Combined Sewer Overflow Simulator (2D Plan View)

Storm Controls

Rainfall intensity 0 mm/hr

Green infrastructure retention 0%

Interceptor capacity 1.50 m³/s

Live State

No overflow — within capacity

Combined flow Q

0.35 m³/s

Interceptor use

23%

CSO discharge

0.00 m³/s

CSO volume (event)

0 m³

BOD load discharged

0.0 kg

Storm elapsed

0 s

How it works

This is the 2D plan-view companion to the 3D Combined Sewer Overflow simulator: the same rational-method hydraulics, viewed from directly above the pipe network instead of in perspective. A combined sewer carries sanitary sewage and street stormwater in the same pipe. In dry weather an interceptor easily carries the flow to the treatment plant. During a storm, runoff is added on top — and if the combined flow exceeds the interceptor's fixed capacity, a regulator structure spills the excess, untreated, straight into the river through a CSO outfall.

Q_storm = C_eff · i · A / 360        (rational method, m³/s)
C_eff   = C_base · (1 − retention/100)
Q       = Q_dry + Q_storm            (combined flow)
CSO     = max(0, Q − Q_cap)          (overflow, m³/s)
Load    = CSO · 150 mg/L ≈ CSO · 0.15 kg BOD/s

i — rainfall intensity (mm/hr); A = 25 ha fixed catchment; C_base = 0.65 typical urban runoff coefficient.
Retention slider — permeable pavement, bioswales and rain gardens that intercept rain before it reaches the pipe, lowering C_eff.
Interceptor capacity — the fixed conveyance rating of the trunk sewer to the treatment plant; historically undersized in older combined systems.
Once Q exceeds Q_cap, the regulator diverts the excess — drawn as the reddish-brown stream leaving the outfall into the river, distinct from the blue treated-flow branch.
Drag the plan to pan, scroll (or pinch) to zoom — the schematic is drawn at true relative scale, so the catchment, interceptor chamber, treatment plant and river outfall keep their positions as you move around.

Real-world relevance: this is the same rational-method sizing and overflow-triggering logic used by cities (e.g. under the US EPA's CSO Control Policy) to plan interceptor upsizing, storage tunnels and green infrastructure to cut annual overflow events.

Rain / clean stormwater Sewage in combined flow CSO discharge to river

drag to pan · scroll to zoom