Glossary of Terms and Acronyms

[Bold terms are FEQ or FEQUTL output that are not echoed from input terms.]

**AL** : Cross-sectional area of flow in
the steady-flow computations at the station. The steady-flow computations
proceed from downstream to upstream and are printed in that order.

**AREA** : Cross-sectional area of flow
in the unsteady-flow computations. The unsteady- flow results are printed
from upstream to downstream in the output.

BACKWATER (4): Water surface of stream raised above its normal level by a natural or artificial obstruction.

**BC **: Balance computation summary label.
A system-wide water-volume balance is maintained by tracking the inflows
and outflows at the boundaries of the system and comparing the sum to the
change in storage within the system. If the relative error in the balance,
**R**,
is larger than a fraction of 1 percent, then an error is likely.

**BOTM ELEV**: Bottom elevation for free
nodes and level-pool reservoirs in the summary of extremes at the end of
a simulated event. The elevation may be an actual bottom elevation or it
may be the datum for the depth variable associated with the free node or
level-pool reservoir. In most cases, it is convenient to make the elevation
and depth the same value for the free and level-pool reservoir nodes; thus,
the bottom elevation is zero.

BOUNDARY CONDITIONS: The stage, discharge, or rating curve data needed at one or more terminating branches of an unsteady-flow model in order to solve the equations of flow for the system.

BRANCH: The FEQ representation of a reach of a channel or other watercourse between hydraulic features that cannot be represented by the governing equations for gradually varied flow.

**BRA** (iteration log): The branch number
in which the maximum relative correction **RCORECT**
occurred. If the branch number is zero, then the node number in the **NODE**
column is an exterior node number or name; otherwise, the node number is
the number of the node on the branch.

**BRANCH NUMBER** : Branch number of the
output of detailed results for each time step.

**BRANCH PONDING VOLUME**: Volume of water
ponded above a branch if the storm-sewer option is invoked by inputting
CF and YC to represent the path for inflow and outflow of water from a
storm sewer in the branch.

CHANNEL: A natural or artificial waterway that periodically or continuously contains moving water.

**COMPUTATION TIME** : Computer processing
time spent to complete unsteady-flow computations including function table
lookup, network matrix content, solving network matrix, updating variables,
output of results, and so forth. Excludes the input processing and the
initialization time.

CONVEYANCE : A measure of the flow carrying capacity of a channel section.

CROSS SECTION : A series of coordinates representing the elevations and distances of points across a stream channel, perpendicular to the direction of flow.

**CSUR:** The maximum relative change in
storm-sewer surcharge storage for the system. See **BRANCH
PONDING VOLUME**.

**D** (end of time step output) : Balance
error in cubic feet or cubic meters. The balance error is computed by the
equation **D **=** S2 **+** Q **-**
S1 **-** I** , where S2 is the water volume in the system
at the current time; Q is the sum of the outflows from the start of the
event to the current time; S1 is the water volume in the system at the
start of the event; and I is the sum of the inflows from the start of the
simulated event to the current time.

**DEPTH** (each time step): Maximum water
depth for the time step. The water depth is the difference between the
water-surface elevation and the minimum elevation point in the cross section.

**DT/ITER** (each time step): Number of
seconds of simulation time per iteration since the start of the computations
for the simulated event.

**DX** : Length of each computational element
in a branch in the steady-flow computations.

**DZ** : Change in elevation across each
computational element in a branch in the steady-flow computations. A negative
value indicates a drop in the downstream direction.

**ELEV** : Water-surface
elevation in both the steady-flow computations and in the detailed output
for a time step.

**FLOW** (each time step): Flow rate in
cubic feet per second. A negative value indicates that the flow is moving
from downstream to upstream at a node.

**FR** : Square of the Froude number in
both the steady-flow computations and in the output for each time step.

FROUDE NUMBER : Dimensionless parameter that is the ratio of inertial to gravitational force. The Froude number value is one for critical flow, where the specific energy is minimum for a given depth.

**I** : The sum of the inflows to the system,
used in the water-balance computation. See also **BC,
Q, D, S1, S2, and R**.

**IFRZ**: The number of frozen time steps
not yet completed. A frozen time step is a time step where the time is
held constant while the time step is greater than zero. It is used to reduce
the small differences between the initial condition as given by the steady-flow
computations and the steady flow that would result if the unsteady-flow
computations were continued with the boundary conditions held fixed. Freezing
the time step results in fixed boundary conditions.

**INITIALIZATION TIME**: The computer time
spent processing the input to FEQ and computing the initial conditions.

**IT**: The number of iterations required
to reach convergence in the steady-flow computations.

**JTIME**: The time in Julian time as defined
in FEQ. FEQ takes the beginning of January 1, 1901 as Julian time 15385.0.
Thus, JTIME=15385.5 is the same as noon on January 1, 1901. The relations
used to compute JTIME and also to invert JTIME (compute the year, month,
day, and hour from a given JTIME) are valid from November 17, 1858 through
December 31, 25000. JTIME is used to create a strictly increasing and uniform
index for time. All the dates given in FEQ are converted to Julian time
to make comparisons both easier and faster. JTIME is based on modified
Julian time (as defined astronomically) but with changes for convenient
use in FEQ.

**LAT IN**: This column gives the lateral
inflows when DIFFUS=YES. These flows are averaged over the time step.

LEVEL-POOL RESERVOIR:** **A body of water
with a water surface that has no slope and no momentum.

**LOC**: The location of the maximum residual
given in the column headed by MXRES. The location is the equation number
in either the exterior or interior system. A negative number denotes an
equation in the exterior system and a positive number an equation in the
interior system. This is sometimes useful in diagnosing problems with the
solution when debugging the software.

MANNING'S *n*: The roughness coefficient
used in Manning's formula for computing conveyance in an open channel.

**MAX DEPTH**: Appears in the extreme value
summary at the end of the event and given the maximum depth reached during
the event.

**MAX ELEV**: Appears in the extreme value
summary at the end of the event and gives the maximum depth reached during
the event.

**MAX VELOC**: Appears in the extreme value
summary at the end of the event and gives the maximum velocity reached
during the event. This is the absolute value of the velocity so that high-velocity
flows that are reversing also are included as a positive velocity.

**MXRES**: Appears in the iteration log
and gives the maximum absolute value of the residual in solving the network
matrix. MXRES will be small relative to the other terms in the equation.

**ND**: Used with CSUR and RLTQ to denote
the branch and node location. It consists of two numbers: the first is
the branch number and the second, following the colon, is the node number
on the branch.

**NETWORK PONDING VOLUME**: Appears after
the branch results in the detailed output at a time step and is the ponding
volume above storm sewers for the entire network.

**NODE**: Labels the column of node numbers
on a branch in the branch output and the column of exterior node numbers
in the exterior node output. Note that the exterior nodes in the new input
style are names for nodes and not numbers.

**NODEID**: Labels the column of the alphanumeric
string giving the node identification taken from the input.

**NUMGT**: If the user has given a value
to NUMGT in the input in the Run Control Block, the NUMGT is the number
of nodes that fall outside the primary tolerance for convergence but meet
the secondary tolerance for convergence. The values given under this column
in the iteration log will never exceed the input value of NUMGT.

**Q**: The sum of outflows from the system
in the balance computations from the beginning of the event to the current
time. See BC.

**QE1**: The flow at the exterior node
in the output of the detailed exterior node information given at a time
step.

**QL**: Appears in the steady-flow profile
output and is the flow at the node.

**QMAX**: Appears in the summary of extremes
output and is the maximum flow rate. This is the true maximum with regard
to sign. That is, negative flows are considered to be smaller than any
positive flow.

**QMIN**: Appears in the summary of exter
me output and is the minimum flow rate. This is the true minimum with regard
to sign. Any negative flow is considered to be smaller than any positive
flow.

RATING CURVE: The plot representing the relation of stage or elevation and discharge at a particular structure or point in a stream.

**R**: Appears in the balance check output
and gives the error in balance relative to the sum of the current storage
and the cumulative outflow of water from the hydraulic system (*S*2
+*Q*).

**RCORECT**: The maximum relative correction
in the iteration log for the entire stream system. Used for applying the
primary convergence criterion that the maximum relative correction in absolute
value must be less than the tolerance specified by the user.

**RES**: Appears in the output for the
steady-flow profiles and is the residual in the function used to define
the root of the equation being solved. A large residual at convergence
may indicate some problem in the steady-flow computations.

**RESULTS AT TIME**: Appears in the detailed
output for a time step. The elapsed time since the beginning of the event
in seconds.

**RLTQ**: The maximum relative lateral
inflow for the system. Computed as the ratio of the current rate of lateral
inflow to the current average flow in the element receiving the lateral
inflow. Large values often indicate computational problems where any value
greater than one can be considered.

**S1**: The initial storage in the stream
system at the beginning of the event used in the balance check. This storage
includes the water in the branches and in reservoirs.

**S2**: The current storage in the stream
system used in the balance check. This storage includes the water in the
branches, reservoirs, and in storm-sewer surcharge storage.

**SIMULATION COMPLETE**: Message given
when the simulation of an event has been completed. The final time point
in the simulation is printed in detail to show the final state of the stream
system.

**SIMULATION ENDING AT**: The time in terms
of year, month, day, and hour and fraction of an hour at the end of the
current time step. The length of the current time step is given in seconds.

**STAT**: The station of each node on a
branch in the detailed output for a time step.

**STATION**: The station of each node on
a branch in the steady-state profile computation output.

**STORAGE**: The amount of water stored
in each level-pool reservoir. Two numbers are given: the first is the storage
in internal units, cubic feet or cubic meters, and the second is the storage
in acre-feet in English units and thousands of cubic meters in metric units.
In the output of extreme values, only the values in units or acre-feet
or thousands of cubic meters are given.

SUBCRITICAL FLOW: The flow condition at which gravitational acceleration is the dominant governing force. The Froude number is less than 1.0.

SUPERCRITICAL FLOW:** **The flow condition
for which inertia is the dominant governing force. The Froude number is
greater than 1.0.

**SURF AREA**: The surface area of each
reservoir corresponding to the maximum water-surface elevation in the output
of extreme values. Acres in English units and square kilometers in metric
units.

**SUMSQR**: Appears in the iteration log
and is the sum of the squared residuals of all the equations in both the
interior and exterior system. Used internally for controlling the size
of the correction used in the iterative solution.

**TIME IN COMPUTING NETWORK MATRIX**: The
elapsed time in computing the contents of the network matrix. This may
be an underestimate for small networks because the timing software resolution
is sometimes too coarse for accurate timing.

**TIME IN SOLVING NETWORK MATRIX**: The
elapsed time in solving the network matrix. This may be an underestimate
for small networks because the timing software resolution is sometimes
too coarse for accurate timing.

**TIME OF MAX Q**: Heading for the column
of the times of maximum flows in the summary of extremes. The time is given
in year (first two digits dropped to save space), month, day, and hour
in fractional form.

**TIME OF MAX Z**: Heading for the column
of the times of maximum elevations in the summary of extremes. The time
is given in year (first two digits dropped to save space), month, day,
and hour in fractional form.

**TIME OF MIN Q**: Heading of the column
of times of the minimum flows in the summary of extremes. The time is given
in year (first two digits dropped to save space), month, day, and hour
in fractional form. The minimum flow is defined algebraically considering
the sign of the flow. Thus, the minimum flow could be the maximum flow
if the absolute value is considered.

**TIME STEP RESET IN MANTIM TO**: The ending
time specified by the user in the Run Control Block is used in FEQ. However,
there is no guarantee that the sequence of time steps selected by FEQ will
exactly match the ending time. The subroutine used to manage the time step,
MANTIM, resets the final time step to match the ending time specified by
the user.

**TL**: The top width of the wetted cross
section in the steady-flow profile output.

**TOP**: The top width of the wetted cross
section in the detailed output for the time step.

**VEL**: The average velocity for the flow
in the cross section in the detailed output for a time step.

**WT**: The current value of the time integration
weight factor. When
*WT*=0.5, the trapezoidal rule is used to approximate
the integrals with respect to time. Values of *WT*>0.5 reduce the
accuracy of the approximate integration but reduce the effect of non-linear
oscillations that sometimes distort the numerical solution.

**YE1**: The depth at each exterior node
in the detailed output for exterior nodes at a time step.

**YL**: The depth at each node on a branch
in the steady-flow computation.

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