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Part 624, Chapter 10, Water Table Control United States Department of Part 624 Drainage Agriculture National Engineering Handbook Natural Resources Conservation Service Chapter 10 Water Table Control (210-VI-NEH, April 2001) Chapter 10 Water Table Control Part 624 National Engineering Handbook Issued April 2001 The U.S. Department of Agriculture (USDA) prohibits discrimination in all its programs and activities on the basis of race, color, national origin, sex, religion, age, disability, political beliefs, sexual orientation, or marital or family status. (Not all prohibited bases apply to all programs.) Persons with disabilities who require alternative means for communication of program information (Braille, large print, audiotape, etc.) should contact USDA’s TARGET Center at (202) 720-2600 (voice and TDD). To file a complaint of discrimination, write USDA, Director, Office of Civil Rights, Room 326W, Whitten Building, 14th and Independence Avenue, SW, Washington, DC 20250-9410 or call (202) 720-5964 (voice and TDD). USDA is an equal opportunity provider and employer. (210-VI-NEH, April 2001) Acknowledgments National Engineering Handbook Part 624, Chapter 10, Water Table Control, was prepared by Ken Twitty (retired) and John Rice (retired), drainage engineers, Natural Resources Conservation Service (NRCS), Fort Worth, Texas, and Lincoln, Nebraska respectively. It was prepared using as a foundation the publication Agricultural Water Table Management “A Guide for Eastern North Carolina,” May 1986, which was a joint effort of the USDA Soil Conservation Service, USDA Agriculture Research Service (ARS), the North Carolina Agriculture Extension Service and North Caro- lina Agricultural Research Service. Leadership and coordination was provided by Ronald L. Marlow, national water management engineer, NRCS Conservation Engineering Division, Washington, DC, and Richard D. Wenberg, national drainage engineer, NRCS (retired). Principal reviewers outside NRCS were: James E. Ayars, agricultural engineer, USDA-ARS, Pacific West Area, Fresno, California Robert O. Evans, assistant professor and extension specialist, Biological and Agriculture Engineering Department, North Carolina State University, Raleigh, North Carolina Norman R. Fausey, soil scientist-research leader, USDA-ARS, Midwest Area, Columbus, Ohio James L. Fouss, agricultural engineer, USDA-ARS, Baton Rouge, Louisiana Forrest T. Izuno, associate professor, agricultural engineering, University of Florida, EREC, Belle Glade, Florida The principal reviewers within NRCS were: Terry Carlson, assistant state conservation engineer, Bismarck, North Dakota Chuck Caruso, engineering specialist, Albuquerque, New Mexico Harry J. Gibson, state conservation engineer, Raleigh, North Carolina David Lamm, state conservation engineer, Somerset, New Jersey Don Pitts, water management engineer, Gainesville, Florida Patrick H. Willey, wetlands/drainage engineer, National Water and Cli- mate Center, Portland, Oregon Nelton Salch, irrigation engineer, Fort Worth, Texas (retired) Paul Rodrique, wetland hydrologist, Wetlands Science Institute, Oxford, Mississippi Rodney White, drainage engineer, Fort Worth, Texas (retired) Jesse T. Wilson, state conservation engineer, Gainesville, Florida Donald Woodward, national hydrologist, Washington, DC Editing and publication production assistance were provided by Suzi Self, Mary Mattinson, and Wendy Pierce, NRCS National Production Services, Fort Worth, Texas. (210-VI-NEH, April 2001) 10–i Chapter 10 Water Table Control Part 624 National Engineering Handbook 10–ii (210-VI-NEH, April 2001) Chapter 10 Water Table Control Contents: 624.1000 Introduction 10–1 (a) Definitions ................................................................................................... 10–1 (b) Scope ............................................................................................................ 10–1 (c) Purpose ........................................................................................................ 10–1 624.1001 Planning 10–3 (a) General site requirements .......................................................................... 10–3 (b) Considerations ............................................................................................ 10–3 (c) Management plan ........................................................................................ 10–3 624.1002 Requirements for water table control 10–4 (a) Soil conditions ............................................................................................. 10–4 (b) Site conditions ............................................................................................. 10–9 (c) Water supply .............................................................................................. 10–10 624.1003 Hydraulic conductivity 10–12 (a) Spatial variability ...................................................................................... 10–12 (b) Rate of conductivity for design ............................................................... 10–14 (c) Performing hydraulic conductivity tests................................................ 10–17 (d) Estimating hydraulic conductivities ....................................................... 10–25 (e) Determine the depth to the impermeable layer .................................... 10–27 624.1004 Design 10–27 (a) Farm planning and system layout ........................................................... 10–27 (b) Root zone ................................................................................................... 10–33 (c) Estimating water table elevation and drainage coefficients ............... 10–34 (d) Design criteria for water table control ................................................... 10–39 (e) Estimating tubing and ditch spacings .................................................... 10–41 (f) Placement of drains and filter requirements ......................................... 10–55 (g) Seepage losses ........................................................................................... 10–56 (h) Fine tuning the design .............................................................................. 10–68 (i) Economic evaluation of system components ....................................... 10–74 624.1005 Designing water control structures 10–82 (a) Flashboard riser design ............................................................................ 10–82 (210-VI-NEH, April 2001) 10–iii Chapter 10 Water Table Control Part 624 National Engineering Handbook 624.1006 Management 10–83 (a) Computer aided management ................................................................. 10–83 (b) Record keeping ......................................................................................... 10–83 (c) Observation wells ..................................................................................... 10–84 (d) Calibration ................................................................................................. 10–86 (e) Influence of weather conditions ............................................................. 10–87 624.1007 Water quality considerations of water table control 10–89 (a) Water quality impacts ............................................................................... 10–89 (b) Management guidelines for water quality protection .......................... 10–89 (c) Management guidelines for production ................................................. 10–90 (d) Example guidelines .................................................................................. 10–91 (e) Special considerations ............................................................................. 10–91 624.1008 References 10–93 Tables Table 10–1a Effective radii for various size drain tubes 10–43 Table 10–1b Effective radii for open ditches and drains with gravel 10–43 envelopes Table 10–2 Comparison of estimated drain spacing for 10–73 subirrigation for example 10–6 Table 10–3 Description and estimated cost of major components 10–75 used in economic evaluation of water management alternatives Table 10–4 Variable costs used in economic evaluation of water 10–76 management options Table 10–5 Predicted net return for subsurface drainage/ 10–81 subirrigation on poorly drained soil planted to continuous corn Table 10–6 Water table management guidelines to promote water 10–92 quality for a 2-year rotation of corn-wheat-soybeans 10–iv (210-VI-NEH, April 2001) Chapter 10 Water Table Control Part 624 National Engineering Handbook Figures Figure 10–1 Flow direction and water table position in response to 10–2 different water management alternatives Figure 10–2 Determining site feasibility for water table control 10–4 using soil redoximorphic features Figure 10–3 Location of the artificial seasonal low water table 10–5 Figure 10–4 A typical watershed subdivided by major drainage 10–6 channels Figure 10–5 Excellent combination of soil horizons for 10–7 manipulating a water table Figure 10–6 Soil profiles that require careful consideration for 10–7 water table control Figure 10–7 Good combination of soil horizons for water table 10–8 management Figure 10–8 A careful analysis of soil permeability is required before 10–8 water table management systems are considered Figure 10–9 Good soil profile for water table control 10–8 Figure 10–10 Careful consideration for water table control required 10–8 Figure 10–11 Uneven moisture distribution which occurs with 10–11 subirrigation when the surface is not uniform Figure 10–12 A field that requires few hydraulic conductivity tests
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