**1. Introduction**

In search of better livelihoods and facilities more people are moving towards urban centers. At present approximately half the world population resides in cities. Cities provide greater social and economic benefits to their inhabitants as compared to rural areas and this has resulted in massive demographic shift especially in the developing world which in turn has threatened the environmental stability.

According to the UN Reports, 2008, roughly 75 percent of the population lives in urban areas in the industrialized nations and will continue to grow at a rate of less than half a percent in the coming twenty years. On the other hand cities in the developing world will see about 95 percent growth in urbanization in the coming twenty years mainly due to migration, population increase and conversion of rural settlements into urban areas. A combined increase of this urbanization in the developed and the developing world will be that about 60 percent of the world's population will be living in cities by 2030.

Though cities occupy less than three percent of the world area, the high density of population and industrialization has resulted in severe environmental degradation. The worst environmental issues are faced close to the homes in the developing nations. They include inadequate domestic water supply, excessive waste accumulation and lack of proper hygiene and sanitation. The main reason for these environmental issues is that the infrastructural development has not kept pace with the increasing population. Other environmental issues associated with urbanization include severe air pollution, ground and surface water pollution, habitat loss, soil erosion, loss of bio-diversity and ecological disruption.

Arid regions of the world, especially those of middle-east Asia are not far behind as far as this demographic shift from rural to urban areas are concerned. The petroleum based economy of these regions have led to the springing up of major urban centers in countries like Saudi Arabia, United Arab Emirates, Oman, Qatar, Kuwait and Bahrain,(Bonine, 2009).

With proper planning and management cities can actually reduce pressure on the natural resources and increase energy efficiency. Innovative building designs, better waste management and improvement in transportation infrastructure can help in building sustainable cities. However often hydrological and climatological parameters such as the

Assessing Hydrological Elements as Key Issue for Urban Development in Arid Regions 131

obtain the different ratios such as Drainage Density, Bifurcation Ratio, Stream Frequency,

Ground surveys include essentially preparation of a geologic map of the area, showing the main structural elements of the earth that may affect the units of urbanization such as buildings, roads etc., and gathering information on the subsurface stratum to depth in the order of few meters to some 30 meters. The subsurface picture can be elucidated using geoelectrical techniques, (Reynold, 2011). A number of instruments are available to achieve this goal. Nonetheless the use of SYSCAL-Pro 72 unit proved to be very useful. Resistivity surveys using multi-electrode resistivity technique gave good results. Dipole-Dipole configuration with the unit electrode spacing ranging from 2.5 meters to 5 meters depending upon the ground clearance can be adopted. Dipole-Dipole configuration is selected for the survey as it gives the best horizontal resolution as compared to all the other methods present. RES2DINV Software, (Loke, 2002) can be used for inverting the apparent resistivity values to a resistivity model section. The least square fitting technique (Loke and Barker,

Infiltration is another important hydrological element for urban development studies. Field measurements of both infiltration capacities and infiltration rates of the different soil types in the area are necessary to accomplish the hydrological picture of the water budget in the

All these accomplishments and measurements, as mentioned earlier, should be GIS based so that the different layers can be compared and inter-layer relationships can be worked out. Based upon these relationships the area under study can be zoned according to hazard

**3.1 Delineating the wet/dry zones in the Qassim province of Saudi Arabia (Faisal K.** 

Central Saudi Arabia experiences an arid type of climate with mean annual rainfall rarely exceeding 150 mm. The low rainfall has resulted in scanty vegetation in the region except for the wadis where farms and date palm plantations can be seen due to the availability of groundwater. However the chance of flash floods increases to a great extent due to lack of

The city of Buraidah which is the administrative capital of the Qassim province has undergone rapid urbanization in the recent years and due to lack of proper urban planning a lot of low lying areas and stream channels have been allotted to housing colonies. During the heavy rainfall in the month of November 2008 and March 2009, many such housing

The stagnant water in the lakes became a threat for the environment by providing the breeding ground for mosquitoes and other water borne disease. Thus it was decided to drill a few bore wells in these manmade lakes with the dual purpose of recharging the aquifer and getting rid of the stagnant surface water thereby preventing environmental

1996) is used for getting the best fit for the resistivity model by iterations.

prone areas as far as hydrological elements are connected to urbanization.

Form Factor, Elongation Ratio, and Circulatory Ratio.

area, (Hopmans, 2011).

**3. Case studies** 

**Zaidi et al, 2010) 3.1.1 Introduction** 

degradation.

vegetation cover in the events of heavy rainfall.

colonies in the low lying areas were inundated by flood water.

amount of rainfall, the volume of runoff generated, infiltration rates and drainage basin characteristics are neglected during urbanization process. These features are more commonly neglected in the arid regions mainly due to the lack of sufficient data which restricts the modeling capacity for extreme events. Topography is one important parameter which is not taken into consideration during town planning in these regions and instances of flash floods and water logging are becoming common due to such negligence.

Use of satellite imageries, digital elevation models, field observation and geophysical and hydrological investigations can help in reducing the complications related to urbanization in arid regions.

This book chapter focuses on the elements of hydrology which should be taken care of during urban planning and development with special emphasis on arid regions. A few case studies assessing the hydrological elements for urban planning have been cited as examples for arid region models.
