GIS Framework for Spatiotemporal Mapping of Urban Flooding and Analyze Watershed Hydrological Response to Land Cover Change
Creators: name: Abedin, Sayed Joinal Hossain
Publisher: name: University of Nevada, Las Vegas
Year: 2014

description: Urban flooding is a manmade disaster, and a recurrent problem in cities around the globe. Increased surface imperviousness due to urbanization along with inadequate drainage infrastructure system are the chief culprits for urban flooding. Flooding in an urban area brings about severe economic, structural, and environmental damages, and can be associated with casualties too. In order to evade flooding, an efficient flood model is imperative to study current flooding, and analyze flooding behavior to urban surface characteristics. 
This research aims to develop a framework using Geographic Information System (GIS) to perform modeling and mapping of flood spatiotemporal variation in urban micro-watersheds. Moreover, watershed hydrologic response to the flood remediation measures through land cover changes is analyzed. The GIS-framework includes a workflow of several methods and processes including delineating urban watershed, generation of runoff hydrograph, and time series mapping of inundation depths and flood extent. The developed GIS-framework is used to study urban watershed hydrologic response to the change in land surface characteristics. This framework is tested in areas previously known to have experienced flooding at the University of Nevada Las Vegas (UNLV) main campus including Blacklot parking lot and East Mall. Calibration is performed with Digital Elevation Model (DEM) resolution, rainfall temporal resolution, and clogging factors whereas validation is performed using news reports and photographic evidence. 
The testing at Blacklot site resulted in calibration at 5m DEM resolution and clogging factor of 0.83. The flood model produces a peak flood depth error of 24% between the estimated (26 inches) and actual flood depth (34 inches) for the Blacklot. The observed inundation points are found to be within the estimated flood extents. The flood beginning time (1:53 PM) is found consistent with the actual timing of 2:00 PM. East Mall site shows consistent results. The GIS framework provides spatiotemporal maps of flood inundation for visualization of flood dynamics. Through the calibration against DEM and rainfall resolution, it is observed that DEM resolution follows an irregular trend against errors, while rainfall resolution produces higher errors with increasing resolution. 
The response of an urban watershed to land cover change is also analyzed. The tests are conducted in the Blacklot area, and the land cover types include porous asphalt, gravel and grass swale strips, grass pavers, and concrete grid pavers. The analysis shows that the watershed flooding reduces with a decrease in curve numbers of the surface materials. Flooding is reduced by 26% for porous asphalt, and only 2.90% for grass and gravel swale strips. The flooding is most reduced for grass pavers (by 46%), while flooding is reduced to none for concrete grid pavers. Concrete grid pavers are found to be the optimum land cover in the Blacklot area to avoid flooding. 
This research provides insight into flood modeling, and mapping for a storm drain inlet based watershed. It also provides intuition on calibration against DEM and rainfall temporal resolution, and on soft validation techniques. Finally, it provides understanding on watershed hydrologic response to flood remediation land surfaces.