Journal of Spatial Analysis

Abstract

Coastal areas are dynamic and complex multi-function systems. A wide number of often conflicting human socio-economic activities occur in these areas. These include urbanization, tourism and recreational activities, industrial production, energy production and delivering, port activities, shipping, and agriculture. Coastal systems are also characterized by important ecological and natural values; their high habitat and biological diversity is fundamental to sustain coastal processes and provide ecosystem services which are essential also for human well-being. Human activities often conflict with the need to preserve natural coastal systems and their ecological processes.

   One of the most important applied problems in coastal geology today is determining the physical response of the coastline to sea-level rise. Predicting shoreline retreat and land loss rates is critical to planning future coastal zone management strategies and assessing biological impacts due to habitat changes or destruction. Presently, long-term (>50 years) coastal planning and decision-making has been done piecemeal, if at all, for the nation's shoreline. Consequently, facilities are being located and entire communities are being developed without adequate consideration of the potential costs of protecting or relocating them from sea-level rise-related erosion, flooding and storm damage.

   Research on major natural disasters and related technologies has become an important subject in geography and its application. The complexity analysis of the issue is possible in a system approach to theoretical and applied geography also in the integrity of physical and human geography.

Due to the Caspian Sea water-level fluctuation in coastal zone of Babolsar which happens very quickly in decade scale, the observance of safety element will be possible in light of the integrated coastal zone management with determine of sea frontage. In this context, geography and especially geomorphology is a main basic in this kind of coastal management.

   Detection of sea level fluctuations causing morphological changes in the earth surface and damage to facilities, clarifies the necessary of the present research to study the role of geomorphological indices in Babolsar coast zone constructions. The Coastal Vulnerability Index (CVI) is one of the most commonly used and simple methods to assess coastal vulnerability to sea level rise, in particular due to erosion and/or inundation. The CVI provides a simple numerical basis for ranking sections of coastline in terms of their potential for change that can be used by managers to identify regions where risks may be relatively high. The CVI results can be displayed on maps to highlight regions where the factors that contribute to shoreline changes may have the greatest potential to contribute to changes to shoreline retreat.

In this study, coastal vulnerability index (CVI) is used as effective geomorphic index on Babolsar coast zone constructions. In first, primary and secondary vertical frontages were detect using topographic data (digital elevation model with cell size 10-meter) and Caspian Sea water-level fluctuations.

   The primary vertical frontage includes areas which have the lower height of -24.7 meters and secondary vertical frontage consists of areas which are placed between -24.7 and -23.5 meters. Following this issue, within the primary and secondary vertical frontage, coastal vulnerability index was performed based on five parameters, elevation, slope, landform, land use and distance from main road. According to the coastal vulnerability based on natural (NCVI), human (HCVI) and total vulnerability index (TCVI), large parts of the Babolsar coastal zone (especially in Fereidoonkenar and Babolsar city areas) placed in classes of high and very high vulnerability.

   With respect to detection of the primary (level -24.7 m) and secondary (from level -24.7 to -23.5 m) frontages in Babolsar township area, 345 and 7177 hectares of the township lands are located in the primary and secondary vertical frontages, respectively. The most area of the township land uses in primary frontage belongs to natural structures that have 153 hectares of area. Survey of lands distribution in the height of -24.7 to -23.5 m (secondary vertical frontage) shows that agriculture land use has the most extent in this area; the area of this land use is 5293 hectares that equivalent to 74 percent of all lands which are located in the secondary frontage. Urban and industrial structures have 45 and 522 hectares of area in the primary and secondary frontages of Caspian Sea in Babolsar Township, respectively.

Flood as a natural disaster follows certain erratic patterns which was made confounding factor. Flood risk is variable and complex that depends on very phenomena such as rainfall, runoff concentration and high exposure of the flooding downstream areas.

    This are changes over time and from regions due to natural conditions, human activities, and damage culture of the community at risk. Occurrence of chaos at flood risk changes the trend of predictable processes. In the other words, although flood is a disaster, the occurred irregularities in its patterns can reveal its complicated nature. Flood pattern irregularities are the incident evidence of chaos in the system which can be studied by fractal geometry. The occurred events in spatial variability of floods in the last 50 years show they can be occur as unusual urban flood in Tehran.

    Tehran city may experiences the difference life and property damages because the high varieties in the socio-economic and the life quality level in regions, also structural varieties in the city fabric??. Ignoring the natural factors in spatial planning, overrun and destruction of natural morphology as a result of urban activities and subsequently disturbing urban drainage system lead to unpredictable and destructive floods in Tehran.

    The Tehran precipitation layer was prepared based on 27 weather stations data in the period of 10 years (1998-2009) and Kriging model with a Gaussian function. The runoff is calculated by Soil Conservation Service Curve Number (SCS-CN) and precipitation layer. The flood hazard potential map has been created by 8 variables and Analytic Hierarchy Process (AHP). This map as an index to define the said complexity was prepared in 5 categories of risk by combination of Tehran metropolis flood hazard and vulnerability maps. Then it was divided into hydrological basins and 12 basins were selected randomly. The Perimeter-Area Fractal and Number-Area Model were used to study the chaos and turbulence in the Tehran’s flood pattern.

     Explanation of locational changes of risk between the basins needs to calculate the weighted average risk and the independent variables in 12 basins that obtained by zonal statistics. Based on these average values the factor analysis used to determine the Varifactors or main components of the variability in flood risk between the basins. Finally, fractal geometry models (perimeter-area and cumulative number-area) were used to demonstrate the chaos of the flood risk value in 5 categories of risk.

    In this research the Tehran flood zoning map was calculated at 5 hazard categories. The fractal of sample basins had increased by increasing in the level of hazard map. Generally, the higher DAP values from 1 represented increasing in the chaos or irregularities of Tehran floodhazard. The obtained DAP from very low to very high risk levels are 1.206, 1.216, 1.23, 1.263 and 1.293 respectively. The increasing of DA indicated that turbulence hazard increases based on Perimeter-Area fractal model, thus, with the increase in hazard the DAP and DP values were greater. Also, the results of Number-Area Model showed turbulence floods in the five classes of hazard. The area cumulative number of risk levels are 0.74, 0.79, 0.85, 0.86 and 0.88 respectively; this trend showed the less size of flood risk polygons from very low to very high risk levels. In the other words, by increasing the risk level the polygons gets smaller and indicates the increase the flood risk chaos.

    The occurrence pattern of natural phenomena and even natural hazards have a regularity type in normally condition; if this regularity disrupts for any reason, irregularities or chaos happens. In present study, the results of fractal analysis in sample basins presented the chaos pattern in Tehran floods. Also the heavy rainfall can be predicted in Tehran but the prediction of the flooding distribution was not provided. According to the recorded floods in Tehran the flooding begins always in the northern valleys of Tehran, like Darband, Kan or Golabdareh basins,  are not similar to damage pattern. As a result, despite several studies and projects which have been implemented about flood phenomenon in Tehran, this is unpredictable and uncontrollable in the city.