Application of a digital filter method to separate baseflow in the small watershed of Pengchongjian in Southern China

Abstract

Baseflow plays a crucial role in maintaining the stability of streamflows, especially in watersheds. To reveal the evolution of baseflow in watersheds in southern China, this study investigated the variation in baseflow across the small watershed of Pengchongjian in Jiangxi Province. A digital filter method was applied to separate baseflow from local daily streamflow records for 1983-2014 using different values of filtering parameter (β) and filtering times (T). The separation results were validated by the baseflow index (BFI) method to determine the optimal parameters. When β = 0.90 and T = 2, the baseflow separation results conformed to the actual field situation in the watershed. The average monthly baseflow increased at first and then decreased, being unevenly distribution within a year, whereas average monthly BFI followed the opposite trend. On the seasonal scale, baseflow was ranked as spring > summer > winter > autumn, and the BFI as winter > spring > autumn > summer. Both the annual baseflow and BFI decreased at a rate of 2.30 mm/year and 0.0005/year, respectively. When considered on the annual scale, the BFI was lower in the wet years and higher in the dry years compared with normal years, averaging 0.22 in the watershed for the 1983-2014 period. This study obtained key optimal parameters for baseflow separation and revealed baseflow variation in the Pengchongjian watershed. These results provide a useful reference for studying the patterns of baseflow evolution in watersheds in southern China.