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Stormflow response and ‘effective’ hydraulic conductivity of a degraded tropical Imperata grassland catchment as evaluated with two infiltration models
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  • Zhuo Cheng,
  • Jun Zhang,
  • Bofu Yu,
  • Nick A Chappell,
  • Ilja H.J. van Meerveld,
  • Leendert Adrian Bruijnzeel
Zhuo Cheng
Department of Geography, Beijing Normal University
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Jun Zhang
Institute of International Rivers and Eco-Security

Corresponding Author:[email protected]

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Bofu Yu
Griffith University
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Nick A Chappell
Lancaster University
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Ilja H.J. van Meerveld
University of Zurich
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Leendert Adrian Bruijnzeel
VU University
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Predicting catchment stormflow responses after tropical deforestation remains difficult. We used five-minute rainfall and storm runoff data for 30 events to calibrate the Green–Ampt (GA) and the Spatially Variable Infiltration (SVI) model and predict runoff responses for a small, degraded grassland catchment on Leyte Island (the Philippines), where infiltration-excess overland flow is considered the dominant storm runoff generating process. SVI replicated individual stormflow hydrographs better than GA, particularly for events with a small runoff response or multiple peaks. Calibrated parameter values of the SVI model (i.e., spatially averaged maximum infiltration capacity, Im and initial abstraction, F0) varied markedly between events, but exhibited significant negative linear correlations with (mid-slope) soil water content at 10 cm (SWC10) – as did the ‘catchment effective’ hydraulic conductivity (Ke) of the GA model. SWC10-based values of F0 and Im in SVI resulted in satisfactory to good predictions (NSE > 0.50) for 18 out of 26 storms for which data on SWC10 were available, but failed to reproduce the hydrographs for six events (23%) with mostly small runoff responses. Median values of field-measured near-surface Ksat (~2–3 mm h-1, depending on method) were distinctly lower than the median Im (32 mm h-1) and, to a lesser extent, Ke (~8 mm h-1), confirming previously suspected under-estimation of field-measured Ksat. Using pre-storm topsoil moisture content and 5-min rainfall intensities as the driving variables to model infiltration with SVI gave more realistic results than the classic GA approach or the comparison of rainfall intensities with field-measured Ksat.