Drainage Particular Columns


In calculating drainage networks, beyond common columns, several columns appear, they are:
TC
Time runoff (inlet time)
It is time that the particle of water takes longest to reach the structure in the basin.

Only available for editing the parameter Calculation of TC is set to Arbitrated .

Otherwise, a value will be calculated by the equation defined in this parameter. In general function of basin area (AREACONTR), the length (LT) and slope (H) of thalweg.

H
thalweg Drop.

Is diference between the elevation and the elevation farthest discharge point.

It is used in the calculation of TE by various formulas, it will be selected in parameters frame.

LT
Thalweg length.
Is the distance between the farthest point and the discharge point, in the course of the thalweg.

It is used in the calculation of TE by various formulas, it will be selected in parameters frame.

QSP
Flow to the full section.
Flow when the water height is 100%. In general it is less than the maximum flow, since the wetted perimeter is the maximum.
Important: upstream pipe without load, that is, the power line coincides with the upper inner generatrix of the pipe.


VSP
Flow speed to the full section.
Flow when the water height is 100%.
QESC
Real flow flowing.

QESC is calculated by:

DNIT method:

QESC = QIN + Sum(QESC upstream pipes)

other methods:
QESC = CR * SCXA * I


Where:
SCXA, is the sum of C multiplied by AREA
I, is precipitation from rain
CR, is retardation coefficient

C
Run Off coefficient.

In any precipitation of rain, only a portion actually reaches the network, since a portion infiltrates the soil.
This coefficient can be given by this table:

Location Value
roofs and paved surfaces 0.7 to 0.95
Cobblestone, tiles, blocks and taken together 0.85 to 0.90
uneven paving stone 0.5 to 0.7
Roads and rides boulder 0.15 to 0.30
Parks, gardens, lawns 0.01 to 0.2

can further simplify this table, making up:

C = ((Covered Area) * 0.7 + (Discovery Area) * 0.3)/((Covered Area) + (Discovery Area))


Understand covered area as being urbanized stretch and discovery as rural areas.
In truth, many local governments impose values of C. Curitiba (Brazil) for example, determines that use C = 0.95 to 1.00 in central areas and 0.8 in the other regions.

F
Number of Fantoli
In the DNIT calculation method, the flow is calculated by:
Qesc = CR * I * ( F * A )


F = 0.0725 * C * (I * TCMAX) ^ (1 / 3)

The formula for the Fantoli coefficient is presented on page 11 of the document Instruções Técnicas Rio-Águas (2019) and in the book Drenagem Urbana: Do Projeto Tradicional Á Sustentabilidade, on page 238

The coefficient C can be given by:

Type of Area C
Urban Zone 0.80
Residential Zone 0.60
Sub Urban Zone 0.40
Rural Zone 0.25


AREA
Basin contribution.
Obtained from design. You must define the areas of contribution of each structure with the CAREA command. In this case, the cell will be read-only.

HLAM
Height of water height

yh
Hydraulic height

yh = AreaMolhada / B

Where:
AreaMolhada is the wet section area
B, width of the surface in contact with the atmosphere

FR
Froude number. Says that the flow is critical (FR = 1) subcritical (FR < 1) or supercritical (FR > 1).

is given by:

fr = VESC /(g * yh) ^ 0.5


Where:
VESC is the flow velocity
g is the gravity acceleration
yh is the hydraulic height

SCXA
Calculated by:
SCXA = (C * AREA) + SUM (SCXAupstream)

Where:
SCXAupstream is the corresponding value in each pipe of the amount of considered pipe
AREATOTAL
Sum of the basin.
It is the sum of the contribution areas in the basin. Will be used in the calculation of delay coefficient (CR)

DECMEDTAL
Average slope of all thalweg.
Will be used in the calculation of delay coefficient (CR)

TP
Course Time
It is the travel time in the pipe in the stretch. Calculated by:

TP = EXT/VESC


Where:
EXT is the length of the pipe in plant
VESC is the flow speed in the stretch.

TCMAX
Time of arrival to the amount
It is the time that it takes to get in structure. If more than one pipe reaches this structure, takes the biggest.

TCMAX = Max (TC, Max(PipesIn.TCMAX+PipesIn.TP))
QIN
Parcial flow rate
In DNIT method)
is given by:
QIN = CR * I * F * AREA

All other methods:
QIN = CR * I * C * AREA


Where:
I is the equation precipitation
CR is the delay coefficient
D is the Fantoli Number
C is the runoff coefficient

VESC
Flow speed

The C3DRENESG evaluates the actual water height leaking iteratively, as follows:
  1. Refereeing the height of the water height, the procedure is the calculation of the wet area (AreaMolhada) and wetted perimeter (PerimetroMolhado) depending on the geometry of the cross section.
  2. Calculate hydraulic radius (rh):
    rh = AreaMolhada / PerimetroMolhado
  3. Calculate the flow velocity (VESC)

    VESC = rh ^ (2/3) * INC ^ 0.5/NMAN
  4. Calculate the flow (qcalc):
    QCALC = VESC * AreaMolhada
  5. Compares if QCALC equals QESC. if they are equal, stops, if different, arbitrates another value for water height and restart process

I
Rain Precipitation
Rain precipitation is calculated according to the recurrence time (TR) and concentration time (tc)

tc, is the higher of the arrival times upstream (TM) and the arrival time for the amount structure (TE)

The rain equation  should be chosen in parameters frame.

CR
Delay coefficient.
Applied on pipe out. It is function of AREATOTAL and DECMEDTAL
It reduces the flow rate obtained by rational method, that is, transforms the rational method in modified rational method.

See: Drain Parameters for clarification.

DECTAL
Medium basin slope.
has influence on the calculation of the CR coefficient, when the calculation method is original method.

is given by:

DECTAL = H/LT
where:
See also Common Columns.