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Spilling Nodes

Any manhole or basin can be defined as 'spilling'. If the water level in a node defined as a spilling node reaches the ground level, the water will start spilling irreversibly out of the system. The flow will be computed using the free overflow formula, according to the following:

\[ \text{for } H \leq \left(H_{gl} + \Delta P\right): \quad Q_{spill} = 0; \qquad \text{for } H > \left(H_{gl} + \Delta P\right): \quad Q_{spill} = \text{Relative Weir Coefficient} \cdot 0.63 \cdot B \cdot \sqrt{2g} \cdot \left(H - \left(H_{gl} + \Delta P\right)\right)^{3/2} \]

Equation: Spill discharge from a spilling cover, zero below the buffer pressure level and a weir formula above it.

where:

  • Qspill — the spill discharge [m3/s]
  • B — a conceptual spill width [m]
  • H~~ — the water level in the manhole [m]
  • Hgl — the ground level in the manhole [m]
  • DP — the “Buffer Pressure Level” for the spill [m]
  • g — the acceleration of gravity [ms-2) RelativeWeirCoefficient = the linear scaling coefficient for the spill.

The level (i.e. head) at which the spill starts can be controlled by optionally specifying the 'Buffer Pressure Level' as a relative elevation above (or below) the ground surface (default value = 0).

For circular manholes, the spill width B equals to 1.5 times the manhole diameter for the water level H = Hgl+DP. With increasing water level, the spill width B increases, following the same functional relation as used for the area above expanding nodes (i.e. increases exponentially to approximately Max. 1000 times the manhole diameter), see Section A.4.1.

The spilling capacity of a spilling manhole can be controlled by specifying the Relative Weir Coefficient (default value = 1).