Drainage Design Manual, Hydrology - Flood Control District of ...

Drainage Design Manual for Maricopa County
Hydrology: Acknowledgements, Comments & Revisions
Document Page Numbering - Page numbering has changed to section numbering rather than
consecutive (i.e., 1-1, 2-1, 3-1, etc.).
Chapter 2 - The rainfall chapter has been substantially condensed. The computer program PRE-
FRE has been added to ease development of rainfall statistics for sites outside the Phoenix metropolitan
area. The PREFRE user's manual is included with the manual as Appendix J. An
additional isopluvial map with 2-hour, 100-year depths has been added.
Chapter 3 - New roughness factor descriptions were developed. “C" coefficients will now be
adjusted to reflect storm frequency, and a new table is included. A computer program RATIO-
NAL.EXE is included for development of discharges and volumes using the Rational Method.
Chapter 4 - The methodology used to develop Green and Ampt loss parameters has been substantially
modified and simplified. The section on the Initial plus Uniform Loss Rate Method has
been reduced, and limitations for the use of that method are provided. An equation is provided for
calculation of the XKSAT vegetation adjustment coefficient.
Chapter 5 - New land classification descriptions are provided to facilitate selection of parameters
in the K b equation. An error was corrected in the Lag equation (the Corps of Engineers uses
C = 24K n instead of C = 20K n ). The MCUHPl and MCUHP2 computer programs were revised to
reflect our change of address, some data inputs were added to facilitate revisions and an error
was corrected in the 2-hour storm distribution (the program was underestimating T c because of
an incorrect summation of the first three rainfall excess values).
Chapter 6 - The routing chapter now includes guidance on using the Muskingum-Cunge routing
option recently available in HEC-l. A sample problem is included in the Examples section.
Chapter 7, the Appendices, and the Examples - All have been updated to incorporate the
changes outlined above.
Overview of Changes Made in the Third Edition
In addition to the correction of a few typographical errors, changes of January 1, 1995 revision of
the Drainage Design Manual, Volume I, Hydrology included the following:
Chapter 2 -The SCS Type II rainfall distribution is recommended for use for the 24-hour general
design storm. Areal reductions of point rainfall are to be made with Table 2.1, which is based on
the NWS-HYDRO 40 data. Guidelines have also been added as to when to select the general
storm for use in design hydrology in Maricopa County.
August 15, 2013
iii