Routing (attenuation)

Hydrological routing is the process of converting a hydrograph that passes through some part of a flow system to allow for the changes that occur during its passage. There are three main types of routing:

1. catchment routing, which converts a rainfall excess (rainfall - losses) hyetograph into a hydrograph at the catchment outlet, allowing for the distribution of rainfalls over the catchment surface, and various lags or delays along flow paths;

1. river routing, which allows for the changes in hydrographs as they flow along river reaches, caused by variations in the river channel geometry causing storage effects, reservoir routing, which allows for storage effects in a concentrated, 'level pool' reservoir.

Routing includes changes such as translation (the movement of the hydrograph in time) and attenuation (the spreading out of the hydrograph, and consequent reduction in its peak).

​

This is caused by a number of effects.  On a catchment is mainly due to time effects, with rainwater falling on all parts of a catchment taking different times to flow to the catchment outlet, and so spreading out the runoff hydrograph.  Storage and roughness effects also play a minor part.

In a stream, routing effects are mainly due to changes in the stream cross-section creating a number of storages, with roughness playing a minor part, unless there are significant overbank flows.  In a reservoir, storage effects are the sole cause of attenuation.

Within DRAINS, catchment routing occurs in the Horton (ILSAX) time-area calculations and in the non-linear storage routing calculations in the storage routing models.  Stream routing can be carried out in the RAFTS-type storage routing model, in which stream routing reaches offer simple translation and a hydraulic routing procedure.  Translation can also be effected by overflow routes. Detention basin    routing is undertaken using the detention basin facility.

• Related Articles

• Storage routing models

  (a) General As well as the standard Horton (ILSAX) hydrological model for simulating flows from urban areas, DRAINS has optional storage routing models based on procedures applied in three hydrological models that have been used in Australia since ...

• Storage routing calculations

  These are carried out over a series of time steps, with the information obtained from solving equations at one time step being used as an input to the next step. In reservoirs, the information needed is: a relationship between storage and outflow, ...

• Stream routing reach tool

  This link type, , is used to connect nodes and sub-catchments in RORB and WBNM storage routing models that can be used to model broad-scale rural and urban catchments. It performs non-linear routing in these models (the RAFTS storage routing model ...

• Stream routing reach

  This link type, , is used to connect nodes and sub-catchments that form parts of the RORB and WBNM storage routing models which can be used to model broad-scale rural and urban catchments (the RAFTS type model employs the same overflow routing link ...

• Layout for WBNM type storage routing model

  A catchment is divided into sub-catchments that depend on junctions of streams and internal ridge lines. Nodes should be placed at the outlets of self-contained sub-catchments - those at the top of the catchment, with no streamflow from upper ...