---
title: "Cohesive Sediment Option | Sediment Transport"
slug: "cohesive-sediment-option"
description: "Learn about the cohesive sediment option, why they must be flagged in the model input, and the datafile format. "
tags: ["1D river modelling"]
updated: 2022-11-01T15:42:49Z
published: 2022-11-01T15:42:49Z
canonical: "help.floodmodeller.com/cohesive-sediment-option"
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.

# Cohesive Sediment Option

Cohesive sediments are not adequately described by the non-cohesive sediment transport computations in 1D Sediment Transport Solver. Cohesive sizes must therefore be flagged in the model input. This option allows certain of the sediment sizes to be set as cohesive, and enables the additional input required.

Cohesive sediment fractions should have had the Westrich-Jurashek sediment transport equation specified in the general input datablock.

Cohesive sediment fractions are usually described in terms of settling velocity, rather than size, so the settling velocities are input directly here. The sizes input previously are used solely as sediment fraction labels and in the output of the D, Detc sizes, they are not used in the simulations. An example of the structure of this section of the file is shown in Figure 6.

## Datafile Format – Cohesive sediment data block

Line 1 keyword 'COHESIVE'

Line 2 to end of datablock size, threshold, Vs

Where

size = a sediment size from the sediment distribution given in the general datablock

threshold= threshold bed shear stress for erosion (N/m2)

V= settling velocity for the cohesive sediment size (mm/s)