Lecture notes on drainage and soil salinity

Theoretical drainage and salinity  
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1. Subsurface drainage.
This articles discusses in general terms the classification of horizontal subsurface drainage systems, their design optimization, the history, and the environment, as well as (vertical) drainage by wells

2. Subsurface drainage criteria.
The article on drainage criteria discusses the aspects that need to be covered, systems analysis, the processes of crop yield response and production to variations of the water table or phreatic surface regime with the aim to formulate the drainage objectives and to provide design criteria.

3. Subsurface drainage and drain spacing equations.
The drain spacing equations refer to the formulas that are used to design a horizontal subsurface drainage system, that is to say a system diches or subsurface pipes (tiles) inccluding the darin spacing.
The equations are also applicable to areas with a gradient, and they are adjustable to the variation of the hydraulic conductivity (permeability) in various soil layers, both in horizontal and vertical direction (anisotropy)
The applicable software is introduced.

4. Well spacing equations for vertical drainage.
Drainage by wells is called vertical drainage.
Like for horizontal drainage, there are also spacing equations for vertical drainage that take into account the variation of the soil's permeabilty in different layers as wel as the anistropy of the hydraulic conductivity.
The applicable software is introduced.

5. Water balances and drain discharge.
Water balances are introduced for four soil layers in the profile, from the surface down to the bottom of the aquifer.
The water balances serve to calculated the design discharge of the drains or wells.
This drainage requirement is important in the design of the drainage system to to determine the capacity hydraulic engineering structures serving the evacuation of the drainage water to the outlet.
The text needs the support of the examples given in continuation below.

6. Examples of water balances.
In this document a series of examples of water balnces is presented regarding the subsurface drainage under varying hydrological conditions.
The examples refer to drainage from the soil surface up to the drainage in the aquifer.

7. Soil salinity control by means of subsurface drainage.
In irrigated lands, soil salinity is a common problem globally.
In many instances salinity control must be done with a subsurface drainage system.
Here, the origin of the soil salinity is explained, the worldwide distribution of saline soils is shown, and the diagnosis, the leaching and the water and salt balances are discussed, while the applicable software and mathematical simulation models are presented.

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