Guidelines and computer programs for the planning and design of land drainage systems / W.H. van der Molen, J. Martínez Beltrán, W.J. Ochs.

Foreword -- Acknowledgements -- List of acronyms and symbols -- 1. Introduction -- 2. Environmental considerations in drainage projects -- 3.Socio-economic and institutional aspects -- 4. Drainage studies and investigations -- 5. Main drainage and disposal systems -- 6. Surface drainage -- 7. Subsurface drainage -- 8. Calculation programs for drainage design -- References -- Annexes -- 1. Estimating soil hydrological characteristics from soil texture and structure -- 2. Statistical analysis of extremes -- 3. Field methods for measuring hydraulic conductivity -- 4. Determining drainable soil porosity -- 5. Determining other soil hydrological characteristics -- 6. Estimating recharge due to irrigation -- 7. Leaching for salinity control -- 8. Procedures for determining soil hydrological characteristics in drained lands -- 9. Procedure for deriving drainage design criteria from drained lands -- 10. Calculations regarding elements of the main drainage system -- 11. Example of the batch method for flat lands -- 12. Cypress Creek formula -- 13. Statistical analysis of measured flows -- 14. Unit hydrograph -- 15. Rational formula -- 16. Curve number method -- 17. Formulae for steady-state flow to drains -- 18. Drainage under vertical seepage -- 19. Formulae for non-steady-state flow to drains -- 20. Diameters of drainpipes -- 21. Interceptor drains -- 22. Drainage by vertical wells -- 23. Computer programs for drainage calculations.

List of CD-ROM contents: Computer programs -- Present publication.

Agriculture and, consequently, food production depend, among other factors, on the proper management of water. Land drainage, an integral component of water management, is well known to have ameliorated salinity and waterlogging problems in rainfed and irrigated agriculture. In so doing, it has contributed substantially to sustainable agricultural development through enabling increased crop production, decreased farming costs, and the maintaining of soil quality. In areas where rainfall is excessive, it is necessary to manage land drainage, both surface and subsurface, in order to prevent waterlogging. In areas where rainfall is deficient, drainage management is still important in order to minimize soil salinization. In the arid and semi-arid regions, soil salinity still limits crop production significantly. Hence, it has a negative effect on food security. This is especially true in irrigated agriculture because of the salts added with the irrigation water and the buildup of saline groundwater where natural drainage is insufficient. Although only approximate figures are available, FAO estimated in 2002 that salinity had damaged about 20–30 million ha of irrigated land worldwide, and that 0.25–0.50 million ha were being lost from production every year as a result of soil salinization. In the wetter regions, flooding and waterlogging still limit crop production in many parts of the world. In the inland valleys of sub-Saharan Africa with shallow groundwater tables, controlled drainage may help to increase crop production and improve the health of rural populations. In certain lands of the humid tropics, drainage is also needed in order to increase rice production and promote crop diversification. As the global population and the demand for food increase, additional new drainage systems will be installed in a broader range of climate, soil and hydrological conditions, and existing systems will be renovated. FAO has already addressed waterlogging and salinity control through its normative and field programmes in the past 50 years. However, the context of land drainage has changed considerably in recent decades. This change has come about owing to concerns for the environment and the recognition of the need to integrate system users into the planning, design, operation and maintenance process. In addition, the experience gained and the research of recent years have led to improvements in the technology and methods. This FAO Irrigation and Drainage Paper is intended to serve as a tool for an integrated drainage approach by providing guidelines for: (i) the appropriate identification of drainage problems; (ii) the planning and design of drainage systems; and (iii) the careful integration of technical, environmental and socio-economic factors. The main text of this paper provides critical general information about the planning and design of land drainage systems and their relationship with technical, socioeconomic and environmental aspects. The annexes provide more detailed information with technical background, appropriate equations, some cross-references for finding appropriate methodologies, and computer programs for applications developed by Professor W.H. Van der Molen, which are included on a CD–ROM.

Available online.

System requirements to use the CD-ROM:
• PC with Intel Pentium® processor and Microsoft® Windows 95 / 98 / 2000 / Me / NT / XP
• 64 MB of RAM
• 50 MB of available hard-disk space
• Adobe Acrobat® Reader (not included on CD-ROM)
• Printout of results available by copying all programs to PC