Test: Infiltration - Civil Engineering (CE) MCQ

Infiltration:

• Some of the water that falls on land soaks into the ground. Water penetrates the ground through joints or small pore spaces between particles via a process known as infiltration.
• Infiltration is the process of water entry into the soil through the earth's surface. The water at the soil surface can originate from rain, snowmelt or anthropogenic activities (e.g. to regulate groundwater formation by artificial infiltration).

Transpiration:

• Transpiration is the process of water movement through a plant and its evaporation from aerial parts, such as leaves, stems, and flowers. Water is necessary for plants but only a small amount of water taken up by the roots is used for growth and metabolism.

Precipitation:

• In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls under gravitational pull from clouds. The main forms of precipitation include drizzle, rain, sleet, snow, ice pellets, graupel, and hail.

Sublimation:

• Sublimation is the transition of a substance directly from the solid phase to the gas phase without passing through the intermediate liquid phase.

Evaporation:
Evaporation is defined as the process in which the liquid changes to the gas state at the free surface, below the boiling point through the transfer of heat energy.
It is a cooling process in which latent heat of vaporization is provided by the water body itself.
The rate of evaporation is dependent on the following factors –
1. The vapor pressures at the water surface and the air above (Vapour Pressure ↑ ⟹ Evaporation ↓).
2. Air and water temperatures (Temperature ↑⟹ Evaporation↑).
3. Wind speed (Wind Speed ↑⟹ Evaporation ↑)
4. Atmospheric pressure (Atmospheric Pressure ↑ ⟹ Evaporation ↓).
5. Quality of water (Quality↑⟹ Soluble Salts↓⟹Evaporation↑)
6. Size of the water body (Size↑⟹Surface Area↑⟹Evaporation↑).
7. Depth of water (Depth↑⟹Evaporation↓).
Evaporation of water may take place in absence of sunlight. During the daytime all the air surrounding us gets heated. This warm air provides heat for the evaporation of water in the absence of sunlight. So, evaporation is high in the Summer season.

Infiltrometer is used for field measurement of infiltration. There are two types of infiltrometer – Single ring infiltrometer and Double ring infiltrometer. Single ring infiltrometer always overestimate because of the lateral movement of water and to overcome this double-ring infiltrometer is used.

Grass cover or vegetation cover increases the field capacity by trapping water and reducing the effect of raindrop compaction. Vegetation and grass cover also reduces the surface compaction of the soil which again allows for increased infiltration.

Rainfall simulators are used for laboratory measurement of infiltration and Infiltrometer is used for field measurement of infiltration. Lysimeter is used to measure evapotranspiration and tensiometer is used to measure capillary potential.

Infiltration is the process by which the water seeps into the surface strata of the earth to meet soil moisture deficiencies. Percolation is the deep vertical movement of water in the ground.

Horton’s equation assumes an infinite water supply at the surface i.e. it assumes the saturation conditions at the soil surface. The infiltration rate at any time‘t’ is given by –
f_t = f_C + (f_O – f_C) e^-K.t
Where f_C = final constant rate of infiltration at saturation, f_O = initial rate of infiltration capacity, k is the decay constant depending upon soil and vegetation and t = time from the beginning of the storm.

Isohyets:

• It is a line joining points of equal rainfall for a given interval or Isohyets are contours of equal precipitation analogous to contour lines on a topographic map.
• In the isohyetal method, precipitation values are plotted at their respective stations on a suitable base map, and isohyets are drawn to create an isohyet map.

∴ In isohyets, the line joining points on a map where the amount of precipitation recorded in a given period is the same.

DAD curve: The areal characteristics of a rain storm are represented by a depth-area-duration curve. Once the sufficient rainfall records for the region are collected the basic or raw data can be analysed and processed to produce useful information in the form of curves or statistical values for use in the planning of water resources development projects.
Many hydrologic problems require an analysis of time as well as areal distribution of storm rainfall. Depth-Area-Duration (DAD) analysis of a storm is done to determine the maximum amounts of rainfall within various durations over areas of various sizes.
Hyetograph: is a graph between rainfall intensity and time. Rainfall intensity progressively increases until it reaches a maximum and then gradually decreases.
Mass curve: is graphical representation between accumulated rainfall v/s time. A mass curve of inflow can be prepared from the flow hydrograph of a stream for a large number of consecutive previous years
Double mass curve: It is used to check consistency of a rainfall for a particular area. The current mass curve is plotted and compared with previous data to check variation over a single curve.

Infiltration Capacity: 
(i) The maximum rate at which a given soil at a given time can absorb water is defined as infiltration capacity. It is denoted as f_p and its unit is cm/hr.
(ii) Hence, if the intensity of rainfall is more than the infiltration capacity then, the infiltration rate will be equal to infiltration capacity (f_p), and the rest of the amount of rainfall will be in the form of runoff.
Important points related to Infiltration capacity:
The intensity of rainfall is “i”. Then, three conditions arise from here:
(i) If the actual rate of infiltration is f such that f = f_p and i > f_p then a certain amount of runoff will be observed.
(ii) If f < f_p then infiltration rate will be f and no runoff will be observed.
Infiltration:
(i) When water is applied to the surface of the soil, a part of it seeps into the soil. This movement of water through soil is called infiltration.
(ii) This infiltration water used in increasing the moisture of soil up to field capacity and extra water goes down and becomes ground water.