Application guide Water stress test for extreme rainfall

From Tygron Support wiki
Jump to navigation Jump to search

Application guide: Water stress test for extreme rainfall

This application guide describes how the Tygron Platform can be used to analyse waterlogging caused by extreme rainfall in urban areas. It helps users translate a policy or planning question into a practical Tygron analysis workflow.

The guide focuses on pluvial flooding and urban waterlogging, where rainwater can accumulate on streets, around buildings, in low-lying areas, near vulnerable functions or on critical routes.

This guide bridges policy questions and Tygron functionality. It does not replace the technical documentation for the Rainfall Overlay, Water Overlay or Water Module.

Purpose

The purpose of this guide is to support users who want to answer the following question:

Where does waterlogging occur during extreme rainfall, and which areas, objects or routes are vulnerable?

Typical follow-up questions are:

  • Which streets or neighbourhoods are most vulnerable to waterlogging?
  • Which buildings are affected at a chosen water-depth threshold?
  • Which roads become difficult or unsafe to use?
  • Which vulnerable functions, such as schools, healthcare facilities or public buildings, are affected?
  • Which measures reduce waterlogging most effectively?
  • How do current and future design scenarios compare?
  • What data is needed for an extreme rainfall analysis?
  • How can results be prepared for a risk dialogue or decision-making process?
  • When is specialist hydraulic, sewer or groundwater software needed?

Target audience

This guide is intended for:

  • policy officers for climate adaptation;
  • municipalities;
  • water authorities;
  • provinces;
  • consultants;
  • GIS specialists;
  • urban planners;
  • hydrologists and modelers;
  • project leaders for public space;
  • stakeholders preparing risk dialogues or climate adaptation plans.

When to use Tygron

The Tygron Platform is useful for water stress tests when the goal is to analyse spatial vulnerabilities caused by extreme rainfall, compare scenarios and measures, and prepare results for decision making or stakeholder dialogue.

The Rainfall Overlay is the main Tygron component for this application. It is a Water Overlay connected to the Water Module. Users can start from the Demo Rainfall Project, follow How to work with the Demo Rainfall Project, or configure their own model using How to manually configure a Water Overlay and How to configure the Water Overlays.

Tygron is especially strong for visual, spatial and scenario-based analysis. It helps users understand where water accumulates, which areas are vulnerable, and how measures affect the situation.

Tygron is less suitable as a full replacement for specialist hydraulic, sewer or groundwater modelling software when detailed calibration, design calculations or formal engineering verification are required. In many projects, Tygron works best alongside specialist software.

Suitable use cases

Tygron fits well when the question is about:

  • spatial analysis of waterlogging;
  • extreme rainfall scenarios;
  • water-depth maps;
  • scenario comparison;
  • measure exploration;
  • vulnerable buildings and objects;
  • road accessibility and critical routes;
  • neighbourhood-level water stress;
  • visualisation for stakeholders;
  • risk dialogue and decision support;
  • reproducible analysis workflows;
  • GIS export and reporting.

Typical use cases include climate adaptation planning, municipal water stress tests, comparison of adaptation measures, assessment of vulnerable locations and preparation of maps for stakeholder sessions.

Less suitable use cases

Tygron is less suitable when the question mainly concerns:

  • detailed sewer design;
  • deep multi-layered groundwater modelling;
  • detailed hydraulic structure design;
  • a prescribed external calculation protocol;
  • purely static reporting without spatial analysis;

Analysis framework

A water stress test for extreme rainfall can contain several sub-analyses. These sub-analyses should not be treated as completely separate workflows when they are actually extensions of the same underlying analysis.

For this Application Guide, the recommended structure is to work with a limited set of main analyses and describe possible extensions underneath each main analysis. This prevents overlap between related topics such as impacted buildings, vulnerable functions, damage indication and critical infrastructure.

The main analyses are:

  1. Water depth during extreme rainfall.
  2. Water on the surface, duration and recovery time.
  3. Accessibility and critical routes.
  4. Impact on buildings and vulnerable functions.
  5. Wadis, storage facilities and blue-green measures.
  6. Plans, measures and scenario comparison.
  7. Validation, uncertainty and model confidence.

1. Water depth during extreme rainfall

Core question:

Where does water occur on the surface during extreme rainfall, and how deep does it become?

This is the central analysis for a water stress test. It shows where water accumulates, which locations are most exposed and how severe the calculated water depth is.

Possible extensions include:

  • maximum water depth per scenario;
  • water-depth classes for viewer, map or risk dialogue;
  • comparison between rainfall events, such as 70 mm, 90 mm or long-duration rainfall;
  • technical control using result types such as Surface max value result type (Water Overlay) or related Water Overlay results;
  • comparison with national or regional stress-test maps;
  • identification of low-lying areas and local ponding locations.

Relevant Tygron components and links:

2. Water on the surface, duration and recovery time

Core question:

Where does water remain on the surface, and how long does it take before the area recovers?

This analysis extends the water-depth analysis by considering duration and recovery. A location with moderate water depth but long duration may still be relevant for nuisance, maintenance, accessibility or public-space use.

Possible extensions include:

  • duration of water on the surface;
  • duration of water on roads, squares, industrial areas or public spaces;
  • remaining water at the end of the simulation;
  • recovery time after the rainfall event;
  • duration classes, such as 0 to 5 minutes, 5 to 30 minutes, 30 to 60 minutes or more than 120 minutes;
  • validation with known waterlogging reports, photos, observations or local field knowledge.

Relevant Tygron components and links:

3. Accessibility and critical routes

Core question:

Which roads, routes or destinations become less accessible because of water on the surface?

This analysis combines water-depth and duration results with road data, critical routes or destination areas. It should include clear assumptions about which water-depth threshold is used for passability and for which road user this threshold applies.

Possible extensions include:

  • traffic nuisance on roads;
  • passability of main roads or exit routes;
  • accessibility of emergency services;
  • accessibility of vulnerable or critical destinations;
  • evacuation routes;
  • blocked roads based on water-depth thresholds;
  • route availability over time;
  • combination of water depth and duration.

Relevant Tygron components and links:

4. Impact on buildings and vulnerable functions

Core question:

Which buildings, objects and functions are affected by water on the surface?

This analysis combines water-depth results with buildings, vulnerable functions and critical infrastructure. It is broader than a simple count of affected buildings. It can include regular buildings, critical buildings and vulnerable objects that may not be represented as standard buildings in the source data.

Possible extensions include:

  • impacted buildings;
  • critical buildings;
  • vulnerable functions;
  • public buildings;
  • schools and healthcare facilities;
  • shelters and municipal buildings;
  • electricity assets, transformer stations and battery storage;
  • pumping stations;
  • telecom facilities;
  • utility assets;
  • threshold heights per building type;
  • impact range around buildings;
  • asset-specific vulnerability;
  • damage indication, if suitable thresholds, fragility curves or local assumptions are available.

Relevant Tygron components and links:

5. Wadis, storage facilities and blue-green measures

Core question:

How do wadis, storage facilities and blue-green measures function during and after the rainfall event?

This analysis focuses on the behaviour and reusability of local water-storage and infiltration facilities. It can be used both for existing facilities and for proposed climate adaptation measures.

Possible extensions include:

  • emptying time of wadis;
  • reusability after a dry period;
  • remaining water at the end of the simulation;
  • maximum water level or maximum load of a storage facility;
  • contribution of blue-green infrastructure;
  • effect of local infiltration capacity;
  • role of overflow structures, drains, pumps or inlets;
  • locations with potential for additional storage or infiltration.

Relevant Tygron components and links:

6. Plans, measures and scenario comparison

Core question:

What changes when a future plan, measure or scenario is calculated?

This analysis compares the current situation with plans, measures or future scenarios. It can reuse the same result types as the base analysis, but compares the results between variants.

Possible extensions include:

  • comparison between current and future situations;
  • terrain changes;
  • additional storage;
  • greening or removal of paved surfaces;
  • wadi or retention measures;
  • effect on water depth;
  • effect on duration;
  • effect on affected buildings and vulnerable functions;
  • effect on accessibility and critical routes;
  • prioritisation of measures;
  • export of difference maps or statistics.

Relevant Tygron components and links:

7. Validation, uncertainty and model confidence

Core question:

Are the results recognizable, plausible and useful for the intended application?

This analysis supports all other analyses. It is not always a separate viewer output, but it should be part of the workflow before results are used for communication, decisions or measure selection.

Possible extensions include:

  • validation with expert judgement;
  • validation with known waterlogging locations;
  • validation with reports, photos or field observations;
  • checking surface-flow directions;
  • checking vulnerable objects and critical routes;
  • checking data sources and model assumptions;
  • documenting uncertainty caused by missing or simplified data;
  • sensitivity to rainfall, infiltration, sewer assumptions, groundwater or grid size;
  • deciding whether specialist modelling is needed.

Relevant Tygron components and links:

Relation between main analyses and extensions

Some topics are best treated as extensions of a main analysis instead of separate analyses.

For example:

  • impact on vital and vulnerable functions is part of "Impact on buildings and vulnerable functions" when the question is whether objects are affected by water;
  • damage indication is an extension of building impact when thresholds or vulnerability assumptions are available;
  • accessibility of emergency services is an extension of "Accessibility and critical routes";
  • duration per road, square or neighbourhood is an extension of "Water on the surface, duration and recovery time";
  • blue-green infrastructure is part of "Wadis, storage facilities and blue-green measures" when the focus is on storage, infiltration or local adaptation;
  • validation with reports or photos is part of "Validation, uncertainty and model confidence".

Separate Application Guides may still be useful when an extension becomes a full application in its own right, such as surface runoff pathways, flood impact analysis, health and environmental quality, or accessibility and critical routes.


Required data

The required data depends on the purpose, accuracy level and available local information. The list below gives an overview of common datasets for an urban water stress test.

Elevation model

Buildings

Building function

Roads

Sewer areas

Sewer overflows

Surface water

Culverts

Weirs

Pumps and inlets

Soil and infiltration

Groundwater

Vulnerable objects

Measures

Validation data

Relevant data import links:


Preferred data for detailed water stress analysis

The general required data list above describes which data layers are commonly relevant for an extreme rainfall analysis. The checklist below describes the preferred data quality and data attributes for a more detailed water stress test.

This checklist can be used as a data intake specification when discussing data availability with a municipality, water authority or other data provider. It also helps connect commonly used Dutch data sources and project assumptions to the corresponding Tygron concepts.

Elevation model

  • Current starting point: AHN6.
  • Preferred data: elevation measurements with a higher resolution than AHN, preferably 0.5 m by 0.5 m or better.
  • Required attributes or values: elevation value per raster cell.
  • Preferred file format: raster, preferably GeoTIFF.
  • Tygron term: Elevation GeoTIFF.
  • Why it matters: the elevation model strongly determines flow direction, local ponding, water depth and the location of waterlogging.

Surface water

  • Current starting point: not always available or project-dependent.
  • Preferred data: water level areas from the water authority.
  • Required attributes or values:
    • summer level, in m NAP;
    • winter level, in m NAP;
    • target level, in m NAP.
  • Preferred file format: polygon dataset, preferably GeoJSON or GeoPackage.
  • Tygron term: Water area (Water Overlay).
  • Why it matters: surface water defines open-water storage, drainage routes and the interaction between rainfall runoff and the water system.

Culverts

  • Current starting point: IMWA or available asset data.
  • Preferred data: municipal and water authority dataset with culvert information.
  • Required attributes or values:
    • culvert location;
    • culvert diameter, or height and width for rectangular culverts;
    • bottom height of the culvert;
    • Manning value.
  • Preferred file format: spatial dataset, preferably GeoJSON or GeoPackage.
  • Tygron term: Culvert (Water Overlay).
  • Why it matters: culverts determine hydraulic connectivity under roads, embankments and other barriers. Missing or incorrect culverts can strongly affect local ponding and flow paths.

Weirs

  • Current starting point: IMWA or available asset data.
  • Preferred data: municipal and water authority dataset with weir information.
  • Required attributes or values:
    • weir location;
    • overflow height;
    • overflow width;
    • weir orientation;
    • weir coefficient;
    • weir shape exponent.
  • Preferred file format: spatial dataset, preferably GeoJSON or GeoPackage.
  • Tygron term: Weir (Water Overlay).
  • Why it matters: weirs control overflow between water areas and can influence water levels, storage and discharge during and after rainfall.

Sewer areas and sewer outflow

  • Current starting point: sewer storage based on neighbourhood characteristics.
  • Preferred data: municipal dataset with sewer area information.
  • Required attributes or values:
    • sewer storage for stormwater, in mm, per sewer area;
    • sewer outflow, in m³/s, from the sewer system;
    • geometry of each sewer area.
  • Preferred file format: polygon dataset, preferably GeoJSON or GeoPackage.
  • Tygron term: Sewer area (Water Overlay).
  • Related Tygron concept: Sewer model (Water Overlay).
  • Why it matters: sewer storage determines how much rainfall can temporarily be stored below ground. Sewer outflow represents water that leaves the model through the sewer system. The storage in mm multiplied by the sewer area surface gives the available storage volume in m³.

Sewer overflows

  • Current starting point: not always available or project-dependent.
  • Preferred data: municipal dataset with sewer overflow information.
  • Required attributes or values:
    • location where stormwater overflows from the sewer system;
    • related sewer area;
    • overflow height, in m NAP;
    • overflow threshold, in m NAP;
    • maximum overflow discharge, in m³/s.
  • Preferred file format: spatial dataset, preferably GeoJSON or GeoPackage.
  • Tygron term: Sewer overflow (Water Overlay).
  • Related Tygron concept: Sewer area (Water Overlay).
  • Why it matters: sewer overflows determine where stored sewer water can return to the surface or connect to the water system. This can be important during intense rainfall events.

Surface infiltration

  • Current starting point: infiltration is derived from the BRO soil map in combination with surface hardening information, for example from the BGT.
  • Preferred data: soil investigations with infiltration measurements.
  • Required attributes or values:
    • permeability of the ground cover, in m/day;
    • permeability of the soil, in m/day;
    • permeability of paved surfaces, in m/day.
  • Preferred file format: polygon dataset, preferably GeoJSON or GeoPackage.
  • Tygron term: Surface infiltration.
  • Related Tygron page: Infiltration model (Water Overlay).
  • Why it matters: surface infiltration determines how much rainfall can infiltrate into the ground before contributing to surface runoff or waterlogging.

Ground infiltration and percolation

  • Current starting point: percolation is derived from the BRO soil map. The unsaturated fraction may be assumed to be fully dry, meaning 0% saturation.
  • Preferred data: soil permeability and information about soil saturation.
  • Required attributes or values:
    • permeability of the soil, in m/day;
    • degree of soil saturation;
    • assumptions for the unsaturated zone;
    • value or assumption for UNSATURATED_FRACTION.
  • Preferred file format: polygon dataset, preferably GeoJSON or GeoPackage.
  • Tygron term: Ground infiltration.
  • Related Tygron page: Infiltration model (Water Overlay).
  • Why it matters: ground infiltration and percolation influence how much water can move from the surface and unsaturated zone into the deeper subsurface. The initial saturation assumption can strongly affect the available storage for infiltrating rainwater.

Water storage constructions

  • Current starting point: not always available or project-dependent.
  • Preferred data: dataset with water storage constructions.
  • Required attributes or values:
    • location;
    • storage capacity, in m³/m².
  • Preferred file format: polygon dataset, preferably GeoJSON or GeoPackage.
  • Tygron term: Water storage m2 (Water Overlay).
  • Why it matters: water storage constructions can temporarily store rainfall and reduce local waterlogging. They can be relevant for both existing infrastructure and future adaptation measures.

Buildings and critical functions

  • Current starting point: BAG. Critical functions may be identified using schools, healthcare facilities and other vulnerable functions. A generic threshold height may be assumed, for example 0.1 m above ground level.
  • Preferred data: building dataset with critical functions and threshold information.
  • Required attributes or values:
    • building location;
    • whether the building is critical infrastructure;
    • building function or vulnerability category;
    • threshold height for impact assessment.
  • Preferred file format: polygon dataset, preferably GeoJSON or GeoPackage.
  • Tygron terms:
  • Why it matters: building data is needed to translate water-depth results into affected buildings, vulnerable functions and critical infrastructure impact.

Priority roads and accessibility

  • Current starting point: roads with more than 400 vehicles per hour may be classified as critical infrastructure. A road may be considered inaccessible for cars when the water depth exceeds 0.20 m.
  • Preferred data: dataset with road categories and critical infrastructure information.
  • Required attributes or values:
    • road location;
    • road category or priority class;
    • whether the road is critical infrastructure;
    • traffic intensity or another prioritisation indicator;
    • water-depth threshold for accessibility.
  • Preferred file format: line or polygon dataset, preferably GeoJSON or GeoPackage.
  • Possible Tygron terms and workflows:
  • Why it matters: road data and accessibility thresholds are needed to analyse blocked roads, critical routes, emergency access and reachability during extreme rainfall.

Wadis and infiltration facilities

  • Current starting point: not always available or project-dependent.
  • Preferred data: design data for wadis and related drainage or overflow structures.
  • Required attributes or values:
    • wadi location;
    • location of the overflow or drainage intake;
    • discharge capacity of the pump, inlet or outlet, in m³/s;
    • threshold height at which the pump, inlet or outlet starts discharging, in m NAP;
    • target location where water is pumped or discharged to, if a pump is used;
    • adjusted infiltration speed if soil improvement has been applied.
  • Preferred file format: spatial dataset, preferably GeoJSON or GeoPackage.
  • Tygron terms:
  • Why it matters: wadis can store and infiltrate water, but may also have overflow or drainage structures. Depending on whether the water must remain inside the project area or may leave the project, an overflow or intake can be represented using a pump, inlet or outlet-like modelling approach.

Groundwater level

Data quality notes

When using this checklist, the following data quality aspects should be checked explicitly:

  • whether all spatial datasets use the correct coordinate reference system;
  • whether polygons, lines and points have valid geometry;
  • whether sewer areas do not overlap incorrectly;
  • whether each sewer overflow is linked to the intended sewer area;
  • whether culverts, weirs, pumps and inlets have plausible orientation and height attributes;
  • whether all heights use the same vertical reference, preferably m NAP;
  • whether units are documented, for example m, m NAP, mm, m³/s, m/day or m³/m²;
  • whether default assumptions are clearly separated from measured or supplied data;
  • whether missing data has been replaced by assumptions, proxies or simplified representations;
  • whether local experts have reviewed the data before results are interpreted.

Assumptions and choices

Assumptions and modelling choices should be documented before results are interpreted. A water stress test for extreme rainfall is strongly influenced by the selected rainfall event, hydrological starting situation, available local data, model settings and impact thresholds.

The following assumptions should be documented for each analysis:

  • rainfall event, for example 70 mm in 1 hour, 90 mm in 1 hour or another local design storm;
  • rainfall duration;
  • dry period after the rainfall event;
  • total simulation duration;
  • return period or policy interpretation of the rainfall event;
  • climate scenario or stress-test scenario;
  • grid size;
  • timeframes and result moments;
  • whether the analysis focuses on urban areas, industrial areas, rural areas or a combination;
  • whether current situation, future design, measures or multiple scenarios are analysed;
  • whether existing stress-test results are reused or new calculations are performed;
  • which local data sources are used instead of default or national data;
  • whether sewer storage and sewer outflow are included;
  • whether sewer overflows are included;
  • whether surface water levels are included;
  • whether culverts, weirs, pumps and inlets are included;
  • whether groundwater is included;
  • which groundwater condition is used;
  • which soil saturation or unsaturated-zone assumption is used;
  • which infiltration assumptions are used;
  • which water-depth threshold defines water nuisance;
  • which water-depth threshold defines road accessibility problems;
  • which water-depth threshold defines affected buildings;
  • which object categories are treated as vulnerable or critical;
  • whether model validation is based on measurements, expert judgement, known problem locations or a combination;
  • whether the analysis is exploratory, planning-level or design-level.

Hydrological starting situation

The hydrological starting situation should be described explicitly. This includes assumptions about surface water levels, groundwater levels, soil saturation, sewer storage, sewer outflow and infiltration capacity.

For example, a project may use a summer water level as the starting water level and compare a relatively dry and wet soil condition. A dry condition may assume a lower saturation of the unsaturated zone, while a wet condition may assume a higher saturation. These choices influence how much rainfall can infiltrate, be stored or be discharged.

Extreme failure situations, such as failure of pumping stations or sewer pumps, should be listed separately. If these situations are not part of the analysis, this should be stated explicitly.

Rainfall scenarios and simulation duration

The selected rainfall scenarios should be documented with at least:

  • scenario name;
  • rainfall depth;
  • rainfall duration;
  • return period or policy interpretation;
  • dry period after the rainfall event;
  • initial condition;
  • purpose of the scenario.

A dry period after the rainfall event can be useful when the analysis also needs to show how long water remains on the surface or when storage facilities, such as wadis, become available again for a following rainfall event.

Example rainfall scenarios that may be used in a municipal water stress test include:

  • a common sewer-design rainfall event;
  • a heavier sewer-design rainfall event;
  • a stress-test rainfall event, such as 70 mm in 1 hour;
  • a heavier stress-test rainfall event, such as 90 mm in 1 hour;
  • a long-duration rainfall event, such as 200 mm in 48 hours;
  • a historical or previously used rainfall event for validation or comparison.

Relevant pages:

Result thresholds

Thresholds should be documented because they determine how water-depth results are translated into impact.

Common threshold choices include:

  • minimum water depth for duration analysis;
  • water-depth threshold for road accessibility;
  • water-depth threshold for affected buildings;
  • impact range around buildings;
  • thresholds for vulnerable or critical functions;
  • duration classes for water on the surface.

For example, a duration analysis may only count water on the surface when the water depth exceeds 0.10 m. This prevents very shallow water films from being interpreted as relevant water nuisance. Road accessibility may use a different threshold, for example 0.20 m water depth for passenger cars. Building impact may use a separate threshold, depending on building type, entrance level or vulnerability.

Relevant pages:

Buildings and vulnerable functions

When analysing affected buildings, the following assumptions should be documented:

  • the water-depth threshold used for building impact;
  • whether the threshold is generic or differs per building category;
  • the impact range around the building;
  • which buildings are classified as vulnerable or critical;
  • which attribute is used to identify critical infrastructure;
  • whether separate analyses are needed for different threshold groups.

Examples of vulnerable or critical objects may include:

  • municipal buildings;
  • healthcare facilities;
  • schools;
  • shelters or reception locations;
  • fire stations;
  • electricity assets;
  • transformer stations;
  • pumping stations;
  • telecom facilities;
  • other locally defined critical infrastructure.

The actual vulnerability of assets may be asset-specific. Thresholds can depend on entrance levels, component height, protective measures and the function of the object.

Relevant pages:

Road accessibility and critical routes

For road accessibility, the following choices should be documented:

  • which road dataset is used;
  • which roads are classified as critical routes or main access routes;
  • which water-depth threshold is used for passability;
  • whether the threshold applies to pedestrians, passenger cars, emergency vehicles or another road user;
  • whether duration of water on the road is included;
  • whether accessibility is analysed as a map, route analysis or indicator.

A road-depth threshold should be interpreted as a practical assumption, not as an absolute safety limit. The selected threshold should be checked with the municipality or relevant road authority.

Relevant pages:

Sewer modelling

The sewer system should be described as a simplified representation unless a detailed sewer model is explicitly used.

The following assumptions should be documented:

  • whether sewer storage is included;
  • how sewer storage is defined, for example in mm per sewer area;
  • whether sewer outflow is included;
  • how sewer outflow is represented, for example as a discharge from the model;
  • whether sewer overflows are included;
  • how sewer overflows are linked to sewer areas;
  • whether different sewer system types are distinguished;
  • whether the sewer system is treated as a simplified storage-and-discharge system rather than a full sewer model.

If local sewer data is missing, default values or typology-based assumptions may be used, but this should be stated clearly.

Relevant pages:

Infiltration and paved surfaces

Infiltration assumptions should distinguish between soil infiltration, surface cover, paved surfaces and special infiltration facilities.

The following assumptions should be documented:

  • which soil or infiltration dataset is used;
  • whether infiltration is derived from national soil data, local soil data or field measurements;
  • whether paved surfaces are treated as closed surfaces;
  • whether water-permeable or water-passing pavements are modelled separately;
  • whether private gardens are represented using a hardening percentage;
  • whether local infiltration values overwrite general soil values;
  • whether grass concrete or similar surfaces are treated as infiltration measures.

Water-permeable or water-passing pavement should only be modelled as such when it is specifically designed and documented as permeable. Otherwise, normal paved surfaces may be treated as closed surfaces.

Relevant pages:

Wadis and water storage facilities

For wadis, retention areas and other storage facilities, the following assumptions should be documented:

  • geometry of the facility;
  • infiltration capacity;
  • whether storage depth or storage volume is included;
  • whether overflow, drain, pump, outlet or inlet structures are explicitly modelled;
  • whether the facility must be empty after a selected dry period;
  • which result types are used to assess emptying and reusability.

A dry period after the rainfall event can be used to assess whether a wadi or storage facility is available again for a following rainfall event.

Relevant pages:

Plans and measures

Plans and measures should only be analysed when their spatial effect can be represented in the model.

The following assumptions should be documented:

  • whether the measure changes elevation, land use, infiltration, storage or hydraulic connectivity;
  • whether future ground levels or design levels are available;
  • whether buildings, roads, green areas and water structures are included;
  • whether wadi, retention or storage facilities are included;
  • whether the plan connects to existing flow routes or surface water;
  • whether the analysis compares current situation, future design and measures.

A flat plan without height information has limited value for surface-runoff analysis, because local elevation strongly controls flow direction and water accumulation.

Relevant pages:

Interpretation and limitations

Results should be interpreted as a spatial indication of water on the surface during the selected extreme rainfall scenario. They should not be interpreted as an absolute prediction of a future event.

The reliability of the results depends on:

  • elevation data;
  • surface water levels;
  • culverts and weirs;
  • sewer storage and sewer outflow;
  • infiltration assumptions;
  • groundwater assumptions;
  • storage facilities;
  • building and road data;
  • selected rainfall scenarios;
  • model settings;
  • validation with local knowledge.

When local data is missing, default data or national datasets may be used. This reduces confidence and should be documented. Validation with local experts, known problem locations and available observations remains necessary before using results for decision making.


Workflow

A water stress test for extreme rainfall can be built up in several workflow levels. The core workflow is the rainfall simulation itself. Additional workflows support data preparation, impact analysis, result processing and reusable templates.

Core workflow: configure and run a Rainfall Overlay

Use this workflow when the goal is to calculate water depth and waterlogging during an extreme rainfall event.

  1. Define the policy question and study area.
  2. Choose the rainfall event and simulation duration.
  3. Add a Rainfall Overlay.
  4. Use the Rainfall Overlay tutorial and Water Overlay Wizard to configure the water system.
  5. Check the elevation model, terrain roughness, water areas, sewer districts and hydraulic structures.
  6. Set relevant simulation settings, timeframes and result type.
  7. Run the calculation.
  8. Inspect maximum water depth and other relevant result types.
  9. Validate the results with known problem locations, expert judgement and system checks.
  10. Export maps or use results in follow-up analyses.

Recommended implementation links:

Example workflow: start from the Demo Rainfall Project

Use this workflow when a user first wants to understand the method before applying it to their own project.

  1. Open the Demo Rainfall Project.
  2. Follow How to work with the Demo Rainfall Project.
  3. Inspect the configured Rainfall Overlay.
  4. Review the input data, such as water level areas, weirs, culverts and sewer areas.
  5. Inspect the resulting water-depth maps.
  6. Use the project as a learning reference before configuring a new project.

Recommended implementation links:

Data workflow: add or prepare external spatial data

Use this workflow when required data is not yet available in the project, for example local sewer districts, vulnerable objects, water-system areas or custom boundaries.

  1. Check which data is missing for the analysis.
  2. Prepare data as WFS, GeoJSON, GeoPackage or another supported geodata route.
  3. Add the data to the project.
  4. Map the imported data to the correct Tygron object type or attribute.
  5. Check whether the data is spatially correct.
  6. Use the data in the Rainfall Overlay, Combo Overlay or impact analysis.

Relevant implementation links:

Impact workflow: calculate affected buildings or vulnerable functions

Use this workflow when water-depth results need to be translated into impact.

Examples:

  • buildings affected by more than 0.10 m water depth;
  • public buildings affected by a lower threshold;
  • road segments affected by more than 0.10 m water depth;
  • vulnerable objects intersecting waterlogging zones;
  • neighbourhoods with a high fraction of built area affected by inundation.

Steps:

  1. Select the relevant water-depth result.
  2. Select the relevant object category, such as buildings, roads or vulnerable locations.
  3. Define thresholds.
  4. Combine water-depth results with object attributes.
  5. Calculate statistics or classify objects.
  6. Check map output against statistics.
  7. Export results for reporting.

Relevant implementation links:

Result-processing workflow: combine multiple calculations into one result

Use this workflow when results from several overlays, scenarios, areas or timeframes must be combined.

Examples:

  • combining multiple limited-area calculations;
  • accumulating results across timeframes;
  • combining water depth with building vulnerability;
  • preparing one output map for reporting;
  • creating a reusable result layer for a template.

Relevant implementation links:

Advanced workflow: connect overlays using prequels

Use this workflow when the result of one overlay needs to be used as input for another overlay.

Examples:

  • using a processed result as input for a Combo Overlay;
  • chaining rainfall results into a follow-up analysis;
  • building reusable calculation chains for templates.

Relevant implementation links:

This is an advanced reusable workflow, not a first-step workflow for new users.

Practical How-to routes

The following How-to pages can be used to translate common user questions into practical Tygron workflows. They are grouped by the type of task a user is trying to perform.

Start with an example project

Use these pages when the user wants to understand the method before configuring their own project:

These pages are especially relevant for questions such as:

  • How do I start a water stress test in Tygron?
  • Is there an example project for rainfall analysis?
  • How can I learn how the Rainfall Overlay works?
  • How do I understand the basic setup of a Water Overlay?

Configure rainfall and simulation settings

Use these pages when the user needs to define the rainfall event, simulation duration or spatial rainfall pattern:

These pages are especially relevant for questions such as:

  • How do I set a simple rainfall event, such as 70 mm in 2 hours?
  • How do I use a custom rainfall event?
  • How do I model a local rain shower?
  • How do I set the simulation time for a rainfall calculation?
  • How do I inspect the initial conditions of a rainfall simulation?
  • How do I use timeframes in a Water Overlay?
  • Can rainfall be limited to part of the project area?
  • Can rainfall vary spatially within the project area?

Add or prepare local spatial data

Use these pages when the user has local datasets, such as sewer areas, buildings, vulnerable objects, water areas or hydraulic structures:

These pages are especially relevant for questions such as:

  • What data do I need for a water stress test?
  • How do I import municipal data into Tygron?
  • How do I import a GeoPackage, WFS or ArcGIS Online layer?
  • How can I prepare reusable data imports for a template?
  • How can imported data be mapped to Tygron objects or attributes?

Add sewer data and sewer overflows

Use these pages when sewer storage, sewer outflow or sewer overflows are relevant for the rainfall analysis:

These pages are especially relevant for questions such as:

  • How do I include sewer storage in a rainfall model?
  • How do I import sewer areas?
  • How do I model sewer overflows?
  • What happens if sewer areas or sewer overflows are missing?
  • How should sewer areas and sewer overflows be represented in Tygron?

Add surface water and hydraulic structures

Use these pages when water areas, culverts, weirs, pumps or inlets influence the flow of water:

These pages are especially relevant for questions such as:

  • How do I add culverts or weirs to a Water Overlay?
  • How do hydraulic structures affect rainfall results?
  • How can I check where water flows through the project area?
  • Why does water accumulate in a certain location?
  • How do waterways and water levels affect extreme rainfall results?

Add groundwater or drainage assumptions

Use these pages when groundwater, drainage or initial groundwater conditions are relevant to the rainfall analysis:

These pages are especially relevant for questions such as:

  • Should groundwater be included in a water stress test?
  • How do I add a groundwater GeoTIFF?
  • How do I use default groundwater information?
  • How do I model drainage?
  • How do I define an initial groundwater situation?

Analyse impact on buildings, roads or vulnerable functions

Use these pages when water-depth results must be translated into impact:

These pages are especially relevant for questions such as:

  • How do I calculate affected buildings?
  • How do I combine water depth with building attributes?
  • How do I apply a water-depth threshold?
  • How do I create an impact map for vulnerable functions?
  • How do I analyse road accessibility during extreme rainfall?
  • How do I mask water-depth results below a threshold?

Analyse accessibility and critical routes

Use these pages when water-depth results need to be translated into accessibility, blocked roads or evacuation routes:

These pages are especially relevant for questions such as:

  • How do I analyse road accessibility during extreme rainfall?
  • How do I calculate which routes are blocked by water?
  • How do I create evacuation routes that avoid flooded roads?
  • How do I combine water-depth thresholds with travel distance?
  • Are critical destinations still reachable during waterlogging?
  • How can water-depth results be used in accessibility analysis?

Combine results from multiple calculations

Use these pages when results from multiple overlays, timeframes, scenarios or calculation areas need to be combined:

These pages are especially relevant for questions such as:

  • How do I combine results from multiple rainfall calculations?
  • How do I combine different overlays into one result map?
  • How do I process multiple timeframes?
  • How do I create a reusable output layer?
  • How can results from limited-area calculations be merged?

Compare measures and future scenarios

Use these pages when the user wants to compare adaptation measures or future designs:

These pages are especially relevant for questions such as:

  • How do I compare the current situation and a future design?
  • How do I add climate adaptation measures?
  • How do I model terrain changes as a measure?
  • How do I edit a measure outside Tygron?
  • How can measures be used to compare waterlogging before and after adaptation?

Validate and inspect model behaviour

Use these pages when the user wants to check whether the model behaves plausibly:

These pages are especially relevant for questions such as:

  • How do I validate a rainfall model?
  • How do I check whether water flows in a plausible direction?
  • How do I inspect output values for hydraulic structures?
  • How do I understand water-system behaviour behind the map result?
  • How do I use the Hydrologic System Overview for plausibility checks?

Export results for GIS, reporting or communication

Use these pages when results need to be exported for further analysis, reporting or stakeholder communication:

These pages are especially relevant for questions such as:

  • How do I export water-depth maps?
  • How do I export results to GIS?
  • How do I share rainfall results through GeoShare?
  • How do I export affected buildings or other objects?
  • How do I export object attributes for reporting?

Expected outputs

Expected outputs should follow the analysis framework. A project does not need to produce every output. The relevant outputs depend on the policy question, available data, selected scenarios and intended use of the results.

Water depth during extreme rainfall

Expected outputs include:

  • water-depth maps;
  • maximum water-depth maps;
  • water-depth classes for viewers or reports;
  • hotspot maps for local waterlogging;
  • comparison maps between rainfall scenarios;
  • GIS exports for further analysis.

Water on the surface, duration and recovery time

Expected outputs include:

  • duration maps;
  • maps showing where water remains after the rainfall event;
  • recovery-time classes;
  • statistics per neighbourhood, road, square, area or object category;
  • indication of locations where water remains for a long time;
  • input for maintenance, design or risk dialogue.

Accessibility and critical routes

Expected outputs include:

  • road accessibility maps;
  • blocked-road maps based on water-depth thresholds;
  • critical-route impact maps;
  • accessibility maps for emergency services or vulnerable destinations;
  • evacuation-route or travel-distance maps, when relevant;
  • tables or statistics showing affected routes or destinations.

Impact on buildings and vulnerable functions

Expected outputs include:

  • impacted buildings;
  • impacted critical buildings;
  • impacted vulnerable functions;
  • impacted utility assets or critical objects, when data is available;
  • statistics per building type, function, neighbourhood or impact threshold;
  • maps that distinguish ordinary buildings, critical buildings and vulnerable functions;
  • input for prioritisation, communication and risk dialogue.

Wadis, storage facilities and blue-green measures

Expected outputs include:

  • duration of water in or around wadis;
  • remaining water at the end of the simulation;
  • maximum water level or maximum water depth in storage areas;
  • indication of whether a storage facility is available again after a dry period;
  • comparison of existing and proposed blue-green measures;
  • locations where extra storage or infiltration may be useful.

Plans, measures and scenario comparison

Expected outputs include:

  • comparison between current and future situations;
  • comparison between base scenario and measure scenario;
  • difference maps;
  • statistics per scenario or measure;
  • change in water depth;
  • change in duration;
  • change in affected buildings or vulnerable functions;
  • change in accessibility or blocked routes;
  • visual material for decision making.

Validation, uncertainty and model confidence

Expected outputs include:

  • validation notes;
  • list of confirmed assumptions;
  • list of remaining uncertainties;
  • comparison with known waterlogging locations;
  • results of expert review;
  • data-quality issues;
  • backlog items for future improvement;
  • decision on whether the results are suitable for the intended use.

Relevant result and output links:

The Water stress (Indicator) can be used to summarize the flood resilience of built areas based on the fraction of built area that inundates beyond a configured threshold. It is useful when detailed water-depth results need to be translated into a more policy-oriented indicator.

Validation

Validation is essential before water stress test results are used for communication, decision making or measure selection.

Recommended validation checks:

  • Check known problem locations.
  • Compare results with municipal reports, complaints or field knowledge.
  • Review results with water managers and local experts.
  • Check whether water accumulates in plausible low-lying locations.
  • Check whether flow paths and ponding locations are influenced by bridges, culverts, road edges or elevation artefacts.
  • Check whether sewer areas, sewer outflow and sewer overflows behave plausibly.
  • Check whether water-depth maps and statistics tell the same story.
  • Check multiple thresholds, for example 0.05 m, 0.10 m and 0.20 m.
  • Compare current and future situations.
  • Test sensitivity to rainfall intensity, grid size and infiltration assumptions.
  • Decide whether specialist modelling or additional data collection is needed.

Validation with the Water Overlay Wizard

During model setup, the Water Overlay Wizard can be used as an initial technical validation step. It provides feedback on the configured water system, imported data and settings. Warnings and errors should be reviewed before interpreting model results.

Use this check for:

  • missing or inconsistent water-system data;
  • incorrectly configured water areas;
  • warnings in imported data;
  • incomplete sewer or hydraulic structure configuration;
  • settings that may prevent the water system from functioning as intended.

Relevant implementation links:

This is a configuration check, not a full validation of model results.

Validation with tracing and measurements

Tracing and measurements can be used to inspect model behaviour after running a Water Overlay. These workflows help users understand where water flows, which objects influence the result and whether calculated object values are plausible.

Use this check for:

  • tracing water through the project area;
  • checking whether flow paths are plausible;
  • inspecting water levels, discharge or other output attributes for hydraulic structures;
  • exporting measurement results for review or reporting.

Relevant implementation links:

Validation with the Hydrologic System Overview

The Hydrologic System Overview plugin can be used as an additional validation and plausibility workflow after running the Water Overlay. It installs a dashboard for analysing Water Overlay results and creates a dashboard instance for each Water Level Area identified by the Water Overlay.

For a water stress test, this is useful when the user wants to understand whether the hydrological behaviour of the model is plausible at water-system level, not only at map level.

Use the Hydrologic System Overview to check:

  • whether water level areas behave as expected;
  • whether inflow and outflow patterns are plausible;
  • whether water is stored, routed or discharged in a logical way;
  • whether hydraulic structures strongly influence the result;
  • whether the model behaviour explains surprising water-depth patterns;
  • whether a result should be trusted, refined or investigated further.

Recommended implementation links:

The Hydrologic System Overview should not replace expert judgement, field validation or comparison with measurements, but it can help users understand the internal hydrological behaviour behind the map output.

Reusable concepts

Reusable concepts for this theme include:

  • Why use scenarios?
  • Why use templates?
  • Why start with a clear policy question?
  • Why separate theme, analysis, data, assumptions and workflow?
  • Why validate before communicating results?
  • Why compare current and future situations?
  • Why define water-depth thresholds?
  • Why combine water-depth maps with buildings, roads and vulnerable objects?
  • Why distinguish exploratory analysis from design-level modelling?
  • How can model results be translated into policy choices?

Useful reference links:

Relevant Tygron components

Relevant Tygron components include:

Comparison with other software

Tygron is strong for:

  • spatial scenario exploration;
  • visualisation of waterlogging;
  • combining water results with spatial objects;
  • measure comparison;
  • stakeholder communication;
  • risk dialogue preparation;
  • fast iteration between current and future situations;
  • integration of water results with buildings, roads and other spatial datasets.

Specialist tools may be more suitable for:

  • detailed sewer design;
  • formal hydraulic calibration;
  • highly detailed 1D/2D sewer and surface-water interaction;
  • detailed groundwater modelling;
  • regulatory design verification;
  • operational flood forecasting.

A practical way to position Tygron:

  • Use Tygron when the main goal is spatial insight, scenario comparison and communication.
  • Use specialist modelling software when the main goal is formal design, calibration or regulatory verification.
  • Use both when quick spatial insight must be checked or refined with specialist modelling.

Useful background links:

External context and comparable use cases

This section provides external context for the application of Tygron to water stress testing, urban waterlogging and pluvial flooding. These links are not Tygron implementation pages. They help connect this Application Guide to broader policy, research and climate-adaptation terminology.

External links should be used selectively. They are useful when they clarify the broader application context, for example DPRA stress tests, climate adaptation, pluvial flooding, road accessibility or upper-regional rainfall events. Technical implementation steps should still primarily link to Tygron documentation and How-to pages.

DPRA climate stress tests and risk dialogue

The Dutch Delta Programme for Spatial Adaptation (DPRA) provides the broader policy context for climate stress testing in the Netherlands. Climate stress tests identify vulnerabilities for themes such as waterlogging, heat, drought and flooding. The results are intended to support risk dialogue and adaptation planning.

Relevant external links:

Relation to this Application Guide:

  • Extreme rainfall analysis in Tygron can support the waterlogging part of a climate stress test.
  • Tygron can help create spatial insight into water depth, affected buildings, road accessibility, vulnerable functions and possible adaptation measures.
  • Tygron results can be used as input for stakeholder dialogue, risk dialogue and decision-making, provided assumptions and limitations are documented.

Useful terminology:

  • climate stress test;
  • waterlogging;
  • extreme rainfall;
  • vulnerability;
  • risk dialogue;
  • adaptation planning;
  • implementation agenda.

Water depth after short-duration heavy rainfall

The Dutch climate adaptation portal describes water depth after short-duration heavy rainfall as a relevant stress-test indicator. This focuses on water depth on streets and squares after intense rainfall. In sloping areas, flow velocity can also be relevant because high surface-flow velocities can create additional safety risks.

Relevant external link:

Relation to this Application Guide:

  • This is one of the closest external equivalents to the Tygron use case for extreme rainfall.
  • The primary Tygron output is a water-depth map, for example through the Rainfall Overlay and Water stress result type (Water Overlay).
  • For sloping areas or flow-path questions, this guide may connect to a separate Application Guide about surface runoff pathways or flow paths.

Useful terminology:

  • water depth;
  • short-duration heavy rainfall;
  • pluvial flooding;
  • surface runoff;
  • flow velocity;
  • streets and squares;
  • local waterlogging.

Klimaateffectatlas water-depth maps

The Dutch Climate Impact Atlas contains national maps for water depth after heavy rainfall events, including rainfall events such as 70 mm and 140 mm in 2 hours. These maps provide broad spatial insight and can be used as national reference context.

Relevant external link:

Relation to this Application Guide:

  • The Climate Impact Atlas provides national reference maps.
  • A Tygron project can provide a more local, scenario-based and data-specific analysis.
  • Tygron can include local elevation data, local sewer assumptions, surface water, hydraulic structures, vulnerable objects and local measures.
  • Differences between national maps and local Tygron results should be explained through differences in input data, assumptions, resolution and model setup.

Useful terminology:

  • national reference map;
  • local analysis;
  • water-depth map;
  • rainfall scenario;
  • scenario comparison;
  • local data.

Upper-regional stress tests for extreme rainfall

Upper-regional stress tests analyse large-scale extreme rainfall events that exceed municipal or regional boundaries. Deltares describes a national water image for large-scale extreme rainfall based on 200 mm in 48 hours. These analyses show expected water depth, duration of water on the surface and regional attention points.

Relevant external links:

Relation to this Application Guide:

  • A local Tygron water stress test and an upper-regional stress test have related but different purposes.
  • A local Tygron analysis is useful for detailed spatial insight, measure comparison and local decision support.
  • Upper-regional stress tests are useful for understanding broader system behaviour, regional disruption and cross-boundary effects.
  • Long-duration events, such as 200 mm in 48 hours, may require additional attention to groundwater, surface water, drainage, storage and regional discharge pathways.

Useful terminology:

  • upper-regional stress test;
  • large-scale extreme rainfall;
  • 200 mm in 48 hours;
  • water depth;
  • water duration;
  • regional disruption;
  • cross-boundary waterlogging.

Pluvial flood risk assessment in urban areas

The Copernicus Climate Change Service describes pluvial flood risk assessment in urban areas as a way to assess risks associated with extreme rainfall events in Europe. Pluvial flooding is flooding caused by intense rainfall that the ground and drainage system cannot absorb or discharge quickly enough.

Relevant external link:

Relation to this Application Guide:

  • This supports the use of the terms "pluvial flooding" and "urban waterlogging" in this guide.
  • The Tygron workflow fits the broader class of urban pluvial flood risk assessment.
  • The Tygron focus is practical scenario analysis, local spatial insight, impact analysis, measure comparison and communication.

Useful terminology:

  • pluvial flood risk;
  • urban flooding;
  • extreme rainfall;
  • risk assessment;
  • inundation;
  • exposure;
  • vulnerability;
  • adaptation measures.

Road accessibility and critical routes during waterlogging

Some waterlogging studies and stress-test datasets translate rainfall results into accessibility or passability of roads. This is relevant when water depth and water duration are combined with road networks, main access roads, emergency routes or critical destinations.

Relevant external context:

  • road passability during heavy rainfall;
  • water depth on roads;
  • duration of water on roads;
  • emergency access;
  • evacuation routes;
  • critical infrastructure;
  • road network disruption.

Relation to this Application Guide:

  • In Tygron, road accessibility can be analysed by combining rainfall results with roads and thresholds.
  • A Combo Overlay can classify flooded or blocked roads based on water-depth thresholds.
  • A Travel Distance Overlay can be used when the question concerns reachability, evacuation routes or access to critical destinations.
  • The threshold for passability should be documented as an assumption and should depend on the road user, such as pedestrians, passenger cars or emergency vehicles.

Relevant Tygron links:

High-resolution urban pluvial flood risk mapping

Research on urban pluvial flood risk often combines high-resolution elevation data, rainfall scenarios, building data, vulnerability information and impact indicators. This is similar to the structure of a detailed Tygron water stress test.

Relevant external context:

  • high-resolution elevation model;
  • rainfall scenario;
  • surface runoff;
  • water-depth map;
  • affected buildings;
  • vulnerable functions;
  • exposure;
  • local impact assessment.

Relation to this Application Guide:

  • The quality of the elevation model strongly affects water depth and flow paths.
  • Building data and critical-function attributes help translate water-depth results into impact.
  • Impact thresholds should be documented, because they determine which buildings, roads or objects are counted as affected.
  • High-resolution local data generally increases confidence, but validation with local knowledge remains necessary.

Relevant Tygron links:

Data-scarce pluvial flood modelling

In many urban waterlogging analyses, detailed sewer, drainage or infiltration data is incomplete. In such cases, simplified assumptions are used. This is acceptable for exploratory or planning-level analysis, provided the assumptions and limitations are documented.

Relevant external context:

  • data-scarce urban flood modelling;
  • simplified drainage representation;
  • rainfall uncertainty;
  • sewer storage assumptions;
  • infiltration assumptions;
  • uncertainty and limitations.

Relation to this Application Guide:

  • Tygron can be used for exploratory spatial analysis when not all specialist data is available.
  • Missing local data can be replaced by default data, national datasets, typology-based assumptions or simplified representations.
  • Reduced confidence should be stated clearly.
  • Detailed sewer design, formal calibration or legal verification may still require specialist hydraulic or sewer modelling software.

Relevant Tygron links:

External links are useful for large language models when they provide context that is not specific to Tygron but important for understanding the application domain.

Use external links for:

  • policy context, such as DPRA climate stress tests;
  • common terminology, such as pluvial flooding, urban waterlogging and risk dialogue;
  • reference rainfall scenarios, such as 70 mm in 2 hours or 200 mm in 48 hours;
  • comparison between local Tygron analyses and national or regional stress-test maps;
  • explaining why assumptions, validation and limitations matter.

Do not rely on external links for:

  • Tygron implementation steps;
  • Tygron attribute names;
  • Tygron model settings;
  • Tygron result types;
  • Tygron import or export workflows.

For implementation, prefer internal Tygron links such as:

A good pattern is:

  • use external links to explain the broader application context;
  • use Application Guides to connect the context to a Tygron workflow;
  • use Tygron How-to pages to explain implementation.

Search terms from comparable use cases

This Application Guide may also be relevant for users searching for:

  • DPRA climate stress test
  • standardized climate stress test
  • waterlogging stress test
  • pluvial flood risk assessment
  • urban waterlogging
  • water depth after heavy rainfall
  • short-duration heavy rainfall
  • water depth on streets and squares
  • 70 mm in 2 hours
  • 90 mm in 1 hour
  • 200 mm in 48 hours
  • upper-regional stress test
  • risk dialogue
  • adaptation planning
  • flood impact on buildings
  • road accessibility during waterlogging
  • critical routes during flooding
  • high-resolution pluvial flood mapping
  • data-scarce pluvial flood modelling
  • simplified sewer modelling
  • rainfall scenario analysis

Key terms from comparable use cases

  • climate stress test
  • DPRA
  • waterlogging
  • pluvial flooding
  • urban waterlogging
  • water depth
  • rainfall duration
  • water duration
  • flow velocity
  • surface runoff
  • critical infrastructure
  • vulnerable functions
  • affected buildings
  • road accessibility
  • passability
  • evacuation routes
  • risk dialogue
  • adaptation planning
  • upper-regional stress test
  • local water stress test
  • uncertainty
  • validation
  • simplified drainage


Frequently asked questions

Can Tygron be used for a water stress test?

Yes. Tygron can be used to analyse waterlogging caused by extreme rainfall, especially when the goal is spatial insight, scenario comparison and communication. See the Rainfall Overlay, Rainfall Overlay tutorial, How to work with the Demo Rainfall Project and How to manually configure a Water Overlay.

Which overlay should be used?

The Rainfall Overlay is the main overlay for extreme rainfall and waterlogging. It is a Water Overlay connected to the Water Module. The broader configuration can be supported by the Water Overlay Wizard, How to configure the Water Overlays and Basic water model use case (Water Overlay).

What data is needed?

The most important data are elevation, land use, buildings, roads, water areas, sewer areas, hydraulic structures, infiltration assumptions and validation data. Local data can be imported using Import Geo data, Geo Data Wizard, How to import a GeoPackage file, How to import data from a WFS or How to import data from ArcGIS Online. See also How to work with the Demo Rainfall Project.

How can I use a custom rainfall event?

A custom rainfall event can be configured using Weather data and simulation time settings. Relevant pages are How to load in dynamic rain and simulation time (Water Overlay), How to set linear rain and simulation time (Water Overlay), Weather (Water Overlay), How to create a Rain area, Rain area (Water Overlay) and Limit rain (Water Overlay).

How do I set a simple rainfall event, such as 70 mm in 2 hours?

A simple rainfall event can be configured using How to set linear rain and simulation time (Water Overlay). For time-varying rainfall, use How to load in dynamic rain and simulation time (Water Overlay). Rainfall and total simulation time are part of the Weather (Water Overlay) configuration.

How can I inspect the starting conditions of a rainfall simulation?

Use How to add a timeframe for initial conditions of a simulation (Water Overlay), Timeframes (Water Overlay) and Timeframe times (Water Overlay) when the initial state of the Water Overlay needs to be inspected or validated.

Can Tygron calculate impacted buildings and vulnerable functions?

Yes. Water-depth results can be combined with building geometry, building attributes and separate object datasets to analyse affected buildings and vulnerable functions. This can include ordinary buildings, critical buildings, schools, healthcare facilities, public buildings, utility assets, pumping stations, electricity assets or other locally defined vulnerable objects. Relevant links are Water stress (Indicator), Combo Overlay, Combo Overlay tutorial, How to edit a Combo Overlay formula, How to use building attributes in a Combo Overlay, Critical infrastructure (Function Value) and Impact flood threshold m (Water Overlay).

Can Tygron calculate road accessibility?

Tygron can support road accessibility analysis by combining water-depth results with road data and threshold assumptions. The threshold should depend on the intended interpretation, such as pedestrians, passenger cars or emergency vehicles. Relevant pages include Combo Overlay tutorial, Combo Overlay with masking, Combo Overlay with distance filtering, How to edit a Combo Overlay formula, Travel Distance Overlay and How to add the Travel Distance Overlay.

Can Tygron analyse evacuation routes or blocked roads during waterlogging?

Yes. Water-depth results from a Rainfall Overlay can be combined with a Combo Overlay to identify blocked cells or roads. These results can then be used with the Travel Distance Overlay, How to create an evacuation routes overlay or How to create a flexible Travel Distance Overlay to analyse accessibility or evacuation routes.

Should impact on vital functions be a separate analysis?

Not necessarily. Impact on vital or vulnerable functions is usually best treated as part of "Impact on buildings and vulnerable functions" when the question is whether a building, object or function is affected by water on the surface. It becomes a separate analysis only when the project also analyses functional failure, cascade effects, service areas, asset-specific vulnerability or dependencies between functions.

How should sub-analyses be structured?

For extreme rainfall, it is usually better to work with a limited set of main analyses and describe extensions underneath them. For example, affected schools, healthcare facilities, utility assets and critical infrastructure can all be grouped under "Impact on buildings and vulnerable functions". Emergency access, evacuation routes and blocked roads can be grouped under "Accessibility and critical routes". This prevents overlap and makes the analysis structure easier to interpret.

Can Tygron compare measures?

Yes. Measures and future designs can be compared by running scenarios and comparing water-depth maps, indicators and impact statistics. See Scenario, Measure, Future Design, Measures tutorial, How to add and remove measures, How to add an Area to a Measure, How to add a Terrain Spatial to a Measure and How to edit a Measure with QGIS.

Can Tygron export results to GIS?

Yes. Water results can be exported for use in GIS workflows, reports or web viewers. See GeoTIFF Overlay, How to export a Grid Overlay as GeoTIFF, How to export a Grid Overlay as GeoJSON, How to export a Grid Overlay to the GeoShare and Export Geo data.

How reliable are the results?

Reliability depends on the elevation model, rainfall event, grid size, infiltration assumptions, sewer assumptions, water-system data and validation. Results should be checked with local knowledge, known problem locations and, where possible, measurements. Relevant pages include Water Overlay Wizard, Configuration Wizard, How to trace water through project area (Water Overlay), How to inspect object output attributes of an overlay using the measurement tool, How to export measurements and How to add the Hydrologic System Overview plugin.

Can Tygron replace specialist hydraulic or sewer software?

Not as a general statement. Tygron is best positioned as a spatial, scenario-based analysis and communication tool. Specialist software may still be required for detailed design, calibration or regulatory verification.

Where does the Hydrologic System Overview fit?

The Hydrologic System Overview plugin fits under validation and plausibility checking. It helps users understand the hydrological behaviour behind Water Overlay results, especially per Water Level Area. See How to add the Hydrologic System Overview plugin, Dashboard, Water level area (Water Overlay) and Water Overlay.

AI summary

Tygron can support water stress testing by helping users analyse spatial vulnerabilities caused by extreme rainfall, compare current and future scenarios, assess water depth, duration, accessibility, affected buildings, vulnerable functions, storage facilities, measures and uncertainty, and prepare results for decision making or stakeholder dialogue. The Rainfall Overlay and Water Module are the core components for calculating rainfall-driven waterlogging. The Water stress (Indicator) can translate water-depth results into a more policy-oriented assessment of built-area resilience.

A good workflow starts with a clear policy question, a defined study area, a chosen rainfall event, required data, preferred data quality, explicit assumptions and a clear analysis framework. Users can start from the Demo Rainfall Project and How to work with the Demo Rainfall Project, configure rainfall using How to load in dynamic rain and simulation time (Water Overlay), How to set linear rain and simulation time (Water Overlay) or How to create a Rain area, inspect timeframes using Timeframes (Water Overlay), add local data using Import Geo data and Geo Data Wizard, include sewer behaviour using How to add sewer data (Water Overlay) and How to import sewer overflows, calculate impact using Combo Overlay tutorial and How to use building attributes in a Combo Overlay, analyse accessibility using Travel Distance Overlay, compare measures using Measures tutorial, and export results using How to export a Grid Overlay as GeoTIFF or How to export a Grid Overlay as GeoJSON.

Results should be validated using known problem locations, expert judgement, configuration checks, tracing, measurements and, where useful, the Hydrologic System Overview plugin. Sub-analyses should be grouped logically: vulnerable functions are part of building and object impact, emergency access is part of accessibility, and damage indication is an extension of impact analysis when suitable thresholds are available. Tygron is strongest for spatial insight, scenario comparison and communication. Specialist hydraulic, sewer or groundwater software may still be needed for detailed calibration, design or formal verification.

Related application guides may include:

  • Rural Water: Flow Paths
  • Flooding: Rapid Flood Impact Analysis
  • Rural Water: Water System Analysis and Water Balance
  • Groundwater and Drought
  • Rainwater Retention
  • Sewer Interaction and Surface Waterlogging
  • Climate Adaptation Measures for Water
  • Accessibility and Critical Routes
  • Water Model Setup with HyDAMO
  • Calibration and Validation of Water Models
  • Hydraulic Structures and Network Connectivity

Useful related Tygron links:

Search terms

This page may be relevant for users searching for:

  • Can Tygron be used for a water stress test?
  • How do I analyse waterlogging in Tygron?
  • How do I configure a Rainfall Overlay?
  • What data do I need for extreme rainfall analysis?
  • What data should a municipality provide for a water stress test?
  • What is the preferred data quality for a Tygron water stress test?
  • How do I translate Dutch water datasets to Tygron Water Overlay concepts?
  • Can Tygron calculate water depth during heavy rainfall?
  • Can Tygron compare adaptation measures?
  • Can Tygron calculate impacted buildings?
  • Can Tygron calculate road accessibility during extreme rainfall?
  • Can Tygron export water-depth maps to GIS?
  • How do I validate a rainfall model in Tygron?
  • Can Tygron replace hydraulic modelling software?
  • How do I include sewer storage in a Tygron rainfall model?
  • How do I import sewer overflows in Tygron?
  • How do I use a custom rainfall event in Tygron?
  • How do I use a Rain area in Tygron?
  • How do I combine rainfall results with buildings or roads?
  • How do I use a Combo Overlay for water stress?
  • How do I export rainfall results as GeoTIFF?
  • How do I compare measures for waterlogging?
  • What sub-analyses are relevant for extreme rainfall in Tygron?
  • How should water stress test analyses be grouped?
  • Can Tygron analyse vulnerable functions during extreme rainfall?
  • Can Tygron analyse critical infrastructure during waterlogging?
  • Can Tygron analyse wadi recovery time?
  • Can Tygron compare blue-green measures for waterlogging?
  • Can Tygron validate waterlogging results with local knowledge?
  • How do I set linear rainfall in Tygron?
  • How do I set 70 mm rain in 2 hours in Tygron?
  • How do I use timeframes in a Tygron Water Overlay?
  • How do I inspect initial conditions in a rainfall simulation?
  • Can Tygron analyse evacuation routes during waterlogging?
  • Can Tygron analyse blocked roads during extreme rainfall?
  • How do I use the Travel Distance Overlay with waterlogging?

Key terms

Retrieved from "https://support.tygron.com/w/index.php?title=Application_guide_Water_stress_test_for_extreme_rainfall&oldid=89850"