---
title: "Diffusion Data Fields | Definitions"
slug: "diffusion-data-fields"
description: "Learn about data input and the datafile format required for diffusion in the water quality solver. "
tags: ["1D river modelling"]
updated: 2022-09-22T14:47:31Z
published: 2022-09-22T14:47:31Z
canonical: "help.floodmodeller.com/diffusion-data-fields"
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.

# Diffusion Data Fields

## Data Input

In order to input the required information for this pollutant into the Water Quality model, the user needs to make sure that the Tab Diffusion appears in the WQ General Tab (please follow the description on the page [Preparing a Water Quality Datafile](/v1/docs/preparing-a-water-quality-datafile) for this). Then the user needs to select the Tab Diffusion and type in the necessary information for this pollutant in the fields which are shown on this Tab. Alternatively the necessary information for this pollutant can be typed in the .con file opened in a Textpad editor in the datafile format mentioned below.

## Datafile format

Depending on the form of dispersion coefficient which the user wishes to simulate there are five different data formats.

*For constant diffusion everywhere within the model use:*

Line 1 DIFFUSION

Line 2 CONSTANT

Line 3 d0

Where:

DIFFUSION = keyword

CONSTANT = keyword

d0= Value of constant dispersion coefficient, D0(m2/s).

*For a variable value of the constant diffusion coefficient use:*

Line 1 DIFFUSION

Line 2 VARIABLE

Line 3 label, d0

Above line is repeated for each node in the model.

Where:

DIFFUSION = keyword

VARIABLE = keyword

label = Node label

d0 = Value of constant dispersion coefficient, D(m2/s).

*For estuary type diffusion use:*

Line 1 DIFFUSION

Line 2 ESTUARY

Line 3 azero, uzero, szero, dzero

Line 4 d0, d1, d2

Where:

DIFFUSION = keyword

ESTUARY = keyword

label = Node label

d0 = Value of constant dispersion coefficient, D(m2/s).

azero = Representative cross-sectional area at seaward boundary (m2)

uzero = peak tidal velocity at seaward boundary (m/s)

szero = salinity at seaward boundary (ppt)

dzero = representative saline intrusion length (km).

d0, d1, d2 = Value of empirical longitudinal dispersion coefficients D, Dand D(m2/s).

*For river applications use:*

Line 1 DIFFUSION

Line 2 RIVER

Line 3 d0, d1

Where:

DIFFUSION = keyword

RIVER = keyword

d0, d1 = Value of longitudinal dispersion coefficients D(m2/s) and D

*Where the user wishes to use different types of dispersion coefficients in different parts of the model use:*

Line 1 DIFFUSION

Line 2 DYNAMIC

Line 3 azero, uzero, szero, dzero

Line 4 Label, type, d0(n), d1(n), d2(n)

Line 4 is repeated for each node.

Where:

DIFFUSION = keyword

DYNAMIC = keyword

azero = Representative cross-sectional area at seaward boundary (m2)

uzero = peak tidal velocity at seaward boundary (m/s)

szero = salinity at seaward boundary (ppt)

dzero = representative saline intrusion length (km).

Label, type, d0(n), d1(n), d2(n) = Node label, diffusion type (keyword 'RIVER' or 'ESTUARY'), value of longitudinal dispersion coefficients D, Dand D(m2/s). (If type = 'RIVER' then D2 is not used and should be set to zero by the file editor).

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Overview [Diffusion](/v1/docs/diffusion)