| Summary: | 碩士 === 國立臺灣大學 === 農業工程學系 === 85 === In the past time in Taiwan, the canal capacity depended on the
conditions like 20 to 30 days of irrigation interval,
cultivation by cows and the constant rate of land
preparation. However, since machines have been applied
widely in agriculture, land preparation by machines is far
faster than by cows. Land preparation only takes 15
days now whilst it took 30 days before. The maximum water
requirement for land preparation has been increasing.
Moreover, due to the lack of farm laborers, farmers require
convenient operation and easy maintenance on the
irrigation work.
To have a more efficient utility of canals, we shall take the
convenience application of canals into consideration
when designing the facilities. We begin with the
research on reasonable water use plans.
Demand and supply of water must be regarded when we design a
water use plan. First it has to meet the requirement of
plants. Then we improve the facilities, irrigation system and
water management to make the management better.
Accordingly, in this research in order to assure to meet the
requirements of plants, we determine the canal capacity
based on the water requirement of plants first, then the
irrigation requirement in field lots, field blocks and even
tertiary units. And we improve the shape of close section of
canals to keep the head irrigating fluently and use
division boxes to have water distributed properly and
conveniently.
To design the close section of canals, first we consider the
irrigation requirement of a field block for a growing
season and calculate the basic close section of a
supplemental ditch. Then we fix the width of the canal
bottom and by Wen - Cheng's modified formula we get the maximum
current volume during land preparation. Furthermore,
with the information of the height of canal and the
free board, which is one third of the maximum water depth
or daily maximum precipitation, the ideal shape of close section
therefore can be determined.
However, in order to reduce the cost and make it easier during
construction, we can set the minimum allowable head and
minimum allowable velocity as restraint conditions. If
the head and velocity are beyond the restraints, we plan
to apply the same close section to several supplemental ditches
and it will cost less. Besides, the main ditch is divided
into several sections by division works. The volume of
every section needs to include the volume of the
following main ditch and its supplemental ditches. Likewise, we
get the basic bottom width according to the current
volume of the growing season and get the height of canal
according to the maximum current volume. Then with the
information of the free board we have the ideal close section of
each main ditch and plus the restraint conditions we have the
designed close section.
Nowadays Irrigation Associations or irrigation groups, which are
organized by farmers, employ common irrigators to operate
water distribution in tertiary units. And the farm
laborers are decreasing and aging and it is characterized in
the labor structure that most of them only devote themselves to
the farming as part time job. As a result, farmers would only
accept the water distribution facilities which are easy to
maintain, convenient to operate and can distribute water
properly. Division works with the characteristics mentioned
above are also generally proposed in this research.
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