Applicability and Limitations of Channel Routing Models

The choice of a channel routing method depends upon the purposes of the study, the desired level of detail, and the physical characteristics of the watershed in question. In some applications, the transformation of precipitation to streamflow at a particular point of interest can be adequately represented without channel routing. Also, some of the aforementioned methods utilize parameters that cannot be estimated using measurable channel characteristics; they can only be determined through the use of observed data. Moreover, only one of the aforementioned methods (Modified Puls) can simulate backwater effects or the impacts of hydraulic structures. Finally, some of the aforementioned routing methods are only appropriate for use in steep streams with bed slopes > 10 ft/mi.

Initial estimates of channel routing parameters should be subjected to a model calibration process where computed outputs are compared against observed data and model parameters are modified in order to achieve an adequate fit. Also, best estimate parameters derived through the aforementioned model calibration process should be tested through a model validation process where computed results, without any further parameter modifications, are used to compute outputs which are compared against observed data for independent events that were not considered during model calibration. Storm events used during both model calibration and validation should be approximately equal to the magnitude of events that are being considered within the particular application.

The following table contains a list of various advantages and disadvantages regarding the aforementioned channel routing methods available for use within HEC-HMS. However, these are only guidelines and should be supplemented by knowledge of, and experience with, the methods and the watershed in question.

Method	Advantages	Disadvantages
Kinematic Wave	Predicted values are in accordance with open channel flow theory (for steep channels). Parameters can be estimated using measurable channel characteristics. Can use multiple cross-section shapes.	Method is less parsimonious than simpler routing methods; it requires many more parameters. Cannot simulate backwater effects or impacts of hydraulic structures. Only appropriate for use in steep streams (bed slopes > 10 ft/mi). HEC-HMS implementation cannot use cross-section shapes that include overbank areas.
Lag	Simple, parsimonious method.	Method may be too simple; no attenuation effects are simulated by this method. Parameters cannot be estimated using measurable channel characteristics. Only appropriate for use in streams that experience no attenuation. Cannot simulate backwater effects or impacts of hydraulic structures.
Lag and K	Well established and documented method through its use by NWS. Simple, parsimonious method. Can simulate variable translation and attenuation.	Similar to disadvantages of the Muskingum method. Numerical errors can arise through the use of flawed inflow vs translation functions.
Modified Puls	Can simulate backwater effects and impacts of hydraulic structures.	Method is less parsimonious than simpler methods; it requires many more parameters. Requires hydraulic simulations to derive accurate storage vs. outflow relationships; consequently, this method can be difficult to parameterize and calibrate.
Muskingum	"Mature" method that has been used successfully in thousands of studies throughout the U.S. Method is parsimonious; it requires only a few parameters.	Method may be too simple to accurately predict floodwave translation and attenuation. Only appropriate for use in moderately steep streams (bed slopes > 2 ft/mi). Cannot simulate variable translation and attenuation. Cannot simulate backwater effects or impacts of hydraulic structures.
Muskingum-Cunge	Similar to advantages of the Muskingum method. Predicted values are in accordance with open channel flow theory. Parameters can be estimated using measurable channel characteristics. Can use cross-section shapes that include overbank areas.	Similar to disadvantages of the Muskingum method. Method is less parsimonious than Muskingum; it requires many more parameters.
Normal Depth	Similar to advantages of the Modified Puls method. Does not require the use of hydraulic simulations to derive storage vs. outflow relationships. Parameters can be estimated using measurable channel characteristics.	Similar to disadvantages of the Modified Puls method. Since normal depth is assumed to derive storage vs. outflow relationships, backwater effects or impacts of hydraulic structures cannot be simulated.
Straddle Stagger	Similar to advantages of the Lag method. This method can simulate attenuation effects.	Similar to disadvantages of the Lag method. Not well documented nor widely used.