The effects of hydrological factors on river suspended solids contamination from a colliery in South Wales

Suspended solids contamination caused by runoff below a working colliery in the Upper Clydach catchment in South Wales, U.K., was investigated in relation to hydrological controls. Field studies over a 16 month period found that concentrations below the colliery ranged from 4 to 8028 mg 1 −1 . Simple correlation and linear regression analysis of spot and storm event samples taken below the colliery gave a correlation coefficient of 0·39 between flow and suspended solids concentration. Because of the lack of explained variance, a multiple linear regression model of within‐storm concentrations was derived using four selected independent variables. X 1 the time relation of the sample to the storm peak; log X 2 the stormflow at the time of sampling; log X 3 the baseflow at the time of sampling; and log X 4 an index of the storm intensity. Analysis of the entire dataset gave an R 2 of 0·34. When the results from three atypical events were excluded however, the R 2 value improved to 0·65. Beta coefficients indicated that rising limb conditions (X 1 ) and intense storms (log X 4 ) along with dry antecedent conditions (log X 3 ) represent the worst combination of hydrological factors for producing suspended solids contamination.