Nature-based management of urban floods to decline risks with case studies

This paper discusses devastating urban floods in the year 2019 that caused human and socioeconomic losses in many countries, including Iran. The main question addressed by this paper is the choice between two flood management models, namely, the optimal and naturebased flood management or the existing hazardous situation that damage the ecosystem and natural resources. The analysis of this paper will find the main responsible factors in the mentioned floods in Iran. For this reason, it examines the impacts of the existing flood management that neglects the ecosystems, environmental components, and nature. The method of this research includes theoretical studies, case studies with the help of structured interviews, and observations. A benchmarking technique compares the two alternatives. The comparisons use seven indicators abstracted from successful global experiences and local knowledge. Finally, this research presents a model for optimal flood management that is applicable everywhere in the world.

Overall, the flood-affected regions experienced catastrophic human, financial, infrastructure, and urban and rural causalities. The quantity of the total damages has not been determined, but there are many reasons to claim that the hazards are widespread and heavy costly. The floods affected the political, social, and economic situations of Iran extensively. Of course, these floods could increase the groundwater resources of Iran. Nevertheless, due to the lack of necessary technologies and infrastructure to direct the waters into groundwater, the beneficial side of the floods has been shrunk (Pakmehr et al 2020). Therefore, the extent and severity of the floods highlight the importance of flood control and management. In common with Tockner and Standford, we believe that flood management is a vital task now (Tockner & Stanford, 2002). From the other side, the effects of ever-expanding urban developments on the hydrological cycle are large. Amid the mentioned massive floods in Iran, debates about the causes of the floods have increased. Some scholars are saying that the neglecting of the environment, lack of knowledge-based urban planning, absence of funding for standard constructions caused the hazardous floods (Pourghasemi et al 2020). They argue that forests are declining and the incompetent authorities do not respect the structural standards, urban building codes, and regulations. Therefore, floods have become so mortal and destructive. On the contrary, others are saying that climate changes and sudden rains are only responsible for the recent fatal floods (Yadollahie, 2019).
The question addressed by this research is which factor is the reason for the hazardous floods? In other words, the question is whether poor control and management of floods lead to devastating floods or climate changes. To answer this question, this paper will look at how the authorities treated the ecosystems and the natural cycle of water flows in Iran. Do they behave abusively with Iran's nature? This paper also investigates whether a significant climate change has happened in Iran.
The purpose of this research is to introduce an optimal model for the control and management of floods to prevent hazards in advance.
The methods of this research are both theoretical studies and field observations to achieve the goal some classic methods and a benchmarking technique have been applied as well.
The outcome of this study is an optimal model for flood control projects to minimize the harms of the floods.

Theoretical studies
This part studies the causes of floods with mortal hazards in the urban built environments in the views of water and flood engineering and management. The purpose of theoretical studies is to provide a theoretical guide for field observation. It is necessary to understand to what degree human activities cause the floods. Earlier, scholars discussed the concept of optimal management of floods (Ghobadi & Kaboli, 2020;Raso et al 2019 andShahraki, 2015). In common with the scholars, with optimal flood management we mean using knowledge-based methods thru minimal budget, maximal ecosystem maintenance, and maximum damage prevention. According to a definition of the Webster Dictionary flood is 'a rising and overflowing of a body of water especially onto normally dry land'. Floods occur in rivers, waterways, channels and water storages like lakes, swamps and dams. Thus, the definition means that an overflow of water can take place on usually dry lands. Shortages of natural or artificial drainages lead the excess of surface runoff (Müller et al, 2019;Singh, 2019;Hong et al 2018;Chan et al 2018 andSpaans &Waterhout, 2017). The shortages of drainage systems cause major human, infrastructure, economic, and socio-psychological hazards. The increase in the population and the simultaneous increase in urbanization has been a fast-paced trend in the developing countries (Zhang, 2016). World Bank studies In Iran show that the percentage of the urbanization trend in recent decades has increased. Please see the fact in Figure 2.  (Rogger et al, 2017, Walsh et al, 2016and Fetter, 2018. One major impact of the urbanization is degrading of the ecosystems and natural environments. Scholars examined the effects of population growth and urbanization on the ecosystems. They evaluated ongoing water supply projects. The evaluations have proven that the majority of the current water supply policies are destructive. The results of the studies state that water procurement policies should not include projects that harm natural watercourses nor ecosystems (Peng et al 2017). One explicit result of the expansion of urbanization is the reduction of soil quality. The other is the coverage of the earth's surface with the building materials. The expansion of the urban built environments narrows the watercourses and rivers. It shortens the water shelf life on the lands. Consequently, the rains are moving rapidly towards low-lying urban areas (Corbau et al, 2019 andFekete &Bogárdi, 2015). The covering of the land surface by a greater share of impervious building materials means that a plentiful bigger proportion of any rainfall forms directly floods. In addition, the grounds covered by buildings in a city, the paved streets and car parks cover large surfaces.
Considering the local topographic characteristic, any slope of the land also enhances the overflow response of a paved area. In every catchment area, the effect on the stream discharge is dependent on the degree of the impervious area. The influence of groundwater is limited to rainfall infiltration into the soil. Thus, after major urban developments in a catchment, the following differences in the river flow will be identified. The emergence of water in the streets and residential areas, a steeper rising curve of the flow, increase in the flood peak magnitude, and decline of water quality by pollutions.
The expansion of urbanization makes essential structural changes to drainage channels and declines their capacity. Flood information can help communities reduce their vulnerability to floods (Han et al 2016 andMetal, 2017). Therefore, by increasing the urban areas, the volume of the water flow in the city increases, while the drainage capacity is reduced.
Rapid urbanization is making people vulnerable to the effects of climate variability. The most obvious change in climate caused by urbanization is an increase in the sudden and sharp floods. An increase in the average temperature happens too. Miller and Hutchins studied the impacts of urbanization on climate change and consequently the situations of urban flooding.
They concluded that urbanization poses climate change with high spatial-temporal variability and uncertainty in climate (Miller and Hutchins, 2017). The majority of the scholars agree that the increased urbanization made global warming. They believe that global warming is caused by -based greenhouse gases. Human activities affect climate change through greenhouse gas emissions and land-use changes (Wang et al, 2014).  (Shaw, 2005). In urban development, hydrological knowledge is required in two phases. The first is the planning stage to consider a higher elevation for the buildings. The second step of the hydrological involvement occurs at the detailing stage, the designing of the drainage channels and pipes to carry the surface water into the rivers. The design of the drainage system is dependent on a careful assessment of the flood size and return period of the flood. When cities are becoming increasingly vulnerable to flooding, the design of the drainage channels is vital.
Until now, we analyzed dialectically urban expansion effects on urban hydrology and floods multidimensional. We recognized that urban development has multifaceted effects on the floods. The studies illustrated that urban development is influential on the aquifers, the drainage systems, the climate characteristics, and the area of the forests.
Theoretical studies guide us that essential projects in the urban development process are needed to manage the floods optimally. We concluded that planners, designers, entrepreneurs, and urban management must take certain actions to make optimal use of the rains and floods. Their ultimate goal is to protect the cities against highly destructive floods.
The required projects are determined through workshop experiences and exploration of the ideas of the relevant scholars and practicing. Please see Table 1for a list of required projects to manage and control the floods optimally. At the same time, we use the situation of the projects as indicators to assess the degree of success in flood management. Build cities resilient and respect the indices and standards of resilient cities to control floods.

Methodology
The theoretical studies of this research provided a framework to guide field studies in the form of a case study strategy. The field studies are knowledge-based as earlier has been presented by Shahraki for the sake of regional/urban sustainable development (Shahraki, 2019). This research supposes that when the flood management model is knowledge-based and optimal, it will not be hazardous. On the contrary, the flood will be beneficial in sustainable urban development. Thus, the main method of this research is to suggest an optimal natural-based flood management model. This research examines the current flood management procedures as one alternative model to introduce its failures and weaknesses.
Procedures to manage floods optimally include projects that have been listed in Table 1.
Theoretical studies on seven indicators had both generic and local features. The indicators are suitable for the characteristics of the case study areas. A benchmarking technique has been used to compare the current flood management model to the optimal natural-based model. Shahraki applied the technique in a work titled "Analyzing economic policies related to effects of immigrant labor" (Shahraki, 2017). In this case study, the indicators have been evaluated and scored for the two alternatives with the help of structured interviews and bad, bad, no idea, good, and very good equal to -10, -5, 0, +5, and +10 respectively. Then, the benchmarking technique as a comparative tool has been used. The benchmarking technique has also been used to analyze all suggested and recommended projects in the two flood control alternative models. Finally, some projects under the umbrella of natural-based optimal flood control and management model have been suggested to meet the goal.

Case studies
The case studies are concerning two subjects. First, to see how much climate change influences the floods. Second, to see to what degree the seven indicators have been respected in urban flood management.

Climate change in Iran
Iran's environment has become critical due to the increased population and urbanization.

i Analysis of the seven indicators
The population of Iran has increased steadily. The increased demands for the required urban places degrade the rivers, drainages, and forests. Table 2 shows the responses of the questioned people about the success of the demographic development programs in Iran. There are some hydraulic structures such as 588 dams, some tidal barrage diversion canals, and coastal defenses in Iran, but they have major shortages. Some lack is short feasibility studies, structural corruption, inefficiency, and none environmental standards. Regarding this index, the responders evaluated it as Figure 3 illustrates. Our observation and experiences reveal that the quantity and quality of preventive projects in terms of the aquifers and watersheds to control the floods in the primary areas are very low.
The authorities did neglect the importance of watershed management over the past decades.
The reductions of water resources, conflict of interests, and neglect of local communities have caused floods and major losses. The responders evaluated the indicator as Figure 4 illustrates.  The above table states a high degree, 93%, of dissatisfaction among the flooded people about the PP index. Before the flood, rivers, water channels, and valley floods were full of mud and sediments like cities of Aghala and Gomishan in the northern strip of the country. In the southeastern part of Iran like the city of Shiraz, the flood revealed that the corrupted municipality had constructed in the riverbed. About this index (DP), the responders evaluated as Figure 5 shows.   In recent decades, there has been no investment in urban knowledge-based projects.
Generally, the population of Iran has suffered greatly from a lack of proper regional/urban planning. The increased density puts pressure on the built environments in coastal lowlands, along with unstable slopes, and in hazard-prone areas are some of the risks. Another significant risk driver in Iran is the corrupted and weak local governance and insufficient public participation. Inadequate and incompetent water resources management is one more important risk driver. The short drainage and waste management cause floods and landslides too. The decaying infrastructure and unsafe building stocks that lead to collapsed structures in flooding times are also risk drivers in Iranian urban areas. During the last floods in Iran, uncoordinated emergency services that decreased the capacity for swift response and preparedness has been revealed as well. Worse, urban management in Iran has no plans to create resilient cities! The responders assessed this indicator as Figure 8 illustrates.

Discussions and comparisons
The observations and field studies concerning the seven indicators proved that urban flood management in Iran has been unsuccessful. Although Iran has always faced destructive floods, the authorities have not come up with any proper remedial plan for this problem.  The boundary covers -98 to +100 and shows the necessity to progress the situation of the existing flood management in Iran up to the natural-based optimal situation without any risk.
The progress shall be in all the seven mentioned indicators. The comparison of the two flood management alternatives exhibited that the increased populations, the expansion of urban areas, and human behaviors against the ecosystems and natural resources caused the destructive and deadly floods. This finding proves the validity of the hypothesis of this research that poor flood management led to the deadly, devastated, and hazardous floods. The case studies have also shown us that the slight climate change caused by environmental degradation has also been the result of inefficient management.

Conclusions
The deadly and destructive floods in the Middle East, including Iran in late March and April 2019, have raised many debates to identify the causes of the floods in the cities. We theorized that poor official flood management was the major reason. This study aimed to prove the hypothesis. This research applied the theoretical studies to provide a guideline for the sake of the case studies in Iran and to present an optimal and nature-based flood management model.
We examined seven indicators in the flooded areas. The guideline was supported by theories of the relevant scholars and global successful experiences. This study noticed that the natural environmental components of Iran have been destroyed continuously. With the introduction of the two flood management alternative models and the use of a benchmarking technique, we found that the existing flood management in Iran is very weak. This fact was revealed by referring to the ideas of the flooded people. We found that the major responsible factor for the floods was the official authorities. This paper suggested a knowledge-based, wellfounded, and successful flood management model with the help of certain indicators. Since the indicators have general features, the model is applicable to flood control and management everywhere in the world.