Urban Flood Modelling – A comparative study for 1D and 2D models
Chitranjan
Kaushik
March 2006
Abstract
Flooding in urban areas is a natural
phenomenon and cannot be prevented. With experts predicting that extreme
rainfall events are likely to become more frequent, we must learn to live with
flooding. However urban flood involves peoples’ lives and property and
socio-economic consequences associated with flooding in urban areas are
significant. These impacts can be minimised through timely planning for the protection
and advance warnings. Knowledge about responses of the urban areas to flooding
event will be a very useful tool and for effectiveness of such system which will
help a smooth and fast passage of flood event. Acquiring the knowledge of this process
by modelling will sure help to establish a comprehensive and effective system in
place to manage the risk of flooding in urban areas.
Modelling of flooding in urban areas encompasses a complex set of several
processes like rainfall-runoff, flow on surface area,
drainage system and in underground sewage network. In absence of measured data
for urban flooding it is usually impossible to verify the model. Efforts are
being made in this direction and lot of work has been done mainly by modelling
street network by one-dimensional approach. However 2D modelling is also
picking up in this field. This study aims at understanding the need for better
modelling for flooding in urban areas and comparing the modelling of urban areas
by 1D and 2D approaches. It will help in answering the question that weather efforts
for the complexities of two-dimensional model will bring in some useful inputs for
decision making and planning for unfortunate events. Issue of interaction of underground
pipe network and overland street network which is an important aspect of integrated
urban flood modelling has also been taken up for comparison in this study along
with the comparison of various coupling options in 1D - 2D coupling model.
The models used for comparison in this case study were built using commercial packages developed by DHI Water and Environment (MOUSE and MIKE 21). It is found that apart from inability to give the details across the street, and details of hydraulic conditions within junctions, MOUSE model appears to have significant differences when it comes to the distribution of discharge at junctions. The interaction of MOUSE and MIKE21 by different coupling options (weir and orifice) gives approximately same results except small differences for marginal flooding when underground pipe network reaches to its full capacity and small amount of flooding occurs in the streets.
Keywords: Urban flooding, 1D2D modelling, flood management, coupling, depth-damage function, urban flood modelling