Flooding takes place after excessive water in a river’s channel exceeds its holding volume resulting in overflow of the water onto the adjacent area, the flood plain. The excessive rise in water can be caused by various factors, among which is extended periods of rainfall. In the case of Pakistani floods, the continual, heavy rain that lasted for an entire week contributed significantly to the flood ( Gronewold, 2010) . After long periods of rainfall, the ground becomes saturated hence the soil unable to contain water resulting in excessive runoff water. The runoff mixes with river water at a much faster rate than in times when the ground is not saturated. As a result, the river receives high volumes of water that leads to floods. In conjunction with extended periods of rainfall, there are other physical factors that trigger flooding, some of which can be controlled through human activities especially the vegetation cover. On the other hand, natural disasters, which are life threatening events of nature have also been noted to contribute to flooding. Thus, this paper asserts that physical factors have a major influence on flooding.
One of the significant physical factors that play a role in floods is the shape and size of the drainage basin of a river. The shape dictates the time taken or the lag time for rainwater to reach the river and affect the holding capacity ( Smith, 2013) . In case of a river having a circular basin, much of the precipitation finds its way into the river’s channel almost at the same time since a circular basin allows fairly equal distance for the precipitation to reach the river. A circular basin is undesirable as it tends to result in massive precipitation in a river without much time and could lead to flash floods. On the other hand, the size of a river’s basin determines the amount of precipitation that the river is capable of keeping in its channel. A river with an extensive drainage basin implies that it has the capacity to hold much water before breaking its banks.
Delegate your assignment to our experts and they will do the rest.
Another physical factor is the perviousness of rock bed and the soil in a river’s drainage basin. The best situation in reducing flooding is where the rock bed and the soil are pervious to allow the infiltration of as much precipitation as possible. However, if the drainage basin of a river has impermeable soil and impervious rock bed, less precipitation is likely to percolate. As a result, the surface runoff is likely to increase and implicate a high likelihood of flooding. Other physical factors may have a role to play in determining the permeability of the soil. For instance, if the soil had been saturated by the previous precipitation, with a short interval between the periods of rainfall, then the soil’s permeability stands to be significantly reduced. In turn, the soil is less likely to allow rainwater through, thus increasing the surface runoff. On the other hand, prolonged heat in an area may coagulate soil particles and reduce the soil’s permeability ( Office of the Queensland Chief Scientist, 2017) . As a result, the rainfall that falls on the soil is less likely to infiltrate and instead, the rain water finds its way into the river, causing massive swelling of the river’s waters and initiating floods.
The other significant physical factor that influences flooding is the cover of vegetation in a river’s basin. A river basin with a highly dense cover of vegetation is less likely to experience massive flooding. The reason is that the vegetation cover has been observed to intercept the runoff from rain water for storage and thus reduces the amount of water flowing into the river. On the contrary, a river basin with sparse vegetation leaves much room for surface runoff to flow without much interception. Consequently, more water is likely to flow into the river and increase the chances of flooding ( Smith, 2013) . In a different perspective, vegetation serves a crucial role in binding soil particles through the network of roots. As a result, less soil erosion is likely to take place in a densely vegetated river basin, ensuring that less silt finds its way into the river’s channel. As such, the river is less likely to have a reduction in its size and capacity to hold water within its channel. On the other hand, a river basin with little or no vegetation increases the chances of soil erosion and mass wasting during the rainfall seasons. This often occurs due to human activities such as deforestation and clearing land for farming or construction ( Entwistle & Heritage, 2016) . Once the rains pour down, most of the eroded soil is carried away by the surface runoff and into the river channel. As a result, the river’s capacity is reduced with a subsequent increase in the likelihood of flooding.
Similarly, the steepness and relief of the river basin influences the speed at which the surface runoff flows into the river. In situations where the valley of a river has sharp and steep sides, the rate of flow of the surface runoff into the river is much faster. A faster rate of flow implies that the discharge in the river is likely to increase significantly within a short period of time after a heavy downpour thus increasing the likelihood of flooding. Conversely, rivers with valleys characterised by gentle sides and undulating relief experience lower rates of flow of the surface runoff into their channels. Lower rates of flow of the surface runoff indicates that more time is required before the river gains a significant amount of water in its channel and thus reduces the likelihood of flooding ( Smith, 2013) . Thus, rivers with gentle valleys and undulating relief are less likely to experience flooding than rivers whose valleys have sharp and steep sides with a smooth relief.
Another important physical factor that influences flooding is the number of streams emptying into a river. Where a river has a high number of tributaries emptying in its channel, the river is likely to have high amounts of water due to the high inflow of water from the tributaries. Following a heavy downpour, the river is likely to have high amounts of water in its channel from the tributaries. Progressively, the water in the river’s channel is likely to constantly rise and implicate a high probability of flooding particularly at the confluences where much water is flowing from the tributaries ( Smith, 2013) . On the other hand, a river with few tributaries supplying water to its channel is less likely to flood. Less tributaries mean that lower amounts of water flow into the river’s channel and as a result, a lower likelihood of flooding.
The next important physical factor is climate change. In the case of Pakistani, the change in climate was evident as they experienced high levels of humidity accompanied with stifling heat that gave way to rainfall for a month ( Gronewold, 2010) . Further investigations into the floods pointed out that massive deforestation had played a part in augmenting the effects of climate change and the subsequent floods. Moreover, the physical infrastructure for handling the surface run off had been less considered and gave way to the floods. It seemed that the country had overlooked the effects of climate change and the results were the devastating floods. Another aspect of climate change in Pakistani was the altered pattern of the monsoon. Unlike during other years, the monsoon had drifted far northwards to one of the driest regions in Pakistan. Since these areas had never experienced the monsoon before, the result was the flash floods that had a devastating outcome ( Gronewold, 2010) . Another feature of climate change is that it caused high temperatures which resulted in the melting of glaciers, releasing massive volumes of water. Before the rains begun, the rivers were already full of the melt water hence were unable to hold the water from the heavy downpour and as a result, flooding was inevitable.
From a different perspective, flooding can be attributed to natural disasters. For instance, the cyclones experienced in Bangladesh result in massive amounts of precipitation that leads to flooding (Jonkman, 2005). Similarly, the occurrence of hurricanes and tornadoes results in huge amounts of water that result in flooding with massive destruction of property and loss of lives. In the US, various hurricanes have hit the nation resulting in pronounced flooding beyond the control of human beings (Jonkman, 2005). In fact, these disasters continuously strike and massive efforts have been dedicated towards monitoring their occurrence to mitigate the impact of flooding. Other natural disaster such as high tides result in tsunamis that bring much precipitation and ocean water to the nearby areas, resulting in massive flooding.
In conclusion, from the discussion, physical factors have a major influence on flooding. Factors such as the shape and size of the drainage basin of a river influence flooding. The shape dictates the time taken for rainwater to reach the river and affect the holding capacity while the size of a river’s basin determines the amount of precipitation that the river is capable of keeping in its channel before flooding occurs. The permeability of the soil and rock bed influences flooding where impermeable soil and impervious rock bed result in increased the surface runoff and implicate a high likelihood of flooding. Similarly, the cover of vegetation in a river’s basin influences flooding where a river basin with a highly dense cover of vegetation is less likely to experience flooding. Other physical factors such as the steepness and relief of the river basin, the number of streams emptying into a river and climate change have been found to have a significant influence on flooding. Nevertheless, natural disasters such as tornadoes and cyclones have also been found to cause flooding but nit in the same magnitude as the physical factors. Thus, physical factors have a major influence on flooding.
References
Entwistle, N. & Heritage, G. (2016). Changes to our rivers and floodplains have exacerbated flooding. The conversation. Retrieved on August 12, 2017. http://theconversation.com/changes-to-our-rivers-and-floodplains-have-exacerbated-flooding-52876
Gronewold, N. (2010). What caused the massive flooding in Pakistan? Scientific American . Retrieved on August 12, 2017. https://www.scientificamerican.com/article/what-caused-the-massive-flooding-in-pakistan/
Jonkman, S. N. (2005). Global perspectives on loss of human life caused by floods. Natural hazards , 34(2), 151-175.
Office of the Queensland Chief Scientist. (2017). What factors contribute to floods? Retrieved on August 12, 2017. http://ww w.chiefscientist.qld.gov.au/publications/understanding-floods/what-factors-contributenrfa.ceh.ac.uk/nrfa-data
Smith, K. (2013). Environmental hazards: assessing risk and reducing disaster . Routledge.
