Culvert formula (Water Overlay): Difference between revisions

Revision as of 08:53, 9 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})

For circular culverts, the flow height $h_{f}$ is:

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

For rectangular culverts, the flow depth h is:

h_{f}=\max(0,\min(H,\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}}}

For circular culverts, the flow area $A$ and the wetted perimeter $P_{w}$ is calculated using the formula's in the image below.

Where the radius of the culvert:

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

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

A=h_{f}\cdot D

$P_{w}={\begin{cases}D+2h_{f},&{\text{if }}h_{f}<H\\2D+2H,&{\text{if }}h_{f}\geq H\end{cases}}$

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, representing either the inside diameter of a circular culvert or the inside width of a rectangular culvert.
$H$ = The CULVERT_RECTANGULAR_HEIGHT attribute of the culvert, representing the inside height of a rectangular culvert.
$h_{f}$ = The (flow) height of the water inside 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.
$R_{h}$ = 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 4: / Line 4: @@
 : <math>B_c = \max( T_c , B_l , B_r )</math>
-For circular culverts, the flow depth h is:
+For circular culverts, the flow height <math>h_f</math> is:
-: <math>h = \max(0,\min(D,\max (w_{l}, w_{r})-B_c)))</math>
+: <math>h_f = \max(0,\min(D,\max (w_{l}, w_{r})-B_c)))</math>
 For rectangular culverts, the flow depth h is:
-: <math>h = \max(0,\min(H,\max (w_{l}, w_{r})-B_c)))</math>
+: <math>h_f = \max(0,\min(H,\max (w_{l}, w_{r})-B_c)))</math>
 The loss coefficient for the culvert is calculated:
@@ Line 21: / Line 21: @@
 For rectangular culverts, the flow area and wetted perimeter is calculated as followed:
-: <math>A = h \cdot D</math>
+: <math>A = h_f \cdot D</math>
 <math>
 P_w =
 \begin{cases}
-D + 2h, & \text{if } h < H \\
+D + 2h_f, & \text{if } h_f < H \\
-D + 2H, & \text{if } h \ge H
+D + 2H, & \text{if } h_f \ge H
 \end{cases}
 </math>
@@ Line 39: / Line 39: @@
 * <math>D</math> = The [[Culvert diameter (Water Overlay)|CULVERT_DIAMETER]] attribute of the culvert, representing either the inside diameter of a circular culvert or the inside width of a rectangular culvert.
 * <math>H</math> = The [[Culvert diameter (Water Overlay)|CULVERT_RECTANGULAR_HEIGHT]] attribute of the culvert, representing the inside height of a rectangular culvert.
+* <math>h_f</math> = The (flow) height of the water inside the culvert.
 * <math>T_c</math> = The [[Culvert threshold (Water Overlay)|CULVERT_THRESHOLD]] attribute of the culvert.
 * <math>B_c</math> = The [[Terrain height (Water Overlay)|surface height]] of the base of the culvert.
 * <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</math> = The water height inside the culvert.
 * <math>R_h</math> = The hydraulic radius in the culvert<ref name="hydradius"/>.
 * <math>R_w</math> = The wetted perimeter.

Culvert formula (Water Overlay): Difference between revisions

Revision as of 08:53, 9 October 2020

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