Technical details

This part gives some insight on how Itzï works. More details about the implementations could be find in the articles cited in Publications section.

Overland flow

General equation

The surface model of Itzï is using an explicit damped local inertia numerical scheme described in the following articles:

De Almeida, G. a M., Bates, P., Freer, J. E., & Souvignet, M. (2012). Improving the stability of a simple formulation of the shallow water equations for 2-D flood modeling. Water Resources Research, 48(5), 1–14.

De Almeida, G. a M., & Bates, P. (2013). Applicability of the local inertial approximation of the shallow water equations to flood modeling. Water Resources Research, 49(8), 4833–4844.

This numerical scheme is using a simplification of the Barré de Saint-Venant equations that neglect the convective inertia term. It is applied on a regular staggered grid. The time-step duration is calculated at every time-step.

Automated flow routing

When the water depth is under a user-defined threshold, the flow is calculated using a user-given velocity, following a methodology described here:

Sampson, C. C., Bates, P. D., Neal, J. C., & Horritt, M. S. (2013). An automated routing methodology to enable direct rainfall in high resolution shallow water models. Hydrological Processes, 27(3), 467–476.


Infiltration could be calculated using the well-known Green-Ampt model. Alternatively, the user could set the infiltration rate as a forcing.