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Consider the following statements regarding loss of water in canals : 1. The water lost by evaporation is generally very small, as compared to the water lost by seepage in certain channels. 2. In percolation, there exists a zone of continuous saturation from the canal to the water-table and a direct flow is established 3. In absorption, a small saturated soil zone exists around the canal section and is surrounded by a zone of decreasing saturation. Which of the above statements are correct ? 

Consider the following statements regarding loss of water in canals : 1. The water lost by evaporation is generally very small, as compared to the water lost by seepage in certain channels. 2. In percolation, there exists a zone of continuous saturation from the canal to the water-table and a direct flow is established 3. In absorption, a small saturated soil zone exists around the canal section and is surrounded by a zone of decreasing saturation. Which of the above statements are correct ?  Correct Answer 1, 2 and 3

Explanation:

(i) Losses of water in canals may be defined as the process in which a considerable amount of water is lost as it passes through the canal from the starting of the headwork to the final point where it is supplied to the agricultural field or elsewhere.

(ii) The loss of water in canals is also commonly referred to as transit loss or transmission loss.

The major types of canal losses are listed as follows:

  • Evaporation Losses in Canal
  • Seepage Losses in Canal
  • Transpiration Losses in Canal

Evaporation Losses in Canal:

(i) Evaporation loss in the canal is inevitable as the water flowing through any canal is exposed to the atmosphere.

(ii) Evaporation losses are less than the seepage losses in the canals. So, statement 1 is correct

(iii) The evaporation losses depend upon several factors such as temperature, humidity, wind, etc. But, the most dominant factor is temperature. On account of this, the evaporation losses are higher in summer than in winter.

Seepage Losses in Canal:

The seepage loss in the canal is the most significant loss of water in the canals. Such loss mainly depends upon the following factors:

  • The porosity of the soil.
  • Existing underground water table conditions
  • The existing condition of the canal system.
  • Physical properties of the water canal such as turbidity of water.
  • Amount of silt carried by the water.

Types of seepage losses are:

(i) Seepage Losses due to Percolation:

  • It is the seepage loss in a canal in which the water is lost through a continuous zone that is formed between the canal and the water table. Such a zone that is formed consists of fully saturated soil that is capable of establishing continuity in the flow of water from the canal to the underground reservoir.

So, Statement 2 is correct.

The loss of water through percolation is greatly affected by the difference in level between the topwater surface level of the channel to the water table level.

(ii) Seepage Loss due to Absorption:

  • In the canals, usually, a zone of saturation is present below the canal that is accompanied by a zone of soil with decreasing saturation which is further bounded by a zone that is saturated by the capillary action of water rising from the adjacent water table level.​

So, statement 3 is correct.

(iii) Transpiration Losses in Canal:

  • Some amount of water flowing through the canals is lost by the process of transpiration.
  • The plants, grasses, weeds, or other vegetation that grow on the banks of the canal undergo transpiration thereby resulting in loss of water from the canal.

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