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Open AccessArticle

Understanding of Storm Runoff Generation in a Weathered, Fractured Granitoid Headwater Catchment in Northern China

1
Department of Hydraulic Engineering, State Key Laboratory of Hydroscience and Engineering, Tsinghua University, Beijing 100084, China
2
Department of Environmental Health and Engineering, Johns Hopkins University, Baltimore, MD 21210, USA
3
College of Resource Environment and Tourism, Capital Normal University, Beijing 100048, China
4
Changjiang Institute of Survey, Planning, Design and Research, Wuhan 430010, China
*
Author to whom correspondence should be addressed.
Water 2019, 11(1), 123; https://doi.org/10.3390/w11010123
Received: 28 November 2018 / Revised: 28 December 2018 / Accepted: 29 December 2018 / Published: 11 January 2019
(This article belongs to the Section Hydrology)
Few of the classical field studies of streamflow generation in headwater watersheds have been conducted in catchments with thin soils and deeply weathered crystalline silicate bedrock. As such, the role of the (potentially very large) storage capacity of weathered, fractured rock in baseflow and storm event discharge remains poorly characterized. Here we present a study of streamflow generation in an upland semi-humid watershed (Xitaizi Experimental Watershed, XEW, 4.22 km2) dominated by baseflow feeding one of the main water supply reservoirs for the city of Beijing, China. This catchment is relatively dry (625 mm/yr precipitation, 480 mm/yr Evapotranspiration), but has strongly seasonal precipitation that varies in phase with strongly seasonal potential evapotranspiration. The catchment was instrumented with four weather stations and precipitation collectors, 11 deep wells drilled into the bedrock along three hillslopes, and additional soil moisture sensors and water samplers along one hillslope. In six storm events over two years, samples of rainfall, soil water (10–80 cm depth), groundwater, and stream water were collected with high frequency and analyzed for stable water isotopes (δ18O and δ2H). Tracer-based hydrograph separation showed that event water (precipitation) makes up the majority of the hydrograph peak above baseflow, and pre-event water contributions (on average) simply represent the steady release of groundwater. The quantity of event water corresponded to a very small effective contributing area (<0.2% of the catchment) that nevertheless showed a clear dependence on catchment wetness as measured by the streamflow. The streamflow itself was isotopically identical to the deep groundwater in wells. This suggests that the fractured, weathered, bedrock system dominates the production of streamflow in this catchment. View Full-Text
Keywords: semi-humid; runoff generation; hydrograph separation; weathered semi-humid; runoff generation; hydrograph separation; weathered
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Zhao, S.; Hu, H.; Harman, C.J.; Tian, F.; Tie, Q.; Liu, Y.; Peng, Z. Understanding of Storm Runoff Generation in a Weathered, Fractured Granitoid Headwater Catchment in Northern China. Water 2019, 11, 123.

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