Getting Started

A five-minute tour of HydroDesign. This page walks through the full workflow — from account creation to downloading a finished report — in enough detail to produce your first real calculation. For deep method theory see the Design Flood Estimation umbrella article; for the HydroDesign home page see the Knowledge Base landing page.

A five-minute tour

HydroDesign is a design-flood-estimation platform built around a single pipeline: pick a location on the map, choose which calculation methods and return periods you want, submit the request, and receive a full set of engineer-ready deliverables. The platform handles catchment delineation, rainfall extraction, and runoff-parameter lookup automatically — you do not need to assemble the inputs by hand.

The fastest way to understand HydroDesign is to run through one calculation end-to-end. This guide covers the seven steps of that workflow. Expect about five minutes of hands-on time per calculation once you are familiar with the interface.

Prerequisites

You will need a HydroDesign account with at least a small credit balance. New accounts start on the free Stream plan, which includes trial credits sufficient for a first calculation.

Step 1 — Create an account and pick your project

Sign up at app.deltahydro.tech using your work email address. Accounts are verified via a one-time email link; once confirmed, you are taken to the dashboard. From the dashboard you can:

• See your current credit balance — each calculation consumes one credit regardless of how many methods or return periods it contains.
• Browse your existing projects (a project groups related calculations — for example all locations in a road-crossing study).
• Start a new calculation request via the “New Request” button.

How credits work

Calculations are purchased in credit packs. A single request — one catchment, any combination of methods, any combination of return periods — consumes one credit. Credits never expire. The free Stream plan includes enough credits to evaluate the platform; the Pro (River) and Team (Delta) plans include larger monthly allocations.

If you are working as part of a team, switch the active context from the top-right menu: solo projects draw from your personal credit balance; team projects draw from the team’s shared credit pool.

Step 2 — Choose your tool

HydroDesign offers a family of tools rather than a single one-size-fits-all calculator. Which one to use depends on what you are trying to answer. The most common tools are:

Tool	Best for
Rational Method	Small urban catchments (< 25 km²); sizing stormwater pipes and road drains
SCS Method	Small to medium catchments with known Curve Number data
Unit Hydrograph	Medium rural catchments where a full hydrograph is needed
DRH Method	Medium rural catchments with a design rainfall hyetograph
SDF Method	Medium to large rural South African catchments
QRT Calculator	Ungauged rural catchments; regional flood-frequency regression
RMF Calculator	Upper-bound envelope flood for critical infrastructure
Flood Frequency Analysis	Gauged catchments with a long annual-maximum record

If you are not sure which method to choose, the Design Flood Estimation umbrella article includes a full decision guide. As a rule of thumb, the platform’s integrated request flow lets you run several methods at once — it is common and recommended to run at least two independent methods and compare the results.

Standalone tools

In addition to the peak-flow methods, HydroDesign includes standalone tools for Design Rainfall, Watershed Delineation, Watercourse Profile, Flood Routing, Culvert Designer, Channel Analysis, and several more. These can be used on their own or as intermediate steps in a larger workflow.

Step 3 — Select a catchment location

Every calculation begins with a location on the map. This is the outlet point — the downstream end of the catchment you want analysed — and HydroDesign uses it to automatically trace the contributing area upstream.

Select the location by either:

• Clicking on the interactive map. Zoom in using the mouse wheel or pinch gesture; click once on the outlet point. A marker appears and the latitude / longitude is populated.
• Typing coordinates directly in decimal degrees (e.g. -25.7461, 28.1881) or in degrees-minutes-seconds via the coordinate-format toggle.
• Importing a point from a previous calculation or from an external CSV file.

Place the outlet accurately

The outlet point drives everything downstream — catchment area, slope, rainfall, and ultimately the computed peak flow. A few hundred metres of positioning error can change the delineated catchment by an order of magnitude if the outlet sits near a drainage divide. Zoom in to at least 1:5 000 scale and verify the point lies on the correct watercourse.

HydroDesign currently supports outlet points within South Africa’s borders plus a small buffer into neighbouring SADC states. Selecting a point outside the supported region will return an error before credits are consumed.

Step 4 — Configure methods and return periods

Once the location is set, the request form prompts you to choose:

• One or more calculation methods from the Step 2 table. Checking multiple methods runs them all within a single request (still one credit).
• One or more return periods from the seven standard intervals (1:2, 1:5, 1:10, 1:20, 1:50, 1:100, 1:200 year).
• Optional project-level metadata — project name, client reference, notes. These are not used in the calculation but appear in the report.

For a first run, a sensible default is:

• Methods: Rational, SCS, Unit Hydrograph (three independent methods, easy to cross-check)
• Return periods: 1:10, 1:50, 1:100 year (covers typical stormwater, major infrastructure, and critical-facility design points)

Step 5 — Submit the calculation

Click Submit. The platform debits one credit, queues the request, and shows a progress indicator. Behind the scenes HydroDesign:

1. Delineates the catchment upstream of the outlet point.
2. Extracts physiographic parameters (area, slope, flowpath length, land cover, soil group).
3. Queries the rainfall database for the station or grid cell relevant to the catchment.
4. Runs each requested calculation method against the extracted inputs.
5. Assembles the results.

Most calculations complete within a couple of minutes. You will receive an in-app notification and (if configured) an email when the result is ready.

While you wait

Calculations run asynchronously — you can close the tab, start another calculation, or log out entirely. The results remain in your dashboard indefinitely.

Step 6 — Read the results

When the calculation is complete, open the results from the dashboard. The result page is organised as a set of panels, each covering one aspect of the calculation:

• Overview — headline peak flows, catchment area, outlet coordinates, and the methods that were run.
• Peak Flow Comparison — side-by-side table and bar chart of peak flows by method and return period. This is where you check whether the methods agree.
• Hydrographs — time-series plots for methods that produce a full hydrograph (Unit Hydrograph, SCS, DRH).
• Catchment Information — area, centroid, boundary on the map.
• Land Cover & Soils — derived land-cover breakdown and hydrologic soil groups.
• Flowpath — longest flowpath, elevation profile, slope metrics.
• Rainfall — extracted IDF values used in the calculation.
• Per-method panels — detailed intermediate values for each method run.

A comprehensive walk-through of each panel is in Understanding Your Results.

Interpreting disagreement between methods

If two methods give very different peak flows, that is a feature, not a bug — it tells you something about the uncertainty in the design flood estimate. Read the Peak Flow Comparison panel carefully, consider which method’s assumptions are best suited to your catchment, and document the rationale for the adopted design value in your engineering report.

Step 7 — Export deliverables

Engineering studies need engineering-grade deliverables — not just a number on a screen. HydroDesign exports:

• Word report (.docx) — a fully-formatted report including catchment map, parameter tables, method-by-method calculations, hydrograph plots, and references. Ready to be inserted into a larger submission document.
• Excel workbook (.xlsx) — tabular export of every numerical input and result. Useful for bespoke post-processing and for inclusion in calculation spreadsheets.
• GIS package — catchment boundary, flowpath, and outlet point as shapefiles (or GPKG, depending on the tool). Opens directly in QGIS, ArcGIS Pro, or Civil 3D.
• CAD (.dxf) — catchment boundary and flowpath as layered DXF lines. Drops straight into a CAD drawing at the project coordinate system.

Full details of the export formats and how they are structured are in the Exports & Deliverables section of the umbrella guide.

Reproducibility

Every exported report includes a calculation hash — a short fingerprint of the inputs and outputs. Cite this hash in your project file when the design flood is adopted; it lets a reviewer recreate exactly the same calculation by submitting the same request with the same parameters.

Next steps

You have now run a complete HydroDesign calculation end-to-end. From here, the natural next steps are:

• Go deeper on a method. Every peak-flow method has a dedicated guide linked from the Knowledge Base landing page. The Rational Method is the most commonly-used starting point.
• Explore the standalone tools. Watershed Delineation, Design Rainfall, and Flood Routing can all be used independently of the main request flow.
• Read the decision guide. The Design Flood Estimation umbrella article includes a method-selection decision guide that will save you time on subsequent projects.
• Check the FAQ below, or email the support team.

FAQ

How do credits work?

One calculation request = one credit, regardless of how many methods or return periods the request contains. Standalone tools (Design Rainfall, Watershed Delineation, etc.) typically consume one credit per run. Credits never expire; monthly allocations on Pro and Team plans are topped up on the billing anniversary.

Which method should I use?

There is no single correct answer — the choice depends on catchment size, land use, and what question you are answering. As a rule of thumb:

• Small urban catchment, sizing a pipe: Rational Method.
• Rural catchment, full hydrograph needed: Unit Hydrograph or SCS.
• Ungauged rural catchment: QRT plus SDF, compared.
• Upper-bound flood for critical infrastructure: RMF plus PMP.
• Gauged site with a long record: Flood Frequency Analysis on the observed series.

See the full decision guide in Design Flood Estimation.

What data sources does HydroDesign use?

HydroDesign is built on authoritative South African and international datasets:

• DEM — MERIT-Hydro (90 m), used for catchment delineation, flowpath, and slope.
• Rainfall — WR2012 / Smithers & Schulze (2003) design rainfall surfaces.
• Land cover — national land-cover classification (most recent version).
• Soils — national hydrologic-soil-group layer derived from the land-type inventory.
• Gauged flow records — DWS hydrological station archives.

Each calculation reports the specific dataset versions used, so your report is explicit about provenance.

Is my data private?

Yes. Your calculation inputs, outputs, and project metadata are visible only to you (and to other members of your team, for team projects). HydroDesign does not resell or anonymise customer data for third parties. Standard GDPR / POPIA protections apply.

Where do I go for help?

Email support@deltahydro.tech. Responses are typically within one working day. For engineering-interpretation questions (“I ran this calculation, the result looks wrong — can you check?”), attach the calculation hash and a brief description of what surprised you.