

Depth of the watertable (X) and crop production
(Y), field data



1  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 shallow water table inside the soil
(at a
depth of say less than 0.5 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).

2  What is the tolerance or senstivity of crops to
shallow watertables?

Field measurements of crop yield and depth to
water table are scarce and it is therefore not
easy
to present crtiical watertable depths for various
crops. Data found in literature for wheat,
banana,
sugracane and cotton have been analysed on the
water tolerance page,
giving also a classification on
tolerance/sensitivity that may give a help with
the formulation of a drainage criterion for
these crops.

3  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
agroclimatologic conditions.
See also Wikipedia:
Drainage sytems, or:
WaterWiki (Land drainage).


4  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?
5  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

6  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 (see
the software page).

7  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 the 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
(see the
software page).

8  What is the optimimum depth of the water table
and how can we develop suitable drainage
criteria
to design a subsurface drainage system
9  How can surface drainage (runoff) be
calculated without using the complicated method
with an instantaneous unit hydrograph (IUH) and
convolution?

On this website there is a method that uses
a model of a nonlinear reservoir
and the corresponding software can be found
on the
RainOff page.
In addition there exists the method of a
cascade of linear reservoirs, all
having the same raction factor, as
elaborated
by Nash. The software is to be found on the
NashMod page.
Further, on request, one can obtain software
of a computer program for the method using
two linear resrvoirs in series with
different reaction factors (response
functions).

10  What envelope materials (filters, wraps) are
used for pipe drains?

This is a
pdf file
made of scannned pages on the subject taken from
an ILRI publication.

11  How is the river and surface water pollution
tackled in The Netherlands?

I am not a lawyer nor a specialist on pollution
with organic compounds. Yet I made a summary of
the Dutch "Law Pollution Surface Water" to the
best of my ability.
This is the
summary.
Further a powerpoint presentation of the summary
("summary of the summary") can be
downloaded or
viewed online.



Controlled drainage




(B) Irrigation subjects


Women high up the the Andean mountains
are good irrigators. See this
paper.


"Over the surface irrigation" with furrows
Of the almost 300 million ha of irrigated land in the
world, 94% is irrigated by "over the surface
irrigation" methods, see
Wikipedia



12  Is there global information on irrigation
statistics, management, and environmental
impact?
13  What about water management and soil salinity
in alluvial fans or inland delta's?

On this website there are 3 papers on water
management and soil salinity in alluvial
fans (inland delta's):
1. Flood recession cropping in the
molapo's of the
Okavango Delta,
Botswana.
2. Irrigation projects in the
alluvial fan of
Punata in Bolivia.
3. Water management and soil salinity control in
the alluvial fan
of Garmsar in Iran.

14  Is irrigation high up in the mountains
feasible?

This is a paper discussing the importance of
irrigation at high altidues in the
Andean mountains.

15  What is spate irrigation, how effective is
it, and what is its potential?

This article discusses the problems and potential
of spate irrigation in the
NWFR province of
Pakistan.

16  What is tidal irrigation and how does
it work?

This is a paper in tidal irrigation of date
palms in the
Abadan Island
in SW Iran.

17  What does the irrigation in Egypt look like
after construction of the Aswan High Dam?

Please consult this report on irrigation
improvement along the
Nile river in Egypt.

18  What is the development of river salinity in
downstream direction when, in arid and semi
arid regions, the salty river water is used
for irrigation of agricultural land and the
drainage flow and effluent are returned to the
river, and what are the effects on soil
salinity and how can eventual problems of
salty soils be tackled?


(C) Soil subjects

Looking over the shoulder of a farmer to his
salinized land with poor crop stand.



19  What are saline and salty soils, how do they
originate, where are they found, what is their
problem, how can the problem be solved?

This is the paper on
soil salinity
There is also a programmed selfhelp exercise on
water and salt balances and leaching
(reclamation)
of a saline, salty and sodic, soil in Chacupe,
Peru. Soil salinity, sodicity and alkalinity are
analysed:
Chacupe case study
A description of salinity development and control
in a small
coastal delta in
Peru can be can be consulted here.
See also "Salinity control" in
Wikipedia, or:
WaterWiki.

20  What is salt tolerance of crops and are there
determinations of crop response to soil
salinity under farming conditions?

In this tolerance
paper examples are given of determination
of salt tolerance based on measurements in
farmers' fields on the relation between crop
production and soil salinity in 3 subtropical
countries.

21  What are alkali, alkaline sodic and acid
sulphate (sulfate) soils (cat clays), how do
they originate, where are they found, what is
their problem, how can the problem be
solved?


22  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 (see
the software page).



(D) Statistical subjects

23  What are the principles of cumulative frequency
analysis and (discontinuous, composite)
probability distributions (used in the CumFreq
program, see the
software page),
and what to do if there is a discontinuity?
What is return period and how reliable is it?

This is the lecture note on
frequency analysis.
The table of contents
can be inspected here.
An article on the use of the binomial distribution
for the determination of confidence intervals and
belts for cumulative probability distributions can
be downloaded from this
place, while a summary of it can be found
over here.

24  What are the principles of linear regression
analysis (used in the SegReg program, see the
software page)
) and how are confidence statements and
intervals determined. What is breakpoint (break
point), threshold, and coefficient of explanation
(determination)?
25  The SegReg model (see the
software page
) provides confidence intervals
of the breakpoint in segmented linear
regression
analysis to test its statistical significance.
Is it necessary to additionally perform an
analysis of variance (ANOVA) and Ftest and how
is this done?

The wheat crop tolerates soil salinity (measured
in electric conductivity, ECe) up to a level of
7.1 dS/m, beyond which the yield declines.



26  Is there a calculator available for the Ftest
described under the previous question?

Yes, one may download the calculator from the
Ftest page here.

27  Is there a away to determine the longest
horizontal stretch while fitting a relation
with a horizontal and sloping part to a number
of data? This stretch is needed to find out
the range over which there is no effect of
the influential variable on the goal variable.
Recently I developed a method called "partial
regression" eactly for this purpose. It can be
found on the
PartReg page.

28  Is there a calculator available for the ttest
using Student's tdistribution in determining
the confidence intervals in (segmented) linear
regression anlysis?

Yes, one may download the calculator from the
ttest page.


29  Is there also a calculator available for the
cumulative frequency in the normal distribution?
30  Is there a technique to compare averages of
different data series and to determine the
significance of the difference between them.

For this one uses Student's ttest. See the
ttest page from
where a ttest calcuator can be downloaded.



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