Branching points

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BlueM.Sim theory

Table of Contents

• Einleitung
• Modellierungstechnische Grundlagen
  • Begriffsdefinitionen
  • Programmstruktur und Datenhaltung
  • Bildung der Zuflussbelastung
  • Berechnungsreihenfolge
  • Simulation types
  • Time series management
• Hydrological Basics
  • Rural Catchments
    • Soil moisture calculation
    • SCS-Method
  • Urban Catchments
  • Individual discharges
  • Transport elements
  • Consumers
  • Branching points
  • Talsperren
    • Betriebsregelkonzept
    • Grundlegende Typen von Betriebsregeln
    • Grundsätze zur Beschreibung von Betriebsregeln
    • Umsetzung der Gesetzmäßigkeiten für die Simulation
    • Anwendung an einem Beispiel
  • Storm-water overflows
  • Regenüberlaufbecken
• Systemübergreifende hydrologische Methoden
  • Speicherbaustein
  • Systemzustände
    • Steuern und Regeln

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 Q_krit 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: [math]\displaystyle{ \mbox{Trennschaerfe} = \frac{Q_{ab}(Q_{zu}=5 \cdot Q_{krit})}{Q_{krit}} }[/math]

Abbildung 47: Definition selectivity parameter in BlueM

Percentage distribution (Option 2)

Independent of inflow a constant distribution into two outflows _ab1 and Q_ab2 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 Q_ab1 and inflow, which was derived through hydraulic calculations or operating instructions, is utilized as a polygon course. The second outflow Q_ab2 is calculated as the residual value of inflow - Q_ab1.