# A Saint-Venant shallow water model for overland flows with precipitation and recharge

## TL;DR

This paper introduces a one-dimensional Saint-Venant model for overland flows that incorporates recharge from rainfall and infiltration, derived from Navier-Stokes equations, with new friction terms and a novel entropy function.

## Contribution

It presents a new overland flow model including recharge effects, a novel entropy function, and a finite volume scheme validated with numerical and experimental data.

## Key findings

- Model recovers existing models as special cases
- Incorporates water-mixing friction dependent on recharge rate
- Validated through numerical comparisons and experimental data

## Abstract

We propose a one-dimensional Saint-Venant (open channel) model overland flows including a water input--output source term modelling recharge via rainfall and infiltration (or exfiltration). We derive the model via asymptotic reduction from the two-dimensional Navier--Stokes equations under the shallow water assumption, with boundary conditions including recharge via ground infiltration and runoff. This new model recovers existing models as sepcial cases, and adds more scope by adding a water-mixing friction terms that depends on the rate of water recharge. We prospose a novel entropy function and its flux, that are useful in validating the model's conservation or dissipation properties. Based on this entropy function we propose a finite volume scheme extending a class of kinetic schemes and provide numerical comparisons with respect to the newly introduced mixing friction coefficient. We also provide a comparison with experimental data.