WORLD METEOROLOGICAL ORGANIZATION 
HOMS COMPONENT 

Explanation of the criteria for classification and numbering of components  K35.3.14 (DEC 99) 

Explanation of the dates on the component's description  
FLOW MODEL FOR A ONE DIMENSIONAL SYSTEM OF OPEN CHANNELS BASED ON THE DIFFUSION ANALOGY (DAFLOW) 

1. Purpose and objectives DAFLOW is a computer code that can be used to simulate flow through a network of onedimensional 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 waterquality 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 onedimensional channels with unsteady, unidirectional flow. The restrictions of the model include unstratified flow, fixedchannel 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,  Branch information including number of grids to be used, fraction of  Subreach information including river mile to the grid, initial flow  Time series of discharge at each external boundary. 4. Output Tables or graphs of discharge, crosssectional 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 MSDOS as well as larger machines. A mathematical coprocessor is highly recommended. The system must be onedimensional, 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 WaterResources Investigation Report 894133) 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 10. Conditions on use Program is available free of charge; there is a charge for documentation.


(First entered:01 FEB 93  Last updated: 01 FEB 94) 