Program FLUSS

The program FLUSS features both one dimensional water level calculations and two dimensional flood modeling.

FLUSS-1D The program FLUSS calculates backwater curves and flow profiles along a series of chosen cross sections. Profile forms (open or closed) are entered simply through the use of a coordinate system. This allows arbitrary profile shapes (symmetric or asymmetric) to be calculated. FLUSS then determines the water levels for a given flow rate.

FLUSS-2D is a two-dimensional finite element (FE)-flow model and is a part of FLUSS program. The program FLUSS-2D consists of both a graphical and a numerical module. The graphical module is used for generating and post-processing the computational mesh, defining the initial and boundary conditions, assigning roughness values, and including in-flow structural elements. The numeric module imports point coordinates, handles all record management tasks, establishes the required run parameters, and carries out the hydraulic calculation within the defined conditions. Calculation results such as surface water level, water depth and velocity vectors are graphically depicted. FLUSS-2D requires the installation of AutoCAD R2007 or above.

1D-Model

Basics of design

The calculation assumes stationary, non-uniform flow conditions.

The program makes use of the following calculation methods:

•	MANNING-STRICKLER
•	DARCY-WEISBACH with the following options: ♦ Compound/composite roughness after MERTENS ♦ Compound/composite roughness after PASCHE ♦ Compound/composite roughness after NUDING

FLUSS calculates both sub- and supercritical flow conditions. The state of flow can be calculated either after KNAUF / KÖNEMANN or using the energy equation.

Profiles can include the river channel and left and right overbank areas, each with their own distinct hydraulic characteristics. Calculations are carried out after MANNING-STRICKLER, where each of the three profile subsections can be assigned separate roughness k_st values. Additionally, FLUSS makes it possible to include vegetation effects after FELKEL (using a correction factor for the k_st - value).

The procedure after MERTENS PASCHE allows the input of a sand k_s roughness between any two points. This takes into account transitioning flow conditions between the vegetated overbank areas and the river channel itself using compound/composite roughness calculations.

The program calculates standard open channel profiles, profiles including in-flow structural elements (such as bridge piers), and closed profiles. Backwater effects due to piers are calculated after REHBOCK. Sudden expansions automatically include loss calculations after BORDA-Carnot.

In addition, branched flow can also be calculated. The water level is calculated interactively using a mass balance approach, until the branching profiles satisfy a user-defined accuracy (in terms of the difference in the respective energy grade lines).

When carrying out hydraulic calculations after MANNING-STRICKLER, the roughness coefficients k_st can be determined using measured flow rates and water depths. This aids greatly in the calibration of river reaches and cross-sections for which new calculations are to be carried out.

Additionally, the program itself contains several useful sub programs:

•	Single profile calculations including the specific energy curve showing the critical depth, critical velocity, and critical slope
•	Weir flow calculations after POLENI
•	Hydraulic drop loss calculations after BÖSS-BELANGER
•	Calculation of flow regulating sections
•	Quantity take-offs after Elling by superimposing two FLUSS project file results

In addition to the profile can also form another (field) Profile captured. The cross sections including terrain are graphically displayed on the screen. The program allows for the user to directly modify profiles, terrain data, overbank boundaries, compound/composite areas, etc. through the use of the graphics module.

Data output

Lists can be created for viewing, printing, or can be output in ASCII file format. FLUSS provides the following list types:

•	Input data for individual cross sections
•	Calculation results in a condensed format
•	Calculation results in a detailed format
•	Calculation results for individual profiles, (including the rating curve) showing weirs, falls, and flow regulating sections

Structure performance (1D)

•	Max.	4,000	Cross sections
•	Max.	10	Branches

Data exchange

Data taken from FLUSS hydraulic calculations can be used directly in AutoCAD for the creation of river profile and cross section drawings.

User Interfaces:

•	DA 54	Data import und -export after REB-data type 54
•	DA 66	Data import und -export after REB-data type 66
•	ASCII	Variable ASCII-interfaces with templates to facilitate data transfer with the following programs: ESNA (RWTH Aachen), WSP (TH Darmstadt), HYDRA-WSP96 (Knauf), and to import point data (2D)

2D-Model

In addition to one-dimensional water level calculations, FLUSS performs flood flow modelling with a 2D FEM model as well. The computational approach is based on the depth-averaged shallow water equations (Navier-Stokes equations) and requries the use of a digital terrain model (DTM), roughness values and boundary conditions (rating curve and water depth). FLUSS-2D then provides simulations which can be used to estimate the areal extent of flooding, along with water depths, flow direction and velocities.

There are a total of three program modules: Scatter Point, Design, and Mesh Modules. Each of the modules are available to the user as menu items and buttons displayed directly in AutoCAD.

Key to flood flow modelling is the use of a digital terrain model (DTM) either from a FLUSS-2D generated point cloud, or imported though the user interface

1) Scatter Point-Module: Importing and editing survey topographic data

•	Import scatter point data (x, y, and z values of the survey data)
•	Duplicate point data can be checked, and the data points can be inserted/deleted.
•	Mesh generation (triangular) using the Delaunay-Method
•	Data management (copy, split, merge, delete)
•	Directly insert scatterpoints into the mesh
•	Alternatively to using the DTM, the user can also import AutoCAD file types (*.dxf, *.dwg).

2) Design-Module: Classify investigation reach sub areas, generate mesh

•	Define sub areas based on points, polylines, and polygons
•	Refine sub areas (modify/add/delete points, polylines, and polygons).
•	Roughness values (after Manning-Strickler) input based on sub areas
•	Create mesh points according to sub area polygons, scatter point elevation interpolation, mesh generation

Solving the system of differential equations with the finite element method (FEM) requires that the mesh is as uniform as possible. For this reason, the scatter point module produced TIN is usually not ideal for performing hydraulic calculations, as the point positions correspond to the topographic survey and are not optimal from a hydraulic standpoint.

An important task of the design module is the mesh generation. First, the study area is divided into polygons representing the overbank and river channel sections. Next, roughness values are assigned. The mesh generation algorithm is then run (using either a patch or paving method). All elements within a polygon are then assigned the appropriate roughness type.

3) Mesh – Module: mesh optimization, define boundary conditions, carry out the hydraulic calculations and visualize results

•	carry out refinements to the mesh (insert/delete points, manually build new elements, delete elements)
•	Modify a roughness classification table (150 values max)
•	Change the roughness value of individual elements
•	create a new reach/delete a reach
•	boundary conditions (defined flow rate on upper reach and water surface elevation on the lower reach)
•	define initial conditions - water surface, flow velocity in x and y direction
•	carry out the hydraulic calculations, compare results/visualization/print

Modifying points, segments, and elements:

The extensive data processing features of RIVER-2D allow you to insert, delete, and move points, and add and delete node segments and elements. Designed with the design engineer in mind, modifications can be done quickly and efficiently with just a few mouse clicks.

For better design and project orientation, the use of orthophotos is highly recommended. A quick and easy source is Google Earth–Pictures (External Link).