---
title: "Routing Velocity Calculation | Technical Reference"
slug: "routing-velocity-calculation"
description: "Learn about the routing velocity calculation and the power law function. "
tags: ["1D river modelling"]
updated: 2022-08-22T09:22:22Z
published: 2022-08-22T09:22:22Z
canonical: "help.floodmodeller.com/routing-velocity-calculation"
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.

# Routing Velocity Calculation

If the flood routing model is to going be used with a water quality simulation, then an approximate formula must be used to calculate nodal velocities.

The node types forming the flood routing model are:

- [Muskingum Routing](/v1/docs/muskingum-routing)
- [VPMC Routing](/v1/docs/vpmc-routing)
- [VPMC Cross-Section](/v1/docs/vpmc-cross-section)
- [VPMC Routing Section](/v1/docs/vpmc-routing-section)

The velocity is then used to determine flow area at each timestep. This value is stored in the Mode results field for the node and will be used for future water quality runs.

The following options are available to specify velocity as a function of flow.

## **Power Law Function**

|  | For Q > Qo \| V = Vo + a( Q - Qo )b \| (1) \| \| --- \| --- \| and for Q £ Qo \| V = Vo \| (2) \| \| --- \| --- \| where: V = Velocity defined in the Rating Curve (VQ Rating) Vo = Minimum Velocity Q = Flow defined in the Rating Curve Qo = Minimum Flow a = Velocity Scaling Parameter b = Velocity Power Parameter The second formulation is introduced to avoid potential problems when the flow dips initially, possibly attaining a negative value; a property associated with the Muskingum algorithm. These parameters are defined in the data fields topics for each of the flood routing node types. |
| --- | --- |
| V = Vo + a( Q - Qo )b | (1) |
| V = Vo | (2) |

## **User Supplied Relationship**

In this case you provide a rating curve relating velocity and flow and the Flood Modeller linearly interpolates between these values.

## **Derivation from Section Geometry**

This method is only available for the [VPMC Cross-Section](/v1/docs/vpmc-cross-section) node.

The velocity is determined from the supplied section details using Manning's equation in the usual way.