STRUCTURAL DESIGN OPTIMIZATION OF MODERN INFRASTRUCTURES MODERN DESIGNS FOR HIGHER INSTITUTIONS

CHAPTER ONE

• INTRODUCTION
  • BACKGROUND TO THE STUDY

Floods are among the most recurring and devastating natural hazards, impacting upon human lives and causing severe economic damage throughout the world, Khan et al (2011). It is understood that flood risks will not subside in the future, and with the onset of climate change, flood intensity and frequency will threaten many regions of the world Jonkman and Dawson (2012). Floods occur because of the rapid accumulation and release of runoff waters from upstream to downstream, which is caused by very heavy rainfall. Discharges quickly reach a maximum and diminish almost as rapidly.

The occurrence of flooding is of concern in hydrologic and natural hazards science due to the top ranking of such events among natural disasters in terms of both the number of people affected globally and the proportion of individual fatalities, Borga et al (2014). The potential for flood casualties and damages is also increasing in many regions due to the social and economic development, which imply pressure on land-use, e.g., through urbanization. Flood hazard is expected to increase in frequency and severity, through the impacts of global change on climate, severe weather in the form of heavy rains and river discharge conditions Dihn et al (2014). The current trend and future scenarios of flood risks therefore demand for accurate spatial and temporal information on the potential hazards and risks of floods. As reported by Chang and Guo (2006), heavy convective rainfall often results in flooding in urban areas. Urbanization results into conversion of agricultural land, natural vegetation and wetlands to built-up environments and construction on natural drainages as well increase in the population of those living in flood vulnerable areas such as flood plains and river beds.

In addition to population growth and the ongoing accumulation of value assets, both the frequency and magnitude of floods due to climate change are expected to increase in the future, therefore aggravating the existing flood risk in urban areas. This scenario implies that urban areas in particular suffer from a comparatively high flood risk due to their high population number and density, multiple economic activities and many infrastructure and property values, which in turn interferes with the natural infiltration processes.

Some of the causal factors of flood disasters in Nigeria include land inundation from heavy rainfall, climate change, and blockage of drainages with refuse, construction of buildings across drainages, inadequate drainage networks, and population increase in urban areas. These  factors do  not  act  independently  and  flood  disasters  usually occur  from a combination of  several of  them, Adeoye et al, (2009). Moreover, urbanization results  into  conversion  of  agricultural  land,  natural  vegetation  and  wetlands  to  built-up environments  and  construction  on  natural  drainages  as  well  increase  in  the  population  of those living in flood vulnerable areas such as flood plains and river beds (Adeoye et al, 2009).

Adequate geographic information on hazards and  areas  vulnerable  to  hazards  is  required  to  be  able  to  prepare  for  disasters. Hazard risk vulnerability mapping is considered one of the most important steps in disaster risk reduction because it identifies areas vulnerable to disaster so as to plan for disaster risk management. Remotely sensed imagery and GIS can be very effective in identifying the spatial component of flood for management. Remote sensing offers a synoptic view of the spatial distribution and dynamic of hydrological phenomena such as flood and erosion.

They are used to measure and monitor the extent of flooded areas, provide a quantifiable estimate of the land area and infrastructure affected by flooding and erosion, Izinyon et al (2011). Mitigation of flood disaster can be successful only when detailed knowledge is obtained  about  the  expected  frequency,  character  and magnitude of hazardous  events  in  an area  as  well  as  the  vulnerabilities  of  the  people,  buildings,  infrastructure  and  economic activities in  a  potentially  dangerous  area. Goel et al (2005) presented the technique for preparation of flood hazard maps which include development  of  digital  elevation  model  and  simulation  of  flood  flows  of  different  return periods. Bhadra, et al (2011)  proved  that GIS  technique  is effective  in  extracting  the  flood inundation extent in a time and cost effective manner for the remotely located hilly basin of Dikrong, where conducting conventional  surveys  is very difficult. Thilagavathi  (2011) used GIS  to  demarcate  the  flood  hazard  prone  areas  in  the Papanasam Taluk  into  five  zones  of varying degrees of  flooding.

Moreover, Ishaya, et al (2009) created digital terrain maps and flood vulnerability maps of Gwagwalada in Abuja showing the areas that were highly vulnerable, less vulnerable and areas vulnerable to flood disaster. The high risk potential of floods in particular may be related to their rapid occurrence and to the spatial dispersion of the areas which may be impacted by these floods. Both characteristics limit the ability to issue timely flood warnings. In flood prone areas, runoff rates often far exceed those of other water flow types due to the rapid response of the catchments to intense rainfall, modulated by soil moisture and soil hydraulic properties.

The small spatial and temporal scales of floods, relative to the sampling characteristics of conventional rain and discharge measurement networks, make also these events particularly difficult to observe and to predict Borga, et al., (2014). Small streams in urban areas can also rise quickly after heavy rain due to higher generated run off and less concentration time Ozcan and Musaoglu, (2010). Changes in the urban area and in storm intensity produce higher flows that exceed the capacity of small culverts under roads designed for non-urbanized areas. Although such structures can be adequate when designed, their capacity may turn out to be inadequate and thereby cause overflows onto the roads creating new water paths and flood the built up areas. In developing countries, inadequate maintenance of the drainage channels, and debris and solid waste disposed into such drainage systems may accentuate the situation. The rainfall runoff process, however, is highly complex, non-linear and temporally and spatially varying because of the variability of the terrain and climate attributes, Chang and Guo (2006)).

Flood vulnerability maps need therefore to be created as they provide a basis for the development of flood risk management plans. What is more, these plans needed to be effectively communicated to various target groups (including decision makers, emergency response units and the public) as a measure to reduce flood risk by integrating different interests, potential and conflicts over space and land use in a city.

Reduction of the risk of flooding will depend largely on the amount of information on the flood that is available and the knowledge of the areas that are likely to be affected during a flood event. Therefore, it is necessary to use modern day technique in developing measures that will help relevant authorities and relief agencies in the identification of flood prone areas and in planning against flooding events in the future. Determining the flood prone area is important for effective flood mitigations. For this study, flood simulation model was introduced which involved the use of ArcGIS which simulates and models the depth and extent of the flood prone areas within the state. Remote sensing images will be obtained, using the SRTM data of the state, a contour map and DEM were produced which will be used to demarcate flood areas in the study area. Some of the causative factors of flooding in the study area will be taken into consideration, examples include: Elevation and Land use.

1.2 STATEMENT OF THE PROBLEM.

Seasonally, Anambra State especially Local Government Areas within the river basins are faced with flooding to the extent that damages are caused to human lives and other properties, whenever it rained heavily. Due to the topography of the state, river basins around the state and some blocked drainage systems overflow their banks within the urban and rural regions of the state thereby causing devastating floods in Anambra State which results in destruction of properties, lives and other facilities which include damaging of the Awka – Onitsha road and other roads within the state; destruction of farmlands within the river basins and forceful migration of people from flood risk zones. In 2012, a large portion of the state settlements, agricultural lands and other landed properties were flooded after torrential rains (or intense rainfall) which has been the highest recorded in the state. This brought a lot of difficulties and untold hardship on the affected victims in the state who were displaced from their houses, caused damages to agricultural farms and so on; hence to effectively handle the dynamics of flood disasters in the state, there is the need to find geospatial method of identifying and mapping potential flood risk zones.

Thus, the use of flood simulation model which involves the use of ArcGIS software for spatial analyses and identifying flood prone zones within the state will serve as a valuable tool in proper management of this devastating environmental hazard which affects the state annually.

1.3 SCOPE OF RESEARCH

This research involves flood vulnerability assessment of Anambra State using flood simulation model. The flood model adopted for this research is developed through ArcGIS software which specifically models the extent and depth of the prone areas with emphasis on land use and height.

1.4 AIM AND OBJECTIVES

The aim of this research is to carry out a flood vulnerability assessment of Anambra State using flood simulation model.

This can be achieved through the following objectives,

1. To identify a systematic approach that will provide effective decision support framework for evaluating flood simulation;
2. To identify the different steps that determines flood vulnerable areas;
3. To identify factors in a GIS environment in order to carry out spatial analysis and mapping of these factors;
4. To produce a flood vulnerability map of the study area.