MODELING HILLSLOPE WATER J. J. van Tol, S.A. Lorentz & P. A. L. Le Roux Hydropedology dialogue Pretoria 2014

INTRODUCTION  Catchments are ideal management units  Hillslope determine hydrological response  Fundamental landscape unit  Common form of organization and symmetry  Interaction between: Topography Climate Vegetation Geology Soils  Ideal scale for understanding and simulating hydrological process  Basic building block for some hydrological models

 Progress in hillslope hydrology declined modellers experimentalists  Modellers: Small scale physical descriptors Don’t incorporate the experimentalist’s knowledge into model structure HILLSLOPE HYDROLOGY

Hydrological modeling problem  Dominant paradigm in hydrological modelling  a priori set of small scale theories and process descriptions  splitting the catchment into small enough uniform elements for these theories to work  Models require mapping of heterogeneities and process complexities  Impossible!!

Hydrological modeling problem  Models rely on calibration  Models ‘work’ but for wrong process reasons  Overparameterized  Equifinality  Large degree of modeling uncertainty  Unsuitable for PUB’s!!

 Progress in hillslope hydrology declined modellers experimentalists  Modellers: Small scale physical descriptors Don’t incorporate the experimentalist’s knowledge into model structure  Experimentalists Unconventional behaviour of new hillslopes No intercomparison Extrapolation value is low No minimum set of measurements to characterize a single hillslope!! HILLSLOPE HYDROLOGY

Hydrological modeling problem  Paradigm shift required  Accept landscape heterogeneity and process complexity  Find common threads, patterns, concepts and laws  Identify, classify and quantify

Hydrological soil typeSymbol Recharge Interflow (A/B) Interflow (soil/bedrock) Responsive (shallow) Responsive (saturated)

Weatherley: 5 hillslopes Bedford: 2 hillslopes Two Streams: 3 hillslopes Cathedral Peak: 2 hillslopes Baviaans: 2 hillslopes Letaba: 4 hillslopes Skukuza: 4 hillslopes Bozrah: 2 hillslopes Bloemfontein: 5 hillslopes Riversdale: 1 hillslope Mokolo: 5 hillslopes Craigieburn: 3 hillslopes PAP: 1 hillslope Thaba Nchu: 2 hillslopes Taylors Halt: 1 hillslope Hogsback: 2 hillslopes Noord Kaap: 2 hillslopes Loeriesfontein: 2 hillslopes Schmitsdrift: 2 hillslopes Newcastle: 3 hillslopes

Observations and measurements CatchmentHillslopePedologySoil physicsHydrometricsGeologyAI Craigieburn3 √√√ Granite0.28 Letaba4 √√√ Granite0.2 Skukuza4 √√√ Granite0.25 Mokolo5 √xx Aeolian0.2 New Castle3 √xx Sandstone/dolerite0.35 Two Streams3 √√√ Sandstone0.4 Taylor’s Halt1 √√x Sandstone0.45 Noord Kaap2 √√x Aeolian<0.1 Taba Nchu2 √xx Sandstone/mudstone0.28 Schmitsdrift2 √xx Alluvium0.15 Bloemfontein5 √xx Shales/dolerite0.25 Cathedral Peak2 √√√ Basalt>0.6 Weatherley5 √√√ Mudstone/dolerite0.5 Loeriesfontein2 √xx Shales0.2 Hogsback2 √xx Shales/dolerite>0.6 Fort Hare2 √√x Shales0.26 Bedford2 √√√ Shales0.2 Riversdale1 √xx Sandstone0.5 Baviaans kloof2 √xx Conglomerate0.2 PAP1 √xx Granite0.3

Framework of hillslope classification

Van Tol JJ, Le Roux PAL, Hensley M & Lorentz SA. Hydropedological classification of South African hillslopes. Vadose Zone Journal, 2013

Application – distributed modelling

Application – wetlands (Hogsback) Class 1 Class 4

Conclusions  We can: Indentify Classify  Dominant hydrological responses  We need to:  Quantify!

THANK YOU!!  WRC