Influence of the in-stream structures and parameters variation on transient storage

In-stream structures are designed to mimic natural topographic features in rivers and have emerged as an effective method for ecological restoration in recent years. However, there is a lack of studies exploring the impact of these structural designs on transient storage characteristics. We implemented a series of weirs and groynes in a stream and conducted conservative tracer experiments to quantify the influence of these structures on solute transport within the stream. Additionally, we utilized the one-dimensional transport with inflow and storage (OTIS) solute diffusive transport model to assess variations in solute transport parameters and characterize transient storage. Our analysis of the OTIS parameters and transient storage index revealed that in-stream structures can enhance the interaction between flowing water in the mainstem area and the transient storage area, consequently improve the stream's transient storage capacity. Notably, weirs had a greater effect on the transient storage characteristics of streams parameters than groynes. Furthermore, the effect of this impact intensified with an increase in the number, spacing, and height of the in-stream structures. However, it was observed that the coupling between the structures decreased simultaneously, resulting in a gradual weakening of the enhancement in transient storage capacity. This study deepens our understanding of how the design factors of in-stream structures influence transient storage characteristics, and provides a theoretical basis for optimizing instream structures in ecological restoration projects.