Flood Inundation Modeling
For flood modeling studies in a river basin, Saint-Venant equations of gradually
varied unsteady flow are generally used. The flood modeling approach is done in two
ways, by one-dimensional (1-D) and two-dimensional (2-D) methods. The 1-D flood
modeling approach is simple and the 2-D approach is appropriate. In urban flood
modeling the modeling approach requires high-resolution data to distinguish complicated urban topography. This type of modeling requires high-resolution grids of
the order of 1–5 m to acquire appropriate topographic features (Mark et al. 2004).
The high-resolution remote sensing data available are LIDAR (light detection and
ranging) and Ordnance Survey (OS) Master Map digital map data (Mason et al.
2007), recently used for providing accurate LULC classes, and these types of data
can be used in hydrologic and hydraulic models in urban areas.
A number of studies have considered the application of 2-D hydraulic models to
urban problems, including numerical solutions of the full 2-D shallow-water equations (Mignot et al. 2006), 2-D diffusion wave models (Hsu et al. 2000; Yu and Lane
2006a; Yu and Lane 2006b), and analytical approximations to the 2-D diffusion
wave equations using uniform flow formulae (Schmitt et al. 2004). The most
common approach to urban flood modeling is to employ a 2-D approach at high
resolution and calibrate the friction parameters to observed data. The dynamic wave
models are found to produce more efficient results in urban flood modeling simulations. These models can be coupled to 1-D flow models for accurate simulations.
Modeling Urban Drainage Systems
As per European Standards EN 752, ‘flooding’ is defined as a ‘condition’ where
wastewater or surface water escapes from or cannot enter a drain or sewer system
and either remains on the surface or enters buildings. Flooding in an urban drainage
system is classified as separate or combined sewers. For design of flood flow in
urban drainage systems, urban storm water drainage modeling is required. The
modeling approach may be hydrologic or hydraulic or a combined modeling
approach. The hydrologic model simulates surface runoff from rainfall and the
hydraulic model describes the flood extent and depth in the basin. For computations
of surface runoff, a standard rainfall runoff simulation model is required. The
one-dimensional urban storm drainage models such as MOUSE, info works,
Storm Water Management Model (SWMM), EPA SWMM, MIKESHE,
HEC-HMS, and HEC-RAS are used for flood modeling purposes (Hunter et al.
2007).
3 Flood Risk Assessment for a Medium Size City Using Geospatial Techniques with. . .
43
For flood modeling studies in a river basin, Saint-Venant equations of gradually
varied unsteady flow are generally used. The flood modeling approach is done in two
ways, by one-dimensional (1-D) and two-dimensional (2-D) methods. The 1-D flood
modeling approach is simple and the 2-D approach is appropriate. In urban flood
modeling the modeling approach requires high-resolution data to distinguish complicated urban topography. This type of modeling requires high-resolution grids of
the order of 1–5 m to acquire appropriate topographic features (Mark et al. 2004).
The high-resolution remote sensing data available are LIDAR (light detection and
ranging) and Ordnance Survey (OS) Master Map digital map data (Mason et al.
2007), recently used for providing accurate LULC classes, and these types of data
can be used in hydrologic and hydraulic models in urban areas.
A number of studies have considered the application of 2-D hydraulic models to
urban problems, including numerical solutions of the full 2-D shallow-water equations (Mignot et al. 2006), 2-D diffusion wave models (Hsu et al. 2000; Yu and Lane
2006a; Yu and Lane 2006b), and analytical approximations to the 2-D diffusion
wave equations using uniform flow formulae (Schmitt et al. 2004). The most
common approach to urban flood modeling is to employ a 2-D approach at high
resolution and calibrate the friction parameters to observed data. The dynamic wave
models are found to produce more efficient results in urban flood modeling simulations. These models can be coupled to 1-D flow models for accurate simulations.
Modeling Urban Drainage Systems
As per European Standards EN 752, ‘flooding’ is defined as a ‘condition’ where
wastewater or surface water escapes from or cannot enter a drain or sewer system
and either remains on the surface or enters buildings. Flooding in an urban drainage
system is classified as separate or combined sewers. For design of flood flow in
urban drainage systems, urban storm water drainage modeling is required. The
modeling approach may be hydrologic or hydraulic or a combined modeling
approach. The hydrologic model simulates surface runoff from rainfall and the
hydraulic model describes the flood extent and depth in the basin. For computations
of surface runoff, a standard rainfall runoff simulation model is required. The
one-dimensional urban storm drainage models such as MOUSE, info works,
Storm Water Management Model (SWMM), EPA SWMM, MIKESHE,
HEC-HMS, and HEC-RAS are used for flood modeling purposes (Hunter et al.
2007).
3 Flood Risk Assessment for a Medium Size City Using Geospatial Techniques with. . .
43