Frequently Asked Questions (FAQ)

What is the difference between MODRAT and MORA and if not significant difference, Does LADPW will take analysis from MORA?

The MODRAT and MORA software programs both do modified rational hydrology calculations. Both were developed from the same source code (F0601) developed by the Los Angeles County Flood Control District in the 1970s. Woodcrest Engineering obtained the source code and developed it for personal computers. This program has been the main hydrologic program since the early 1980s. However, over the last 7 years, Public Works has modified the rainfall input parameter methodology. The MODRAT module was developed to interface with GIS in the Watershed Modeling System to take advantage of spatial data for populating hydrology model input parameters. During development of the MODRAT module, several problems were found in the F0601 source code. Woodcrest was contacted to correct their MORA software. However, when approached, Woodcrest indicated that they no longer wished to sell or support the software. The changes were not made and the differences are significant enough that Public Works no longer accepts models created using the MORA software. Approved software for use in Los Angeles County are found in Chapter 15 of the 2006 Hydrology Manual. The manual is found on-line at:

  2006 Hydrology Manual