HIGHLIGHTS or Main points of Soil and Water Conservation Engineering
Useful for objective / MCQ question of any related exam like PSC, GATE, IOE entrance.
- Hydrology is the science, which deals with the occurrence, circulation and distribution of the water and earth's atmosphere.
- Sun is the source of energy for the hydrologic cycle. The area of land draining into a stream or a watercourse at a given location is called catchments area.
- All forms of water that reach the earth from the atmosphere is known as precipitation. The magnitude of precipitation varies with time and space.
- The net precipitation at a place and its form depend upon a number of metrological factors. tropical cyclone, also called cyclone in India, hurricane in USA and typhoon in South- East Asia.
- The centre of storm is called eye.
- The precipitation is collected and measured in a rain gauge. Mass curve of rainfall are very useful in extracting the information on the duration and magnitude of a storm.
- Intensity of storm decreases with increase in storm duration. The parts of precipitation, which infiltrates and moves laterals through upper layer of soil and meets to stream is called inter flow.
- The rate of evaporation is proportional to the difference between the saturation vapour pressure at the water temperature and actual vapour pressure in the air. Rate of evaporation increases with wind speed upto a critical speed.
- Energy-budget method is an application of the law of conservation of energy.
- The maximum rate at which a given soil at a given time can absorb water is defined the infiltration capacity.
- Average infiltration rate is called infiltration index.
- Wire gauge is used to measure the water-surface elevation from above the surface.
- Dilution method of flow measurement depends upon continuity principle.
- A perennial stream is one which always carries some flow.
- An intermittent stream has limited contribution to the ground water.
- An ephemeral stream is one, which does not have any base flow contribution. The flow-duration curve is also known as discharge -frequency curve.
- The total catchments area of all the rivers in India is approximately 30.5 million square kilometres.
- Minor catchments have an area less than 2000 square kilometre. Medium catchments have an area between 2000 to 20000 square kilometre.
- Large catchments have an area greater than 20000 square kilometre.
- The missing data of rainfall can be computed by hydrology budget method. Flood hydrograph is useful for analyzing the stream characteristics.
- The time interval between centre of mass of rainfall to the centre mass of hydrograph is called as lag time!
- S-curve is also known as S-hydrograph.
- S-hydrograph is a hydrograph produced by a continuous effective rainfall at a rate for an infinite period.
- The limiting case of a unit hydrograph of zero duration is known as instantaneous unit hydrograph
- An imaginary surface representing the artesian pressure in artesian aquifer is called piezometric surface.
- The hydrostatic pressure within artesian aquifer is some times greater enough to cause the water to rise in a well.
- The hydraulic resistance is also called reciprocal leakage factor. The vc ume leakage factor of semi-pervious layer generally ranges between 100 to 40,000000 min.
- High value of leakage factor indicates a greater resistance of the semi-pervious strata to flow as compared to the resistance of strata itself.
- Low head water lifts are suitable when the depth to water surface does not exceed 1.2 meter
- Medium head lifts are suitable when the height of lift is within the range of 1.2 to 10 meters.
- The height of high head lift is above the 10 meter.
- Specific speed is often used as an index to the operating characteristics of pump. The part of rainfall, which enters the stream immediately after the rainfall, is called surface runoff.
- That portion of rainfall which first leaches into the soil and moves laterally without joining the water table, to the stream is known as subsurface runoff.
- Ratio of total channel length in the watershed to total watershed area is called drainage density.
- The unit hydrograph method used to compute the direct runoff, is limited to the watershed area of about 5000 square kilometre.
- The top 30 cm soil depth is very useful for the human being and wild life.
- Accelerated erosion is in excess of geologic erosion Raindrop erosion is also known as splash erosion.
- The soil may splash into the air up to a height of 50 to 70 cm depending upon size of raindrop.
- Splash erosion is caused by impacting the raindrop.
- Uniform removal of soil in the form of a thin layer by the flowing of water from a given width of slopping land is called sheet erosion.
- Gully erosion is the advance and last stage of water erosion.
- In other words gully erosion is the advance stage of rill erosion.
- Glacial erosion is found where mean temperature is below zero degree Celsius. Photogenic erosion is the destruction of soil, caused by plants root system.
- Zoogenic erosion is caused by animals.
- Anthropogenic erosion is associated with the activities of human beings.
- The annual soil loss from 0.05 to 0.5 mm depth or 0.5 to 5 cubic meters per hectare is count as week erosion.
- In medium erosion the annual soil loss ranging from 0.5 to 1.5 mm of soil depth or 5 to 15 cubic meters per hectare per year.
- The range of soil loss in serious erosion varies from 1.5 to 5 mm of soil depth or 15 to 50 cubic meters per hectare per year.
- The rates of extent of gully development are closely related to the amount and velocity of runoff water.
- U-shape gullies are generally found in the alluvial plains.
- V-shape gullies are often developed where the subsoil are tough to resist the rapid cutting of soil by runoff flow.
- Drop spillways are used where head drop is 1.2 to 2.4 meter.
- Chute spillways are used at the locations where head drop is fairly large ranging from 5 to 6 meter.
- Wind erosion is the process of detachment, transportation and deposition of soil particles by the action of wind. The desert areas are the severely affected by wind erosion problem.
- Soil erosion due to wind is mainly the result of creation of wind turbulence over the ground surface.
- Suspension is the movement of very fine soil particles generally less than 0.1 mm in diameter
- In saltation process, the size range of particles may be from 0.05 to 0.5 mm in diameter. Among the all type of soil movement the saltation is responsible for transporting the maximum amount of soil particles along ground surface by rolling and pushing action which ranges from 55 to 72% of total soil erosion.
- The size of soil particles associated with surface creep are ranges from 0.5 to 1 or 2 mm in diameter.
- The extent of total desert in India is about 20.7 Mha
- Wind breaks and shelter belts are used for control the wind erosion. Erosivity is defined as the potential ability of rain to cause the erosion.
- Erosivity depends upon the physical characteristics of rainfall include raindrop size distribution, kinetic energy and terminal velocity etc
- Erodibility is the susceptibility of soil to get erosion.
- In low rainfall regions the primary purpose of contour cultivation is to conserve the rain water into the soil as much as possible.
- In humid regions the basic purpose of contour cultivation to reduce the soil erosion by retarding the overland flow.
- Terracing is the engineering soil conservation practice, used to control the soil erosion in highly slopped areas.
- Bench type terraces are generally constructed on the land of 6 to 33% slope.
- Graded terrace is also known as channel type terrace.
- Level terraces are constructed for conserving the moisture and controlling soil erosion.
- Level terraces are also known as conservation terraces.
- The conservation terraces are normally, found most suitable where rainfall is low and land slope is less than 6 percent.
- Bunding is used for retaining the water, creating obstruction and thus to control erosion.
- Bunding practices are found most suitable for the land having the slope ranges from 2 to 10 %.
- Contour bunding is not technically feasible on the land slopes greater than 6 percent.
- Graded bunding used in the area having rainfall greater than 700 mm per year.
- Pipe culverts are used for very small drainage works.
- Box culverts are preferred for the construction, especially in loose soil condition and for larger spans
- Box culvert can be used for a single span of 3 meter for a double span of 6 meter width.
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