Comparison of Different Grid Cell Ordering Approaches in a Simplified Inundation Model

Abstract

This study proposes a simplified model for non-riverine flood routing using a digital elevation model. The model has the advantage of running with only a few types of input, such as topographic data and cumulative rainfall. Given its ease of use, the model is stable and reliable for developing a real-time inundation forecasting system. This model uses two approaches to determine the collection of cells from which flooding is assumed to originate: (1) A traditional "lowest-elevation approach" that assumes flooding originates from the lowest elevations and that is only based on topographic data; and (2) a novel "D-infinity contributing area approach" that assumes flooding originates at the cells toward which the flow moves and that considers in situ topography and upslope information. The flood water is transferred based on the flat-water assumption that the water levels of adjacent cells are equalized.

A New Rapid Simplified Model for Urban Rainstorm Inundation with Low Data Requirements

“…In TRSFM, Equation (2) can be solved by establishing a volume-level function [17] or flood routing algorithm [23,24] for water inside each impact zone according to the DEM data. For the NRSFM proposed in this study, the interior inundation space of each cell is simplified to a regular spatial geometry according to its topographic features, and the volume-level function can then be easily derived in a geometric way, which reduces the computational complexity.…”

“…Because NRSIM is not able to determine the detailed inundation extent, all of the storm gates located in the study area served as monitoring points for the comparisons. Generally, the inundation extent with a maximum depth less than 30 cm has little impact on people's lives and properties [23]. Therefore, the monitoring points with maximum inundation depth over 30 cm were defined as a flooded point, whereas other points were defined as dry points.…”

“…Generally, the inundation extent with a maximum depth less than 30 cm has little impact on people's lives and properties [23]. Therefore, the monitoring points with maximum inundation depth over 30 cm were defined as a flooded point, whereas other points were defined as dry points.…”

“…This is because the numbers of flooded points in both LISFLOOD and the testing models would be decreased if the thresholds of flooded depth became higher and thus lead to a further reduction in the number of overlapped points. Yang et al [23] described that critical services in urban settings are typically vulnerable to a water depth of 30 cm or greater. Moreover, based on the experimental results of an evacuation test provided by Ishigaki et al [35], the walking speed of a normal person would decrease by approximately 50% when walking in water with over 30 cm depth.…”

“…With the total surface runoff volume of each zone serving as input to the model, the flood inundation is calculated by spreading the total volume over the regular storage cells (regular DEM cells) distributed in each zone [20][21][22]. The flood sources of each zone are determined by identifying the cells with lowest elevation or highest flow accumulation values [23]. However, RSFMs are typically designed for the general basin rather than urban floodplains, and the influences of drainage infrastructure on the urban rainfall-runoff processes are not considered in the model structure, which poses significant challenges to the application of RSFMs for urban rainstorm inundation.…”