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;
formal calibration against measurements;
specialist groundwater modelling;
detailed hydraulic structure design;
legal engineering verification;
a prescribed external calculation protocol;
purely static reporting without spatial analysis;
a calculation where the sewer system, groundwater system or hydraulic network must be modelled in detail according to a specialist standard.

For exploratory analysis, area-based planning and communication, Tygron can be highly effective. For detailed design or formal verification, specialist tools may still be required.

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

Preferred source: AHN or preferably a higher-resolution local elevation model.
Why it matters: Determines flow direction, local ponding and water depth.
If missing: Use the available terrain model and state reduced confidence.
Tygron component or term: Elevation GeoTIFF.
Relevant links:

Buildings

Preferred source: BAG and municipal building data.
Why it matters: Needed to analyse impacted buildings and vulnerable functions.
If missing: Use building footprints only and document simplification.
Tygron component or term: Buildings.
Relevant links:

Building function

Preferred source: BAG, municipal data or custom classification.
Why it matters: Needed to distinguish homes, shops, public functions or critical buildings.
If missing: Use generic categories or building footprints only.
Tygron component or term: Building attributes.
Relevant links:

Roads

Preferred source: BGT, municipal road data or traffic datasets.
Why it matters: Needed for accessibility and road-impact analysis.
If missing: Use main roads only.
Tygron component or term: Areas or road attributes.
Relevant links:

Sewer areas

Preferred source: Municipal sewer data with storage and outflow values.
Why it matters: Determines how much rainfall is stored or removed by the sewer system.
If missing: Use typology-based assumptions or omit sewer storage.
Tygron component or term: Sewer area (Water Overlay).
Relevant links:

Sewer overflows

Preferred source: Municipal overflow data.
Why it matters: Determines where sewer water reaches the surface.
If missing: Use simplified overflow representation or omit.
Tygron component or term: Sewer overflow (Water Overlay).
Relevant links:

Surface water

Preferred source: Water board data, water level areas and target levels.
Why it matters: Defines storage, drainage and water levels.
If missing: Use simplified water areas and document assumptions.
Tygron component or term: Water area (Water Overlay).
Relevant links:

Culverts

Preferred source: Municipal and water board asset data.
Why it matters: Determines connectivity under roads and barriers.
If missing: Include only major culverts first.
Tygron component or term: Culvert (Water Overlay).
Relevant links:

Weirs

Preferred source: Water board data.
Why it matters: Controls overflow between water areas.
If missing: Use simplified barrier behaviour.
Tygron component or term: Weir (Water Overlay).
Relevant links:

Pumps and inlets

Preferred source: Water board or municipal asset data.
Why it matters: Represents active water movement or drainage.
If missing: Simplify or omit if not relevant.
Tygron component or term: Pump / Inlet.
Relevant links:

Soil and infiltration

Preferred source: BRO, BOFEK or local soil data.
Why it matters: Determines how much rainfall infiltrates.
If missing: Use soil-class defaults.
Tygron component or term: Infiltration.
Relevant links:

Groundwater

Preferred source: BRO, local groundwater model or measurements.
Why it matters: Relevant for longer events or shallow groundwater.
If missing: Use simplified groundwater assumptions or omit.
Tygron component or term: Ground water (Water Overlay).
Relevant links:

Vulnerable objects

Preferred source: Municipal, provincial or custom datasets.
Why it matters: Needed to translate water depth into impact.
If missing: Use buildings and roads as proxy.
Tygron component or term: Attribute Overlay / attributes.
Relevant links:

Measures

Preferred source: Design data or conceptual measures.
Why it matters: Needed to compare scenarios.
If missing: Use schematic measures.
Tygron component or term: Measures / Future Design.
Relevant links:

Validation data

Preferred source: Known problem locations, photos, reports or measurements.
Why it matters: Needed to check plausibility.
If missing: Use expert review.
Tygron component or term: Local validation input.
Relevant links:

Relevant data import links:

Assumptions and choices

The following assumptions should be documented before results are interpreted:

rainfall event, for example 70 mm in 2 hours;
climate scenario or return period;
simulation duration;
grid size;
timeframes and result moments;
whether sewer storage and sewer outflow are included;
whether sewer overflows are included;
whether groundwater is included;
which infiltration assumptions are used;
which water-depth threshold defines water nuisance;
which water-depth threshold defines affected buildings;
which water-depth threshold defines road accessibility problems;
whether the current situation, future design or both are analysed;
which measures are compared;
whether the analysis is exploratory, planning-level or design-level.

Common example thresholds are:

water nuisance: 0.05 m water depth;
road accessibility problems: 0.10 m water depth;
building impact: project-specific, depending on building type, entrance level and vulnerability.

Relevant pages:

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.

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

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.

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

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.

Check which data is missing for the analysis.
Prepare data as WFS, GeoJSON, GeoPackage or another supported geodata route.
Add the data to the project.
Map the imported data to the correct Tygron object type or attribute.
Check whether the data is spatially correct.
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:

Select the relevant water-depth result.
Select the relevant object category, such as buildings, roads or vulnerable locations.
Define thresholds.
Combine water-depth results with object attributes.
Calculate statistics or classify objects.
Check map output against statistics.
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.