It is efficient for the model flood routing to calibrate n-values for reasonable Froude numbers. When the limiting Froude number is exceeded in a particular grid element, the model will increase the roughness value to suppress numerical surging. Limiting Froude numbers can be assigned to the channels, streets and floodplain grid elements. This distributary flow improves the time of concentration on alluvial fans.
The small distributary channels expand as more flow enters the gully. Overland flow can be simulated in small rills and gullies instead of sheet flow. Grid element flow exchange can be partially or entirely obstructed in all of the eight flow directions. A portion or the entire element can be removed from potential inundation. Levee breaches can be initiated with fragility curves.įloodplain storage loss due to buildings or features can be modeled. There a several levee failure options including a comprehensive breach erosion model. Levees, road embankments and dams can be simulated by specifying crest elevations on a grid element boundary. Culvert flow can occur between grid elements that are not contiguous. Hydraulic structures are simulated by user specified discharge rating curves or tables assigned to either channel or floodplain elements. Hydraulic structures can represent bridges, culverts, weirs or other hydraulic control features. Streets can intersect and exchange flow with the floodplain. Streets are simulated as shallow rectangular channels with a curb. The GDS can convert HECRAS cross sections into a data file formatted for FLO-2D. For detailed simulations the channel can be larger than the grid element. Overbank flow or return flow to the channel is simulated for each timestep. Unconfined floodplain flow is simulated in eight directions (4 compass directions and 4 diagonal directions). One-dimensional channel flow is simulated with rectangular, trapezoidal or surveyed cross sections. FLO-2D can also perform as a rainfall runoff model and rain can occur on the flooded surfaces.Įxchange of Channel and Floodplain Discharge Any ASCII data format hydrograph can be used as input. The number of inflow nodes are unlimited. Inflow hydrographs can be assigned to either the channel or floodplain nodes. Computational timesteps are incremented or decremented according to numerical stability criteria. Numerical stability is linked to volume conservation and when the model conserves volume the model runs faster. FLO-2D tracks and reports on volume conservation.
The key to accurate flood routing is volume conservation. Volume Conservation, Routing Algorithm Stability and Timesteps
The number of square grid elements is unlimited.Īerial images can be imported to the GDS as background to assist graphical editing. A typical grid element size will range from 10 ft (3 m) to 500 ft (150 m). A processor program called the Grid Developer System (GDS) generates the grid system and assigns the elevations. The grid element elevations are assigned from an interpolation of the DTM points. Topography can be represented by a digital terrain model (DTM) points, contour mapping or survey data.
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The model uses the full dynamic wave momentum equation and a central finite difference routing scheme with eight potential flow directions to predict the progression of a floodwave over a system of square grid elements.įLO-2D requires two sets of data: topography and hydrology.
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