Guidelines and computer programs for the planning and design of land drainage systems /

Need for and benefits of land drainage 1
Current context of land drainage 1
Need for guidelines and computer programs for planning
and design 3
Importance of following a planning and design procedure 3
Scope of this publication 4
Introduction 7
Environmental problems 9
Changes in hydrological peaks 9
Water quality management 9
Soil conservation 11
Wetland and wildlife habitat areas 11
Water conservation and recycling within the project area 11
Improving on-farm irrigation management 12
Shallow water table management 12
Drainage water reuse 14
Groundwater management 15
Land retirement and dry drainage 15
Biological drainage 16
Drainage outlet and disposal to avoid or minimize
downstream effects 17
General remarks on outlet structures 17
Disposal to the sea and tidal waters 17
Disposal to a lake 18
Disposal to a river 19
Evaporation ponds 19
Constructed wetlands and related systems 20
Groundwater recharge wells 21
Options for drainage water treatment 21
Removal of organic compounds and nutrients 22
Water desalination 22
Trace element treatments 23
Adsorption of soluble pesticides 23
Removal of heavy metals 23
Scope for drainage development 25
Farmer participation 25
The need for a participatory approach 25
Considerations for participatory planning and design 26
Drainage system modifications to facilitate participatory
management 27
Socio-economic investigations 27
Procedures 27
Costs and benefits 28
Life expectancy of drainage systems 29
Cost recovery 29
Operation and maintenance costs 30
Social evaluations 30
Introduction 33
Drainage master plans at national or river basin level 34
Identification of problem areas 36
Climate information 36
Landforms, soils and land use 37
Hydrology and irrigation practices 38
Soil salinity 38
Drainage development in the studied area 40
Feasibility study for planning new drainage projects 41
Topography and land use 42
Climate data 42
Soil information 42
Natural and present hydrological conditions 44
Hydrological conditions associated with the project 48
Crops and crop drainage requirements 52
Environmental procedures 52
Socio-economic evaluation 53
Example of the planning at feasibility level of a new
drainage system in an irrigation sector 54
Detailed studies for drainage design 56
Example of a map with the layout of a designed
drainage system 58
Investigations in drained lands 60
Introduction 63
Structural elements 64
Layout 64
Channels and ditches 65
Bridges and aqueducts 66
Culverts 67
Weirs and drop structures 67
Pumping stations and sluices 68
Connection with field drainage systems 68
Design requirements and criteria 69
Water level requirements 69
Specific discharge 69
Design discharges of channels 70
Exceptional discharge 71
Hydraulic gradients and head differences 71
Longitudinal profile 71
Introduction 73
Surface drainage systems for flat lands 74
Furrow at the downstream end of a field 74
Ridges and furrows 75
Convex raised beds and furrows 75
Parallel surface drains at wide spacings 76
Parallel small ditches 77
Systems for sloping and undulating lands 77
Cross-slope drain systems 77
Random field drainage systems 78
Surface drainage in undulating lands 78
Cross-sections of surface drains 79
Design discharges 80
Basic concepts concerning overland runoff 81
Methods to determine design discharges 83
Introduction 87
Layout of singular and composite drainage systems 87
Design concepts and approaches 90
Drainage criteria 92
Design groundwater depth 92
Design outflow 93
Groundwater lowering 94
System parameters 95
Drain depth 95
Drain spacing 95
Drain slope and allowed head loss in the pipes 96
Drain diameter 97
Drainage materials 97
Pipes 97
Pipe accessories and protection structures 98
Envelopes 98
Auxiliary structures 99
nterception drainage 99
Vertical drainage 100
Introduction 103
General structure 103
Specific programs 104
Extreme values 104
Calculation of permeability 105
Spacing of drainpipes and wells 105
Drain diameters 107