Abstract
This study aims to examine the flood propensity of the main watercourse of Porto da Cruz drainage basin and, if relevant, to propose two methodologies to alleviate the impacts (i.e., detention basin sizing and riverbed roughness coefficient adjustment). Geomorphological data were obtained from the watershed characterization process and used through the SIG ArcGIS software for the flood propensity assessment and then for the calculation of the expected peak flow rate for a return period of 100 years through the Gumbel Distribution. Subsequently, the drainage capacity of the river mouth was verified using the Manning‐Strickler equation in order to establish whether the river mouth of the watershed has the capacity to drain the entire volume of rainwater in a severe flood event. In conclusion, the results demonstrate that the river mouth of the Porto da Cruz watershed does not have the capacity to drain the rain flow for the predetermined return period; thus, the detention basin was sized through the Dutch method and the simplified triangular hydrograph method.
TopIntroduction
While people were civilizing, they took care to establish their settlements on the banks of rivers and streams. For this reason, floods and overflows have been one of the most destructive natural disasters on human settlements (Wetherald & Manabe, 2007). Especially after the industrial revolution, the increase in temperature and the climate change seen as a result of it have also been the trigger of extreme natural events. In parallel with this, floods and overflows gradually cause great material and moral losses on societies (Trenberth & Dai & Rasmussen & Parsons, 2007).
Today, flood and overflow events are not limited to rivers and streams, but they have also started to be effective in densely populated metropolises (Barichivichi & Gloor & Peylin & Brienen & Schöngart & Espinoza & Pattnayak, 2018). The reason for this is that the rain waters cannot drain fast enough in the city centers. Due to the high rate of concretization, the connection of the soil with water is cut off and the soil loses its ability to absorb water to a great extent (Gonçalves & Lousada, 2020). Especially the settlements established around the flood areas are frequently faced with floods today. In addition, mountainous regions can be exposed to destructive floods because they are suitable for high-speed flows due to gravity (Gonçalves & Rodrigues & Curitiba & Torres & Lousada, 2020).
Today, as a result of the increase in flood disasters due to extreme natural events, communication and technological interventions have become necessary (Gonçalves & Lousada & Lis, 2020). Traditional methods are based on changing the direction of the flow from the source of the flood (Tucci & Porto & Barros, 1995). Although this method works in the source area, it causes further exacerbation of floods in the downstream areas. For this reason, it has become essential to find a solution to the problem with more technological and effective interventions without directing the flow from one region to another (Lousada & Gonçalves & Atmaca, 2022).
Taking all of this into consideration, this study aims to perform a hydrological analysis of the parish of Porto da Cruz, estimating its peak flowrate for a recurring period of 100 years, and establish a comparison with its watershed´s river mouth drainage capacity. Based on the premise that the streams river mouth hydraulic features are insufficient to drain the expected peak flow rate, it was designed a detention basin to further control the downstream flowrate and avoiding the need to change the stream cross section. This structural measure was also chosen as it results in considerably reduced urban effects and can be complemented with small changes of the streambed and walls roughness coefficient, thus increasing the drainage capacity of the river mouth without affecting its cross section.
Key Terms in this Chapter
Insular Territories: Independent territory that is composed of an island or an archipelago.
Hydrology: A science dealing with the properties, distribution, and circulation of water on and below the earth's surface and in the atmosphere.
Urban Planning: Is a technical and political process concerned with the control of the use of land and design of the urban environment, including transportation networks, to guide and ensure the orderly development of settlements and communities. It concerns itself with research and analysis, strategic thinking, architecture, urban design, public consultation, policy recommendations, implementation, and management.
Spatial Analysis: Is the process of extracting or creating new information about a set of geographic features to perform routine examination, assessment, evaluation, analysis, or modeling of data in a geographic area based on pre-established and computerized criteria and standards.
Territorial Management: Mean the decision-making processes of economical and institutional social actors of a particular space in the process of appropriation and the use of territories.
Hydraulics: Branch of science concerned with the practical applications of fluids, primarily liquids, in motion. It is related to fluid mechanics, which in large part provides its theoretical foundation. Hydraulics deals with such matters as the flow of liquids in pipes, rivers, and channels and their confinement by dams and tanks. Some of its principles apply also to gases, usually in cases in which variations in density are relatively small. Consequently, the scope of hydraulics extends to such mechanical devices as fans and gas turbines and to pneumatic control systems.