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重要职能

求解算法

• 选取完 全动态颠簸量方程和中 心有限差分法

• 基于8向潜在流方向的方形网格系统进行洪水演进推算

网格系统构建

1. 数据需要

   • 地形数据：数字地形模型（DTM）点、等高线或测绘数据

   • 水文数据：通过预处置法式网格开发系统（GDS）自动天生网格并插值高程

   • 典型网格尺寸：3米（10英尺）到 150米（500英尺），网格数量无限度

2. 布景图像

   • 支持导入航拍图像辅助图形编纂（需配套世界文件定位）

水量守恒与推算不变性

• 通过严格的水量守恒节造确保精度（模型实时追踪并汇报水量平衡）

• 数值不变性与水量守恒直接关联，守恒性越好推算速度越快

• 凭据漫滩、河路及街路流的不变性准则动态调整推算功夫步长

输入水文过程线与降雨

• 支持肆意数量输入节点（河路或漫滩）

• 兼容ASCII体式水文过程线

• 可作为降雨径流模型运行（允许洪水面上叠加降雨）

• NEXRAD雷达降雨数据利用：

  • 通过GDS将NEXRAD网格降雨数据插值到模型网格

  • 天生RAINCELL.DAT文件实现时空变降雨仿照

  • 需结合雨量站数据校准雷达降雨

损失推算

• 下渗：支持Green-Ampt法、SCS曲线数法或Horton法，可组合使用

• 蒸发：别离推算漫滩和河路的水面蒸发损失

河路与漫滩水流互换

• 河路流：一维仿照（支持矩形/梯形/实测断面）

• 漫滩流：8向非约束流动仿照（4主方向+4对角线方向）

• 支持漫滩与河路间每步长的溢流/回流仿照

• 特殊职能：

  • 河路可大于网格尺寸

  • 支流输入数量无限度

  • GDS支持HEC-RAS断面体式转换

街路流与水力构筑物

• 街路流：仿照为引路缘石的浅矩形渠路，支持与漫滩交互

• 水力构筑物：

  • 桥梁/涵洞/堰等通过用户界说的流量-水位曲线仿照

  • 支持逆向流、非陆续网格间的涵洞流（含进出口节造方程）

雨水排水系统

• 完 全耦合的地表与地下排水系统仿照

• 组件蕴含：

  • 无限管路系统

  • 5种雨水口节造类型

  • 可"顶起"的查抄井盖

  • 基于管路压力与地表水位比力的入流节造

  • 多种出水口类型（含水下出水口和止回阀）

堤坝/大坝溃决

• 通过指定网格天堑顶高程仿照堤防/路堤/大坝

• 溃决选项：

  • 9种泥沙输移方程选择的侵蚀模型

  • 支持基于脆弱性曲线触发溃决

构筑物与流动故障

• 仿照构筑物导致的蓄水容量损失

• 支持部门/完 全阻断网格8向水流互换

屋顶径流与低影响开发（LID）

• 屋顶径流：

  • 思考落水管节造和女儿墙蓄水

  • 凭据屋顶坡度将径流叠加到构筑周边地表

• LID措施：

  • 通过空间变容水深（TOL）仿照生物滞留池/绿色屋顶/ permeable pavement等

  • 单个网格可代表复合LID技术

泥石流与泥沙输移

• 泥石流：

  • 二次流变模型（含黏滞应力/屈服应力/紊流应力项）

  • 支持流动滞碍与稀释仿照

• 泥沙输移：

  • 11种方程选择

  • 按粒径分级仿照输移与装甲效应

  • 网格级泥沙量守恒

地下水耦合

• 运行时与USGS的MODFLOW模型耦合

• 支持地表水-地下水双向互换

临界弗劳德数节造

• 可为河路/街路/漫滩网格指定临界弗劳德数

• 超限时自动增长糙率值抑造数值振荡

了局输出与后处置

• 文本输出：ASCII体式

• 后处置法式MAPPER：

  • 天生等值线图/流向图/灾害图

  • 支持洪灾损失评估与洪水动画

  • 自动导出ArcGIS兼容的shapefile

• 二进造输出：

  • 支持HDF5/NetCDF4体式（通过ITIMTEP变量节造）

  • 输出功夫步长与变量数量可调

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【英文介绍】

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.

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• 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 pre-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.

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• Backgound Images

Aerial images can be imported to the GDS as background to assist graphical editing. The GDS requires a world file to read images.

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• 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 for floodplain, channel and street flow.

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• 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.

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• Replicate Historical Rainfall Events with NEXRAD data

Model calibration can be performed with NEXRAD rainfall data. NEXRAD ASCII grid rainfall data can be interpolated to the grid elements using the GDS. A file RAINCELL.DAT is generated so that each grid element distinct rainfall data in the NEXRAD recorded intervals (typically 5 or 15 minutes). A historical rainfall event can then be simulated with spatially and temporally varied rainfall. Adjusted NEXRAD data to rain gages is necessary to compile rainfall data.

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• Infiltration and Evaporation Losses

Spatially variable infiltration for the channel or floodplain can be computed with either Green-Ampt, SCS curve number or Horton methods. Combined Green-Ampt and SCS methods will enable curve number rainfall losses to be model with transmission losses. Surface water evaporation can computed for both floodplain and channel flow.

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• Channel Flow and 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.

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• Street Flow

Streets are simulated as shallow rectangular channels with a curb. Streets can intersect and exchange flow with the floodplain.

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• 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. Reverse flow is possible. Culvert flow can occur between grid elements that are not contiguous. The generalized culvert equations will account for inlet and outlet control.

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• Storm Drain System

There is a fully integrated surface water and storm drain system. The storm drain components can include an unlimited pipe system, inlet, outfalls and manhole covers. Inlet control is simulated with five storm drain inlet types. Manhole covers can be popped. Outflow through the inlets or junction boxes with manholes is based on the comparison between pipe pressure and surface water elevation. There are numerous types of outfalls which may include underwater outfalls and flapgates.

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• Levees and Levee and Dam 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 with a choice of nine sediment transport equations. Levee breaches can be initiated with fragility curves.

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• 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.

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• Roof Runoff

Rainfall runoff from roofs can be simulated with downspout inlet control and parapet wall storage. Variable depth tolerance values (TOL) can be assigned to accommodate other roof storage. The rainfall runoff from the roof will be added to the ground water surface around the building based on the roof slope. A positive roof head enables the flow to be added to the ground surface water while the flooding will still go around the building.

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• Low Impact Development

Lot-size flood retention storage for site development can be simulated with a spatially variable tolerance depth (TOL) value. This may include bio-retention, green roofs, rain gardens, permeable pavement, drainage disconnection, swales, and on-site storage. TOL values are assigned to represent composite Low Impact Development (LID) techniques on a given grid element. Different grid elements may represent different LID techniques.

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• 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 for floods progressing over alluvial fans.

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• 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.

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• Sediment Transport

Sediment transport is computed for both channel and overland flow using one of eleven 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.

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• 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.

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• 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.

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• Model Output, Results and Mapping

Text output is written to ASCII files. The Post-processor MAPPER programs create shaded contours, line contours 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.

Results can be written now to the TIMDEP output file using a HDF5 or NetCDF binary format. FLO-2D PRO writes the TIMDEP output file in different formats according to the value specified on the ITIMTEP variable:

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0: NO TIMDEP.OUT RESULTS

1: ONLY TIMDEP.OUT IS WRITTEN

2: TIMDEP.OUT and HDF5 ARE WRITTEN

3: TIMDEP.OUT and NETCDF4 FILES ARE WRITTEN

4: ALL OUTPUT FILES ARE WRITTEN

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For options 0, 1, 2, 3 or 4 the output timestep TIMTEP must be specified. The number of output variables printed in the TIMDEP files was also expanded.