Culvert formula (Water Overlay): Difference between revisions

Revision as of 15:22, 8 October 2020

Flow through culverts is based on an open channel flow calculation.

The actual height of the culvert is at least the height of the terrain on either end of the culvert and the provided threshold height:

B_{c}=\max(T_{c},B_{l},B_{r})

The radius of the culvert:

r={\frac {D}{2}}

The height of the water column at either end of the culvert, relative to the culvert, is calculated:

w_{l}=\max(0,w_{l}-B_{c})

w_{r}=\max(0,w_{r}-B_{c})

Flow depth d is:

d=\max(0,\min(D,\max(w_{l},w_{r})-B_{c})))

The loss coefficient for the culvert is calculated:

U={\sqrt {\frac {1}{1+{\frac {2g\cdot n^{2}\cdot length}{R_{h}^{\frac {4}{3}}}}}}}

The hydraulic radius $R_{h}$ is calculated as:

R_{h}={\frac {A}{P_{w}}}Forcircularculverts,theflowarea<math>A

and the wetted perimeter

P_{w}

is calculated using the formula's in the image on the right.

For square culverts, the flow area and wetted perimeter is calculated as followed:

The potential flow through the culvert is then calculated:

C=U\cdot K\cdot {\sqrt {2g\cdot \Vert w_{l}-w_{r}\Vert }}

Finally the actual amount of water flow is calculated:

\Delta f={\frac {\Delta t\cdot C}{\Delta x}}

Where:

$D$ = The CULVERT_DIAMETER attribute of the culvert.
$T_{c}$ = The CULVERT_THRESHOLD attribute of the culvert.
$B_{c}$ = The surface height of the base of the culvert.
$w_{l}$ = The water level on the left end of the culvert, relative to datum.
$w_{r}$ = The water level on the right end of the culvert, relative to datum.
$h_{l}$ = The relative water height on the left end of the culvert.
$h_{r}$ = The relative water height on the right end of the culvert.
$R_{h}$ = The hydraulic radius in the culvert^[1].
$R_{w}$ = The wetted perimeter.
$A$ = The flow area.
$K$ = Circular flow area, based on the height of the water in the (circular) culvert.
$g$ = Acceleration factor of GRAVITY, defined for the Water Overlay.
$L$ = The length of the culvert, calculated as the distance between the culvert's endpoints.
$U$ = Loss coefficient for culverts.
$n$ = The CULVERT_N attribute of the culvert.
$C$ = The potential rate of water flow through the culvert.
$\Delta f$ = The water flow which takes place.
$\Delta t$ = Computational timestep.
$\Delta x$ = Cell size.

References

↑ Hydraulic Radius Equations Formulas Calculator ∙ found at: https://www.ajdesigner.com/phphydraulicradius/hydraulic_radius_equation_pipe.php ∙ (last visited 2019-02-11)

Models

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Model formulas

Timestep • Season • Surface water level • Groundwater level
Flow formulas

Surface flow • Surface infiltration • Ground flow • Ground infiltration • Surface evaporation • Ground evaporation • Ground bottom flow
Hydraulic structure formulas

Culvert • Weir • Breach growth • Breach flow • Pump • Sewer Overflow • Inlet • Drainage
Related

Building attributes • Hydrological features • Hydraulic structures • Terrain attributes • Model attributes • Results • Simulation data

[hydradius-1] Hydraulic Radius Equations Formulas Calculator ∙ found at: https://www.ajdesigner.com/phphydraulicradius/hydraulic_radius_equation_pipe.php ∙ (last visited 2019-02-11)

[1]

@@ Line 17: / Line 17: @@
 : <math>U = \sqrt{ \frac{1}{ 1 + \frac{2g \cdot n^2 \cdot  length }{  R_{h}^{\frac{4}{3}}} }}</math>
-The hydraulic radius <math>R_h</math> is calculated using the formula's in the image on the right.
+The hydraulic radius <math>R_h</math> is calculated as:
+: <math>R_h = \frac{A}{P_w}
+For circular culverts, the flow area <math>A</math> and the wetted perimeter <math>P_w</math> is calculated using the formula's in the image on the right.
+For square culverts, the flow area and wetted perimeter is calculated as followed:
 The potential flow through the culvert is then calculated:
@@ Line 31: / Line 37: @@
 * <math>w_{l}</math> = The [[Surface water level formula (Water Overlay)|water level]] on the left end of the culvert, relative to {{datum}}.
 * <math>w_{r}</math> = The [[Surface water level formula (Water Overlay)|water level]] on the right end of the culvert, relative to {{datum}}.
+* <math>h_{l}</math> = The relative water height on the left end of the culvert.
+* <math>h_{r}</math> = The relative water height on the right end of the culvert.
 * <math>R_h</math> = The hydraulic radius in the culvert<ref name="hydradius"/>.
-* <math>K</math> = Flow area, based on the height of the water in the (circular) culvert.
+* <math>R_w</math> = The wetted perimeter.
+* <math>A</math> = The flow area.
+* <math>K</math> = Circular flow area, based on the height of the water in the (circular) culvert.
 * <math>g</math> = Acceleration factor of [[Gravity (Water Overlay)|GRAVITY]], defined for the Water Overlay.
 * <math>L</math> = The length of the culvert, calculated as the distance between the culvert's endpoints.

Culvert formula (Water Overlay): Difference between revisions

Revision as of 15:22, 8 October 2020

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