Irrigation & Hydrology (General Engineering) (SSC JE)

When the water is pumped out from a tube well in an aquifer, the piezometric surface formed surrounding the tube well is known as cone of depression. A cone of depression is formed where the water table sinks at an exact point because of heavy pumping.

Depression head–Depression head is defined as the difference of level of water table and the water level in the well when the pumping is generally stop.

The precipitation caused by natural rising of warmer lighter air in colder and dense surroundings is known as convective precipitation.
• Cyclonic precipitation–It occurs due to pressure difference.
• Orographic precipitation–Due to mountain barrier.
• Frontal precipitation–It is a type of cyclonic precipitation, which occurs due to warm and cold air masses.

Channel routing–The process of determining the flow of water through a river or stream over time. In channel routing the prism storage is the function of both inflow discharge and outflow discharge. In inflow is more than outflow then storage increase while if outflow exceeds inflow then prism storage decreases.

As per the recommendations of the Bureau of Indian Standard the shape of lined canal is trapezoidal.

Advantage of the line of the canal–
• Prevents seepage loss and hence more area can be employed for irrigation.
• Helps in the prevention of water logging.
• Increased velocity in a canal prevents silting of the canal.

Outlets– Outlet is a small structure or device, built at the head of the water course to facilitate flow of water from distributing channel to the water course.

Classification or types of outlets– The outlets may be divided into following three categories–
Non-modular outlet
• Mostly pipe outlet is used as non-modular outlet.

Semi-modular Outlets
(a) Pipe outlet free fall
(b) Kennedy's gauge outlet or venturi flume outlet
(c) Open flume outlet
(d) Orifice semi modules
Modular or rigid Outlet–
(a) Gibb's Module
(b) Khanna’s rigid Module

Furrow irrigation is a method of laying out the water channels in such a way where gravity plays the role of providing just enough water for suitable plants to grow.
• It is usually made by the planned placement of ridges and furrows. It is a kind of surface irrigation system.
• According to given option furrow methods of irrigation results in less evaporation losses.

Furrow method or furrow irrigation–
• The water is applied to the land to be irrigated by a series of long, narrow field channels called furrows which are dug in the land at regular interval.
• The water flowing in the furrows infiltrates into the soil and spreads laterally to irrigate the land between the furrows.
• The crops are usually grown on the ridges between the furrows.

Sprinkler irrigation–In the sprinkler irrigation method of irrigation water is sprayed into the air and allowed to fall on the ground surfance somewhat resembling rainfall.

Advantages of sprinkler irrigation–
1. Suitable to all types of soil except heavy stay.
2. May also be used for undulating area.
3. Areas located at a higher elevation than the source can be irrigated.
4. Closer control of water application convenient for giving light and frequent irrigation and higher water application efficiency.