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 type Symbol

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

Catchment Hillslope Pedology Soil physics Hydrometrics Geology AICraigieburn 3 √ √ √ Granite 0.28

Letaba 4 √ √ √ Granite 0.2

Skukuza 4 √ √ √ Granite 0.25

Mokolo 5 √ x x Aeolian 0.2

New Castle 3 √ x x Sandstone/dolerite 0.35

Two Streams 3 √ √ √ Sandstone 0.4

Taylor’s Halt 1 √ √ x Sandstone 0.45

Noord Kaap 2 √ √ x Aeolian <0.1

Taba Nchu 2 √ x x Sandstone/mudstone 0.28

Schmitsdrift 2 √ x x Alluvium 0.15

Bloemfontein 5 √ x x Shales/dolerite 0.25

Cathedral Peak 2 √ √ √ Basalt >0.6

Weatherley 5 √ √ √ Mudstone/dolerite 0.5

Loeriesfontein 2 √ x x Shales 0.2

Hogsback 2 √ x x Shales/dolerite >0.6

Fort Hare 2 √ √ x Shales 0.26

Bedford 2 √ √ √ Shales 0.2Riversdale 1 √ x x Sandstone 0.5

Baviaans kloof 2 √ x x Conglomerate 0.2

PAP 1 √ x x Granite 0.3

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