--- title: "Flash and urban floods monitoring | Nexus Observatory" description: "A flash flood or a flooded street gives minutes, not hours. Rain gauges, depth sensors in streets and culverts and cameras at known flood points report…" url: https://observatory.global/industries/public-safety/flash-floods/ publisher: Nexus Observatory Inc. updated: 2026-11-02 --- [Nexus Observatory](https://observatory.global/) / [Public safety](https://observatory.global/industries/public-safety/) / [Specialized fields](https://observatory.global/industries/public-safety/fields/) / **Flash and urban floods** # Flash floods, warned in the minutes they allow. A flash flood or a flooded street gives minutes, not hours. Rain gauges, depth sensors in streets and culverts and cameras at known flood points report to one record the city and the emergency services act on, and warnings go out through the authority's own channels. [Plan a deployment](https://observatory.global/contact/deployment/) How it works [Station Builder](https://observatory.global/studio/builder/) **Industry**: Public safety **Measurements**: 5 **Sources cited**: 5 1. Public safety · Flash and urban floods Minutes, not hours A storm cell parks over a city and an underpass fills before the drains can take the water. A small stream rises faster than any river forecast can follow. Depth sensors at the places that flood, and rain gauges above them, give the minutes a road closure or a warning needs. 2. What is measured Rain, depth and levels Rain gauges across the city measure intensity. Ultrasonic or radar sensors on poles measure water depth at underpasses and dips, level sensors watch culvert inlets and small streams, and cameras confirm what the numbers show when an alarm sounds. Every reading names its street and point. InstrumentsRain gauges · Street depth sensors · Culvert levels · Cameras 3. The base node Faster as the water rises Each endpoint sleeps between readings until water appears, then reports faster. The gateway's node compares depths with the city's thresholds, raises alarms with images at once and keeps every value signed, so the review after the storm has the whole event. 4. Radio and links LoRaWAN on the streets Battery sensors on street poles reach a gateway on a high building over LoRaWAN, with no cabling and years on a battery. Gateways reach the operations centre over cellular, with a satellite path at the centre for when terrestrial networks fail. LinksLoRaWAN · Public cellular · Satellite 5. How it works From water in an underpass to a closed road A depth sensor sees water in an underpass and starts reporting faster. The gateway's node sees the depth cross the closure threshold, raises the alarm with an image to the operations centre, and the road is closed. The authority warns, and the record keeps every step. 6. From order to operation · Order Scope the flood points and the warning The scope reads the flood risk plan, the history of flooded streets and underpasses, existing gauges and the city's warning procedures. Nexus Observatory Inc. returns the flood point plan, the radio design, the integration with operations and warning systems and a price per point and per service. [Plan a deployment](https://observatory.global/contact/deployment/) 7. From order to operation · Survey Walk the low points Crews walk known flood points with the city's engineers: underpasses, dips, culvert inlets and streams. They choose poles above the highest recorded water, check gateway coverage from high buildings and note where cameras can see the water without filming homes. 8. From order to operation · Permits Poles, streets and privacy Sensors on street poles need the owner's consent; cameras follow the city's privacy rules. Warning roles are agreed in writing, so the authority that warns decides. Every consent is kept with the point it covers. Residents near cameras are told what is measured and why. 9. From order to operation · Build Build for the street Depth and level sensors, endpoints, gauges and gateways are built, tested together and enrolled with their identities. Thresholds come from the city's warning plan, and every part is labelled with the street and the point it serves. Spares are kept at the depot for quick swaps after storms. [Open the Station Builder](https://observatory.global/studio/builder/) 10. From order to operation · Install Install between storms Crews mount sensors on poles above the flood level and set their reference to the road surface, install rain gauges on rooftops clear of obstructions and gateways on high buildings. Every point is photographed and located for the record. Each sensor’s height above the road is measured and kept. 11. From order to operation · Commission Test thresholds with the city Each endpoint proves its identity. Depth readings are checked against a measured reference, rain gauges with a measured volume, and alarms are tested to the operations centre and the warning authority with a staged threshold crossing. Each point joins the live map only when its checks pass. 12. From order to operation · Operate Close, clear and warn on evidence Operators see rain and water depth across the city as a storm arrives. Underpasses are closed when depth crosses the threshold, crews clear blocked culverts, and the authority issues warnings through its own channels. Every event is reviewed afterwards with the record. 13. From order to operation · Maintain Check after every storm After each storm, points are checked for debris and damage; references are rechecked yearly and after road works; batteries are changed on plan. Every change is recorded, so thresholds stay true to the street. Sensors damaged in a flood are replaced first, because the next storm may come soon. [Book field services](https://observatory.global/contact/field-service/) 14. Data products For operators, crews and planners City operations and road authorities receive depth alarms; meteorological services and engineers receive rain intensity; drainage teams receive culvert and stream levels; flood risk planners and insurers receive event records. Each product carries its reference and siting. Event records are kept for the review after every storm. [See the data products](https://observatory.global/data-products/) 15. Evidence Every storm reviewed Every reading, alarm, closure and warning is signed and kept. Measurements follow WMO practice, flood management follows the floods directive, warnings follow the multi-hazard early warning checklist and travel in the Common Alerting Protocol, so each event can be reviewed and thresholds improved. Drawn againstWMO-No. 8 · Directive 2007/60/EC · WMO early warning checklist · Common Alerting Protocol 16. What you get Hydrometeorological and flood observing networks Stream gauges, rain gauges, weather radar and automatic weather stations built to WMO practice, reporting through WIS 2.0 where the agency requires it. Delivered as hardware + software, managed service and build-operate-transfer, for national meteorological and hydrological services, river-basin agencies, utilities. [Talk to sales](https://observatory.global/contact/sales-enquiry/) 17. Next step Plan flash and urban floods with us Tell us the site, the measurements and the rules it answers to. We reply with a survey proposal, a design and a scope for flash and urban floods. An engineer replies with a survey proposal and a scope, and the plan grows from one site to the network you need, at your pace. [Plan a deployment](https://observatory.global/contact/deployment/) [Open the Station Builder](https://observatory.global/studio/builder/) [Open the Studio](https://observatory.global/studio/) **01** The place and its hazards ## Where it runs, and what can go wrong. Operating contextIntense rain on steep small catchments and on paved cities floods streets, underpasses and streams within minutes, faster than river forecasting can follow. Cities, road authorities and emergency services close roads, open drains and warn people, and flood risk plans set out who does what. Hazards - Underpasses and streets flooding within minutes - Vehicles and people swept away in small streams - Blocked culverts and drains - Sensor loss in the flood itself - Warnings that arrive after the water **02** What must be measured ## What, where, how often, and under which rules. Each measurement names where it is taken, how often, and the public standard or regulation behind it. Numbers in the sources column open the cited source below. | Measurement | Where | Cadence | Sources | | --- | --- | --- | --- | | Rainfall intensity | Gauges across the city and small catchments | Continuous, reported at short intervals | 1 | | Water depth in streets and underpasses | Ultrasonic or radar sensors on poles at known flood points | Continuous, faster when water appears | 2 | | Level in culverts and small streams | Culvert inlets and stream sections | Continuous | 3 | | Visual confirmation | Cameras at flood points | Images on alarm | 2 | | Warnings issued | The authority's warning channels | Each event | 45 | **03** The observation stack ## From one base unit to a network. The same blocks at every scale: instruments and a base node, a site with its radio, a fleet run as one, and a network federated on the open protocol. 1. **01** Base unit A flood point: a depth or level sensor on a LoRaWAN endpoint that signs every value, on a street pole above the water. [Build a station →](https://observatory.global/studio/builder/) 2. **02** Site A district: flood points, rain gauges and a gateway on a high building with a cellular link. [Plan a site →](https://observatory.global/contact/deployment/) 3. **03** Fleet Every flood point of a city run as one fleet, with one record. [Managed offers →](https://observatory.global/industries/public-safety/solutions/) 4. **04** Network Cities, road authorities, emergency services and meteorological services exchange levels and warnings through open standards. [The open protocol →](https://observatory.global/protocol/) - **01** Water level gauge - **02** Compact weather station - **03** LPWAN endpoint - **04** LoRaWAN gateway - **05** Cellular modem/router - **06** Battery case - **07** Pole Radio and links ### LoRaWAN Battery sensors on street poles reach a gateway on a high building, with no cabling and years on a battery. Radio and links ### Public cellular Gateways reach the operations centre over cellular, with a second operator where the city requires it. Radio and links ### Satellite A satellite path at the operations centre's gateway keeps alarms moving when terrestrial networks fail. Edge computeEach sensor reports faster when water appears; the gateway's node compares depths with thresholds set by the city and raises alarms with images at once. PowerFlood points run on long-life batteries; gateways on building power with a battery. **04** How it works ## From the instrument to the product. One observation's path, tier by tier, with the interface on every link and a bill of materials below; then how the one node grows to a site, a fleet and federated networks. Flash and urban floods: data path – of 07 01 Instruments Measurement with sensor identity andcalibration 02 Field radio 03 Gateway 04 Backhaul 05 Site Consumer inbox deduplicates and applieseach record once into governed data 06 Data store Governed product through API, map orexport, correction-aware 07 Products Common Alerting ProtocolOGC SensorThings APILoRaWAN 08 Power and structure Supplies 12 V DC to the field equipment 01 Water level gauge SDI-12 · RS-485 · Ethernet 02 Compact weather station SDI-12 · RS-485 · Ethernet 03 LPWAN endpoint Analogue I/O · SDI-12 · RS-485 04 LoRaWAN gateway Ethernet · RF · GNSS antenna 05 Cellular modem/router Ethernet · USB · RS-232 Site MQTT 5 with Sparkplug B Governed data store Versioned, correction-aware Street and underpass depth alarms Rain intensity across the city Culvert and stream levels Event records 06 Battery case USB 07 Pole SDI-12 SDI-12 LoRaWAN Ethernet LTE/NR From the instrument to the published product: each band is a tier, each connector names its interface, and the numbers match the bill of materials. Hover or focus a block to trace its path; scroll or step to follow one observation. | Item | Equipment | Data ports | Protocols | Power in | | --- | --- | --- | --- | --- | | 01 | **Water level gauge** Radar, pressure or float gauge for river, lake, reservoir or tide level. | SDI-12RS-485Ethernet | SDI-12, Modbus, MQTT 5, OGC SensorThings API | 12 V DC | | 02 | **Compact weather station** All-in-one or compact station for temperature, humidity, pressure, wind and rain at a site. | SDI-12RS-485Ethernet | SDI-12, Modbus, MQTT 5, OGC SensorThings API | 12 V DC | | 03 | **LPWAN endpoint** Battery-powered endpoint on LoRaWAN, NB-IoT or LTE-M that carries one or more sensors. | Analogue I/OSDI-12RS-485 | LoRaWAN, OMA LwM2M, CoAP | Internal battery, Energy harvesting | | 04 | **LoRaWAN gateway** Multi-channel LoRaWAN gateway that forwards uplinks to a network server and schedules downlinks within duty limits. | EthernetRFGNSS antenna | LoRaWAN, MQTT 5 | PoE, 12 V DC | | 05 | **Cellular modem/router** LTE or NR modem or router that uses a public carrier or private network as backhaul. | EthernetUSBRS-232 | 3GPP E-UTRA air interface, 3GPP NR air interface, OMA LwM2M | 12 V DC, PoE | | 06 | **Battery case** Portable battery pack with DC outputs for field kits. | USB | Modbus | AC mains, HV DC, USB PD | | 07 | **Pole** Utility, street or dedicated pole with clamp positions. | — | — | — | How it scales 01 Instruments Arbitrary qualified sensors and instruments whosemeasurements are ingested with calibration, units,geometry, time, custody and uncertainty. ×n 02 Node The minimum useful deployable unit: server, ruggedappliance, radio node, sensor gateway, satelliteterminal, AI, scientific, vehicle or virtual node. Node Node agent 03 Site The minimum independently operable localgovernance and failure domain: one or more nodesplus local network, identity, policy, evidence,storage, products and operator surfaces. SITE Node Node Node ×n 04 Cluster An optional scale or specialisation domain forscheduling, shared storage, accelerators or datalocality. CLUSTER ×n 05 Fleet Coordinates plans, acknowledgements,convergence evidence, update campaigns andcorrection propagation across nodes and sites. FLEET Fleet controller ×n 06 Federation An exchange of products, capabilities, events orwork across approved, independently administeredtrust domains, using explicit trust, policy,data-locality, version and correction contracts. TRUST DOMAIN TRUST DOMAIN TRUST DOMAIN ×n Verifier Applications Data in the field Telemetry Control Data upstream Control Data upstream Control Exchange Evidence Events Exchange The smallest deployable unit is one node; the same unit is replicated to meet the demand. Nodes form a site, sites may form a cluster, sites and clusters are coordinated as a fleet, and fleets exchange across independently administered trust domains. Each plane is a separate channel with its own open binding. **Data in the field**: MQTT 5 with Sparkplug B; connectors for LoRaWAN, OPC UA and instrument buses. **Telemetry**: OpenTelemetry OTLP. **Control**: TLS 1.3 with mutual authentication; protobuf messages over gRPC or HTTP/2. **Data upstream**: At-least-once publication with repeat-safe keys over the control channel or NATS JetStream; QUIC MAY be used on lossy links. **Evidence**: DSSE-signed in-toto statements; SLSA provenance; SCITT transparency receipts. **Events**: Event envelopes mapped to CloudEvents 1.0; channels described in AsyncAPI 3. **Exchange**: OpenAPI 3.1; the OGC API family; SensorThings; STAC; WIS 2.0. **05** From order to operation ## Every step, from the first call to a running site. The same crew and the same record carry the work from scope to maintenance. 1. 01 Order Scope the flood points and the warning The scope reads the flood risk plan, the history of flooded streets and underpasses, existing gauges and the city's warning procedures. Nexus Observatory Inc. returns the flood point plan, the radio design, the integration with operations and warning systems and a price per point and per service. 2 2. 02 Survey Walk the low points Crews walk known flood points with the city's engineers: underpasses, dips, culvert inlets and streams. They choose poles above the highest recorded water, check gateway coverage from high buildings and note where cameras can see the water without filming homes. 3. 03 Permits Poles, streets and privacy Sensors on street poles need the owner's consent; cameras follow the city's privacy rules. Warning roles are agreed in writing, so the authority that warns decides. Every consent is kept with the point it covers. Residents near cameras are told what is measured and why. 4. 04 Build Build for the street Depth and level sensors, endpoints, gauges and gateways are built, tested together and enrolled with their identities. Thresholds come from the city's warning plan, and every part is labelled with the street and the point it serves. Spares are kept at the depot for quick swaps after storms. 5. 05 Install Install between storms Crews mount sensors on poles above the flood level and set their reference to the road surface, install rain gauges on rooftops clear of obstructions and gateways on high buildings. Every point is photographed and located for the record. Each sensor’s height above the road is measured and kept. 1 6. 06 Commission Test thresholds with the city Each endpoint proves its identity. Depth readings are checked against a measured reference, rain gauges with a measured volume, and alarms are tested to the operations centre and the warning authority with a staged threshold crossing. Each point joins the live map only when its checks pass. 4 7. 07 Operate Close, clear and warn on evidence Operators see rain and water depth across the city as a storm arrives. Underpasses are closed when depth crosses the threshold, crews clear blocked culverts, and the authority issues warnings through its own channels. Every event is reviewed afterwards with the record. 5 8. 08 Maintain Check after every storm After each storm, points are checked for debris and damage; references are rechecked yearly and after road works; batteries are changed on plan. Every change is recorded, so thresholds stay true to the street. Sensors damaged in a flood are replaced first, because the next storm may come soon. **06** Data products and integration ## What it delivers, to whom, and into which systems. Data products - **Street and underpass depth alarms** City operations and road authorities - **Rain intensity across the city** Meteorological services and engineers - **Culvert and stream levels** Drainage teams - **Event records** Flood risk planners and insurers Integration - **City operations** Alarms with images reach the operations centre's screens and road closure procedures. - **Warning systems** The authority issues warnings in the Common Alerting Protocol from its own system. - **Drainage asset management** Culvert events open work orders for clearing. Exchanged through Common Alerting Protocol, OGC SensorThings API, LoRaWAN. **07** Questions buyers ask ## Before you scope it. Who warns the public? The warning authority, through its own channels; the network supplies the evidence. Will sensors survive the flood? They are mounted above recorded water and keep their data through any lost link. Do cameras film people? Cameras are aimed at the water and follow the city's privacy rules. How fast are alarms? Sensors report faster as water rises, and alarms are raised by the gateway at once. **08** Resources ## The sources behind this page. Public standards, regulations and guidance, cited where they apply. Each applies only where its jurisdiction or scope does. 1. **1** [Guide to Instruments and Methods of Observation (WMO-No. 8)](https://library.wmo.int/) World Meteorological Organization 2. **2** [Directive 2007/60/EC on the assessment and management of flood risks](https://eur-lex.europa.eu/) European Union · 2007 3. **3** [Guide to Hydrological Practices (WMO-No. 168)](https://library.wmo.int/) World Meteorological Organization 4. **4** [Common Alerting Protocol Version 1.2](https://www.oasis-open.org/) OASIS 5. **5** [Multi-hazard Early Warning Systems: A Checklist](https://library.wmo.int/) World Meteorological Organization · 2018 **09** Related ## Use cases and solutions. [Use case Street flood observatoryUltrasonic depth sensors on poles report street-level water depth as open data and alerts.The full use case →](https://observatory.global/use-cases/street-flood/) [Solution Hydrometeorological and flood observing networksStream gauges, rain gauges, weather radar and automatic weather stations built to WMO practice, reporting through WIS 2.0 where the agency requires it.Solutions for public safety →](https://observatory.global/industries/public-safety/solutions/#hydromet-networks) [Solution Municipal sensing and connectivity layersCity-wide LPWAN or private 5G as a shared layer for public sensors and services.Solutions for public safety →](https://observatory.global/industries/public-safety/solutions/#municipal-connectivity) **10** Public safety: specialized fields ## Other fields of this industry. [Specialized field Wildfire detection and responseSmoke detection from towers, fire weather and danger, thermal confirmation and satellite hotspots, on microwave and satellite to the fire agency's dispatch, so a start is seen in minutes.The full field →](https://observatory.global/industries/public-safety/wildfire/) [Specialized field Landslides and debris flowsGround movement by GNSS, pore pressure and rainfall thresholds, ground vibration for debris flows, on LoRaWAN and satellite from unstable slopes to the agency that warns and closes roads.The full field →](https://observatory.global/industries/public-safety/landslides/) [Specialized field Earthquakes and early warningStrong-motion and broadband seismometers, GNSS for large events, structural response in key buildings, on fibre and cellular with timing that lets a warning outrun the shaking.The full field →](https://observatory.global/industries/public-safety/earthquakes/) [Specialized field Avalanches and mountain roadsSnow and weather on the slopes, avalanche detection by radar and infrasound, cameras on the paths, on microwave and satellite to the road and the avalanche service, so roads close before the snow comes down.The full field →](https://observatory.global/industries/public-safety/avalanches/) [Specialized field Incident response and deployable networksA network that arrives with the crews: cell on wheels, satellite, mesh, drones, gas and thermal sensing at the scene, so incident command sees and talks when local networks are down.The full field →](https://observatory.global/industries/public-safety/incident-response/) ### Bring us the site. 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