---
title: "Junction | Technical Reference"
slug: "junction"
description: "Find the data, theory and guidance for the junction unit. "
tags: ["1D river modelling", "junction"]
updated: 2022-08-08T09:17:58Z
published: 2022-08-08T09:17:58Z
canonical: "help.floodmodeller.com/junction"
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.

# Junction

The Junction unit is applied at the division of a single channel into several channels or the confluence of many channels into one. It may also be used to connect an open channel directly to a conduit if entry and exit losses are insignificant. It may also be used when adding bypass/overspill structures or adding structures in parallel.

## Data

| Field in Data Entry Form | Description | Name in Datafile |
| --- | --- | --- |
| Node 1 | First connecting node name | Label1 |
| Node 2 | Second connecting node name | Label2 |

## Theory and Guidance

The Junction models an open channel junction.

The Junction is applied at the division of a single channel into several channels or the confluence of many channels into one or both. It may also be used where structures in parallel or bypass/overspill structures are being modelled. The Junction may also be used to connect an open channel directly to a conduit if entry and exit losses are insignificant.

### Equations

The equations used to model junctions are flow continuity:

|  | \| Q1 + Q2 + Q3 + .... = 0 \| (1) \| \| --- \| --- \| |
| --- | --- |
| Q1 + Q2 + Q3 + .... = 0 | (1) |

and equality of water surface level:

|  | \| h1 = h2 = h3 .... \| (2) \| \| --- \| --- \| |
| --- | --- |
| h1 = h2 = h3 .... | (2) |

### General

Junctions must not be connected to other junctions or reservoirs.

Bifurcating junction outflows may be connected to [Abstractions](/v1/docs/abstration). The abstractions typically define logical rules to govern the split of flow.

## Datafile Format

Line 1 - Keyword 'JUNCTION' [comment]

Line 2 - Keyword 'OPEN'

Line 3 - Labels for the junction (two or more)

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