HEC-RAS Description and Input

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HEC-RAS Description and Input Powered By Docstoc
   HEC-RAS is a modeling program for one-dimensional flow (e.g. open channel flow, where the water
only flows in one direction). It can model streams, rivers, flooding in channel overbanks, culvert flow,
flow under bridges, and flooding over in-channel structures (bridges/culverts).

Input parameters:

Cross sectional geometry – A two dimensional “plot” of the channel cross section perpendicular to flow.
Each cross section will consist of data point where the station (x) and elevation (y) are measured.
Manning’s n values for the main channel and the overbanks are needed when entering cross sectional
geometry. Any obstructions or hydraulic control structures need to be defined and associated with
nearby cross sections as defined in the HEC-RAS user’s manual. HEC-RAS can interpolate intermediate
cross sections based on surrounding cross sections. The slope will be determined by the lowest points in
the main channel cross section and the distance between cross sections.

Distance from one cross section to the next – The distance along the flow path between cross sections.
Three distances are required, (1) the distance between the left overbanks (linear), (2) the distance
between right overbanks (linear), and (3) the distance between the centers of the main channels, this
distance is not linear, but must instead follow the flow path.

Hydraulic data – You can use steady and unsteady flow. For steady flow we will likely require estimated
maximum flow or the flow for given return periods. For each flow a boundary condition is required (e.g.
if the river/stream is subcritical then the boundary will be defined by the flow at the most downstream


Input values needed:
     Cross sectional geometry
            o Stations and elevations
            o Distance between cross sections
                    Left overbank distance
                    Main channel distance
                    Right overbank distance
            o Manning’s n values
                    Main channel
                    Overbanks
     Hydraulic Data
            o Flow rate(s)
            o Boundary conditions
                    Supercritical, subcritical, or both
                           Helpful Translations
                               English                    Español
                           Geometric data           Datos geométricos
                            Cross section         La sección transversal
                             Station (x)               La abiscisa (x)
                            Elevation (y)                La cota (y)
                            Main Channel             El canal principal
                              Overbank            llanura de inundación
                              Upstream                 aquas arribas
                            Downstream                  aguas abajo
                                 Right                    Derecha
                                  Left                   Izquierda
                              Distance                    Distancia
                                 Slope                 La Pendiente
                             Manning's n                Manning's n
                           Hydraulic data            Datos Hidráulicos
                              Discharge                   El caudal
                         Boundry conditions      Condiciones de contorno
                          Supercritical flow            supercrítico
                           Subcritical flow              subcrítico
                            Critical depth           profunidad crítico
                            Normal depth           profundidad normal
                         Water surface profile      Perfiles de láminas
                           Elevation view          El perfil longitudinal

Phrases and Translations

Cross sectional geometry
Datos geométricos de la sección transversal

Distance between cross sections
La distancia entre secciónes transversales

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