Level

All Variables from Level 1. Level 2 includes additional hydraulic parameters used in the sediment model (which may be different than the HEC-RAS hydraulic output).

Flow (cfs) (m³/s) – The flow at the cross section at the time step.

Velocity (ft/s) (m/s) – Average channel** velocity – the flow between the channel banks divided by the area of eht channel.

Shear Stress (lb/ft²) (Pa or N/m²)– Channel average shear stress. The is the computational shear stress from the sediment computations:
                 
       where,

            is the unit weight of water
            EfD is the Effective Depth in the channel ( between the channel banks see level 3 for the EfD equation) and
           S_f is the friction slope (which can be local or averaged from the bounding cross sections – see Section on Sediment Energy Slope).♱

Level 3 includes gradation data, some additional hydraulic parameters, and a sediment flux term.

d₅₀ Cover/Subsurface/ Inactive Layers (mm) – the median grain size of the specified mixing layer at that cross section. (Note: Layer names can change base on the mixing method – see Table 1 5)

Note:

All particle sizes are always in mm in input and output even if the model is in US customary units.

 d₁₀ Cover/Subsurface/ Inactive Layers (mm)

d₉₀ Cover/Subsurface/ Inactive Layers (mm)

Effective Depth (ft) – A weighted average depth that often reflects the total cross section shape and change more than the invert change. This is also used in the shear stress equation.

            where:

                  D_i is the average water depth in each cross section element (the trapezoid subsection "i" associated with each station elevation point),

                  A_i is the area of that element, and n is the number of subsections.

Effective Width (f–) - Effective width is the comparable channel width that preserves cross section area given the Effective Depth - (Units: ft or m)

Manning's n Channel (s/ft^1/3 or s/m^1/3) - This is the Manning's n value in the channel (between the channel banks). If the channel has laterally varied n values, it is the composite channel n. It can be dynamic in time if the water surface weights the composite n-values differently, if there is a flow, or seasonal n value dependency, or if a dynamic, sediment bed roughness predictor is selected. Unlike the Chezy equation the manning coefficient is not dimensionless.

Froude Number Channel - The Froude number in the channel (between the channel banks). HEC-RAS computes the Froude Number as:

              where:

                     Q_ch is the flow in the channel,

                     W_chis the top width of the channel,

                     g is the acceleration of gravity and

                    A_ch is the area of the channel, where the channel is the portion of the cross section between the channel banks.
Mass (Vol) In Cum (tons or ft³) (tonnes or m³) – The total sediment flux into the control volume since the beginning of the simulation (Cum is "cumulative" in time. Mass In Cum at the upstream cross section should reflect the model boundary and the runtime sediment budget report. Only Total in Level 3. For Grain Class specific results, increase to level 4.

Mass (Vol) Dredge Cum (tons or ft³) (tonnes or m³) – The total mass or volume dredged from that cross section since the beginning of the simulation. Note: This variable will only populate if the model has a dredging event. This output has also changed from version 5, which only reported instantaneous results.  See and example in the Dredging section.

Includes variables from levels 1-3. This is the default level, so it includes the most used variables.

Starting in level 4, the Mass and Volume results include total and each active grain class.+ This includes new Mass and Volume variables in this level as well as mass and volume variables (e.g. Mass Bed Change, Vol in CUM) inherited from previous levels.

Sediment Concentration (mg/L) – HEC-RAS reports concentration of the flux out of the control volume. Therefore, Concentration is:

Slope (no units, ft/ft or m/m) – This is the Energy Slope used in the shear stress equation, which is either computed locally at the cross section (Q/Conveyance)^0.5 or the slope between the EGLs at the bounding cross sections. See the section on Sediment Transport Energy Slope.

Lateral Load Mass (Volume) In (tons or ft³) (tonnes or m³) – This variable records the sediment entering the model through lateral boundary conditions at each cross section and time step. It is only the lateral loads for the computation increment, not a cumulative value. Total and by grain class.

Lateral Structure Mass (or Vol) Div (ton or ft³) (tonnes or m³) – This tracks the sediment that is removed from each control volume (or added) by sediment associated with flow over a lateral structure. Total and by grain class.

Mean Eff Channel Invert (ft) (–) - This is a measure of representative bed change. The Effective Channel Invert is the maximum channel elevation (the elevation associated with the higher channel bank station) minus the Effective Depth (see description in level 3).

Mean Eff Channel Invert Change (ft) – This is the net change in the Mean Effective Invert since the beginning of the simulation. It is similar to the Invert Change variable, reporting bed elevation change (an intuitive measure of morphologic change) but is a more robust reflection of total cross section change than Invert Change, which can generate idiosyncratic results depending on how one node responds to the simulation.

Invert Elevation Max (ft) (m)^◊ – The maximum channel invert (lowest elevation point between the channel banks) since the beginning of the simulation. The final profile indicates the maximum deposition at each cross section during the simulation.

Invert Elevation Min (ft) (m)^◊ – The minimum channel invert (lowest elevation point between the channel banks) since the beginning of the simulation. The final profile indicates the maximum erosion at each cross section during the simulation.

Mass (or Volume) Bed Change Cum: Max (tons or ft³) – The maximum (positive) deposition in mass or volume since the beginning of the simulation. This result is monotonic. It only increases with time.

Mass (or Volume) Bed Change Cum: Min (tons or ft³) - The maximum negative mass or volume change since the beginning of the simulation. This result is monotonic. It only decreases (larger negative value) with time.

Toffaleti Sub Zone Capacities:

Toff Zone Capacity U (tons/day) (tonnes/day) – The fraction of the Toffaleti transport capacity computed in the "Upper Zone" – the top 60% (above 1/2.5 Depth from the bottom) of the water column. Only written if the Toffaleti function is selected. Modelers sometimes compare the upper three zones of Toffaleti Capacity to suspended load measurements (which exclude bed load).

Toff Zone Capacity M – The fraction of the Toffaleti transport capacity computed in the "Middle Zone" – approximately 31% of the water column in the zone between 1/2.5 Depth and 1/11.24 Depth (from the bottom of the channel). Only written if the Toffaleti function is selected.

Toff Zone Capacity L – The Toffaleti transport capacity computed in the "Lower Zone" – approximately the bottom 8-9% of the water column, excluding the bed zone. Only written if the Toffaleti function is selected.

Toff Zone Capacity B – The "Bed Zone" portion of the Toffaleti transport capacity. This is the MPM capacity if the Toffaleti-MPM function is selected.

Level 5 is intended to be a "mixing" level, which includes the more detailed results to help understand/troubleshoot the bed mixing algorithms. It also includes all of the terms required to balance the sediment budget for each control volume (or sub-reach). Level 5 also includes some preliminary (station movement and total mass) of BSTEM results (including all of the grain-class specific results) if the model includes any BSTEM cross sections. For BSTEM variable descriptions see the Output section of the BSTEM manual and Table 41.

Includes all the variables from Levels 1-4

Mass Bed Change^▲: (tons or ft³) (tonnes or m³) – The sediment eroded or deposited from the control volume in that computational increment (the Cumulative version of this variable is included in Level 1. Total and by grain class.

Mass Out^▲: (tons or ft³) (tonnes or m³) – Sediment flux leaving the control volume in that computation increment. The cumulative version of this result is included in Level 3. Total and by grain class.

Mass In^▲ and Mass In Cum: (tons or ft³) (tonnes or m³) – Sediment flux into the control volume, in the specific time series and for all time since the beginning of the simulation respectively. Total and by grain class. The mass balance for each control volume (for the simple Continuity approach) should be :

                                   Mass Bed Change = Mass In - Mass Out

Mass (Vol) Capacity and Mass (Vol) Capacity Cum (tons/day or ft³/day) (tonnes/day or m³/day) – this is the sum of the transport capacity computed for each grain class. This is before limiters like fall velocity or armoring are applied, so, usually:

                                  Mass Bed Change ≠ Mass In  -Mass Capacity
However, it provides a sense of how transport varies with the hydrodynamics and bed evolution. The Cumulative version of this parameter sums the total capacity for all time steps since the beginning of the simulation. Level 5 only includes the totals. HEC-RAS reports these by grain class in level 6.

Temperature (^oF) (^oC) – Water temperature. Current versions of the model only allow one temperature per time step, so this can vary in time but not space.

Thickness Cover (Active)^● (ft) (m) – The vertical thickness of surficial layer of the bed mixing (sorting and armoring) algorithm. This is the Active Layer or the Cover Layer (in the Thomas or Copeland mixing methods).

Thickness Subsurface (ft) (m) – The vertical thickness of an intermediate layer between the cover and inactive layer in the Thomas and Copeland mixing algorithms. The Active Layer method does not have a comparable layer.

Thickens Inactive (ft) (m) – The vertical thickness of the deepest layer of the bed mixing (sorting and armoring) algorithm. All three methods use the same terminology for this.

Mass Cover (Active) (Volume): (tons or ft³) (tonnes or m³) – The sediment mass or volume (total and by grain class) in the surface mixing layer (Active or Cover Layer) of the control volume. The other layers are included in Level 6.

Fall Velocity – (ft/s) (m/s) Reports the fall velocity computed for each grain class. Also reports a "total" fall velocity which is a weighted average:

Where i is each grain class, and n is the number of grain classes in the model. This weighted fall velocity is just a summary heuristic, however. It has no physical analogue and is not used anywhere in the computations. The individual fall velocities can be useful, and vary with temperature. Because HEC-RAS currently only allows one temperature per time step, these values will be constant in space in only vary in time.

Level 6 includes some more detailed results and a wider suite of BSTEM results (including all of the grain-class specific results) if the model includes any BSTEM cross sections. For BSTEM variable descriptions see the Output section of the BSTEM manual and Table 41.

Includes all variables from Levels 1-5.

Mass (or Volume) Capacity (for every grain class) (tons/day or ft³/day) – This is the transport capacity computed by the transport function for each grain class (which is the transport HEC-RAS actually uses in its grain-class independent rout

Long. Cum Mass (or Volume) Movable Limits (tons or ft³) - This is the same as the Longitudinal Cumulative Mass or Volume change in Level 1, except it excludes any bed change outside the movable bed limits. The Longitudinal Cumulative Mass (Volume) change sums the mass or volume change from the beginning of the simulation and from upstream-to-downstream, so that the downstream cross section at the last time step of the Longitudinal Cumulative Mass Curve (LCMC) is a summary of the total aggradation or degredation in that reach for the simulation. Comparing the full LCMC (or LCVC) to this one, that only reports the result in the movable bed limits, is a helpful way to differentiate between overbank and channel processes (e.g. determine what percentage of deposition is floodplain deposition or identify overbank deposition offsetting channel erosion). (Total and by grain class)

Mass Subsurface (Volume): (tons or ft³) (tonnes or m³) – The sediment mass or volume (total and by grain class) in an intermediate mixing layer between the cover (which is in Level 5) and inactive layers in the Thomas and Copeland mixing methods. The Active Layer method does not have this layer.

Mass Inactive (Volume): (tons or ft³) (tonnes or m³) – The sediment mass or volume (total and by grain class) in the deepest mixing layer of the control volume. The deepest mixing layer has the same name for all mixing algorithms.

Hydraulic Radius – The area of the channel (the part of the cross section between the movable bed limits) divided by the wetted perimeter of the channel.

Movable Elv L and Movable Elv R: (ft) (m) – These are the elevations of the movable bed limits. Tracking the MBL movement relative to the channel can be useful, but these are mainly used to track toe migration in BSTEM models.

Movable Sta L and Movable Sta R: (ft) (m) – These are the stations (lateral stations of the station-elevation points) of the movable bed limits. These will remain constant unless the cross section has BSTEM parameters. Only the BSTEM algorithms move cross section station-elevation points laterally.

Reduce Armor Factor (decimal between 0 and 1) – The Armor Reduction Factor determines how effective the cover layer is in the Thomas and Copeland mixing algorithms. It is the "Armoring Ratio" in Figure 217 and Figure 220. HEC-RAS multiplies the capacity deficit of each grain class by this ratio (computed from the "equivalent particle diameters" of coarser particles in the cover layer). An armor ratio of 1 is no armoring, 0 is complete armoring (for that grain class) and anything in between is partial armoring. For example, in the figure below, all the grain gravel and cobble grain classes remain unarmored throughout the simulation (RAF=1). Very Fine Sand and finer grain classes are all completely armored after the first time step (RAF=1). Three sand size classes gradually armor over time, with fine sand fully armoring (goes to zero) during the simulation and Coarse Sand eventually reducing erosion by ~50% because of armoring effects (RAF=0.5).

Shear Velocity (ft/s) (m/s) – Shear velocity (u_*) is an expression of the shear stress with velocity units:
             
where τ is the bed shear stress and ρ  is the density of the fluid.
The shear velocity is a popular way to express shear and shows up in many of the equations and algorithms included in HEC-RAS because the ratio of fall velocity to shear velocity becomes a dimensionless parameters that has a range of meaningful transport applications.

d₁₆ Cover/Subsurface/ Inactive Layers (mm) – The 16^th percentile particles size of the specified mixing layer. Some practitioners prefer the d₁₆ to d₁₀ because it is two standard deviations below the mean.

d₈₄ Cover/Subsurface/ Inactive Layers (mm) The 84^th percentile particles size of the specified mixing layer. Some practitioners prefer the d₈₄ to d₉₀ because it is two standard deviations above the mean.