Modern land drainage : planning, design and management of agricultural drainage systems / Willem F. Vlotman, Lambert K. Smedema & David W. Rycroft.

Contents
List of tables xv
List of figures xix
List of boxes xxv
Preface xxvii
About the authors xxix
PART I
Introduction 1
1 Land drainage for agriculture 3
1.1 Drainage objectives; Scope of the book 5
1.2 Global drainage zones 8
1.2.1 Temperate zone 8
1.2.2 Arid and semi-arid zone 9
1.2.3 Humid and semi-humid zone 9

1.3 Agro-hydrological regimes 9
1.4 Waterlogging control 11
1.4.1 Positive and adverse impacts 11
1.4.2 Responses to improved drainage 13
1.5 Salinity control 17
1.6 Drainage systems 17
1.7 Bio-drainage 19
1.8 Environmental impacts 20

1.8.1 Stream flow regimes 21
1.8.2 Water quality 21
1.8.3 Wetlands and conservation drainage 24
1.8.4 Public health 28
1.9 Drainage development considerations 28
2 Planning and design considerations 31
2.1 Design rainfall 33
2.2 Percolation of excess irrigation water 37
vi Contents
2.3 Design of field drainage systems 38
2.4 Determination of design criteria 39
  3   Remote   sensing  and  field  reconnaissance  41
3.1 Need for drainage and problem diagnosis 41
3.2 Remote sensing and aerial survey 42
3.3 Field investigations 44
3.4 Planning stakeholder engagement 44
3.5 Stages of project preparation 45
3.6 Operation, management and maintenance 46
4 Assessment of costs 49
4.1 Required information 49
4.2 Discounting 51
4.3 Evaluation indices 52
4.4 Cost evaluation of open and pipe drainage systems incl. O&M 52
4.5 Cost calculations for pipe drainage systems 54
PART II
4.5.1 Cost structure for pipe drainage construction 54
4.5.2 Guidelines for cost calculations 54
4.5.3 Example cost calculation 55
Investigations 57
5 Climate, land, soil and environment 59
5.1 Climate 59
5.1.1 Climate; soil moisture balance calculations 59
5.1.2 Climate: rainfall depth-duration-frequency studies 62
5.2 Topography 62
5.3 Soil and land conditions 63
5.4 Soil parameters and properties 65
5.4.1 Texture 65
5.4.2 Plasticity index 68
5.4.3 Bulk density and soil moisture content 69
5.4.4 Sample quantity and density 70
5.4.5 Data requirement for drain envelope design 70
5.5 Watertable and groundwater 71
5.5.1 Watertable observation wells 71
5.5.2 Piezometric studies 72
5.5.3 Groundwater sampling 73
5.6 Hydrology and geohydrology 74
5.6.1 Runoff and flooding 74
5.6.2 Outlet conditions 74
5.6.3 Geohydrological conditions 74
5.7 Agriculture and irrigation 75
5.8 Pilot areas and field testing 75
5.8.1 Types of pilot areas 76
5.8.2 Analysis of results of pilot areas 77
5.8.3 Visual drainage need assessment 77
5.8.4 Statistical analysis 78
5.9 Environmental impact 79
5.9.1 Environmental impact assessment 80
5.9.2 Miscellaneous investigations 80
6 Water in the soil 83
6.1 Forms and nature of occurrence of water in the soil 83
6.2 Pressures in the soil water 85
6.3 Soil moisture characteristics 86
6.4 Soil water potential and soil water movement 88
6.5 Unsaturated zone; soil moisture constants 90
6.6 Infiltration and percolation 92
6.7 Groundwater flow; Laplace Equation 94
7 Hydraulic conductivity 97
7.1 Laboratory measurement 98
7.2 Field measurements below the watertable 100
7.2.1 Augerhole method 100
7.2.2 Piezometer method 105
7.2.3 Drain outflow method 106
7.3 Field measurements above the watertable 108
7.3.1 Infiltrometer-method 108
7.3.2 Inverted augerhole method (Porchet method) 110

7.4 Composed K-values 111
7.5 Surveys and data processing 113
PART III
Systems and technology 117
8 Subsurface drainage systems 119
8.1 Pipe drain systems 120
8.2 Deep ditch systems 123
8.3 Drainpipes 124
8.4 Envelopes 129
8.4.1 Envelope need 129
8.4.2 Material selection 133
8.4.3 Envelope thickness 135

Contents vii

viii Contents
8.5 Envelope design guidelines and criteria 136
8.5.1 Granular envelopes 136
8.5.2 Organic envelopes 140
8.5.3 Synthetic envelopes 140
8.6 Structures in pipe drain systems 144
8.6.1 Surface water inlets 144
8.6.2 Inspection, junctions and control 144
8.6.3 Crossings 146
8.6.4 Outlet of a pipe drain into a ditch or canal 146
8.6.5 Sump outlet 146
8.7 Construction of pipe drain systems 149
8.7.1 Setting out, depth and grade control 149
8.7.2 Installation methods and machinery 151
8.7.3 Construction and quality control 156
8.7.4 Timing of installation 157
8.7.5 Installation below the watertable 157
8.7.6 Backfill 158
9 Surface/shallow drainage systems 161
9.1 Bedding systems 162
9.2 Shallow ditch systems 164
9.2.1 Types of shallow ditch systems 164
9.2.2 Some technical aspects of shallow ditch systems 169
9.3 Mole drainage systems 172
9.4 Pipe drainage systems 175
9.5 Complementary measures 176

9.5.1 Sub-soiling 176
9.5.2 Deep ploughing 178
9.5.3 Chemical amendments and organic matter 178
9.5.4 Land levelling 178
10 Main drainage systems 179
10.1 Main features 179
10.1.1 Drainage basin (watershed, catchment) 180
10.1.2 Types and alignment of drainage canals 181
10.1.3 Outlet and water levels 183
10.1.4 Outlet structures 185
10.2 Lowland and upland drainage 187
10.2.1 Lowland polder 187
10.2.2 River polders 188
10.2.3 Upland discharges 190
10.2.4 Drainage of urban areas 191
PART IV
Design 193
11 Design of pipe drainage systems 195
11.1 Flow patterns 195
11.2 Drain spacing formulae 199
11.3 Hooghoudt formula 200
11.3.1 Use of the Hooghoudt formula 201
11.3.2 Notes on the Hooghoudt formula 201
11.3.3 Drain spacing determination in anisotropic soils 204
11.4 Non-steady state drainage formulae 205
11.4.1 Falling watertable (Glover-Dumm formula) 206
11.4.2 Fluctuating watertable (de Zeeuw and Hellinga formula) 209
11.5 Basic design criteria 212
11.5.1 Criteria for off-season drainage 212
11.5.2 Criteria for crop-season drainage 214
11.5.3 The impact of drain depth and drainable pore space 217
11.5.4 Drainage criteria determined by simulation 217
11.6 Drain depth 218
11.7 Pipe diameter 221
12 Design discharges 227
12.1 Discharge transformation 227
12.2 Design considerations 231
12.3 Statistical analysis of observed discharges 233
12.4 Flat basins 234

12.4.1 Subsurface drainage 235
12.4.2 Shallow drainage 237
12.4.3 Further guidance for flat basins 239
12.5 Sloping basins 240
12.5.1 Rational formula 240
12.5.2 Curve number method 244
12.5.3 Synthetic hydrographs 246


12.6 Area reduction formulae 249
12.7 Discharge reduction through storage 250


12.7.1 Retention reservoirs 251
12.7.2 Canal storage 256
13 Design of drainage canals, pumps and structures 261
13.1 Drainage canals 261
13.1.1 Discharge rate 263
13.1.2 Hydraulic gradient and water levels 265

Contents ix

x Contents
13.1.3 Permissible flow velocities 267
13.1.4 Cross-section 267
13.1.5 Roughness coefficient 268
13.1.6 Freeboard 268


13.2 Structures in drainage canals 270
13.2.1 Culverts and bridges 270
13.2.2 Weirs 271
13.2.3 Backwater curves 272
13.2.4 Example canal design 274

13.3 Tidal outlets 276
13.3.1 Local variations in tide 276
13.3.2 Dischar ge through a sluice 278
13.3.3 Example of calculations 279
13.4 Pumps 280
13.4.1 Types of pumps 282
13.4.2 Pumping head and characteristics 283
13.4.3 Pump selection 285
13.4.4 Sump and intake design 287
13.4.5 Power and cost calculations 287
13.4.6 Example cost calculations of an electrically driven pump 288
PART V

Salinity control 291
14 Soil salinity 293
14.1 Forms of occurrence and distribution of salts in the soil 293
14.1.1 The soil solution 295
14.1.2 Adsorbed cations 295
14.1.3 Equilibrium relationships 297
14.1.4 Distribution of salts in the soil 298
14.2 Agricultural impacts; diagnosis and assessment 298
14.2.1 Osmotic problems 299
14.2.2 Toxicity problems 304
14.2.3 Dispersion problems 306
14.2.4 Corrosion problems 307
14.3 Classification 308
14.3.1 Classification systems 308
14.3.2 Field appearance 310
14.4 Conventional mapping and sampling 311
14.4.1 Sampling 311
14.4.2 Laboratory analysis 312
14.5 New salinity measurement and mapping techniques 315
14.5.1 The EM38 316
14.5.2 Time Domain Reflectometry 316
14.5.3 Remote Sensing methods 317
15 Irrigation induced salinisation 319
15.1 Salinisation by the applied irrigation water 319
15.2 Salinisation from the groundwater (capillary salinisation) 320
15.2.1 Critical watertable depth 321
15.2.2 Factors influencing capillary salinisation 321
15.3 Sodification 323
15.4 Salt balance of irrigated land 323
15.4.1 Leaching requirement calculations 326
15.4.2 Regional salt balances 327
15.5 Irrigation water quality 328
15.5.1 Salinity hazard 329
15.5.2 Sodicity hazard 330
15.5.3 Toxicity hazards 331
15.5.4 Examples of irrigation water quality appraisal 332
16 Drainage of irrigated land 335
16.1 Waterlogging and salinity 335
16.2 Surface drainage 336
16.3 Pipe drainage systems 338
16.3.1 Drain depth 339
16.3.2 Design criteria 341
16.3.3 Layout patterns 345
16.3.4 Pipe diameter 347
16.4 Well or vertical drainage 348
16.4.1 Types of aquifers 348
16.4.2 Design of well (vertical) drainage 350
16.5 Main drainage 351
16.5.1 Design discharge 352
16.5.2 Disposal of saline drainage water 352
PART VI
Special topics 355
17 Seepage and interception 357
17.1 Drainage systems for sloping land 357
17.1.1 Longitudinal drainage 358
17.1.2 Transverse drainage 358
17.2 Interception 360
17.2.1 Interception of seepage down the slope 360
17.2.2 Interception of canal seepage 362
Contents xi
xii Contents
17.3 Natural drainage of river valleys 363
17.4 Seepage into a polder 364
17.4.1 Semi-confined flow 364
17.4.2 Phreatic flow 366
17.5 Seep zones and springs 367
18 Reclamation and drainage of unripened soils 369
18.1 The soil ripening processes 369
18.1.1 Physical ripening 369
18.1.2 Other ripening processes 371
18.2 Reclamation and drainage methods 371
18.2.1 Early reclamation stage 371
18.2.2 Development of the hydraulic conductivity (K-value) 372
18.2.3 Advanced reclamation stage 372
18.2.4 Drainage, evaporation and ripening 373
18.3 Acid sulphate soils 374
18.3.1 Acidification processes 374
18.3.2 Neutralisation and reclamation 374
18.3.3 Diagnosis 375
18.4 Subsidence prediction 375
18.4.1 Ripening subsidence 376
18.4.2 Settlement subsidence due to lowering of the watertable 376
18.4.3 Oxidation of peat soils 378
18.4.4 Experiences in the Netherlands 378
19 Drainage of rice lands 381
19.1 Surface drainage 381
19.2 Subsurface drainage 386
19.3 Crop diversification 387
19.4 Flood control 388
20 Controlled drainage 391
20.1 Issues and developments 391
20.2 Design considerations 392
20.2.1 Layout and technical provisions 393
20.2.2 Drain depth 395
20.2.3 Reuse arrangements 396
20.2.4 Discharge control and watertable management 397
20.3 Operation and maintenance by farmers 400
20.4 Controlled drainage at the regional level 403
21 Computer applications 405
21.1 Drainage design applications 405
21.1.1 Field systems 406
21.1.2 Canal systems 406
21.1.3 Preparation of drawings and documents 408
21.2 Rainfall discharge models 408
21.2.1 TR-20 model 409
21.2.2 HEC-HMS 409


21.3 Ground water flow models 409
21.3.1 Spreadsheet models 410
21.3.2 MODFLOW and integrated programs 410
21.3.3 SGMP and SOURCE 410
21.4 Agrohydrological models 411
21.4.1 DRAINMOD version 6 412
21.4.2 SWAP 413
21.5 Salinity prediction models 414
21.5.1 SALTMOD 414
21.5.2 WATSUIT 415
PART VII
Management and New Developments 417
22 Research and innovation 419
22.1 Hydroluis pipe-envelope drainage 419
22.2 Capiphon drain 420
22.3 Precision agriculture for water quality control 420
22.4 Bi-level subsurface drainage 421
23   Institutional,  organisational   and  financial  arrangements   425
23.1 Drainage laws 425
23.2 Development and management models 426
23.2.1 Public/private good model 426
23.2.2 Participatory development 426
23.2.3 Management Transfer 428
23.3 Public drainage organisation 428
23.4 Financing 430
23.4.1 Investments 430
23.4.2 Operation and maintenance costs 431
23.4.3 Fee systems 431
24 Maintenance 435
24.1 Classification 435
24.2 Organisation, planning and execution 436
24.3 Maintenance of open drainage canals 436
24.3.1 Problems 436
24.3.2 Requirements 437

Contents xiii
xiv Contents
24.3.3 Methods and equipment 440
24.3.4 Environmental considerations 442
24.4 Maintenance of pipe drains 442
24.4.1 Pipe cleaning 443
24.4.2 Entry of roots 444
24.4.3 Chemical clogging (iron ochre, gypsum) 444
24.4.4 Access facilities 445
24.4.5 Costs 446
24.5 Developing countries 446
25 Performance assessment and benchmarking 449
25.1 Drainage design and performance 449
25.2 Indicators 450
25.3 Performance assessment procedure 452
25.3.1 Preliminary investigations (first step) 453
25.3.2 Primary investigation (second step) 453
25.3.3 Cause analysis (third step) 453
25.4 Performance checking of pipe systems 454
25.5 Causes of under-performance of drainage systems 455
References and further reading 457
Index 473