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

Drainage Design Manual for Maricopa County
Hydrology: Channel Routing
7.4.1 Parameter Selection
Application of Muskingum routing requires input values for parameters X and K. Parameter X
has a range of values from 0.0 to 0.5, where 0.0 represents routing through a linear reservoir and
0.5 indicates pure translation. Parameter K indicates the travel time of a floodwave through the
entire routed reach. There are several methods which can be used to estimate K such as average
flow velocity adjusted by a celerity factor, the time difference between peak inflow and peak
outflow, or by using stage-discharge relationships. For more details the reader is referred to the
HEC-1 manual and Section 9.5 of this manual. Once again, since the computational method
within HEC-1 may result in an unstable solution, parameters K, X and NSTPS (number of steps)
must be checked to insure that an adequate number of subreaches is used.
In those rare situations that observed inflow and outflow hydrographs are available, K, X and
NSTPS can be calibrated by trial and error to enable simulation of known outflow hydrographs.
Chapter 5 of the USBR’s Flood Hydrology Manual (Cudworth, 1989) is an excellent source of
Muskingum routing information.
7.5 MUSKINGUM-CUNGE ROUTING
The Muskingum-Cunge routing method is based on the principle of hydraulic diffusivity, which
simulates an attenuation of the flood peak through the routing reach. This method can be used
for both man-made and natural channels where overbank flow is expected, provided the conveyance
can be accurately described with an eight-point cross section. A complete description of
Muskingum-Cunge applications and guidelines for parameter selection can be found in the September
1990 and later versions of the HEC-1 Flood Hydrograph Package User’s Manual.
7.5.1 Parameter Selection
Input data for Muskingum-Cunge routing include energy slope (or bed slope), reach length, and
either the channel shape and a single Manning’s n for a man-made channel, or an eight-point
cross section with channel and overbank roughness coefficients for a natural channel.
7-4 August 15, 2013