1.   Purpose and objectives

     DAFLOW is a computer code that can be used to simulate flow through a network of one-dimensional upland open channels. The program outputs a file of hydraulic information that can be used to drive a transport model such as BLTM, HOMS component K55.2.04

2.   Description

     Predictions of the fate and movement of dissolved constituents in rivers are needed to understand many water-quality problems. Making such predictions depends on being able to predict the time dependent rate of flow in the river system. DAFLOW has been designed to simulate flow in upland stream systems where flow reversals do not occur and backwater conditions are not severe. If these two conditions are satisfied, the diffusion analogy form of the flow equations can be applied with acceptable accuracy even with minimal field data. DAFLOW is designed to be used in conjunction with a transport modelling system but it can be used alone for flood routing and other applications.

     The Lagrangian reference frame is used in solving the diffusive form of the flow equations because of the accuracy, stability, and simplicity of this approach.

     DAFLOW can simulate the flow in a network of interconnected one-dimensional channels with unsteady, unidirectional flow. The restrictions of the model include unstratified flow, fixed-channel 
geometry, and no backwater. The discharge at all external boundary points (upstream ends of external branches and tributary inflows) must be specified as a function of time. When more than one branch originates at a single junction, the percentage of flow to enter each branch must also be specified.

     DAFLOW uses a simplification of the dynamic wave equations and therefore should be used with caution. It is most accurate in steep channels where there is a unique relation between stage and discharge, that is where the frictional resistance term in the momentum equation is large. These are the conditions for which numerical solutions to the full dynamic wave equations tend to be most nonlinear and unstable.

3.   Input

     DAFLOW requires 4 types of input:

     - General information including time step size, number of time steps, 
       system of units to be used, output frequency, number of branches, 
       and accuracy tolerance.

     - Branch information including number of grids to be used, fraction of 
       flow leaving the junction to enter the branch, upstream and  
       downstream junction numbers of the branch.

     - Subreach information including river mile to the grid, initial flow 
       in subreach below grid, output flag, hydraulic geometry coefficients 
       and wave dispersion coefficient for the subreach.

     - Time series of discharge at each external boundary.

4.   Output

     Tables or graphs of discharge, cross-sectional area, top width or tributary inflow at any grid point as a function of time. The output from DAFLOW can be used as input to BLTM, HOMS component K55.2.04.

5.   Operational requirements and restrictions

     The program is written in FORTRAN 77 and can be used on any microcomputer with MS-DOS as well as larger machines. A mathematical co-processor is highly recommended.

     The system must be one-dimensional, so no stratification should be present. Flow must be unidirectional and no backwater should be present.

     A general understanding of hydraulics and open channel flow is needed.

6.   Form of presentation

     Documentation (USGS Water-Resources Investigation Report 89-4133) and programs with dialogue are written in English. Both the source and executable code are on a 3 1/2" floppy diskette or via the Internet.

7.   Operational experience

     DAFLOW has been applied in a number of river systems in the US.

8.   Originator and technical support

     U.S. Geological Survey, Office of Surface Water.

9.   Availability

     From the HOMS National Reference Centre for USA for 3 1/2" floppy or printed documentation; or electronically on the Internet at: http://water.usgs.gov/software/ or
http://www.geogr.uni-jena.de/software/

10.  Conditions on use

     Program is available free of charge; there is a charge for documentation.