Presentation is loading. Please wait.

Presentation is loading. Please wait.

Vadose Zone Hydrology (Land Surface to Phreatic Surface) Matthys Dippenaar Engineering Geology and Hydrogeology Department of Geology University of Pretoria.

Similar presentations


Presentation on theme: "Vadose Zone Hydrology (Land Surface to Phreatic Surface) Matthys Dippenaar Engineering Geology and Hydrogeology Department of Geology University of Pretoria."— Presentation transcript:

1 Vadose Zone Hydrology (Land Surface to Phreatic Surface) Matthys Dippenaar Engineering Geology and Hydrogeology Department of Geology University of Pretoria 17 November 2014 Water Research Commission Khuluma Sizwe Series: Hydropedology in support of Hydrology and Eco-hydrology

2 What happens (OFTEN) in Joburg Increased golf course irrigation on JDG – Waterlogged soils – Increased interflow & unsaturated seepage – Damage to infrastructure 2

3 What happens (OFTEN) in Joburg Increased golf course irrigation on JDG – More common problem than expected as “recreational developments” allow development of areas where large portions are zoned for no development – Insurance company in court with developer as this is poor planning – Ca. 50 units affected in affluent golfing development 3

4 The South African Vadose Zone (Geological Perspective)

5 5 Ca. 4 m depth Lanseria tonalite gneiss, Midrand

6 The Vadose Zone 6 Transported Soils Residuum Ferruginized/ ferricrete Completely Weathered Erodible Highly Weathered Fresh Jointed Bedrock Regolith Saprolite Pebble Marker Ferruginized/ ferricrete

7 The Vadose Zone South African vadose zone is thick (easily tens of meters) Includes soil and rock, and often different lithologies with depth Given the age of our rocks and the intricate geomorphological past, geological profile development is often distinct throughout the depth Similarly, all hydrological parameters (porosity; conductivity; permeability; specific yield) vary with spatially and depth Remember: engineers call weak rock soil (UCS < 1 Mpa) 7

8 Karoo dolerite sill at Gariepdam 8

9 9 Colluvium Ferruginized Horizon Granite Saprolite Porosity ca Pore size small Connectivity poor Adhesion dominates Porosity ca Pore size large Connectivity good Cohesion dominates Possibly periodically saturated Quartz Feldspar Clay/ Mica Goethite Water Limited deep percolation due to smaller pore sizes in saprolite

10 10 Translocated downslope with shallow flow Weathers further into expansive clays Deposited at footslope as duplex soil Often waterlogged at surface Smectite Quartz Feldspar Clay/ Mica Goethite Water Limited deep percolation due to smaller pore sizes in saprolite Kaolinite leached

11 11 Expansive clay Quartz Feldspar Clay/ Mica Goethite Water

12 Land Use Changes and the Impacts Thereof?

13 Volume Change Variable and partial saturation affect and are affected by land use change Variable moisture contents triggering mechanism for – Heave (frequent swell-shrink cycles) – Collapse (threshold moisture content to weaken; saturated soils are more self-supporting; permanent reduction in porosity post-development) Significant roleplayer in – Karst subsidence (ingress-scenarios >90% of all recorded) – Dispersivity and erodibility – Settlement 13

14 Effects of Urbanisation Stormwater – reduced overall recharge, localised recharge, decreased stream runoff Irrigation and landscaping – changes in infiltration vs runoff Leaking underground services – increased subsurface water Subsurface drainage – interruption of natural hydrology Reductions in stream flow – loss of connectivity between channels and possibly between surface water and groundwater Aquifer vulnerability – variable and dense sources of contamination coupled with all of the above 14

15 Effects of Urbanisation Compaction – reduced infiltration, permeability and porosity Surface sealing – reduced infiltration, increased runoff, interruption of connectivity of stream channels and wetlands Artificial ground – altered and highly variable hydraulic properties Manmade materials – altered properties of concrete, geotextiles, etc. 15

16 The Next Step?

17 Some Ideas… Better investigation focused around all impacts of land use change – Consider the impacts of changing water budgets to the subsurface – Anticipate the long-term effects on runoff versus infiltration – Realize the impacts on surface ecology, surface drainage and groundwater – Design for impacts on infrastructure development Sort out the bedrock interface – (How) does water enter saprolite from soil? – Variably saturated fracture flow – Epikarst (dolomite vadose zone) 17

18 Thank You! Questions? Bibliography and more information available in WRC report TT 584/13 | 18


Download ppt "Vadose Zone Hydrology (Land Surface to Phreatic Surface) Matthys Dippenaar Engineering Geology and Hydrogeology Department of Geology University of Pretoria."

Similar presentations


Ads by Google