Preferential flow (PF), which has long been proposed as a common and significant hydrological process, has seen increasing interest in recent years. However, the comparison of PF among different headwater catchments is often missing. Part of the reason lies in the fact that co-variants controlling PF often interact, which increases the difficulty of identifying the main factors controlling PF. By installing soil moisture sensors at the same depths (10cm, 20cm and 40cm) between a shale site and a sandstone site in SSHCZO at four slope locations (ridge-top, south- and north-facing mid-slopes, toe slope), it was possible to uncouple potential interactions between slope position and lithology. PF frequency was calculated by inferring the lag time of soil moisture response order with depth. At south-facing mid-slope position, the shale site had a much higher PF frequency compared with the sandstone site (38.1% vs. 7.7%). Even though the sandy soils at the sandstone site tend to be more porous, the clay-rich soils at the shale site typically undergo more shrink-and-swell processes that create denser fissures among soil aggregates. In contrast to the mid-slope position, PF frequencies were more similar at toe slope (10.5% for shale and 14.5% for sandstone). At this site, instead of direct water percolation, the rise of groundwater often shortened deeper soil moisture response time at both catchments, which is further corroborated by water table depth measurements. Lastly, pedon-scale preferential flow processes were linked to catchment scale hydrological processes by comparing soil moisture dynamics with discharge (Q) fluctuation measured by a flume gage at the watershed outlet. The Q dynamics differed between PF events and non-PF events, which could be explained by favorable rainfall conditions that initiated PF. This study helps develop lithologic and topographic controls on PF and Q dynamics in contrasting catchments.
Qicheng Tang*, Jonathan M Duncan, Dacheng Xiao, Li Li, Li Guo, Henry Lin, David M Eissenstat (2018): Comparing preferential flow between two catchments with contrasting lithologies. Abstract H41O-2310 presented at 2018 AGU Fall Meeting, Washington, D.C., 10-14 Dec .
This Paper/Book acknowledges NSF CZO grant support.