|License||As-is, use at your own risk|
The tank model is a very simple model, composed of four tanks laid vertically in series as shown in Figure 1.
Precipitation is put into the top tank, and evaporation is subtracted sequentially from the top tank downwards. As each tank is emptied, the evaporation shortfall is taken from the next tank down until all tanks are empty.
The outputs from the side outlets are the calculated runoffs. The output from the top tank is considered as surface runoff, output from the second tank as intermediate runoff, from the third tank as sub-base runoff and output from the fourth tank as baseflow.
Despite this simple conceptualisation the behaviour of the tank model is not so simple. The behaviour of the model is strongly influenced by the content of each of the stores. Under the same rainfall and different storage volumes the runoff generated is significantly different.
The tank model is applied to analyse daily discharge from daily precipitation and evaporation inputs. The concept of initial loss of precipitation is not necessary, because its effect is included in the non-linear structure of the tank model.
Figure 1. RRL Tank model
Using the plugin
Load the plugin and use like a standard Rainfall runoff model.
Source code available from http://hg.ewater.com.au/sourceplugin.tankmodel (login required).