Since the opening of the website a number of questions
about soil problems, reclamation, drainage systems,
irrigation, land and water management, and statistics
have reached me.
Sometimes I was unable to provide an adequate answer.
However, there were questions I could categorize and
answer collectively through generalized texts that
were made for the occasion.
More papers can be found on the "articles" page and
the "reports &cases" pages.
The following 26 questions were frequently asked.
They are arranged by subject: (A) Drainage, (B) Irrigation, (C) Soils, and (D) Statistics.
5 - How can hydraulic conductivity (permeability) of the soil be measured and determined?
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?
(B) Irrigation subjects
10 - Is there global information on irrigation statistics, management, and environmental impact?
11 - What about water management and soil salinity in alluvial fans or inland delta's?
12 - Is irrigation high up in the mountains feasible?
13 - What is spate irrigation, how effective is it, and what is its potential?
14 - What is tidal irrigation and how does it work?
15 - What does the irrigation in Egypt look like after construction of the Aswan High Dam?
16 - 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
(D) Statistical subjects
20 - 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?
21 - What are the principles of linear regression
analysis (used in the SegReg program, see the
) and how are confidence statements and
intervals determined. What is breakpoint (break
point), threshold, and coefficient of explanation
22 - The SegReg model (see the
) provides confidence intervals
of the break-point in segmented linear regression
analysis to test its statistical significance.
23 - Is there a calculator available for the F-test
described under the previous question?
24 - Is there a calculator available for the t-test
using Student's t-distribution in determining
the confidence intervals in (segmented) linear
25 - Is there also a calculator available for the
cumulative frequency in the normal distribution?
26 - Is there a technique to compare averages of different data series and to determine the significance of the difference between them.
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