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The water level in the entrance tank is designed to meet requirements for rapid mix, as well as head loss due to flow from the entrance tank to the flocculator. These variables can be found in the Rapid Mix, Flocculation, Sedimentation Inlet Slopes, and User Inputs design programs.

{latex}
\large
$$
HW_{EtTotal}  = HW_{EtMax}  + HL_{FlocEntryOrifice}  + HL_{Floc}  + HW_{Sed}  + HW_{EtWaterFall}  + HW_{EtChannel}
$$
{latex}

{latex}
\large
$$
HW_{EtMax} = HW_{EtMin} + HL_{Lfom}
$$
{latex}

The height of the entrance channel is based on the elevation of the tank and providing a distance of two pipe diameters beneath the tank, along with room for a pipe radius and thickness of concrete. The tank's base does not need to extend to the base of the flocculator. Because it can be elevated, the flocculator can be dug into the ground and less concrete needs to be poured.

{latex}
\large
$$
H_{Et}  = Z_{Et} - H_{Sed} - H_{InletChannel} + H_{SedWeirExit} + 2*ND_{RMPipe}
$$
{latex}

The length of the entrance tank (L.Et) is the square root of the entrance tank area, which is determined from plant flow rate and required up-flow velocity through the entrance tank. The width of the entrance tank is chosen so that it meets the geometry requirements, as well as the width required for rapid mix. In the Rapid Mix, the width of the entrance channel needs to be at least the the spacing between the floc baffles in the first channel (S.FlocBaffle0).

{latex}
\large
$$
W_{Et}  = \max \left( {{{A_{Et} } \over {L_{Et} }},W_{EtChannel} } \right)
$$
{latex}

Rapid Mixer

The rapid mix system is designed to mix the alum and raw water on both the macro and micro-mixing scale.

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