Bengaluru
Large-scale land conversion, loss of lakes, and the occupation of floodplains have
resulted in many problems such as urban heat islands, depletion of groundwater, and
more importantly, flash floods. The impervious surfaces of urbanization led to
accelerated runoff and reduced water recharge in Bengaluru city. The LULC changes
and conversion of land surface to impervious surface and the loss of water bodies led
to urban flood. Recently, 280 locations in the city were identified as areas vulnerable
to flash floods. Apart from LULC changes, the other factors responsible for frequent
floods are dumping of solid waste and the allotment of floodplains for housing
purposes. Increased urbanization with intensified vertical growth of the city has led
to liquid waste disposal along the storm water drains, making the runoff models
unpredictable. Because of LULC changes, even a short rainfall of 30 mm/h causes
greater flood depth. For the proper assessment of vulnerable areas affected by floods,
a multicriteria evaluation of spatial layers in GIS was adopted for flood assessment in
the city. For proper flood risk assessment, self-sufficient eco-friendly buildings with
proper conservation of rainwater by harvesting structures are recommended (Rama
Prasad and Narayan 2016).
Hyderabad
In Hyderabad city, LULC changes and their impacts on surface runoff were studied
by a 2-D hydraulic model integrated with GIS. In this study a simple approach was
adopted to analyze the flood events that occurred in the city by analyzing extreme
rainfall events with changing LULC conditions. Extreme rainfall can occur in a
single day in the city. The synthetic hyetographs were developed from IDF curves
and HEC-RAS freely available hydraulic model is used with GIS to generate flood
depth over underlying terrain and hazard maps for different return periods. From the
analysis it was identified that 17% of total area is liable to floods, of which 9% of the
area indicates high risk, 52% of the area shows medium risk, and the remaining 35%
has low risk of flooding (Rangari et al. 2018).
Chennai
In Chennai city, flood studies were done in the Tirusoolam area, a part of Chennai
city. This method examines the different available methods to trace the flood damage
and illustrates the methodology to explore the economic loss through social investigation in the Tirusoolam area. In this study the CN was generated for Indian
conditions, and flood peak discharge was generated through HEC-HMS software.
From the generated peak discharge, flood hazard maps were generated for the study
area. The flood risk maps generated were used to identify the areas subject to greater
50
S. Natarajan and N. Radhakrishnan
Large-scale land conversion, loss of lakes, and the occupation of floodplains have
resulted in many problems such as urban heat islands, depletion of groundwater, and
more importantly, flash floods. The impervious surfaces of urbanization led to
accelerated runoff and reduced water recharge in Bengaluru city. The LULC changes
and conversion of land surface to impervious surface and the loss of water bodies led
to urban flood. Recently, 280 locations in the city were identified as areas vulnerable
to flash floods. Apart from LULC changes, the other factors responsible for frequent
floods are dumping of solid waste and the allotment of floodplains for housing
purposes. Increased urbanization with intensified vertical growth of the city has led
to liquid waste disposal along the storm water drains, making the runoff models
unpredictable. Because of LULC changes, even a short rainfall of 30 mm/h causes
greater flood depth. For the proper assessment of vulnerable areas affected by floods,
a multicriteria evaluation of spatial layers in GIS was adopted for flood assessment in
the city. For proper flood risk assessment, self-sufficient eco-friendly buildings with
proper conservation of rainwater by harvesting structures are recommended (Rama
Prasad and Narayan 2016).
Hyderabad
In Hyderabad city, LULC changes and their impacts on surface runoff were studied
by a 2-D hydraulic model integrated with GIS. In this study a simple approach was
adopted to analyze the flood events that occurred in the city by analyzing extreme
rainfall events with changing LULC conditions. Extreme rainfall can occur in a
single day in the city. The synthetic hyetographs were developed from IDF curves
and HEC-RAS freely available hydraulic model is used with GIS to generate flood
depth over underlying terrain and hazard maps for different return periods. From the
analysis it was identified that 17% of total area is liable to floods, of which 9% of the
area indicates high risk, 52% of the area shows medium risk, and the remaining 35%
has low risk of flooding (Rangari et al. 2018).
Chennai
In Chennai city, flood studies were done in the Tirusoolam area, a part of Chennai
city. This method examines the different available methods to trace the flood damage
and illustrates the methodology to explore the economic loss through social investigation in the Tirusoolam area. In this study the CN was generated for Indian
conditions, and flood peak discharge was generated through HEC-HMS software.
From the generated peak discharge, flood hazard maps were generated for the study
area. The flood risk maps generated were used to identify the areas subject to greater
50
S. Natarajan and N. Radhakrishnan