| SOIL AND GEOTECHNICAL DEVELOPMENT POTENTIAL An Introduction   |
Geographic Information Very Important Note: |
An
Analysis of Geotechnical Development Potential  |
| Underlying Geology | Determines expected geological properties of soils formed in situ | Granites in north Amphibolite northwest of Roodepoort Quartsite and slate-central Jhb Lavas-Soweto Dolomite-Lenasia |
Soils and thus landuse that can
collapse (settle) on dolomite Excavation difficulties on quartsite and lava Heaving soils Subsidence risk |
Do detailed geological surveys before developing |
| Soil types and properties | Depth (thickness), texture, structure, porosity, permeability, clay percentage, drainage of soil | Grey and sandy in north Deep, red north of Roodepoort Deep, compressible West Rand Shallow – Central Rand Active clays - Klipriviersberg |
Agricultural potential high in
the north and patches in south and west Impacts of soils available for cultivation |
Develop and conserve soils in accordance to their properties |
| Construction material resources | Limited reserves Exploits land |
Brick-making clay-Northcliff,
Roodepoort, Bedfordview Fine building sand from northern granites |
Removal alters the landscape | Seek alternative sources |
| Landforms | Dams, drainage channel, excavations, flood plain, river bank, river channel, vlei/marsh | Klipriviersberg and Witwatersrand
Ridges Rolling plains in central, western and northern areas |
Flood damage Determines cultivation, erosion and housing potential of the land |
Consider the impacts before deciding on landuse type |
| Slope categories | Unstable slopes where steeper than 15º | Mine dumps Witwatersrand and Klipriviersberg Ridges Gatsrand |
Decreases land available for use Development and human activities cause accelerated erosion and rock falls |
Stabilise slopes with vegetation
and engineering Don’t plan landuse (housing/ construction) on unstable slopes |
| Dolomite stability | Sinkholes Dolines Groundwater pollution Risk for informal settlements Risk for development Pollution |
From Doornkop AH eastwards
through Lenasia West of Meadowlands |
Environmental development
problems, property damage and health risk Ground movement events |
Preferably do not develop (housing/ construction, may be used for parks) on dolomite areas |
| Geotechnical properties | Compressible soils Collapsible soils Active clay Dolomite areas Steep/Unstable slopes |
Parallel to Witwatersrand ridges Most areas of GJ Around Klip and Jukskei Rivers East and west of/and Lenasia Witwatersrand and Klipriviersberg ridges |
Structural damage Potential sinkhole formation Excavation problems Increased soil erosion Flood damage Reduced bearing capacity, rising damp in walls, groundwater pollution |
Stabilise soils with constraints
with stable material before development Design foundations |
| Agriculture
|
Wrong farming methods Cultural ecosystem |
Large areas in the north and
northwest Smaller holdings in the south |
Salinisation Waterlogging |
Better practices Conservation agriculture |
| Mining | Ungrassed mine dumps | Mining belt south of the
Johannesburg CBD Less mining than in the past, but older mines are being reworked |
Erosion Toxic soil pollution (Radon) Alteration of the land Siltation of streams and wetlands Groundwater pollution Soils aggressive to concrete |
Rehabilitate mine dumps from
south, southeast Plant indigenous vegetation and recover land for alternative uses Environmental Management Plans Improved extraction technology to reprocess mine tailings |
| Informal Settlements and Poverty | More people living in 1:50 year
flood line Lack of sanitation and regular refuse removal Increase in wood burning and removal of vegetation |
State of Poverty | Flooding and washing away of topsoil Surface soil, water and groundwater pollution Increase in soil erosion and flooding due to increased water flow |
Reduce population growth Environmental awareness and education Eradicate poverty Plant and protect vegetation that protects the soil |
| Urbanisation, Population Growth, Development and Urban Expansion | Higher densities of housing Removal of vegetation and disturbance of steep slopes Destabilisation of slopes due to roads Increase in impermeable surfaces Increase in sewerage and waste |
State of population | Increase in soil erosion Decrease in natural open spaces, soil and agricultural potential Increase in floods and surface water flow |
Decrease population growth Plant vegetation Improve infrastructure to cope with people and their waste, and reduce sewage overflows |
