Getting Started with 1D Urban Modelling

In this guide, we introduce 1D urban modelling. You will load an urban network and visualise aspects of the underlying drainage system. You will learn how to edit the properties of the nodes and links that make up the network, and how to adjust settings in the associated simulation. Finally, you will run a 1D urban simulation and explore a selection of the multiple ways Flood Modeller allows visualisation of the results from this.

The data used in this guide is available below.

Introduction

In this guide, we will look at loading an existing 1D urban network into Flood Modeller, running a simulation and viewing the results from this.

We assume (and highly recommend!) readers of this guide have previously read the Introduction to flood modelling, however the guide can still be followed without having done so.

Please note that there are a variety of ways to undertake different tasks in Flood Modeller. Throughout this guide, we provide details of selected methods only.

We will use data contained in the Urban Network.zip folder for this tutorial. This can be downloaded via the link above.

Let’s get going!

Step 1

Initially open Flood Modeller (or start a new project if already open).

A project file references all the different parts of the model – you might refer to multiple network files and simulation files, among other file types, all within a single project.

Step 2

Let’s add a background map and save the project before progressing.

Background mapping is for visualisation only and is not used as part of the calculations.

Flood Modeller will automatically select the default projection specified in the ‘Application Settings’ window, which will be set at OSGB 1936 as needed (unless you have changed your default projection, in which case you will want to adjust the projection for this tutorial).

If you are having issues with your basemap not displaying, the article here may help.

Step3

Load the network Urban_Network.inp (in the Urban Network folder). This shows the drainage system itself in the map window. This consists of a series of icons, lines and polygons that represent the nodes and links within the network. Save the project again.

The map view shows this urban network consists of a Rain Gage node and various Subcatchment nodes. The Rain Gage node specifies the rain falling on each subcatchment, and thus the flow entering the drainage system. Junction nodes are used through the urban network and Conduit links allow the water to flow between these nodes. These specify details such as the shape and roughness of the pipes. Finally, a boundary is necessary to allow water to leave the system; an Outfall node is used in this case.

Your map will have automatically adjusted to 1D Urban selection mode when you loaded the urban network. This can be switched between urban and river through the right-click menu on the map view. For this tutorial, urban selection mode is used throughout.

Step 4

The urban network has loaded in several areas of the interface.

Turning labels on (using the checkbox on the Home or 1D Urban Build tab) makes it clear which nodes are closer to the Outfall node (such as J1) and which are further (such as J12).

Alongside the nodes and links in the map view, you will also see the urban network loaded into the Project panel on the left of the screen, under both the 1D Urban Networks and Simulations sections.

The urban network is also visible in the 1D Urban Network panel on the right. In this panel, tabs are provided to enable you to change view between the nodes and links that make up the network.

Step 5

View the details of some of the Conduit links. Notice the shape used and the other options provided here.

Check the Manning’s N is set to 0.012 and that the length is provided in metres.

In second-level windows (for example, the Cross-Section Editor window accessed via the Shape field) click the X (top-right) or the Cancel button to close the window and disregard any changes made. Click OK to close the window and retain any changes made.

Step 6

The Rain Gage node specifies the rainfall falling on the Subcatchment nodes, which then is transferred to flow entering the urban network. View the Rain Gage node and look at the time series assigned.

An error has been made in the entry at 05:00; replace the value of 100mm with 200mm and view a plot of the time series this now gives. Also take note of the start and end time of the rain – we will need to ensure the simulation itself runs over the same time period (or longer). Ensure you save this change to your urban network.

The time series defined in a Rain Gage node will affect any Subcatchment node assigned to that Rain Gage, and therefore the placement of the Rain Gage node on the map is not important. In this instance, the node has been placed at the location of a real gage. Rain Gage nodes will always appear at the top of your urban network in the Nodes tab of the 1D Urban Network panel.

Since Flood Modeller prompts you to choose a filename when creating a new file, do not be tempted to choose an existing one (since this will be overwritten) – always choose a new filename.

Step 7

Confirm the details used in the simulation associated to the urban network through the model settings.

Dates are given in the format month/day/year and should match the time series details provided in our Rain Gage node. Check that the timestep used is 2.5 seconds – your timesteps should always be reviewed prior to a run.

Larger timesteps are advantageous for faster simulation runtimes but could be too coarse to capture the detail necessary or could lead to large “jumps” in data calculated (which in turn can lead to instabilities and cause a simulation to crash). When running integrated simulations, it is also necessary to ensure timesteps of the various components are multiples of each other, but this is not something we need to consider for the purposes this guide.

Step 8

The simulation associated to your urban network is ready to run! You initially need to highlight this in the Simulations section of the Project panel.

The simulation itself should be very fast to complete. View the variables displayed and other information output at runtime.

Once your simulation is complete, you can just close the window – the results are automatically saved in the same folder as your project. For urban only simulations, these are contained in a file with extension .out.

Step 9

Now let’s view some of the results. Create a Long Section plot of your results.

If you have selected some nodes within your network beforehand, the plot will show the most direct “route” through these nodes. Otherwise, the plot shows the most direct “route” through all nodes as listed in the 1D Urban Network panel, excluding Rain gage and Subcatchment nodes. In our case, this is from Junction node J1 to the Outfall node. We recall from step 4 that some nodes Junction nodes have a longer “route” to the Outfall node than others.

On opening, the plot shows the data at the start of the simulation. Change the time to automatically update the plot and see water level adjust accordingly.

Step 10

Look at some Long Section plots through some other routes of the urban network. Animate a Long Section plot to see the water levels changing along the route.

Time Series plots are also available for your 1D urban results, with options provided to plot flow, stage, velocity and water depth, alongside other outputs.

Summary

You have now had an initial introduction to 1D urban modelling.

We loaded an urban network into Flood Modeller and noticed how it involved multiple nodes and links. In our particular urban network, a Rain Gage node detailed the water falling on various Subcatchment nodes, and in-turn entering the system through Junction nodes. We edited the rainfall time series assigned to the Rain Gage node, and saw how easily we could view, edit, and plot this data.

Conduit links were used to enable the water to flow between the Junction nodes. We viewed the properties of these links and explored the variety of shapes available and how to change parameters used. We observed the general schematisation of the drainage system; taking note that the network was completed with an Outfall node located near to the river, and that certain Junction nodes had a longer “route” through to the Outfall
node than others.

We explored the settings used in the simulation associated to the urban network, using the tabs to navigate through sections of details such as the routing model selected and the timesteps used. We ensured our start and end times were sufficient (to cover the time of the storm!) and selected a timestep of 2.5 seconds whilst saving the results every 15 minutes. We then ran a 1D urban simulation using settings.

Finally, we visualised the results from our 1D simulation. We created Long Section plots for various “routes” through the drainage system and saw how intuitive it is to adjust the data plotted, through selection of both different nodes and different times. We animated the stage data calculated, showing the water level varying over time. We discussed options provided via Time Series plots to plot flow, stage, velocity and water depth, alongside other outputs. The water exiting the urban network through the Outfall node was completely lost from the system for our simulation. To explore where this water goes, together with any other water leaving the system (for example, flooding out of Junction nodes), we would need to integrate our 1D urban network with other modelling components; connecting to a 1D river network and/or 2D domains. 

What’s next?

You may be interested in more about 1D Urban Modelling

Alternatively, find out more with our other Getting Started guides:

Getting Started with 1D River Modelling

Getting Started with 2D Modelling