When rain crosses the network map
A fictional storm sends runoff towards a low railway cutting and nearby infrastructure. The city has separate stormwater and wastewater networks, but unwanted rainwater can enter its sewers. The chosen locations and impacts are illustrative; no rainfall threshold, flood forecast or public safety decision is calculated.
Start with the land surface
Rain reaches roofs, streets and planted ground before it reaches a network boundary. Hard surfaces can produce runoff that moves towards drains and lower areas. In our fictional district, part of that runoff heads towards a railway cutting. The amount and timing depend on rainfall, ground conditions and drainage. The drawing follows a possible connection across the landscape, not a measured flood extent.
Follow surface slopes across the edges of the water and railway diagrams.
A shared physical environment can connect infrastructure that separate service maps keep apart.
Read the complete journey
- 1Water
Start with the land surface
Rain reaches roofs, streets and planted ground before it reaches a network boundary. Hard surfaces can produce runoff that moves towards drains and lower areas. In our fictional district, part of that runoff heads towards a railway cutting. The amount and timing depend on rainfall, ground conditions and drainage. The drawing follows a possible connection across the landscape, not a measured flood extent.
Notice: Follow surface slopes across the edges of the water and railway diagrams.
Explore Stormwater & urban surfaces
Why: A shared physical environment can connect infrastructure that separate service maps keep apart. - 2Urban rail
Meet a drainage limit
In our selected event, incoming water exceeds what the cutting's drainage can remove. Railway drainage depends on connected flow paths and, where installed, pumping; its capacity is finite. Flooding can affect track support and equipment as well as the space a train occupies. This adds a water-management dependency to the railway, but it does not mean the railway drainage is part of the drinking-water supply.
Notice: Compare incoming water with the available drainage route and the equipment exposed beside it.
Explore Drainage and flood resilience
Why: A transport service can be constrained by a water flow that is outside its passenger route. - 3Electricity
Add a local electrical consequence
We now assume that equipment serving this railway section is affected and its supply becomes unavailable. Floodwater can damage railway power equipment, but the result depends on location, protection and design. This is a chosen consequence, not a rule that rain causes an area-wide blackout. It creates an additional constraint alongside the water on the railway, so removing only one problem may leave the other unresolved.
Notice: Keep the water-affected route and its unavailable electrical supply as two separate conditions.
Explore Substations & protection
Why: One event can create several constraints that require different evidence of recovery. - 4Internet
Question whether two paths are independent
The city diagram offers two possible communications paths. For this teaching example, both pass through equipment exposed to the same flooded area. Two logical lines therefore do not guarantee an unaffected alternative. Real service depends on physical routing, power, network policy and available capacity. A common hazard can affect multiple paths at once, even when a simplified internet drawing makes them look separate.
Notice: Overlay the two logical paths on their shared physical exposure in this example.
Explore Network interconnection
Why: Redundancy helps only to the extent that usable alternatives survive the relevant event. - 5Water
Follow the water that enters the wrong network
Our city's sanitary sewers are separate from storm drains, yet rainwater can enter through infiltration or unwanted connections. Extra inflow can increase the load on collection and treatment facilities. Combined sewer systems intentionally receive both sewage and runoff, but that is a different arrangement. The impact here depends on the amount entering, remaining capacity and support for pumps; no overflow is assumed solely because it is raining.
Notice: Distinguish intended stormwater routes from unwanted entry into the separate wastewater network.
Explore Sewers & lift stations
Why: Network type and actual inflow matter more than a generic label such as 'city drains'. - 6Water
Distinguish a reading from the whole water system
Suppose the storm also changes conditions at the water source. Monitoring can help the utility detect unusual measurements and interpret them alongside treatment and sampling information. A single sensor does not identify every contaminant or certify the entire supply. In our scenario, an unavailable communications link could also leave a remote display without a fresh reading, making the age of the displayed information an important distinction.
Notice: Separate the measured value, its location and its timestamp from the wider condition of the supply.
Explore Water-quality sensing
Why: Knowing what was measured and when prevents missing information from looking like reassurance. - 7Urban rail
Communicate several different service states
The traveller receives a service update once an available communications path delivers it. The railway may still be disrupted even if that page is reachable, because access, track condition, power or train control can remain constrained. The update describes the transport situation; it does not remove those constraints. Our example separates the information channel from the service it reports, including the possibility that they recover at different times.
Notice: Compare successful delivery of an update with the railway status described inside it.
Explore Operations and recovery
Why: Communications recovery can improve understanding before transport recovery is complete. - 8Urban rail
Let the rain end without declaring recovery
When runoff subsides, the visible water may disappear before the railway is ready. Flooding can disturb track support and damage power or signalling equipment, so inspection and any necessary repairs still matter. Other city services have their own conditions to assess. This journey ends with several separate recovery questions, rather than treating clear weather or a dry-looking route as a universal return-to-service signal.
Notice: Look beyond the receding water to track support and the supporting equipment affected earlier.
Explore Track and support
Why: The end of a hazard is different from recovery of every service it affected.
Why might two network paths and a dry-looking railway still fail to establish that services have recovered?
Reveal the explanation
The two paths may share damaged equipment, power or the same physical exposure. A railway may retain damage or operating constraints after water recedes. The example requires evidence about the actual supporting paths and equipment, not just the number of lines or the disappearance of visible water.
Sources & further reading
Original explanations informed by these sources. Diagrams are conceptual; local systems differ.
- Infrastructure Resilience Planning Framework (IRPF) Cybersecurity and Infrastructure Security Agency (CISA) · 2025-03 · Source & rights record
- Stay connected in severe weather Ofcom · 2026-10-22 · Source & rights record
- Sources and Solutions: Stormwater US Environmental Protection Agency · Not stated · Source & rights record
- About Green Infrastructure US Environmental Protection Agency · 2026-09-11 · Source & rights record
- Municipal Wastewater US Environmental Protection Agency · Not stated · Source & rights record
- Primer for Municipal Wastewater Treatment Systems US Environmental Protection Agency · 2004-09 · Source & rights record
- Online Water Quality Monitoring in Distribution Systems US Environmental Protection Agency · 2018-04; second release 2019 · Source & rights record
- Water safety planning World Health Organization · Not stated · Source & rights record
- Flooding Network Rail · Not stated · Source & rights record
- Fourth Adaptation Report Network Rail · 2024-12 · Source & rights record
- Asset Management: Weather Resilience and Climate Change Adaptation Plan Network Rail · 2021-05 · Source & rights record
- How we keep you updated when there’s a delay Network Rail · Not stated · Source & rights record
- The Internet Way of Networking: Defining the critical properties of the Internet Internet Society · 2020-09-09 · Source & rights record
- RFC 4271: A Border Gateway Protocol 4 (BGP-4) IETF / RFC Editor; Y. Rekhter, T. Li, and S. Hares (editors) · 2006-01 · Source & rights record
Another way through the system.
One morning, four systems
Follow an ordinary commute through the services that make it possible.
One interruption, different clocks
Discover why dependent services do not all stop together.
Power is back. What else must recover?
Follow service restoration through several independent conditions.