Agricultural drainage water management in arid and semi ... - FAO.org

viiPageCalculation example of the impact of shallow water table managementon salinity buildup and leaching requirement 67Land retirement 69Hydrologic, soil and biologic considerations 69Selection of lands to retire 70Management of retired lands 716. DRAINAGE WATER REUSE 73Introduction 73Relevant factors 73Considerations on the extent of reuse 74Maintaining favourable salt and ion balances and soil conditions 74Maintaining a favourable salt balance 74Maintaining favourable soil structure 75Maintaining favourable levels of ions and trace elements 79Reuse in conventional crop production 81Direct use 81Conjunctive use – blending 82Conjunctive use – cyclic use 83Crop substitution and reuse for irrigation of salt tolerant crops 85Crop substitution 85Reuse for irrigation of salt tolerant plants and halophytes 85Reuse in IFDM systems 87Reclamation of salt-affected land 897. DRAINAGE WATER DISPOSAL 91Requirements for safe disposal 91Disposal conditions 92Disposal in freshwater bodies 93Disposal into evaporation ponds 95Evaporation ponds in Pakistan 96Evaporation ponds in California, the United States of America 96Evaporation ponds in Australia 97Design considerations for evaporation ponds 98Injection into deep aquifers 998. TREATMENT OF DRAINAGE EFFLUENT 101Need for drainage water treatment 101Treatment options 101Desalinization 102Trace element treatment 103Flow-through artificial wetlands 104Evaluation and selection of treatment options 107PART II – SUMMARIES OF CASE STUDIES FROM CENTRAL ASIA, EGYPT, INDIA, PAKISTANAND THE UNITED STATES OF AMERICA 109Summaries of case studies 111REFERENCES 121