1. Translating Soils Information for Hydrological Modelling Reflecting on the Big Picture from the 1970s to the Present Roland Schulze Professor Emeritus of Hydrology & Senior Research Associate Centre for Water Resources Research School of Agricultural, Earth & Environmental Sciences University of KwaZulu-Natal, Pietermaritzburg, RSA

2. Defining Moments … From Way Back ! 1.“A vital role is played by soil, for it is the capacity of the soil to absorb, retain and release water that is the prime regulator of the evapotranspiration and runoff response of a catchment” (England & Stephenson, 1970) 2.A catchment is not a lumped system in regard to soils, and pronounced differences in magnitude and sequence of hydrological processes have been observed in soil units within a catchment (England, 1970) 3.“Soils of the Tugela Basin” (van der Eyk et al., 1969)

3. Falling in Love …With a Subject Matter Defining Years …1970 -1974 The Drakensberg Cathedral Peak Research Catchments Energy and Water Budgets on Slopes with Different Gradients & Aspects

4. Mapping Energy Budgets on Sloping Terrain Considerations Verification

5. Understanding Soils … Getting Hands Dirty

6. 1979 SCS Manual Effects of SCS Soil Groups on Curve Numbers

7. How Sensitive are Stormflow Volume & Peak Discharge to SCS Soil Groups? Example Example Catchment Area = 2 km² Precipitation = 50 mm Land Cover = Veld in fair condition Catchment Slope = 8 % Length of main Stream = 1 500 m Conclusion Conclusion Highly sensitive

8. Meanwhile, on the Soil Science Front … The “Red Book”: MacVicar et al. 1977 Soil Classification – A Binomial System for South Africa Master Horizons Master Horizons (MacVicar et al., 1977) Diagnostic Horizons Diagnostic Horizons (SCWG, 1991)

9. Early 1980s The beginnings of ACRU A physical-conceptual, process based, daily time step water budget model

10. ? Q IOBSTQ? IOBSPK? PEAK QFRESP IRUN Q P ADJIMP COIAM SMDDEP COFRU P=Precipitation (mm) I a =Initial abstractions (mm) =f (S) S=Soil water deficit (mm) Q = (P – I a ) 2 / (P – I a + S) The ACRU Approach

11. With that, in the mid-1980s, the need to classify soils in South Africa hydrologically Working with Cass, Hutson et al Soils Issues for Hydrologists

12. And, the Advent of Soils LAND TYPES from the Binomial Soil Classification, and their Databases # Based on relatively uniform climate, terrain, soil patterns # With detailed soils inventory on soil series, clay %, texture class, profile thickness… # With the Land Type made up of several soil series # Including information on Terrain Units making up a Land Type

13. “Translating” Land Type Information to Hydrological Model Needs Rules for Partitioning Soil Horizon Thicknesses Drilling Down to Terrain Unit Level

14. BASIC PREMISE Operational hydrological models should be able to be “driven” by standard datasets which are freely available from national networks and by standard (usually non- hydrological) spatial digital information available at national level, suitably “translated” (I.e. converted) into model input variables, for the models then to operate over a range of desired spatial scales

15. Result … Detailed mapping of soil attributes which are critical to hydrological modelling from 16600+ Land Type Polygons (Schulze and Horan, 2008)

16. Result … Detailed mapping of soil attributes which are critical to hydrological modelling (Schulze and Horan, 2008)

17. Result … Detailed mapping of soil attributes which are critical to hydrological modelling (Schulze and Horan, 2008; Schulze, 2012)

18. Quo vadis? An operational hydrologist’s perspective  Operationalising terrain unit delineation  Mapping soil fertility in detail  Getting a better handle on hydraulic conductivity  Towards a general model of interflow  Ringfencing soils with high organic matter content  More detailed delineation of wetlands soils  Delineating unstable soils for hydrological modelling  Getting a better handle on drainage rates of soils