---
title: "How to add a new urban subcatchment | Tutorials"
slug: "how-to-add-a-new-urban-subcatchment"
description: "Learn how to add a new urban subcatchment to your urban model. "
tags: ["1D urban modelling"]
updated: 2022-08-21T11:43:14Z
published: 2022-08-21T11:43:14Z
canonical: "help.floodmodeller.com/how-to-add-a-new-urban-subcatchment"
stale: true
---

> ## Documentation Index
> Fetch the complete documentation index at: https://help.floodmodeller.com/llms.txt
> Use this file to discover all available pages before exploring further.

# How to add a new urban subcatchment

**Note:** If you want the area of your subcatchment to be automatically calculated based on the shape you draw on the map, you must first set the area equal to zero in the **Model Defaults**. Recall how to do this from the [Urban Networks](/v1/docs/1d-urban-networks) section.This must be done **before** adding a subcatchment. Once your subcatchment has been drawn, you cannot set the area equal to zero in the node properties to use this functionality. We also recommend confirming the **Infiltration model** set at this point, as this must be consistent for all **Subcatchment** nodes in the network.

To add a new **Subcatchment**, on the **1D Urban Build tab**, initially confirm you are in **1D Urban selection mode** by ensuring the toggle is coloured blue.

On the **1D Urban Build tab**, locate the **Subcatchment** icon.

![](https://cdn.document360.io/5074bc26-a9ef-4bf4-b1de-a5c6ce628aca/Images/Documentation/1DUrbanimagesaddsubcatchment.png)

Click the **Subcatchment** icon and it will be highlighted. If you have your **1D Urban Network** panel visible, you will also notice this becomes greyed out. On the **map** view, click the location you would like to add the first vertex of your Subcatchment.

![](https://cdn.document360.io/5074bc26-a9ef-4bf4-b1de-a5c6ce628aca/Images/Documentation/1DUrbanimagesaddsubcatchment2.png)

Click again in the location you would like to add the second vertex. A straight line will join these points. Continue clicking to add more vertices. We recommend drawing in the clockwise direction. Double-click to add the final vertex and the tool will automatically add a **Subcatchment node** icon inside the polygon drawn.

![](https://cdn.document360.io/5074bc26-a9ef-4bf4-b1de-a5c6ce628aca/Images/Documentation/1DUrbanimagesaddsubcatchment3.png)

Enter the properties of this node in the same way as other nodes, for example by double-clicking the node icon in the **Map** view.