NSTPS Tool 1.0.0


NSTPS is a software package designed to automatically update the NSTPS parameter (HEC-1 RS card's first field) for flow routing in channels in an HEC-1 input file. The tool is easy-to-use with minimum input from the user. The input data file for the tool is an existing HEC-1 input file where normal-depth storage routing methodology is used. The program creates an updated HEC-1 input file that includes a refined set of NSTPS values updated from two successive model runs.

This program was developed by the Flood Control District staff to assist HEC-1 modelers in refining the values of NSTPS used for flow routing in channels. The channel routing analysis in HEC-1 uses the RS card to define the NSTPS parameter (Field 1).

View the NSTPS Installation Guide (PDF) and download NSTPS 1.0.0 (Beta) (ZIP).


NSTPS is normally evaluated from flow and reach characteristics of the project area. It is usually estimated by the following relation (HEC, 1998): NSTPS = (Channel Reach Length / Average Flow Velocity) /Time Interval

It can also be estimated by: NSTPS = (Difference in Time-to-peak between Channel Inflow and Outflow Hydrograph for Routed Flows) /Time Interval

Determination of Refined Values

The determination of the refined values of NSTPS can be made from several runs of the model, until the values converge. There are rare occasions, however, when NSTPS do not converge (i.e., values swing back and forth between iterations). In these cases, the modeler should look into the matter and use engineering judgment to select appropriate values of NSTPS adequate for his/her modeling purposes.

One possible solution is to manually use Manning's equation to estimate the channel flow velocity and then estimate NSTPS by Equation (1) above. The manually estimated NSTPS can then be entered into an HEC-1 input file for the channel routings whose NSTPS values do not converge. To detect if there are any channel routings whose NSTPS do not converge, users can run the tool twice (the HEC-1 input file for the second-time run is the refined HEC-1 input file for the first-time run) to see if there is any instability in NSTPS value.


  • This program is designed to have a very simple and a user-friendly interface with minimum user input to run.
  • This program only requires an HEC-1 input file to run the program.
  • This program generates two (2) intermediate flow routing summary files that show the computed new NSTPS values.
  • This program generates the updated HEC-1 input file that should contain the refined NSTPS values.


The program is based on two assumptions. The first assumption is that normal-depth channel routings are defined by RS cards with FLOW as a keyword in Field 2. It should be mentioned that there might be some exceptions to this assumption due to many combinations of routing parameters though this assumption is valid for most cases. Users should check to make sure that the intended channel routings are defined by RS card with FLOW as a keyword in Field 2.

The second assumption is that all ID's in KK cards are unique. Users should check to make sure that there are no duplicated KK cards. It is users' responsibility to check and accept the final results.

Useful Reference

Hydrologic Engineering Center (HEC), 1998, "HEC-1 Flood Hydrograph Package User's Manual," Version 4.1, Report No. CPD-1A, June 1998.


If you have questions, please email Dr. Carlos Carriaga.