Branching points

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Branching points serve the purpose of dividing an inflow into two outflows according to a certain distribution specification. Branching points can be an intake structure in rivers for water supply or irrigation purposes,forks in a sewer system, diversions of a part of the inflow or outflow of a dam, storm-water overflows etc..

There are three possible approaches to define the distribution specification.

Threshold model (Option 1)

Abbildung 47b: Outflow distribution using the threshold model approach.

According to the threshold model the second outflow (e.g. storm-water overflow: outlet pipe) is applied only after a critical inflow Qkrit has been reached, due to which the first outflow (e.g. storm-water overflow: throttle)backwater retention reaches the overflow crest. In reality a perfect distribution of the outflows after having reached the threshold value is usually not possible, therefore a selectivity can be specified for the structure to better represent real conditions.

The selectivity is defined as: $\displaystyle{ \mbox{Trennschaerfe} = \frac{Q_{ab}(Q_{zu}=5 \cdot Q_{krit})}{Q_{krit}} }$

Abbildung 47: Definition selectivity parameter in BlueM

Percentage distribution (Option 2)

Independent of inflow a constant distribution into two outflows ab1 and Qab2 according to a certain percentage ratio occurs. Here too, one has the option to influence the distribution through scaling.

Characteristic curve (Option 3)

A dependency between outflow Qab1 and inflow, which was derived through hydraulic calculations or operating instructions, is utilized as a polygon course. The second outflow Qab2 is calculated as the residual value of inflow - Qab1.