A look inside ‘black box’ hydrograph separation models: a study at the Hydrohill catchment
Article first published online: 11 JUL 2001
Copyright © 2001 John Wiley & Sons, Ltd.
Special Issue: Hydrology and Biogeochemistry of Forested Catchments
Volume 15, Issue 10, pages 1877–1902, July 2001
How to Cite
Kendall, C., McDonnell, J. J. and Gu, W. (2001), A look inside ‘black box’ hydrograph separation models: a study at the Hydrohill catchment. Hydrol. Process., 15: 1877–1902. doi: 10.1002/hyp.245
- Issue published online: 11 JUL 2001
- Article first published online: 11 JUL 2001
- Manuscript Accepted: 5 SEP 2000
- Manuscript Received: 15 FEB 2000
- hydrograph separation;
- isotope hydrograph separation;
- chemical hydrograph separation;
- runoff sources;
- water flowpaths;
- mass balance;
- water budget
Runoff sources and dominant flowpaths are still poorly understood in most catchments; consequently, most hydrograph separations are essentially ‘black box’ models where only external information is used. The well-instrumented 490 m2 Hydrohill artificial grassland catchment located near Nanjing (China) was used to examine internal catchment processes. Since groundwater levels never reach the soil surface at this site, two physically distinct flowpaths can unambiguously be defined: surface and subsurface runoff. This study combines hydrometric, isotopic and geochemical approaches to investigating the relations between the chloride, silica, and oxygen isotopic compositions of subsurface waters and rainfall.
During a 120 mm storm over a 24 h period in 1989, 55% of event water input infiltrated and added to soil water storage; the remainder ran off as infiltration-excess overland flow. Only about 3–5% of the pre-event water was displaced out of the catchment by in-storm rainfall. About 80% of the total flow was quickflow, and 10% of the total flow was pre-event water, mostly derived from saturated flow from deeper soils. Rain water with high δ18O values from the beginning of the storm appeared to be preferentially stored in shallow soils. Groundwater at the end of the storm shows a wide range of isotopic and chemical compositions, primarily reflecting the heterogeneous distribution of the new and mixed pore waters. High chloride and silica concentrations in quickflow runoff derived from event water indicate that these species are not suitable conservative tracers of either water sources or flowpaths in this catchment. Determining the proportion of event water alone does not constrain the possible hydrologic mechanisms sufficiently to distinguish subsurface and surface flowpaths uniquely, even in this highly controlled artificial catchment. We reconcile these findings with a perceptual model of stormflow sources and flowpaths that explicitly accounts for water, isotopic, and chemical mass balance. Copyright © 2001 John Wiley & Sons, Ltd.