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).
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
o Flow rate(s)
o Boundary conditions
Supercritical, subcritical, or both
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
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