PROSPECTS FOR THE DRAINAGE OF CLAY SOILS/ DAVID W. RYCROFT

1. Nature and distribution of clay soils. 1.1 Origin. 1.2 Nature of clay soils. 1.3 Classification. 1.4 Distribution. 2. Physical and chemical properties of clay soils. 2.1 Clay-mineral structure. 2.2 Physical properties. 2.1.2 Soil texture. 2.2.2 Soil structure and consistency. 2.2.3 Voids and porosity. 2.2.4 Infiltration and permeability. 2.2.5 Soil moisture storage and soil water content. 2.3. Chemical properties. 2.3.1 Caution exchange capacity. 2.3.2 Exchanges relationship. 2.3.3 Soil reaction- acidity and alkalinity. 2.3.4 Macro-and micronutrients. 2.4. Other properties. 2.4.1 Swelling and shrinking. 2.4.2 Cohesion and dispersion. 3. Movement of water and salts in clay soils. 3.1 Water movement in Clays. 3.1.1 Hydraulic conductivity. 3.1.2 Theories of flow in cracking clay soils. 3.1.3 Infiltration into swelling clay soils. 3.2 Movement of salt in clay soils. 3.2.1 Factors determining the movement of salts in soils and groundwater. 3.2.2 Movement of soluble salts. 3.2.3 Exchangeable. 4. Drainage of clay soils. 4.1 Surface drainage. 4.1.1 Bedding systems. 4.1.2 Furrow systems or row drainage. 4.1.3 Ditch system. 4.2 Groundwater drainage. 4.2.1 Ditches and buried pipe systems. 4.2.2 Drainage of layered alluvial clays. 4.2.3 Groundwater drainage for artesian conditions. 4.2.4 Scale changes to allow for anisotropy. 4.2.5 Artesian anisotropy effects on drain spacing. 4.3 Mole drainage. 4.3.1 Systems. 4.3.2 Installation. 4.3.3 Performance 4.3.4 Gravel tunnel mole drains. 4.4 Subsoiling. 4.5 Vertical chimney drains. 4.5.1 Verticals of the Indian Deccan 4.5.2 Design and layout. 4.5.3 Example of Chimney drain design. 5. Reclamation of salty clay soils. 5.1 Saline and saline sodic clays. 5.2 Leaching. 5.2.1 Quantity of water for leaching. 5.2.2 Water applications methods. 5.2.3 Amendments. 5.2.4 Development of a leaching programmed 5.3 Non-saline sodic clays 5.31 Estimating gypsum requirements. 6. Alternative strategies. 6.1 Rice cultivation. 6.1.1 Reclaiming effects of rice grown in sodic soils. 6.1.2 Types of drainage on rice fields. 6.2 Improved land forming 6.3 Restructuring. 6.4 Cultivation of salt-tolerant plants. 6.5 Water harvesting. 7. Case studies. 7.1 Drainage of heavy clay soils in the Sava valley, Yugoslavia 7.1.1 Background 7.1.2 Soil conditions. 7.1.3 Systems investigated. 7.1.4 Findings. 7.2 Drainage of heavy soils in Lezria Grande, Portugal. 7.2.1 1 Background 7.2.2 Soil conditions 7.2.3 Drainage systems investigated. 7.2.4 Findings. 7.3 Drainage of heavy soils in Spain. 7.4 Drainage of heavy soils in Egypt. 7.4.1 Background 7.4.2 First study. 7.4.3 Second case study. 8. Economics anaylisis of drainage of clay soils. 8.1 Guidelines for economics analysis. 8.1.1 Costs. 8.1.2 Benefits. 8.2 Discounted cash flow. 8.2.1 With or without the project. 8.2.2 Present values of benefits and costs. 8.2.3 Net present value 8.2.4 Benefits / cost ratio. 8.2.5 Internal rate of return. 8.3 Case study 1: costs of drainage heavy soils in the UK. 8.4 Case study 2: Drainage of heavy clays in Eastern Ontario. 8.5 Case study 3: Drainage of irrigated clays in the Guadalquivir Marhes in Spain. 8.6 Case study 4: subsurface and surface drainage in Algeria. 8.7 Case study 5: Drainage and reclamation of heavy clay soils in Egypt. 8.8 Summary. 9. Environmental impact of land drainage. 9.1Hydrology. 9.2 Water quality. 9.2.1 Sediments. 9.2.2 Nutrients 9.3 The disposal problem. 10 Knowledge gaps.

In English