Nodes & Pipes Reference

This section details the physical parameters available for standard manholes (Nodes) and conduits (Pipes) within the platform.

Nodes (Manholes & Chambers)

Nodes represent junctions, changes in pipe direction, changes in pipe diameter, or physical inspection chambers.

• Cover Level (m): The absolute elevation of the ground surface at the node location. If the hydraulic grade line exceeds this level, flooding occurs.
• Invert Level (m): The absolute elevation of the bottom of the chamber. This forms the base elevation for the outgoing pipe.
• Chamber Size (mm): The physical diameter of the manhole ring. While rarely critical for basic hydraulics, it is vital for accurate bill of quantities and ensuring sufficient physical space for multiple incoming pipes.
• Catchment Area (ha): The impermeable area draining directly into this node. Rainfall falling on this area will generate runoff according to the Volumetric Runoff Coefficient ($C_v$).
• Additional Catchment Area (ha): An optional field to manually input extra area, typically used to enforce "Urban Creep" allowances (e.g., adding 10% to account for future paving) without altering the base CAD-measured area.

Outfall Types

The final node in any network must be an Outfall.

• Free: Discharges unimpeded into an empty water body.
• Surcharged (Fixed Depth): Discharges into a water body with a constant water level (e.g., a static lake). The engine maintains a constant head boundary condition based on the specified Depth above Invert.
• Variable Stage / Tidal: Discharges into a water body with a fluctuating level. You can define a continuous sine-wave tide (by specifying minimum and maximum tidal levels) or upload a custom Time-Depth curve to simulate river flood hydrographs.

Pipes (Conduits)

Pipes represent the physical conduits transporting water between nodes. The platform assumes circular cross-sections for standard gravity pipes.

• Diameter (mm): The internal bore diameter of the pipe. Standard UK sizes (150, 225, 300, 450, etc.) should be used.
• Length (m): Automatically calculated based on the physical distance between nodes on the canvas. You can override this if the schematic length differs from the true length.
• Roughness ($k_s$): The Colebrook-White friction factor. A value of $0.6 mm$ is standard for modern concrete pipes. Plastic pipes may use lower values (e.g., $0.3 mm$), while old brick sewers may require significantly higher values ($3.0 mm +$).
• Slopes (1:X): Calculated dynamically using the formula: $Slope = Length / (StartInvert - EndInvert)$. Ensure your slopes meet self-cleansing velocity criteria (typically 1:150 for 150mm pipes).
• Flap Valve: A checkbox to install a non-return valve on the pipe. This prevents flow reversal (backflow), which is essential when discharging into a tidal outfall.