The paper focuses on secondary bio streams which are not captured efficiently in the value supply chain. Specifically, roadside grass clippings were chosen, based on their logistical optimization potential, direct feasibility, locality, biomass potential, and economic valorization value. The main objective is to determine how this secondary flow can be brought to the “factory gate”—through road transport and inland shipping—and at what cost per unit. To this end, various scenarios were developed for a case study in East Flanders, considering multiple combinations of first collection points, secondary collection points, and processing points. The result is a generically applicable Excel-based tool that combines these variations with a solution considering both inland waterways and road transport. These scenarios become valuable in applying the tool for grass clippings and optimizing this value chain located in East Flanders. The results show that reducing the number of collection points is favorable for the utilization of inland waterways, as it reduces costs related to transshipment. Nevertheless, unimodal road transport is still the most cost-effective method for transporting this secondary material stream from the collection point to the processing point. Consequently, a lower weight and a higher density will lead to lower costs, which eventually bottom out, due to regulations and conditions that must be met.