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The purpose if the inlet weir is to regulate the height of water in the inlet channel and flocculator. This is accomplished by a relation between the width of the weir and the head loss over the weir, which is governed by the equation:

{latex}
\large
$$
W = {3 \over 2}{Q \over {K_{VC} \sqrt {2g} H^{{3 \over 2}} }}
$$
{latex}

Where W is the width of the weir and H is the head loss over the weir. The weir can either be placed parallel or perpendicular to the length of the channel.

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The length of the channel is a function of the number of sedimentation tanks, and the thickness of the walls between the sedimentation tanks.

{latex}
\large
$$
L_{Channel} = (N_{SedTanks} )(W_{Sed} ) + (N_{SedTanks} + 1)(T_{PlantWall} )
$$
{latex}

The cross sectional area of the inlet channel on the side of the weir that delivers water to the inlet chimneys is determined using the A.Port function in Fluids Functions

{latex}
\large
$$
A_{InletChannel} = A_{Port} (Pi_{FlocDissipation} ,K_{LTurn90} ,Q_{Plant} ,ED_{SedInlet} ,Pi_{VenaContractaOrifice} )
$$
{latex}

Therefore the height of the water in the inlet channel is equal to the square root of the area of the channel.

{latex}
\large
$$
HW_{InletChannel} = \sqrt {A_{InletChannel} }
$$
{latex}

The first constraint for the width of the inlet channel on the side of the weir that delivers water to the chimneys is to consider the energy dissipation rate. The area of the inlet channel and the height of the water in the channel have already been calculated, and so the width may be determined:

{latex}
\large
$$
W_{InletChannelED}  = {{A_{InletChannel} } \over {HW_{InletChannel} }}
$$
{latex}

Next the size of the ports that take the flocculated water down into the inlet chimneys and to the sedimentation ports is calculated through the A.Port function in Fluids Functions.

{latex}
\large
$$
A_{SedManifoldEntrance} = A_{Port} (Pi_{FlocDissipation} ,K_{PipeEnt} ,Q_{SedManifold} ,ED_{SedInlet} ,Pi_{VenaContractaOrifice} )
$$
{latex}

The diameter of the hole that delivers the water from the inlet channel into the inlet chimneys is calculated using an array that loops through the available pipe size diameters and rounds the needed diameter up to the next available diameter through the function found in the Pipe Database.

{latex}
\large
$$
{D_{SedChimneyPipe}} = {D_{pipelarger}}\left( {2\sqrt {{{{A_{SedManifoldEntrance}}} \over \pi }} ,\left. {{D_{Pipesizes}}} \right)} \right.
$$
{latex}

The circular hole through the inlet chimneys must have at least 3 cm of space around it, and so the second constraint on the width of the inlet channel on the side of the weir that delivers the water to the chimneys is that it must be at least as wide as the diameter of this port, plus the 3 cm of space needed on each side of the port.

Therefore the width of the inlet channel on the side of the weir delivering water to the chimneys is set to be the maximum of the width determined by the allowable energy dissipation in the inlet channel, and the width needed by the circular port in the inlet chimney.

{latex}
\large
$$
{W_{InletChannelEst}} = \max \left( {{W_{InletChannelED}},\left. {{D_{SedChimneyPipe}} + 2{S_{SedInletChannelMin}}} \right)} \right.
$$
{latex}

The height of the inlet channel is equal to the water height in the inlet channel plus the plant freeboard height, so that the water is not at the very top of the channel.

{latex}
\large
$$
H_{InletChannel} = HW_{InletChannel} + H_{PlantFreeboard}
$$
{latex}

As mentioned earlier, the inlet channel weir will serve to regulate the height of the water in the inlet channel. On one side of the weir, the water is being delivered to the inlet chimneys. On the other side of the weir, water will go to waste when the sedimentation tanks are shut off. The width of this side of the weir is determined to be able to handle the flow in the case that all of the sedimentation tanks are shut off and all of the water must go to waste; it must be able to handle the entire flow rate of the plant.

To do this, the inlet channel must have a width that will yield a desired head loss. Taking advantage of the fact that head loss is proportional to the width of the channel, the width of the inlet channel on the side of the weir that delivers water to waste is determined through an iterative solution that compares the channels width and calculated head loss to a target head loss and then adjusts the width until the target head loss is reached. This algorithm can be found in Fluids Functions.

{latex}
\large
$$
W_{InletChannelWaste}  = w_{channel\min HL} (H_{SedWeirInlet} ,H_{SedWeirInlet} ,Q_{Plant} ,L_{Channel} ,Nu_{Water} ,E_{Concrete} ,1,HL_{SedWeir} )
$$
{latex}

The width of the entire inlet channel is now the sum of the width of the channel delivering water to the inlet chimneys, the thickness of the weir, and the width of the channel delivering water to waste:

{latex}
\large
$$
W_{InletChannel}  = W_{InletChannelEst}  + T_{SedWeir}  + W_{InletChannelWaste}
$$
{latex}

Stopping the Flow of Water into the Sedimentation Tank

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