Irrigation & Hydrology (General Engineering) (SSC JE)

When water is not transported by natural flow and is lifted by some mechanical devices it is called lift irrigation.

Drip irrigation–It is also known as trickle irrigation. In drip irrigation water is applied in th form of drops directly near the base of the plant. Water conveyed through a system of flexible pipe lines, operating at low pressure and is applied to the plants through drip nozzles.

The rainwater in the gauge shall be measured every day at 08 : 30 h Indian standard time and the rain gauge shall be examined everyday at that hour even when in the observer's opinion no rain has fallen.
• The observer at each station shall maintain a written record of the rainfall measured at 08 : 30 hr Indian standard time daily.

Isohyetal method– it is a line joining points of equal rainfall magnitude. In the isohyetal method the catchment area is drawn to scale and the rain gauge stations are marked.
• The isohyet method is most accurate method to determine the average rainfall depth over an area. This method is superior to the other two methods especially when the stations are large in number.
• The average value of rainfall indicated by two isohyets is assumed to be acting over the inter isohyet area.

Thus P₁, P₂ ...... Pₙ are the values of isohyet and if a₁ a₂ ....... aₙ are the inter isohyet areas respectively then the mean precipitation over the catchment of area A is given by

Ill effect of irrigation– Excess irrigation and unscientific use of irrigation water may give rise to the following ill-effects

1. Breeding places for mosquitoes–Due to excess application of water and due to leakage of water, ponds and depressions get filled up with water and create breeding places for mosquitoes.

2. Water logging–If the water table is near the ground surface, over-irrigation may raise the water table. This saturates the crop root-zone completely, causes efflorescence and the whole area becomes water logged.

3. Damp climate–The woes which are already damp and cold, become damper and colder due to irrigation.

Following are the main requirements for the success of well irrigation–
• Presence of a suitable aquifer which can yield good quality water in sufficient quantity. • Availability of energy, preferably electric power, for pumps.
• Well distributed demand for irrigation throughout the year.
• Suitable configuration of command area with the highest ground around the centre of the command area.

Tipping bucket type rain gauge–This is a 30.5 cm size rain gauge adopted for use by the US weather bureau. The catch from the funnel falls onto one of a pair of small buckets.
These buckets are so balanced that when 0.25 mm of rainfall collects in one bucket, it tips and brings the other one in position. It may be noted that the record from the tipping bucket gives data on the intensity of rainfall further the instrument is ideally suited for digitalizing of the output signal.
Note : Tipping bucket rain-gauge is used for measuring rain in remote hilly inaccessible area.

A hydrograph runoff due to 1 cm effective rainfall over a catchment for unit duration is called unit hydrograph.

The soil moisture useful for the growth of a plant is called capillary water. • Capillary water is held in pores that are small enough to hold water against gravity, but not so tightly that root cannot absorb it.

Gravity water or free water–This form of water is loosely held in the soil and could be easily lost by gravitational force.

Main purpose of mean water training for rivers is to preserve the channel in good shape by efficient disposal of suspended and bed load.

Hydrograph is similar to chronological load curve. A hydrograph is a graph showing the rate of flow or discharge versus time. The rate of flow is expressed in cubic meter.
• The effective length of steel compression member depend on rotational and translation boundary condition at its ends.
• Effective length is the distance between point of contra-flexure.