OM-MADE: An open-source program to simulate one-dimensional solute transport in multiple exchanging conduits and storage zones

OM-MADE (One-dimensional Model for Multiple Advection, Dispersion, and storage in Exchanging zones) is an open-source python code for simulating one-dimensional solute transport in multiple exchanging conduits and storage zones in steady-state flow conditions. It aims at helping the interpretation of multi-peaked skewed breakthrough curves (BTCs) that can be observed in tracer tests conducted in karstic systems. OM-MADE is based on the resolution of classical mass conservation equations. In OM-MADE, all parallel and exchanging flow zones are divided along the direction of flow into reaches, in which all model parameters are kept constant. The total flowrate may be modified through lateral in and outflows. The solute may also be affected by decay processes either in mobile or immobile zones. Each reach is subdivided into discrete segments of equal length. The partial differential equations can be solved using two second order schemes, one based on an operator-split approach, the other on Crank-Nicholson pondered scheme. A verification is performed against analytical solutions, OTIS software (Runkel, 1998), and the Dual-Advection Dispersion Equation (DADE) proposed by Field and Leij (2012). An application to a tracer test carried out in the karstic area of Furfooz (Belgium) is then performed to reproduce the double-peaked positively skewed BTC that has been observed. It constitutes a demonstration of the software capacities in the case of two reaches and three exchanging zones, among which two are mobile ones and one represents a storage zone. It thus permits to verify numerically the consistency of the conceptual interpretation of the observed BTC.