FLDWAV is a generalized hydraulic routing model that computes the outflow hydrograph from a dam due to spillway, overtopping and/or dam-breach outflows.  The resulting flood wave is simultaneously routed through reservoirs, rivers, canals, and/or estuaries.  FLDWAV is a combination of the NWS dam break (DAMBRK) and dynamic wave (DWOPER) flood forecasting models.  The governing equations are the one-dimensional unsteady flow equations coupled with internal boundary equations representing rapidly varied flow through structures such as dams and bridges/embankments which can develop a time-dependent breach, weirs, waterfalls, and other man-made/natural flow controls.  Also, appropriate external boundary equations at the upstream and downstream ends of the routing reach are utilized.  The system of equations is solved by an iterative, nonlinear, weighted four-point implicit finite-difference method.

Although FLDWAV can model complex river systems very accurately, it can also be used as an emergency management tool to produce fairly accurate results (discharge, elevation, and velocity hydrographs and profiles) when limited data is available.  The FLDWAV model takes advantage of the fact that the governing equations utilize average parameters (e.g., cross sectional area, channel width, discharge, and depth of flow) and simplifies the input data needed for the model.   Cross sections are represented as a table of average top widths vs. elevations at major transitions along a river reach.  Roughness coefficients are averaged along the channel reach as a function of either elevation or discharge.  To satisfy computational requirements, FLDWAV interpolates between reaches to obtain additional cross section and roughness data.  Hydraulic structures are also described in the model input using average parameters (e.g., the effective area of the bridge opening is used instead of describing bridge geometry).

FLDWAV is generalized for wide applicability to rivers of varying physical features, such as irregular geometry, varying roughness, lateral inflows, flow diversions, off-channel storage, local head losses such as bridge contractions and expansions, lock and dam operations, and wind effects.  It is suited for efficient application to dendritic river/floodplain systems or to channel networks consisting of bifurcations with weir-type flow into the bifurcated channel. 

As a dam failure application, FLDWAV is generalized for real-time flood forecasting of dam-break floods and/or natural floods, dam-breach flood analysis for sunny-day piping or overtopping associated with the Probable Maximum Flood, floodplain inundation mapping for contingency dam-break flood planning, and design of waterway improvements. 

Additional features that add to FLDWAV’s robustness include the following.

• Flow Regime – The flow may be either subcritical, supercritical, or a combination of both varying in space and time from one to the other (mixed flow).
• Flow Type – The fluid properties may obey either the principles of Newtonian flow (water) or non-Newtonian flow (mud/debris flows or the contents of a mine-tailings dam).
• Routing Techniques – Multiple user-specified routing techniques (dynamic-implicit/explicit, diffusion, level-pool) may be used throughout the river system,
• Upstream Boundary – The hydrograph to be routed may be user-specified as an inflow, or it may be developed by the model via user-specified breach parameters (size, shape, and time of development).
• Downstream Boundary – Empirical or implicit rating curves may be used to account for the natural condition of the channel (e.g., backwater effects). Also, hydrographs (discharge or stage) made be used to represent a specific condition at the downstream end of the river system (e.g., tidal effects).
• Complex River Systems – The possible presence of downstream dams which control the flow and may be breached by the flood, bridge/embankment flow constrictions, tributary inflows, river sinuosity, levees located along the tributaries and/or downstream river, and tidal effects are each properly considered during the downstream propagation of the flood.
• Units – Model input/output may be in either English or metric (SI) units.

The original FORTRAN code for NWS DWOPER (1974-1988) and NWS DAMBRK (1977-1988) were developed by Dr. Danny Fread and Janice Sylvestre.  The two models were combined and the first version of NWS FLDWAV was released in 1988.  The last NWS release version was in 2000.  Although NWS ceased support for the model in 2005, Janice Sylvestre has continued the development, maintenance, and support of the FLDWAV model.  The name of the model has been changed to FLDWAVE since the continued work is not affiliated with NWS.