FLO-2D 洪水土石流災害模擬軟體
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FLO-2D 模式簡介
FLO-2D 由美國FLO-2D 公司發展之二維洪水災害模擬模式，為美國聯邦急難管理署（FEMA）認可之二維模式，可用於都市淹水、洪水平原管理、工程風險設計、不規則形狀河道水理演算、橋樑涵洞水理演算與滯洪池水理演算，可以處理漫地流、都市水文，泥流及土石流。
FLO-2D 淹水模式採用一維變量模式與二維漫地流模式模擬一維渠道及二維漫地流之流況，並計算發生溢堤時，堤外渠道與堤內地表間水流之互動機制，能有效模擬本計畫區之淹水情形。渠道演算方式為利用連續方程式和動力波模式以有限差分方法進行模擬，能模擬流體流動的速度及深度，並推估合理的淹沒面積，作為災害影響範圍預測之工具。
Key Features
Solution Algorithm
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.
Creating a Grid System
FLO-2D requires two sets of data: topography and hydrology. Topography can be represented by a digital terrain model (DTM) points, contour mapping or survey data. The grid element elevations are assigned from an interpolation of the DTM points. A processor program called the Grid Developer System (GDS) generates the grid system and assigns the elevations. A typical grid element size will range from 10 ft (3 m) to 500 ft (150 m). The number of square grid elements is unlimited.
Backgound Images
Aerial images can be imported to the GDS as background to assist graphical editing.
Volume Conservation, Routing Algorithm Stability and Timesteps
The key to accurate flood routing is volume conservation. FLO-2D tracks and reports on volume conservation. Numerical stability is linked to volume conservation and when the model conserves volume the model runs faster. Computational timesteps are incremented or decremented according to numerical stability criteria.
Inflow Hydrographs or Rainfall
Inflow hydrographs can be assigned to either the channel or floodplain nodes. The number of inflow nodes are unlimited. Any ASCII data format hydrograph can be used as input. FLO-2D can also perform as a rainfall runoff model and rain can occur on the flooded surfaces.
Infiltration and Evaporation Losses
Spatially variable infiltration for the channel or floodplain can be computed with either Green-Ampt or SCS methods. Surface water evaporation can computed for both floodplain and channel flow.
Exchange of Channel and Floodplain Discharge
One-dimensional channel flow is simulated with rectangular, trapezoidal or surveyed cross sections. Unconfined floodplain flow is simulated in eight directions (4 compass directions and 4 diagonal directions). Overbank flow or return flow to the channel is simulated for each timestep. For detailed simulations the channel can be larger than the grid element. Tributary inflow is unlimited. The GDS can convert HECRAS cross sections into a data file formatted for FLO-2D.
Street Flow
Streets are simulated as shallow rectangular channels with a curb. Streets can intersect and exchange flow with the floodplain.
Hydraulic Structures
Hydraulic structures can represent bridges, culverts, weirs or other hydraulic control features. Hydraulic structures are simulated by user specified discharge rating curves or tables assigned to either channel or floodplain elements. Culvert flow can occur between grid elements that are not contiguous. Reverse flow is possible.
Levees and Levee Breach Failure
Levees, road embankments and dams can be simulated by specifying crest elevations on a grid element boundary. There a several levee failure options including a comprehensive breach erosion model. Levee breaches can be initiated with fragility curves.
Buildings and Flow Obstructions
Floodplain storage loss due to buildings or features can be modeled. A portion or the entire element can be removed from potential inundation. Grid element flow exchange can be partially or entirely obstructed in all of the eight flow directions.
Distributary Channel Flow
Overland flow can be simulated in small rills and gullies instead of sheet flow. The small distributary channels expand as more flow enters the gully. This distributary flow improves the time of concentration on alluvial fans.
Mud and Debris Flows
Mudflow is simulated by the FLO-2D model using a quadratic rheological model that includes viscous stress, yield stress, turbulence and dispersive stress terms as a function of sediment concentration. Viscous mudflows may cease flowing and conversely, mudflows can be diluted by inflow.
Sediment Transport
Sediment transport is computed for both channel and overland flow using one of nine available equations. Sediment volume is conserved on a grid element basis. Scour and deposition are non-uniformly distributed on channel cross sections. Sediment routing by size fraction and armoring can be simulated.
Groundwater and surface water exchange
The FLO-2D model is linked with the USGS groundwater MODFLOW model at runtime. Groundwater and surface exchange can occur in both directions.
Limiting Froude Numbers
Limiting Froude numbers can be assigned to the channels, streets and floodplain grid elements. When the limiting Froude number is exceeded in a particular grid element, the model will increase the roughness value to suppress numerical surging. It is efficient for the model flood routing to calibrate n-values for reasonable Froude numbers.
Model Output, Results and Mapping
Text output is written to ASCII files. The Post-processor MAPPER program creates shaded contours, line contour or grid element flow depth plots and hazard maps. Flood damages can be assessed and the FLO_2D output can be viewed as a flood animation . MAPPER will also automatically generate shape files that can be imported directly to ArcGIS. A DFRIM tool is available for FEMA FIS studies. A high resolution, ArcGIS integrated mapping program MAPPER.NET is also available.
Overview (Pro)
FLO-2D is a flood routing model that simulates river, alluvial fan, urban and coastal flooding.
FLO-2D can tackle any diverse flooding problems including:
- River overbank flooding
- Unconfined alluvial fan flows
- Urban flooding with street flow, flow obstruction and storage loss
- Overland progression of tsunami and hurricane storm surges
- Mud and debris flows
- Watershed rainfall and runoff
- Surface and groundwater interaction
- Flood insurance studies
- Flood mitigation design
- NWS Breach embedded
- EPA-SWMM Interface
FLO-2D is a combined hydrologic and hydraulic model so there is no need to separate rainfall/runoff and flood routing. FLO-2D is a FEMA approved hydraulic model for riverine studies and unconfined flood analyses. For a brief overview of the model components For additional information download the Demo Model or Contact Us.
Overview (Basic)
FLO-2D Basic is essentially the v2009 model updated and simplified for free distribution. It is approved for FEMA FIS studies. It is a good tool for Demonstrations, students, training and FIS studies. A basic license is free but does not include training, webinars or technical support.
FLO-2D Basic can tackle many diverse flooding problems including:
- River overbank flooding
- Unconfined alluvial fan flows
- Urban flooding with street flow, flow obstruction and storage loss
- Overland progression of tsunami and hurricane storm surges
- Watershed rainfall and runoff
- Flood insurance studies
- Flood mitigation design