Water Resources Applications Software

Geochemical || Ground Water || Surface Water || Water Quality || General

Summary of NCALC

       ncalc - Manning's n value calculation program

       Computations involving flow in open channels commonly require an
       evaluation of the roughness characteristics of the channel.  The
       Manning equation has been used extensively as an indirect method for
       computing discharge or depths of flow in natural channels.  The U.S.
       Geological Survey engages in a continuing effort to improve the
       understanding of flow resistance, usually in terms of Manning's
       roughness coefficient, n, in channels in the United States.
       Procedures for computing values of Manning's roughness coefficient
       from known discharge, water-surface profiles, and channel cross-
       sectional properties are presented and have been programmed for
       automatic computation.  General theory, procedures for onsite
       investigations and surveys, a description of the use of the computer
       program, an example problem, and additional channel-roughness-
       verification research needs are provided (Jarrett and Petsch, 1985).

       The Manning equation is used as the basis for computing the channel
       reach properties and for calculating n values in this program.  In
       this application, calculations also are assumed to be valid for
       nonuniform reaches usually found in natural channels if the energy
       gradient is modified to reflect only the losses due to boundary
       friction (Barnes, 1967).  The program has the capability to compute
       an n value for single or multiple cross sections.

       Version 2.6 1995/03/30 - code clean-up and minor bug fixes

       1993 version - first version for use on PC's and the Data General

       1985 version - program converted to use on PC's

       1975 version - original version

       Onsite surveys provide data for discharge, water-surface profiles,
       and channel cross-sectional properties.  The program has the
       capability to compute roughness coefficients for 99 subreaches,
       using 99 cross sections.  Each cross section can be defined by 3 to
       999 ground points.  There is no provision in the program for
       subdividing cross sections.  An option is available to include an
       alternate procedure to compute roughness coefficients for an
       individual cross section, based on its localized water-surface
       slope, and is for use in relatively uniform channel reaches.  This
       option is included for comparison and evaluation with basic
       computational procedures.

       The computational results are output in four parts.  The first part
       is a listing of the input data and the computed cross-sectional
       properties of each cross section.  The second part, based on
       multisection analysis, is a listing of the roughness coefficient for
       each successive subreach as well as the roughness coefficient for
       the entire reach.  A roughness coefficient for the entire reach also
       is computed by weighing the subreach coefficients against their
       respective friction heads.  Generally, the accepted n value will be
       from the results for the total reach with all cross sections (the
       friction-head weighted n value).  Consistency of separate subreaches
       is an indication of the reliability of the weighted n value for the
       entire reach.  The third part, which is optional, is the alternative
       method that lists the roughness coefficients computed for each cross
       section.  The fourth part is an option that lists the same items as
       the second part, except that the user may preselect various
       combinations of cross sections.

       NCALC is written in Fortran 77 with the following extensions:  use
       of integer*2 declarations, use of include files, and reference to
       compiler-dependent system date and time routines.  Generally, the
       program is easily installed on most computer systems.  The code has
       been used on UNIX-based computers and DOS-based 386 or greater
       computers having a math coprocessor and 1 mb of memory.

       Jarrett, R.D., and Petsch, H.E., Jr., 1985, Computer program NCALC
          user's manual--verification of Manning's roughness coefficient in
          channels: U.S. Geological Survey Water-Resources Investigations
          Report 85-4317, 27 p.

       Barnes, H.H., Jr., 1967, Roughness characteristics of natural
          channels: U.S. Geological Survey Water-Supply Paper 1849, 213 p.

       Jarrett, R.D., 1985, Determination of roughness coefficients for
          streams in Colorado: U.S. Geological Survey Water-Resources
          Investigations Report 85-4004, 54 p.

       Basic Hydraulic Principles (SW1004TC), offered semiannually at the
       USGS National Training Center.

       Surface-Water Hydraulic Analysis (SW2009TC), offered annually at the
       USGS National Training Center.

       Operation and Distribution:
          U.S. Geological Survey
          Hydrologic Analysis Software Support Program
          437 National Center
          Reston, VA 20192

       Official versions of U.S. Geological Survey water-resources analysis
       software are available for electronic retrieval via the World Wide
       Web (WWW) at:


       and via anonymous File Transfer Protocol (FTP) from:

         (path: /pub/software).

       The WWW page and anonymous FTP directory from which the NCALC
       software can be retrieved are, respectively:


       If you would like to obtain the price of and (or) order paper copies
       of USGS reports, contact the USGS Branch of Information Services at:

                  U.S. Geological Survey
                  Branch of Information Services
                  Denver Federal Center, Box 25286
                  Denver CO 80225-0286

       To inquire about Open-File Reports or Water-Resources Investigations
                  Tel: 303-202-4210; Fax 303-202-4695

       To inquire about other USGS reports:
                  Tel: 303-202-4700; Fax 303-202-4693

The URL for this page is:
Send questions or comments to