4.4. Sewerage

To model the sewerage system you will need different types of structures. A sewerage model can be solely the sewerage system itself (1D), or it can interact with the surface using 2D raster-files (1D/2D). This tutorial shows you what steps you need to take to add these elements to an existing model. The first thing you must do is activate 1D flow in the global settings. Also consider the following parameters in the global or numerical settings:

  • manhole_storage_area
  • advection_1d
  • max_angle_1d_advection
  • max_degree
  • use_of_nested_newton

If you want to make a solely 1D-sewerage model you have to define the inflow parameters. For more information, see Inflow.

4.4.1. Manholes

Manholes are the base of your sewerage model, because they define the locations where the 1D sewerage system can interact with the surface. Each manhole must have a volume and refer to a connection node.

To add a manhole consider the following steps:

  1. First, load the table v2_connection_nodes (point geometry) from the spatialite database if you haven’t already.
  2. Each manhole needs to be linked to a connection node, which determines its geographical location.
  3. Furthermore, each manhole must have dimensions. You have several options to define these dimensions. Check out the the Database overview for more details. Note that manholes do not refer to the cross section definition table (as do the structures). The drain_level determines the elevation at which the manhole can interact with the surface and water can flow in or out of the manhole. This is only used in case of connected manholes.
  4. The manholes must have manhole_indicators (what kind of manhole it is) and calculation_type. The calculation_type defines whether, and how, the water can flow in or out of the manhole.
  5. In case of a purely 1D sewerage model, the manhole storage area has to be defined in the global settings. This determines the size of the ‘storage’ that is used as a substitute to determine the volume at street level when the water rises above the drain_level in case of connected manholes.

4.4.2. Structures (sewerage)

Sewerage structures in 3Di are always a connection between two connection nodes, without their own geometry. 3Di supports four types of structures in sewerage systems:

  1. Pipe
  2. Weir
  3. Orifice
  4. Pumpstation

Check out the Database overview for how use the structure attributes. Below, some specific details are listed.

  • The shape of the pipe, weir and orifice is stored in the cross section definition table. So make sure you have some available before you start adding these structures.
  • To add a structure you have to define the correct start and end connection node id in the sqlite tables. You must work in the v2_structure table, editing in views is not supported.
  • The pumpstation pumps from the start node to the end node. You can choose how it is controlled using the type attribute. It is possible to leave the end node blank (NULL). In that case the pumpstation pumps water ‘out of the model’ and functions as a boundary condition. This could, for example, simulate the final pumpstation that pumps the water to the sewage treatment plant.

4.4.3. Impervious surfaces

It is also possible to use a solely 1D-sewerage model without any 2D component. If that is the case make sure you activate “use_0d_inflow” in the global settings. In this case you force the ‘0D-surfaces’ into the sewerage system. This is done by linking the ‘0D-surfaces’ (v2_impervious_surface) to a connection node (using v2_impervious_surface_map), check the Database overview for more details.

To calculate the dry weather flow, i.e. (household) wastewater, you have to define the ‘nr_of_inhabitants’ and ‘dry_weather_flow’ in the v2_impervious_surface table.

4.4.4. 1D boundary conditions

Boundary conditions for the 1D system are placed on connection nodes. They can only be placed on connection nodes that are connected to a single structure. So not on structures or embedded or connected channels. Check the different types of boundary conditions available in the Database overview.

The timeseries field in the spatialite database can only be filled by copy-pasting your timeseries into the spatialite as QGIS does not allow you to enter a newline. You may use this example:

0,0.000000
15,1.000000
30,2.000000
45,3.000000
60,2.000000
9999,2.000000