The definition of river discharge
River discharge can be understood to be the total volume of water that flows into a given river channel. On the other hand, it could also be viewed as the amount of water volume flowing within a particular channel and at a given point and in most instances; it is measured in cubic meter per second (Di Baldassarre & Montanari, 2009, p. 913).
Background information
Research has established that river discharge is one of the most critical components in as far as the water cycle is concerned, and that this has been playing a vital function of driving the climate system because fresh water movement, usually directed into the ocean, might influence the oceanic circulation patterns (Milliman & Farnsworth, 2013, p. 1). Evidently, drainage basin’s discharge often depends on the evapotranspiration, the storage factors in addition to the precipitation. River discharge further has been shown to have the ability to affect the overall distribution of water resources, the phytoplankton growth more than the nutrient export. Therefore, river discharge can be said to account for water quality particularly in the inland waters and in the coastal oceans. The discharge is also illustrated with the use of hydrographs showing the yearly patterns of flow in response to the various climatic changes. In addition to this, studies have established that the short-term differences in discharges often are represented with the use of flood of storm hydrographs. These storm hydrographs, on the other hand, illustrates the diverse variation in the river discharge within a short time particularly during the rainstorm (Milliman et al., 2008, p. 189).
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Thesis statement
Weather conditions such as storm, high temperature and low temperature, rainfall types and amount and human factors influence river discharges.
The effects of storms on river discharge
During the times of heavy storms, research has established that rainfall tends to be far in excess of the capacity of the infiltration of the soil hence resulting in increased overland flow in addition to a rapid growth in the levels of the river. Studies have further shown that the direction of the movement of the storm about the basin orientation has a significant impact on both the duration and the magnitude of the peak flow of the water surface runoff (Costa, Botta & Cardille, 2003, p. 206). Further, the direction of the storm has also been established to have an enormous impact on the level of the elongated basins. On the same basin, those storms that seem to shift upstream tend to result in lower peaks of long duration than those storms that seem to move downstream. Arguably, the type of storm is also a critical aspect in that; the thunderstorms results into the peak flow on the smaller basins while on the other hand, the large cyclonic or the frontal type storms are simply a determinant in the central basins. If a storm lasts long enough, eventually almost all the precipitation will become runoff. Storm hydrographs have been used for a long time in illustrating how the drainage basins considerably respond to a precise stage of precipitation. They are employed in the process of planning for prospective flood instances and the periods of drought as they illustrate the discharge that originated as precipitation (House & Warwick, 1998, p. 2280). They show a seasonal release pattern of flows about the climate and cover a moderately short time phase, more often than not hours or even days instead of focusing on weeks or months. Additionally, storm hydrographs allow for the investigation of the relationship between a precipitation episode and discharge as storm water enters the drainage basin the discharge rates increase. It is important to note that the highest level of flow within the channel of the storm hydrographs is recognized as the hit the highest point discharge.
Comparison between high temperature and low temperature and River Discharge
Temperature plays a significant role concerning influencing river drainage. The higher rates of evapotranspiration have been shown to lower the average amount of the discharge, and at the same time, lower temperatures have the ability to store water particularly in the form of snow and ice. The high temperatures that are also dry can bake the soil to the extent that when there is rainfall the water cannot easily soak into the soil but instead it will run off the earth surface and directed into the river (Morrison, Quick & Foreman, 2002, p. 230). Further, higher temperatures further result into increasing rates of evaporations from the water surface and the plant transpiration which further reduces the amount of discharge. On the other hand, longer periods of extreme cold weather can result into the frozen grounds to the extent that water cannot easily soak in. In a more generation viewpoint, there is a growing consensus that holds that a warming climate can lead to a hydrological intensification more particularly increase in the evapotranspiration and river flow worldwide. It will be experienced as a result of warming-triggered increases in the overall evaporation and precipitation despite the fact that the debate remains about the enormity and trends of this change.
Rainfall types and amounts that affect river discharge
The amount and type of precipitation have the potential impact on a river's discharge considerably. The intensity of the rainfall tends to affect the overall amount of the runoff and the peak flow rates. Within specified rainfall duration the total rise in the amount rainfall intensity will result into increase in the peak discharges and the volume of the runoff provided that the rates of infiltration to the soil have been exceeded. According to Dawson & Wilby, (1998, p. 48), antecedent rainfall is rain that is believed to have already happened, and this implies that the ground has turned out to be highly saturated and as a result of this, the rainfall will rapidly flow as surface run-off towards the river. A substantial and continuous precipitation or even the snow melting implies increased volume of water flowing into the rivers. Research has shown that torrential rains often results in increased saturation in the soil and the process causing more water to reach the rivers through runoff. Rapid Rain causes the soil to get saturated at higher rates and further, the excessive water will be transferred by surface runoff hence causing a short lag period. The same case might also imply that the water speed has also increased. Slow Light Rain tend to be absorbed through permeation, and the rivers take longer to react to rainfall as water also take longer to seep through the drainage basins through flow and groundwater flow leading to longer lag time (Wei et al., 2007, p. 248).
Human factors that affect River discharge
Numerous human factors have been shown to have a significant impact to the river discharge. Land use can strongly influence the runoff coefficient. Urbanized areas may have a flow coefficient of almost 100 %, whereas natural vegetation may have the low flow. Ploughing, drainage, cropping intensity and a forestation has a considerable effect on runoff. According to Milliman et al., (2008, p. 192), the building of roads, for instance, has been established to have the ability to increase the impermeable surface area which further results in shorter lag time. In most urban regions the surfaces such as the roads are highly impervious; consequently, water cannot easily saturate into the ground, but in its place, it runs into drains, flows swiftly and joins rainwater from several drains which ultimately drip into the rivers (McClelland et al, 2006, p. 6). The building of drains and sewers that are used in the transportation of water rapidly to river channels have a greater effect regarding reducing the lag time. In addition to this, Straightening of river channels and lining with concrete further has the potential of leading to faster delivery of water downstream of the urban area and in the process increases the risk of flooding (Thorstad et al., 2008, p. 345). Focusing on the rural regions, ploughing up and down rather than across the hillsides has been established to create channels that further let rainwater to get directed into rivers much faster resulting in increased river discharge. In addition to this, deforestation might imply less interception, and in the process, the rain water will reach the ground surface much faster, and in the process, the ground is expected to be drenched, and surface run-off will be increased.
The essay has analyzed critically the impact of weather on river drainage taking into consideration specific factors of weather such as storm, high temperature and low temperature, rainfall types and amount and human factors. Future changes in the land used in addition to the weather changes would continue having greater and increasing trends in the river drainage. Human land use is the most significant factor with a more major impact on river drainage. Area of deforestation has been associated with short lag time and increases discharge. Impermeable surfaces as constructed through human activities such as concrete and tarmac roads have been linked to very short lag times.
References
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House, W. A., & Warwick, M. S. (1998). Hysteresis of the solute concentration/discharge relationship in rivers during storms. Water Research , 32 (8), 2279-2290.
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Wei, W., Chen, L., Fu, B., Huang, Z., Wu, D., & Gui, L. (2007). The effect of land uses and rainfall regimes on runoff and soil erosion in the semi-arid loess hilly area, China. Journal of hydrology , 335 (3), 247-258.
