Multi-criteria approach to the infrastructural problems of San Pedro de la Paz - From an urbanistic and hydraulic perspective

Abstract

Part I concerns the analysis of the infrastructural problems at hand in San Pedro de la Paz. To get insight into the problems first an analysis of the location is made. This analysis involves the geographical characteristics of the city, historical development, land use, infrastructure etc. Based on this analysis a problem description is made. The major problem is the congestion of Ruta 160. This problem has different causes: the inter-communal traffic flows, trucks, public transport deficiency, connectivity of the secondary roads and organisational problems. To solve the congestion on Ruta 160 several solutions have been proposed by different parties. These proposed solutions are elaborated upon with figures of the road profiles and tables containing the road characteristics. To improve the congestion on Ruta 160 these solutions are combined into variants by the research team. The most promising variants are filtered using a set of constraints and demands. Finally in Part 1 the criteria that are used in the Multi-criteria analysis (MCA) of Part 4 are introduced and explained. These criteria are: time, costs, environmental impact, social impact, safety, comfort and co-benefits. Part II considers the Biobío River and the Los Batros wetlands north of the Ruta 160 Bridge. The influence of the infrastructure variants Costanera Sur, Puente Industrial and Ruta Humedal on this inland water system is analysed. For this analysis two existing 1D HEC-RAS models of the Biobío River and Los Batros are modified to meet the current and proposed situations. The design conditions that are used for both models are discharges with a return period of 100 years. Also other discharges are used in order to evaluate the effects of the infrastructure for different situations. The results show that the water level in the Biobío River increases with a maximum of 10 centimetres due to the presence of Puente Industrial and Costanera Sur. The water level in (Estero) Los Batros experiences a negligible increase due to the presence of Ruta Humedal. The resulting water levels and LiDAR topography data are also used to create an inundation map for San Pedro de la Paz and the Biobío River. It can be concluded that in the present situation no mentionable floods occur along the southern bank of the Biobío River. This is also the case for the Costanera Sur situation since the riverbanks are heightened. For the design condition flooding occurs for parts of Los Batros. Ruta Humedal does not increase the flooded area in Los Batros but protects a part of the farmland located in that area from flooding. Several roads are also analysed on the tsunami impact with the NEOWAVE model. These roads consist of Ruta Costa (elevated coastal highway), Costanera Sur (elevated road along the riverbank) and Ruta Humedal (through the wetlands). They are combined into three different combinations: (I) Costanera Sur and Ruta Humedal, (II) Costanera Sur and Ruta Costa and (III) Costanera Sur, Ruta Humedal and Ruta Costa.To assess these combinations properly, first the generation of a tsunami by an earthquake is explained. Then an earthquake scenario has to be devised in order to come up with a worst case tsunami scenario. This scenario is derived from multiple major earthquakes that generated tsunamis that affected the coastal area around San Pedro de la Paz over the last centuries.This has led to a scenario MW 8.9 and MW 9.0, which both show inundation of the coastal area of San Pedro de la Paz but in different amounts. Since the amount of inundation of MW 8.9 is not significant enough for a detailed analysis, only the results of MW 9.0 are used. This scenario overtops the dunes and inundates the coastal neighbourhoods. In the case combination (II) and (III) this coastal inundation is completely prevented, only Los Batros has a small amount of inundation. Combination (I) does not prevent coastal inundation and seems to increase the amount of inundation in Los Batros. However, this increase of inundation in Los Batros could be due to deviations in the model itself and needs more research. Part IV starts with the analysis of the different solutions based on the criteria as defined in Part 1. The analysis is followed by the MCA. The MCA consists of three different steps. The first step is the weighting of the criteria. In this step the relative importance of the criteria is determined. This is done using pairwise combination of criteria. The pairwise combination of the criteria is presented in a survey to the research team and students of the UCSC. The weights of the different criteria as determined by both the students and the research team are used in the MCA. The results show major difference in what the students think are important criteria and what the research team thinks are in important criteria. The students view safety, time and costs as most important criteria. But the members of the research prioritize safety, environmental impact and social impact. Step 2 concerns the scoring of the different proposed solutions and the variants. The solutions are given a score for every criterion as defined in Part 1. This scoring is done by the research team and based on the analysis as done in Part 4. The absolutes scores from Part 2 show significant difference on solution level. The two proposed solutions with the highest scores are Ruta Costa and Ruta 160. The improvement of Pedro Aguirre Cerda scores relatively low. On variant level the differences are much smaller. The variants that have the highest scores are variant 1A and 1B. Step 3 of the MCA takes into account the info from the previous both steps by multiplying the absolute scores of step 2 with the weight of the criteria as determined in step 1. This multiplication results in the so-called relative weighted score. By taking into account the relative weights of the criteria the ranking of the variants changes significantly. When using the weights as defined by the students, variant 1A scores the highest. When taking into account the weights of the criteria as defined by the research variant 1B comes out on top.