Chapter 3
Flood Risk Assessment for a Medium Size
City Using Geospatial Techniques
with Integrated Flood Models
Surendar Natarajan and Nisha Radhakrishnan
Abstract Flood is defined as the high stage of a river that flows across the river
banks. Floods are classified based upon the nature of the occurrence, usually as
riverine floods, urban floods, lake fluctuations, and rise of sea level. Factors responsible for floods are topography, rainfall intensity, climate change, and improper
design of drainage facilities. In this study, we discuss urban flooding, because urban
flooding usually differs from other types of flooding where the increase in flood
peaks of 1.8 to 8 fold results in flood volume up to 6 fold. An urban peak flood
occurs quickly as compared to other types of floods. In urban region the factors
responsible for high peak discharge are land use/land cover (LULC) changes,
climate change, and increase in rainfall intensity within a given duration. The recent
floods in major cities in India have raised the awareness for flood modeling studies.
In India, most flood modeling studies are done for major urban river basins passing
through cities, but for this study the Koraiyar River basin that passes through the
medium-sized city of Tiruchirappalli in South India was chosen. The parameter
adopted for analyzing flood volume in this basin is LULC and its impact on urban
surface runoff. LULC changes and their impact on surface runoff are studied by
integrating remote sensing and geographic information systems (GIS) with hydrologic HEC-HMS (Hydrologic Engineering Centre-Hydrologic Modeling System)
and hydraulic HEC-RAS (Hydrologic Engineering Centre-River Analysis System).
Runoff is generated by using LULC, slope, hydrologic soil group, curve number
(CN) maps, and rainfall intensity. The overall performance of the hydrologic model
during calibration was satisfactory, based on the Nash–Sutcliffe Efficiency criteria of
with values of 0.5–0.6. The generated peak discharge is used for developing
floodplain and hazard maps from 1986 to 2036. The floodplain and hazard maps
estimate flood depth and risk in the basin area for changing LULC conditions of
different return periods. Flood plain and hazard maps of 2, 5, 10, 50, and 100 years
return periods were generated to identify flood extent and hazard level in the basin.
S. Natarajan (*) · N. Radhakrishnan
Department of Civil Engineering, National Institute of Technology Tiruchirappalli,
Tiruchirappalli, India
e-mail: nisha@nitt.edu
© The Author(s), under exclusive license to Springer Nature Switzerland AG 2021
M. N. Islam, A. van Amstel (eds.), India: Climate Change Impacts, Mitigation
and Adaptation in Developing Countries, Springer Climate,
https://doi.org/10.1007/978-3-030-67865-4_3
39
Flood Risk Assessment for a Medium Size
City Using Geospatial Techniques
with Integrated Flood Models
Surendar Natarajan and Nisha Radhakrishnan
Abstract Flood is defined as the high stage of a river that flows across the river
banks. Floods are classified based upon the nature of the occurrence, usually as
riverine floods, urban floods, lake fluctuations, and rise of sea level. Factors responsible for floods are topography, rainfall intensity, climate change, and improper
design of drainage facilities. In this study, we discuss urban flooding, because urban
flooding usually differs from other types of flooding where the increase in flood
peaks of 1.8 to 8 fold results in flood volume up to 6 fold. An urban peak flood
occurs quickly as compared to other types of floods. In urban region the factors
responsible for high peak discharge are land use/land cover (LULC) changes,
climate change, and increase in rainfall intensity within a given duration. The recent
floods in major cities in India have raised the awareness for flood modeling studies.
In India, most flood modeling studies are done for major urban river basins passing
through cities, but for this study the Koraiyar River basin that passes through the
medium-sized city of Tiruchirappalli in South India was chosen. The parameter
adopted for analyzing flood volume in this basin is LULC and its impact on urban
surface runoff. LULC changes and their impact on surface runoff are studied by
integrating remote sensing and geographic information systems (GIS) with hydrologic HEC-HMS (Hydrologic Engineering Centre-Hydrologic Modeling System)
and hydraulic HEC-RAS (Hydrologic Engineering Centre-River Analysis System).
Runoff is generated by using LULC, slope, hydrologic soil group, curve number
(CN) maps, and rainfall intensity. The overall performance of the hydrologic model
during calibration was satisfactory, based on the Nash–Sutcliffe Efficiency criteria of
with values of 0.5–0.6. The generated peak discharge is used for developing
floodplain and hazard maps from 1986 to 2036. The floodplain and hazard maps
estimate flood depth and risk in the basin area for changing LULC conditions of
different return periods. Flood plain and hazard maps of 2, 5, 10, 50, and 100 years
return periods were generated to identify flood extent and hazard level in the basin.
S. Natarajan (*) · N. Radhakrishnan
Department of Civil Engineering, National Institute of Technology Tiruchirappalli,
Tiruchirappalli, India
e-mail: nisha@nitt.edu
© The Author(s), under exclusive license to Springer Nature Switzerland AG 2021
M. N. Islam, A. van Amstel (eds.), India: Climate Change Impacts, Mitigation
and Adaptation in Developing Countries, Springer Climate,
https://doi.org/10.1007/978-3-030-67865-4_3
39