Converting a NEXRAD Rainfall Map into a Flood Inundation Map by ...

A subset of NEXRAD time series data for Texas was provided by theGuadalupe Blanco River Authority in Texas as a series of ASCII files. The subsetwas comprised of 552 hourly text files for a storm event in late August of 2002and for the entire state of Texas. Thus, for the current format being used, therainfall data are stored in individual ASCII data files named after the hourly timestamp they contain.A snippet of the file content of one of the text files is shown below for afilename “0701200204.” The filename contains the time stamp embedded in itwith the date format MMDDYYYYHH. Thus, the filename “0701200204”contains a rainfall data for an event occurring on July 01, 2002 at hour 04. Figure3.4 shows a snippet for this data text file. The text file contains a header definingthe first columns as a pixel id (P_ID) and the second column as the precipitationvalue in inches (PRECIP_IN). At the end of the data records, the text file endswith an END statement.The precipitation values on the above Figure are associated with a PixelIDpointing to a NEXRAD cell in the mappable HRAP format. The layer containingthe HydroResponse feature class with the NEXRAD cell definition was providedby the Brazos River Authority in Texas. This layer is a statewide NEXRADHRAP grid in which the “Rfcthsn_ID” field in the grid layer corresponds to theP_ID field (first column Pixel ID) in the above data text file.Given that each of the hourly text files of precipitation contains data for allof the NEXRAD cells in Texas (50,150 cells), the NEXRAD cells covering thespecific study area must be extracted and a new NEXRAD layer for the watershed71