V. Найдите в тексте абзац, в котором рассматриваются преимущества комбинированной оросительной системы.

 

VI Расположите следующие слова и словосочетания в порядке, отражающем процесс движения воды по комбинированной оросительной системе:

 

field furrow, canal, take-off, delivering pipe-line, flexible watering hoses, roots of the plant

 

Vll. Сделайте краткий пересказ текста “Automationin1rrigation Methods”,

Drainage

Getting the water onto the land is only part of the problem that faces the farmer; of almost equal importance is the disposal of water after use. Тоо much water in the soil can be worse than not enough, while inadequate planning and improper irrigation frequently result in salination and waterlogging. Salination occurs because the roots of the plants absorb the irrigation water but exclude most of the salt it contains. The salt remains in the soi1 zone upon which the plant depends for growth and eventually renders the soi1 sterile.

То prevent catastrophic consequences, which are too common in many areas, there rnust be complete and efficient control of irrigation water. It is difficult to overestimate the harm caused by salination and waterlogging; indeed, reclaiming lands ruined through faulty or misused irrigation is almost as -important as bringing new 1ands under irrigation for the first time.

If reclamation is to be successful, the basic problem is to lower the water-table so that it is kept below the root zone. This may be achieved in а number of ways: а grid of deep ditches may be laid along the boundaries of the fields, or lines of tiles 1aid in the fields to collect the water and convey it to а co11ector ditch.

Many areas, particularly in the arid parts of Asia, cannot be conveniently or economically recovered by normal drainage processes. One method of restoration in these circumstances requires the installation of tube wells for pumping the areas to be drained and using the pumped water for further irrigation elsewhere. This method is of growing importance in some countries, but it can be very costly, sometimes proving more expensive than bringing in new irrigated areas. The use of tube wells for this purpose is like1y to increase when cheap hydroelectric power becomes avai1able on а larger scale.

However, it is necessary not only to reclaim areas that have already been spoiled, but also to prevent further ruin. This can only be done by а more efficient use of water, and one way of ensuring this in the future wi11 doubtless be by using automatic control systems. Scientists have recent1y developed an experimenta1 system at the Kirghizia Automation Institute in Central Asia. There an irrigation cana1 is parted into separate sections, and in each section а stable water 1evel is maintained automatica11y. It is held that this system will eliminate disastrous local shortages of water by maintaining stable Ievels of water in the irrigation cana1s serving а large area. Such а system is very expensive, but it is claimed, doubtless under favorable conditions, that the capital costs can be regained in less than two years. Ultimately, it is hoped that large cana1 systems wi11 be controlled by computers. Data on the condition of the irrigated areas, including the humidity of the air and soil, the density of the soil and the nature of the crop, would be fed into а computer, which would then estimate the water requirements for given areas and select optimum water regimes for each section of each canal and for the system as а whole. The first results of recent experiments along these lines suggest that they bring about considerable savings both in the consumption of water and in the cost of irrigation.

То summarize, an efficient, modern irrigation system should properly perform the following functions: 1) store water so that it is available in sufficient quantities whenever required; 2) deliver water to all parts of the cultivated area, in amounts needed to meet crop demands during peak use periods; 3) provide complete control of water; 4) divide water into required amounts for use in different fields; 5) dispose of waste water after use; 6) allow for the free movement of farm machinery. Properly utilized, such а system allows for the most efficient use of water and makes irrigation possible without soil erosion, saline or alkaline accumulation, or waterlogging.

 

Упражнения