Tuflow and estry manual Version 3

3.12.1Nodes and Pits

Nodes or pits are specified as points in a 1d_nwk GIS layer. Note: all points are interpreted as being a node or a pit. Pits were introduced as of Build 2005-05-AN, and extended options were also made available for nodes.

Pits have an additional optional feature of automatically inserting a short channel called a pit channel to transfer water between the 2D domain on the surface and a 1D pipe network underground (see Section 3.12.2 below).

As of Build 2002-08-AC, the digitising of nodes was optional. If a node is not found snapped to the end of a channel a new node is created. The ID of the node is the first ten characters of the channel ID with a “.1” or “.2” extension. “.1” is used if the node is at the start of the channel and “.2” if at the end. If more than one channel is connected to the created node, the channel ID that occurs first alphanumerically is used. The automatic creation of nodes can be switched off using Create Nodes.

Note: The use of the term “node” or “pit” in this manual refers to both manually digitised nodes and nodes automatically created at the ends of channels where no digitised nodes exist. The term “pit channel” refers to the small channel automatically inserted at a pit.

Prior to Build 2005-05-AN, the only attribute required for a manually created node was its ID (see Table 4 .10). Several other attributes are now optionally available as discussed below and detailed in Table 4 .10. It is also now not mandatory to specify an ID.

If an ID is specified it must be unique amongst all nodes, and up to 12 characters in length. It may contain any character except for quotes and commas. As a general rule, spaces and special characters (eg. “\”), should be avoided although they are accepted. The same ID can be used for a channel, but not for another node. The Ignore attribute can be used to ignore a node. It is recommended for the Channel_Type attribute that “Node” is entered to easily distinguish nodes from channels when querying objects in the GIS. Prior to Build 2005-05-AC, all other attributes were not used.

Since Build 2005-05-AN, a number of attributes may now, optionally, be used to more easily create a 1D network. These are described in Table 4 .10 and are listed below:

• 
  Assign upstream and downstream inverts at channel ends using the Downstream_Invert attribute of a node.
  
• 
  Add additional storage (as a surface area) to a node using the Length_or_ANA (previously refered to as Length) attribute, or automatically create a nodal area table if no node storage is specified.
  
• 
  Automatically insert a small, zero length channel, called a pit channel, to convey water to/from a 2D overland domain to a 1D pipe network (see Section 3.12.2 below).
  

For specifying node storages see Section 3.13.2.