Hurricane Maria in Puerto Rico: the Case Background and Impact Caused
Introduction and Overview
Hurricane Maria was a strong Category 5 hurricane that caused serious damage and casualties to the Caribbean region, especially Puerto Rico. In this case study, we are going to look at the case background and point out the major impact caused by this hurricane and do some analysis related to this impact. Then, two feasible solutions will be evaluated based on the selection criteria. A recommended solution will be given at the end of this recommendation report.
At first, I would like to give some background information about a hurricane. The formal name of a hurricane, or typhoon is a tropical cyclone. Tropical cyclones are formed under a few favorable conditions, such a warm sea surface temperature (>=26.5℃) and low wind shear. These favorable conditions would lead to the formation of a tropical disturbance, which is the precedent of a tropical cyclone. If the favorable conditions persist, the tropical disturbance will continue to develop and become a tropical cyclone when the mean sustained wind speed of the tropical cyclone near to the center over a period of time, like 1-min or 10-min, reaches a certain limit. The classification of the tropical cyclone is divided into different categories and varies between different regions. In this case study, Hurricane Maria was formed on North Atlantic. The classification of the tropical cyclone in this region from low to high in terms of wind speed are tropical depressions, tropical storms, and hurricanes from categories 1 to 5.
Hurricane Maria was formed from a tropical disturbance off the African west coast on 16 September 2017 on 1200 in Coordinated Universal Time (UTC) as a tropical depression. The storm moved west-northwest and intensified as a hurricane on 1800 UTC, 17 September 2017. Because of the extremely favorable conditions on the ocean such as warm sea surface temperature and low wind shear, the hurricane intensified quickly from category 1 to 5 just within 30 hours. Hurricane Maria then made its first landfall on the Dominica island just around one hour later, on 0115 UTC, 19 September 2017. After passing through Dominica, the hurricane continued to maintain its intensity and moved west-northwest. The storm weakened slightly just before making landfall on Puerto Rico. Hurricane Maria made its second landfall on the southeastern part of Puerto Rico on 1015 UTC, 20 September 2017. The hurricane passed through the island diagonally from the southeastern to the northwestern part of the island. The hurricane was weakened to category 1 due to the friction with the land mass of Puerto Rico. The hurricane then re-entered the ocean on 1800 UTC, 20 September 2017. After passing through Puerto Rico, the hurricane was strengthened and weakened before turning into an extratropical cyclone on 1800 UTC, 30 September 2017 off the shore of Newfoundland, Canada.
Hurricane Maria created serious havoc to Puerto Rico. The impact and destruction of the hurricane are visible in many places on Puerto Rico. The hurricane’s torrential raining has brought serious flooding to the streets and was only gone just a few weeks later. The strong wind has also knocked down the power lines and caused widespread blackouts. As a result, many people in Puerto Rico did not have electricity supplies and water supplies for weeks. The same also applied to communication lines. Roads were also damaged and numerous were knocked down. Many houses of Puerto Rico citizens have become ruins with some of their rooftops were being blown away by the strong wind, and the citizens had to pick up their personal belongings from their ruined houses after the hurricane has passed through. Last but not least, the hurricane also caused widespread landslides to the mountainous regions of Puerto Rico. This is also the major impact that we will discuss and analyze in this report.
As we have pointed out in the case background, hurricane Maria had a series of negative impacts. However, all of these negative impacts can be linked back to one major root problem —— landslides. Therefore, we must tackle the root problem, which is landslides, in order to prevent a series of negative consequences listed above happen again. The problem of landslides can actually be mitigated by using the current technology and planning using scientific criteria. Therefore, our report will focus on landslides and how to prevent such disastrous events happen again in view of future hurricanes with similar strength.
Before going into the solutions, we must know how landslides are formed. As first we need to know the two forces affecting the stability of the slopes: Shear stress and shear strength. Shear stress is the downward pulling force, which is usually gravitational force, to move the slope materials downslope. This force is usually controlled by the gradient of the slope and the weight of the slope materials. Another force is called the shear strength, which prevents the slope materials to move downslope. This force is affected by cohesion and friction of sliding between slope materials.
Under normal situation, the soil grains are usually held together by a thin film of water and exerts pressure to the surroundings, which is known as pore water pressure. When the soil is not saturated, the pressure force exerts to the surrounding soil grains increase the cohesion force and friction and between the soil materials. This also increases the shear strength. When the soil is saturated with water, like after heavy rainfall, the pore spaces between soil grains are filled with water. The pore water pressure will greatly increase and reduce the cohesion force and friction between the soil grains, which makes them slide very easily. This also reduces the shear strength and increases the shear stress of the slope. When the shear stress has passed the critical point, landslides will occur. This is also an example of energy change between potential and kinetic energy. The gravitational potential energy stored in the soil materials is transferred to kinetic energy when the shear stress is greater than the shear strength. After explaining the formation of landslides, we will look at some feasible solutions to mitigate this problem.
Solution 1: Using Engineering Measures
The first solution for landslides is using engineering measures. In this recommendation report, we will list out two types of engineering measures as an example to explain how this solution works. The first one is constructing a sub-surface drainage system. The sub-surface drainage system can reduce the pore water pressure within the soil after torrential rainfall by draining the excess amount of water inside the soil and discharging them out of the slope. Consequently, the slope is not saturated with water and the friction and cohesion force between slope materials is increased. The second one is using soil anchors to anchor the soil. The unstable soil is anchored to stable bedrock using concrete walls and cables. The anchors add a normal force to the soil, thus increasing the friction between the soil grains. This added force hinders the process of soil grains sliding past one another, so landslides are prevented and mitigated.
Solution 2: Land use planning and restrictions
The second solution is to apply land use planning and restrictions. This might seem to be a purely man-related solution. However, the principle behind determining the high-risk area is very scientific. At first, you need to identify the gradient of that area or slope. The steeper the gradient, the higher the gravitational potential energy of the slope is. When the slope gradient is above 30 degrees, the likelihood of landslides sharply increased. Moreover, the geology of that area is one of considering factors when doing land-use planning. Some of the rocks like granite are more vulnerable to weathering under a hot and wet climate, like Puerto Rico. These rocks are deeply weathered by hydrolysis to become clay. This creates a thick layer of the soil on these slopes, increasing the risk of having landslides. Last but not least, soil moisture data can also be used to analyze whether a region or area is prone to landslides. All these scientific data can help us create a rational land-use planning map and help government officials to plan ahead.
In this part, we will compare two solutions using two selection criteria: Cost-effectiveness and reliability. The first criterion is chosen because the cost-effectiveness can affect the choice for different regions and countries, especially in those developing economies, if the solution is not cost-effective, this may create a heavy financial burden to them. The second criterion is chosen because this can evaluate whether the solution is able to prevent future landslides.
For the first criteria, solution 1 is not cost-effective. Both constructing sub-surface drainage systems and soil anchors are expensive, for example, each soil anchor costs around 600 to 800 US Dollars to install and it requires a specific anchor machine to install the equipment. In contrast, solution 2 is more cost-effective. This is because this solution does not require a huge amount of construction cost. Even though scientific analysis is still needed, the cost is much lower compared to solution 1 and also more effective in mitigating and preventing landslides.
For the second criteria, solution 1 is more reliable. This is because engineering measures can effectively block the slope materials halfway to prevent damage to the built-up area. In contrast, solution 2 is not quite reliable. This is because the solution needs to deal with land owners. (Reyes, 2014) Moreover, the scientific data may still have insufficiencies even though all of these data are collected. As a result, there may be a mismatch between the solution and reality.
Recommendation and Conclusion
After considering all of these selection criteria, we recommend to use land-use planning as the recommended solution. As described in the selection criteria, there might be obstacles to implementing this recommended solution. Therefore, one way to solve this obstacle is to continuously monitor the environment of different areas and adjust the land-use planning map timely according to new scientific data collected.
To conclude, this recommendation report has gone through the introduction, case background, problem analysis, solutions, and selection criteria, and finally gives a recommendation. We hope this report would provide the best solution to prevent the havoc as hurricane Maria happened in Puerto Rico again.
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