Layton City Flooded #CitiesSkylines

City suffers from first major flood


If you have the Rainfall Mod for Cities Skylines what was just cosmetic rain for visual effects now gives real consequences depending how much falls into your City.

This means you have to build a storm water system so that the rain can drain away from your city unless you want the water pooling up after every shower. So you have your inlets for the surface water which drains into the pipes. From there it has to be disposed through one of three options:

  1. Detention Basins (soak holes that allow the rain to soak into the ground)
  2. Gravity outlets (speaks for itself when discharging water in waterways)
  3. Storm pumps (electric-powered pumps that discharge water into waterways meaning gravity is not an issue proving you have power)


I run a two tiered drainage system where storm water is first collected via the inlets into the detention basins scattered throughout the City. Once the basins hit 80% full the storm pumps kick in forcing water out and into the waterways either being a river, harbour or the canal system built-in Layton City.


The Rainfall Mod is set to the south-west Pacific which means it mimics Auckland’s weather. Providing the rain intensity does not go above 4.0mm/hour Layton City’s storm water system handles the rain events very well with localised pooling in a few dips and troughs.

However, a 1-in-100 rain event finally happened where the rain intensity hit 4.6mm/hour. In other words the game threw cats, dogs, monkeys and several kitchen sinks worth of rain in a very short time. For the first time we had city-wide flooding as well as the canal system running in flood mode.


This slideshow requires JavaScript.


The white flood bubbles mean the area is flooding. This always happens in any rain event and will not disrupt the City. It is when you get the red flood bubble that the area is flooded and services become disrupted.

As I said earlier the system is designed to handle intensities of up to 4.0mm/h without overwhelming the inlets (and not all the pumps going into operation). But in this storm event pictured above we had hit 4.6mm/hour for three of the eight hours the storm occurred.



By the end of the third hour of the most intense rainfall all the storm water pumps were actively discharging the water into the canals and the river. And while the river coped the canal for the first time breached its walls (with all those pumps discharging water into it) and had started running up the flood walls either side. The flood waters reached up about 20% of the wall height so there was still capacity spare through the emergency flood systems.

As for the City around 33% of the City was under the red flood bubbles meaning the areas were under water disrupting services and forcing evacuation (citizens abandon the building). Simply put the inlets could not cope with the intensity of rain with 2,500 people “evacuated” out the City. Once the storm had settled back down it took another two hours for the flood waters to clear and the canals to settle (as you need the pumps to stop discharging). The evacuees came back and everything returned to normal not long after all.


In the end it was a very sobering exercise watching the City struggle with a 1 in 100 year storm event. Some more inlets will need to be built as well as a few more detention basins to help handle the flows. However, the emergency systems worked well with the canal system handling the floodwaters within expectations. Because if the canals had failed more than 33% of the City would have been a lake!