---
title: "Modified Parker (1990) Bedload Equation | Sediment Transport"
slug: "modified-parker-1990-bedload-equation"
description: "Learn about the modified Parker (1990) bedload equation and when it's applicable. "
tags: ["1D river modelling"]
updated: 2022-08-21T17:40:19Z
published: 2022-08-21T17:40:19Z
canonical: "help.floodmodeller.com/modified-parker-1990-bedload-equation"
stale: true
---

> ## Documentation Index
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# Modified Parker (1990) Bedload Equation

The modified Parker bedload equation incorporates the method of critical stress calculation of Shvidchenko (2000). The general form of the modified equation is the same as the original one:

![image048 (1)](https://cdn.document360.io/5074bc26-a9ef-4bf4-b1de-a5c6ce628aca/Images/Documentation/image048%20%281%29.gif)

where

![image052(2).gif](https://cdn.document360.io/5074bc26-a9ef-4bf4-b1de-a5c6ce628aca/Images/Documentation/image052%282%29.gif)

![image056(1).gif](https://cdn.document360.io/5074bc26-a9ef-4bf4-b1de-a5c6ce628aca/Images/Documentation/image056%281%29.gif)

and the normalized dimensionless bed shear stress ![image098.gif](https://cdn.document360.io/5074bc26-a9ef-4bf4-b1de-a5c6ce628aca/Images/Documentation/image098.gif) is defied as

![image100.gif](https://cdn.document360.io/5074bc26-a9ef-4bf4-b1de-a5c6ce628aca/Images/Documentation/image100.gif)

where

![image102.gif](https://cdn.document360.io/5074bc26-a9ef-4bf4-b1de-a5c6ce628aca/Images/Documentation/image102.gif)

![image078(1).gif](https://cdn.document360.io/5074bc26-a9ef-4bf4-b1de-a5c6ce628aca/Images/Documentation/image078%281%29.gif)

![ image080(1).gif](https://cdn.document360.io/5074bc26-a9ef-4bf4-b1de-a5c6ce628aca/Images/Documentation/image080%281%29.gif)

and ![image104.gif](https://cdn.document360.io/5074bc26-a9ef-4bf4-b1de-a5c6ce628aca/Images/Documentation/image104.gif) is the reference stress corresponding to a small reference transport rate ![image106.gif](https://cdn.document360.io/5074bc26-a9ef-4bf4-b1de-a5c6ce628aca/Images/Documentation/image106.gif), which is related to the Shvidchenko’s (2000) critical stress as

![image108.gif](https://cdn.document360.io/5074bc26-a9ef-4bf4-b1de-a5c6ce628aca/Images/Documentation/image108.gif)

The value of critical stress ![image110.gif](https://cdn.document360.io/5074bc26-a9ef-4bf4-b1de-a5c6ce628aca/Images/Documentation/image110.gif) is defined as:

![image112.gif](https://cdn.document360.io/5074bc26-a9ef-4bf4-b1de-a5c6ce628aca/Images/Documentation/image112.gif)

a is the particle mobility factor,

![image114.gif](https://cdn.document360.io/5074bc26-a9ef-4bf4-b1de-a5c6ce628aca/Images/Documentation/image114.gif)

b is the mixture mobility factor,

![image116.gif](https://cdn.document360.io/5074bc26-a9ef-4bf4-b1de-a5c6ce628aca/Images/Documentation/image116.gif)

![image118.gif](https://cdn.document360.io/5074bc26-a9ef-4bf4-b1de-a5c6ce628aca/Images/Documentation/image118.gif) is the mixture geometric standard deviation (for bed surface):

![image120.gif](https://cdn.document360.io/5074bc26-a9ef-4bf4-b1de-a5c6ce628aca/Images/Documentation/image120.gif)

![image122.gif](https://cdn.document360.io/5074bc26-a9ef-4bf4-b1de-a5c6ce628aca/Images/Documentation/image122.gif) is the hiding function,

![image124.gif](https://cdn.document360.io/5074bc26-a9ef-4bf4-b1de-a5c6ce628aca/Images/Documentation/image124.gif)

and e is the hiding parameter,

![image126.gif](https://cdn.document360.io/5074bc26-a9ef-4bf4-b1de-a5c6ce628aca/Images/Documentation/image126.gif)

The suggested applicability of the modified Parker equation is for uniform/graded coarse sand and gravel.