@2024 Afarand., IRAN

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ISSN: 2538-4384    Geographical Researches 2021;36(2):217-232

Background
The expansion of cities and the constructions around the historical buildings threaten them. A spatial model for urban sewage networks can be of importance to tackle this problem.
Previous Studies
Conservation of the historical buildings in the time of natural and human disasters are of essential importance [Chen et al., 2016]. The process of conservation is much more difficult when they have various land-uses such as residential, commercial, and museums [Taghvaei et al., 2019]. The aim of using spatial models is to show the efficacy of those methods that have been designed for the conservation of the cultural heritages [Shevlyakova et al., 2019]. Despite the abundance of highly attractive outstanding old buildings, the historical fabric of Isfahan has faced some problems such as overpopulation, traffic jams, and incompatible land-uses that threaten not only the physical structure but also the historical and cultural identity of the city [Ebrahimzadeh et al., 2020]. Dampness is one of the problems damaging the historical buildings in Isfahan.
Aim(s)
This study aimed to design a spatial model in order to evaluate the risk of urban sewage network accidents in the historical fabric of the cities.
Research type
The research type is not mentioned.
Research society, place and time
The current research is carried in high-risk neighborhoods of Isfahan.
Sampling method and number
The sampling method and the number of samples are not mentioned.
Used devices&materials
Analytical Hierarchy Process (AHP) model and Geographical Information System (GIS) using the index of Getis ord GI were combined to design the model.
Findings by Text
High-risk spots locations were found on the GIS map of Isfahan sewage network using the previous records of accidents. Descriptive information of these spots including the precise address, the type of accident, the diameter of the tubes, their depth and material, soil type, and possible cause of the accidents were, also, collected. Figure 7 shows the location of 1459 accidents in a period of five years. All the mentioned data were collected from 122 systems. Clearly, all the streets in one urban zone have the same or similar potential for accidents. Those urban zones with similar situations such as soil type, the age of the network, diameter and depth of the tubes, and the bedding method have similar feasibility of the accidents and are classified into the same groups. Next, the weights calculated using the AHP model are given to all the tubes with the same diameter and material. Hence, the previous accidents' history works as a new collection of the samples. The estimated weights show the importance of that factor and its impact on the occurrence of an accident in the urban sewage network. The calculated weight for every single factor is presented in Table 2. According to the concentration of the historical buildings of Isfahan in one zone and their closeness together such as the buildings assembled in Naghsh e Jahan square, it can be concluded that such buildings are in the same situation of dampness. Then, an accident evaluation and prediction model can have the same attitude toward all the buildings that are close together. Naghsh e Jahan historical monuments need the same strategies to measure their problems in terms of crisis management. Using the Network Analysis process in GIS, the sewage flow in the network can be detected and predict the areas prone to dampness and sewage rising. Table 3 shows the results of accidents' evaluation and the estimation of their causes in different parts of Isfahan. The history of accidents in the urban sewage network in the historical fabric of the city and their causes show that such accidents are more frequent in which zones and what are the most common causes for them. These results help to speculate about the future and detect high-risk areas. This model is generalizable in other cities in order to take the precaution of similar accidents in the regions with a similar situation. Figure 8 shows the accidents hot spots according to the results of Geti ord Gi in the studied area. Light blue spots are low-risk areas and the red ones show high-risk areas in the urban sewage network. In the central parts of Isfahan which is exactly where the historical fabric is located, vehicles movements are more frequent and the number of sewage network accidents is much higher. Such accidents include sewage wells fall, pipe rust, sewage leakage into the foundation and walls of the historical buildings. According to the statistical analysis and the results extracted from SPSS and ArcGIS 10.3, the sewage accidents were evaluated according to the pipes' diameter and age. Kendall & Spearman's non-parametric test was used in the current study because of the shortage of the statistical data about the pipes' age and diameter. The evaluation of the relationship between the accidents and the pipes' diameter According to the collected data, the relationship between the number of accidents and the pipes' diameter is presented in equation 4: Equation 4) Y=-0.0275X+22.44 According to Table 4, statistical analysis shows that there is a negative relationship between the number of accidents and the pipes' diameter. The evaluation of the relationship between the accidents and the pipes' age According to the history of accidents, the relationship between the number of accidents and pipes' age in the range of 20 to 40 years old in the studied area is presented in equation5. Equation 5) Y=0.0225X2-1.0423X+20.791 Table 5 shows the results of the statistical tests.
Main comparison to the similar studies
The results of Mohammadi et al. (2018) are consistent with the results of the current study in terms of the concentration of high-risk areas in the central and historical fabric of the city. Taghvaei et al. (2019) analyzed the vulnerability of the historical fabrics in the central part of Isfahan using the AHP model. They concluded that district 3 is the most vulnerable neighborhood and most of Isfahan's historical monuments are located in it.
Suggestions
- Prepare a data bank about the damp and moisture in the historical buildings. - Update the geographical models related to the cultural heritages in the historical fabric of the cities in order to help the governmental organizations manage the damages and their ownership - Cultural improvements to prevent damages caused by humans. - Using the sensors and portable cameras in the sewage network to monitor the pipes net status quo in the historical fabrics. - Designing proper sewage network with pipes with proper diameter in proper depth - Using pipes such as clay pipes and PE pipes that can be used longer - A homogenous urban management using spatial data infrastructure and the relationship between the relevant organization
Limitations
Lack of an information database about the vulnerability of the historical fabric of Isfahan caused by the dampness from the sewage network accident is one of the main limitations.
Conclusions
Two primary relationships between sewage network pipes and accidents are concluded: 1. The fewer pipes' diameter is, the more probable accidents are. It is mainly due to the recent construction of the residential zone near the historical fabric and consequently over-population. Hence, the available pipes' diameter does not pay off. 2. The leakage of the sewage is more probable in the old rust pipes. To take the precaution of dampness in the historical buildings, it is possible to predict the leakage of the sewage in historically valuable fabrics. According to the importance of Isfahan in terms of the cultural heritages, a comprehensive database that includes spatial data of the surface water and sewage collection network, network's features, history of the accidents particularly in the historical fabric can be of essential importance.
Acknowledgments
We thank all people who helped to do this study.
Conflict of interest
This article has not been published in other journals.
Ethical Permissions
None.
Funding Sources
This study is extracted from a Ph.D. thesis "designing an environmental risk evaluation spatial model in urban sewage network accidents" which is carried out on the student's expense.

TABLES and CHARTS

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