Smart Reservoir · Interactive concept

What if rooftops joined in?

Explore how a small share of roofs could hold back rainwater across a dense Vienna neighborhood.

1 km² reference neighborhood36% roof coverage
A neighborhood of rooftop symbols with participating roofs highlighted The blue roof symbols represent connected rooftop area, and the shared blue tank gauge represents total retained water across all tanks, not a single physical tank. ALL TANKS COMBINED 0% of installed tank space
Connected roofs Other roofs360 connectedEach illustrated roof = 1% of total roof area, not one building.
10%
Conservative deployment scenarioA cautious starting assumption
Assumes 100 m² per equivalent rooftop; maximum is 1,800 rooftops. Labels are scenarios, not measured technical eligibility or adoption forecasts.
0 mm150 mm

P90: 90% of measured rainy days (rain > 0 mm) in our central Vienna April–September 2025–2026 hourly INCA sample had daily totals at or below 11.47 mm. It is not a design-storm threshold.

Roof rainwater temporarily kept out of sewers
1,440 m³
Across 360 connected rooftops during this event.
Without tanks · roof runoff18,000 m³
With tanks · roof runoff16,560 m³
Less runoff from all neighborhood roofs8.0%
Share of all rain falling on 1 km²2.9%

What this tells us — and what it doesn't

These volumes cover rooftop runoff only, not streets, gardens or other surfaces. For comparison we assume all roof rain reaches the combined sewer without tanks. We assume tanks are empty at the start of this event, collect 80% of rain falling on connected roofs, and hold up to 10 m³ per 100 m² roof.

No overflow or treatment-plant benefit is claimed. We do not yet have local sewer capacity or flow timing; storage reduces storm inflow, but that does not automatically mean an overflow was prevented.

Where the reference numbers come from
  • 1 km²: selected hypothetical neighborhood area, not a measured sewer catchment.
  • 36% roof coverage: rounded from the City of Vienna's 2010 MA 22 survey of Rudolfsheim-Fünfhaus (36.07% across the district). Not a current measurement for a particular 1 km² site. Official report, p. 33.
  • P90 11.47 mm: calculated from 167 days with rainfall > 0 mm across April–September 2025 and 2026 at one central Vienna INCA observation point. This is a historical sample, not an official Vienna-wide 90th percentile.
  • 100 m² roof, 80% collection, 10 m³ capacity: hypothetical system-design assumptions, not field measurements.
  • 0–50% connected roof area: a scenario exploration range, with 10% called conservative, 25% ambitious and 50% highly optimistic. These labels are illustrative; technical roof eligibility and actual adoption have not been established.
  • Single-event model: no controlled drainage during the event. Over multi-day storms, results can differ if network capacity allows pre-release between rain pulses.

Educational concept · No connection to Wien Kanal telemetry · No guarantee of flood prevention or combined sewer overflow reduction. Offline-capable once downloaded.