reclamation. Diversions tended to cause statistically significant changes in C-Q relations causing larger chemical concentrations and loads. For some constituents, the sensitivity of chemical concentrations to low and high flows changed from one phase of disturbance to the next. Knowledge of changes in C-Q relations is important because they supply information on the rate of release and supply of chemical constituents in mined and reclaimed watersheds. Duration curves of chemical concentration and loads can be constructed using these mathematical relations with flow-duration curves to give estimates of the percent of time concentrations and loads are exceeded during different phases of disturbance. This study assessed the changes in regression relations due to mining coal seams and reclamation activities for 36 chemical constituents, using two mining methods, three reclamation practices, and three distinct geologic settings. The results are useful to state EPA agencies, regulatory agencies, NRCS, consultants, and university and foreign scientists for further scientific evaluation and development of the duration-curve method, for assessment of stream water quality, and for development of best-management practices. Technical Abstract: Assessment of the impacts of mining and reclamation, and development of best-management practices and total maximum daily load estimates, require knowledge of changing hydrologic conditions and of changing sources and rates of release of chemicals into stream waters. Little is known regarding the watershed-scale effects of mining and reclaiming watersheds on changing relations between surface water chemical concentrations (C) vs. instantaneous discharge (Q). These effects were assessed on three small experimental watersheds in Ohio subjected to surface mining for coal (C06, M09, and J11). Comparisons were made of regression parameter changes between the natural/undisturbed conditions (Phase 1), land disturbances caused by mining and reclamation activities (subphases of Phase 2), incomplete reclamation (subphases of Phase 3), and the final condition of the reclaimed watersheds (Phase 3F). Regression analysis used a total of 5047 laboratory analyses of 36 constituents. Of 429 regressions, 153 (36%) were statistically significant. Surface runoff diversions left in place during Phase 3F at C06 caused many significant differences between Phase 1 and 3F regressions. The return of regression relations from Phase 3F to premine conditions at M09 is attributed to reclamation consisting of straw crimping and no runoff diversions. The haul-back method of mining at J11 contributed to the observed regression changes due to the diverse surface disturbances of ongoing concurrent mining and reclamation. Diversions tended to cause statistically significant changes in regressions causing larger chemical concentrations and loads. The sign of the regression-line slope changed for some constituents from one phase to the next, documenting the changing sensitivity of concentration to low and high flows. Knowledge of changes in regression parameters is important because regressions supply information on the rate of release and supply of chemical constituents in mined and reclaimed watersheds. Duration curves of concentration and loads can be constructed using these regressions with flow-duration curves to give estimates of the percent of time concentrations and loads are exceeded during different phases of disturbance. This study assessed the changes in regression relations due to mining coal seams and reclamation activities for 36 chemical constituents, using two mining methods, three reclamation practices, and three distinct geologic settings. |
