Articles (A), software (B), and FAQ's (C), on (sub) surface land drainage for agriculture and irrigation                                                                                                                                                                
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A) - Articles, papers and lecture notes

1. Agricultural drainage criteria
                    This is a book chapter dealing with drainage systems, effects on agriculture, design criteria and examples in various agro-climatic zones.
The table of contents may be viewed here.

2. Data analysis in drainage research
                    This is a lecture note with examples of application of four software packages on this web site (CumFreq, SegReg, EnDrain and RainOff) and other analysis topics.
View table of contents here.

3. Energy balance of groundwater flow
                    This is copy of an article published earlier. It gives physical theory of groundwater hydraulics.
View abstract.

4. Application of the energy balance of groundwater flow to drains and ditches
                    This is an article giving the mathematical theory and examples of groundwater movement and seepage used in the EnDrain program (see Software on this website).
(view abstract)

5. Well spacing equations for subsurface drainage of agricultural land by pumped wells
                    This paper can be used as a manual of the WellDrain program (see Software page).
For information on well pumping tests for aquifer properties visit the same page.

6. Determining hydraulic conductivity of soils

                    This is a book chapter dealing with the determination of the saturated hydraulic conductivity of soils using small and large scale methods
The table of contents may be viewed here.

7. SaltMod manual

                    This manual gives a description of the Saltmod model (see Software page or below) including its principles, user menu, and case studies.
See table of contents

8. SahysMod manual

                    This manual gives a description of the SahysMod model (see Software page or below)including its principles, user menu, and case studies
SahysMod is a combination of Saltmod and a mathematical (numerical) groundwater model simulating water flow and salinity in unconfined and semiconfined (leaky) aquifers using a polygonal network with nodal points.
See table of contents

 
 
 
 
 
 
 
figure Saltmod
      Water balance factors in SaltMod and
      SahysMod

 
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B) - Free software and models

RainOff
helps in modelling effective rainfall, recharge, water storage, runoff, drainage and discharge relations in hydrological catchment areas (watersheds) using
the concept of a nonlinear reservoir.

 
EnDrain
does calculations on horizontal subsurface drainage systems in agriculture, hydraulic head, depth and level of water-table in agricultural land, and drain spacing using the energy balance of groundwater flow but also the Darcy and continuity equation (mass balance of water). It includes drain entrance resistance and soil anisotropy of hydraulic conductivity (soil permeability for water), i.e. the horizontal and vertical hydraulic conductivity are different. Applicable to pipe/tile drains (drain pipes) and open ditches.

 
WellDrain
Calculates the spacing of wells, the shape, depth, and level of the watertable in vertical drainage systems using pumped wells. Like EnDrain, it permits aquifers with various different properties and, in addition, fully/partially penetrating wells.

 
SaltMod
a mathematical, numerical simulation model describing the relations between agriculture, crop rotation, irrigation, rainfall, potential and actual evaporation (evapotranspiration), climate, hydrology, depth and level of water-table, capillary rise, deep percolation, soil salinity and subsurface drainage by drains or wells, and reuse (conjunctive use) of ground and drain water from wells. It includes farmers' responses to water logging and soil salinity.

 
SaltCalc
A simplified version of SaltMod with the advantage that calculations can be made for shorter time steps (e.g. weekly or monthly). SaltCalc can be used when field observations of irrigation, water table and soil salinity have been made and one wishes to develop a model for that situation. Normally, calibration of unknown values must be done using a range of values of the corresponding variable, running the model repeatedly for a number of time steps, and selecting from the range the value giving model results closest to observed values as the optimal value.

 
LeachMod
This model is somewhat similar to SaltCalc. On the one hand the water management options are fewer (e.g. re-use of drainage or well water for irrigation do not feature here), but the model is more modern in the sense that the variable input for each time step is given in a table so that the calculations over all the time steps are done in one go. Moreover, by inserting the observed values of soil salinity in the data table, the model optimizes the leaching efficiency of the soil.

 
SahysMod
a combination of Saltmod with a model of ground water flow and hydraulics to account for large spatial variation through a network of polygons. It includes phreatic (unconfined) aquifers as well as soil layers with slow vertical hydraulic conductivity (soil permeability for water) resulting in semiconfined (leaky) aquifers.

 

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C) - Frequently asked questions

figure drainage design
Depth of the watertable and crop production, field data

 

    1a - What is waterlogging? (This is probably the most frequently asked question)                            
                    In agriculture, waterlogging means that the soil is considered too wet to cultivate crops profitably (except lowland rice).
Waterlogging can be stagnation of water on top of the soil surface and/or the presence of a high water table inside the soil (at a depth of say 0.7 m on average).
Surface waterlogging can be seen as a flood control problem or a surface drainage problem.
Subsurface waterlogging can be tackled by a subsurface drainage system.
As an alternative one may opt for another kind of land use.
More information can be found in an article on Drainage Criteria and in a paper on world wide cases of Drainage Systems.
See also Wikipedia (watertable control) or WaterWiki (land drainage)

1b - Why is soil drainage required for plant growth? (Also a very frequently asked question)                            
     Drainage is required when the soil is too wet (waterlogged) for optimium crop growth. Then, the soil needs to be made dryer by drainage.
There is a series of reasons why crop growth is hampered in waterlogged conditions.
The article on Agricultural Drainage criteria explains some of the mechanisms and gives examples of crop response to waterlogging and yield increase with drainage (chapter 17.4).
Other examples of crop responses to drainage can be found in: Drainage reseach in farmers' fields

2 - What kind of drainage systems are applicable under what conditions?

     It is difficult to give a generally valid answer to this question, but the paper on surface and subsurface drainage systems gives a summary of practical experiences with different methods under varying agro-climatologic conditions.

3 - How can I calculate drainage discharge needs and irrigation/leaching requirements for salinity control using water and salt balances without resorting to simulation models like SaltMod and SahysMod?

     It is difficult to give a generally valid answer to this question, but the paper on surface and subsurface drainage systems gives a summary of practical experiences with different methods under varying agro-climatologic conditions.

4 - What is the influence of land slope on the spacing of subsurface drains?

     The answer is: for drain spacing calculations the slope of the land has little influence. For this purpose, sloping lands may considered as if they were flat.
This is a paper with mathematical explanations

5 - How can hydraulic conductivity (permeability) of the soil be measured and determined?

     The measurement of hydraulic conductivity can be done in the laboratory or in the field, above or below the water table, using small scale (auger hole method, infiltration method) and large scale methods (e.g. using drainage data in existing experimental fields or in farm land).
A full description is given in the chapter "Measurement of hydraulic conductivity of soils".
See also the table of contents on line.
For well pumping tests to determine aquifer hydraulic properties see the WellDrain model (software page).

6 - Drain spacing equations for horizontal tile/pipe drains are well known. Can subsurface drainage also be done by (tube)wells and how can the required spacing be calculated?

     The calculation of well spacings for subsurface drainage can be done with the WellDrain program (see software page). The theory behind it is discussed in the paper Well spacing equations.
For well pumping tests to determine aquifer hydraulic properties see the WellDrain model (software page).

7 - What is the optimimum depth of the water table and how can we develop suitable drainage criteria to design a subsurface drainage system

     This is the lecture note on Agricultural Drainage criteria.
The table of contents can be seen on line.

 
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