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Sediments, its Measurement and Run Off Agricultural Lands


Date Posted: 3/31/2018 11:12:58 AM

Posted By: franco crick  Membership Level: Gold  Total Points: 2067

Sediments are simply defined as the fragments obtained after degradation of rocks and detachment of soil particles on lands. This is a s a result of physical and biological disintegration.

The main physical disintegration are as a result of heat from the sun, animal’s movements when feeding and tillage practices on land through use of tillage implements and equipments. The biological disintegration is through expansion and growth of plants’ roots, the biological agents of soil weathering. Another process that contributes to increased sediments on farmlands is the chemical disintegration through processes such as hydration, hydrolysis, oxidation and reduction process.The sediments increases production also results to increased bed material, suspended load, wash load, bed load, as well as increased sediment concentration in river beds.

The sediment concentration is mainly defined as the ratio of volume or mass of dry sediment in a sediment-mixture of suspended load to the total volume or mass of suspended load. The sediments are mainly categorized into three i.e.; finer fraction which contains a diameter size of less than 0.075mm, the medium fractions where this particles has a diameter size of between 0.075mm and not greater than 2mm while the coarse fractions has particle with a diameter size greater than 2mm.

Sediment should be measured by the relevant hydrologic engineers concerned. The site containing sediment should be assessed before and measured subsequently. Before sediment measurement is carried out the following factors should be considered;

-The site measurements and conditions-this determines the method of handling a suspended load sampler used in the measurements for example the elevation of the suspended load sampler.

-The flow should also be considered in terms of water depth and the water velocity at specific sites.

-The other factor is sediment concentration and its size.
The main objectives or importance of sediment measurement is;

-They are used in estimation of

catchment erosion conditions/runoff and the relevant conservation measures for the control as well.

-It is also used in studies of river training and river regimes in most institutions and schools.
-It also helps in determining the regime widths and scour depths in river regimes.
-Also helps the engineers in designing and planning a river stage and other hydraulic structures.

Sedimentation constitutes the main component of runoff being carried away from highly elevated places of agricultural farms to low-lying areas. This is mainly through a process called erosion. The runoff has its peak and volume capacity. Both of this is important in that the peak runoff rate helps in designing a diversion ditch and the retention runoff capacity helps in designing a retention structure.

The rate at which runoff in an agricultural land occurs as well as sediment yields in a given farmland is determined by natural factors such as topography, climate, geology and land use. Likewise, human activities are also a determinant of runoff and sediment yield. This human activities include; deforestation, agriculture, urbanization, mining operations and road construction and highways. All these factors are discussed in details as follows:
a) Natural factors

-Land use determines sediment yield in a farm and the rat e of runoff in that the more the eroded a land is the higher the chances of the land being left bare hence soil particle s are easily detached from the ground due to increased runoff rate as there are no obstacles that might help in reducing the runoff rate.

-Topography is also a great concern in runoff determination. The hilly or sloppy agricultural lands tends to have higher gradients at the top/peaks and low gradients at the valleys hence the water runoff moves at a very high speed at steep sides down the valleys carrying away sediments detached in the process. This has mainly contributed to increased sediment yield hence more increased runoff rate.

-Climatic conditions also determine the runoff rate and sediment yield. This is because the higher the amount of rainfall the more the runoff rate washing away the suspended loads in the river beds and also on most farm lands.

-Geology also determines the sediment yield in that the more rocks available the more sediment produced due to disintegration of the rocks.

b) Human activities:

-Agriculture is a major contributor to this because rearing of animals in large herd results to increased land use change hence more physical weathering of rocks resulting to increased sediment which is washed away into water bodies leading to runoff. Increased tillage also leads to mechanical manipulation of soils breaking the soil clods into finer particles that are easily carried by runoff thus increased runoff rate.

-Deforestation is the cutting down of trees thus leaves the land bare hence increased soil particle detached thus more runoff on most farm lands.

-Increased mining activities such as quarries have also led to production of sediments that are washed away during heavy rainfall conditions thus increased runoff rates.

-Increased urbanization and industrialization is also a main contributor of this because the more the increased construction of buildings and structures in urban areas resulting from increased settlements within the areas contributes much in sediments production which lastly is carried into most nearby rivers and streams.

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