Braided rivers are a fluvial class characterized by the presence of multiple channels with different sizes and hydrological properties. The channels diverge and intersect continuously thus forming an extremely complex network. When a substance (like a chemical, a nutrient or a pollutant) is introduced in the watercourse, it undergoes a mixing effect which can be partly attributed to the river geomorphology, i.e. the properties of the network. This phenomenon manifests itself in a spread of travel time distributions at the outlet and is known as geomorphological dispersion. In our thesis work we develop a mathematical model for this dispersion process. Starting from the original geomorphological instantaneous unit hydrograph (GIUH) theory, we adjust the hypothesis to apply it to the case of braided rivers and obtain a closed form to compute outlet discharges with a dependency on geomorphology.