Assessment of the Visual Quality of Sediment Control Structures in Mountain Streams

Sediment control structures such as check dams, groundsills, and revetments are commonly used to balance sediment transport. In this study, we investigated the visual quality of sediment control structures that have been installed to manage mountain streams by analyzing images from the Soil and Water Conservation Bureau (SWCB) of Taiwan. We used visual preference (P) as an indicator in the evaluation of visual quality and considered two softscape elements and four cognitive factors associated with P. The two softscape elements were the visible body of water and vegetation, which were represented by the percentage of visible water (WR) and the percentage of visible greenery (GR). We considered four cognitive factors: naturalness, harmony, vividness, and closeness. Using a questionnaire-based survey, we asked 212 experts and laypeople to indicate their visual preferences (P) for the images. We examined the associations of the P ratings with cognitive factors and softscape elements and then established an empirical relationship between P and the cognitive factors using multiple regression analysis. The results showed that the subjects’ visual preferences were strongly affected by the harmony factor; the subjects preferred the proportion of softscape elements to be 30% WR and 40% GR for optimal harmony, naturalness, and visual quality of the sediment control structures. We discuss the visual indicators, visual aesthetic experiences, and applications of the empirical relationship, and offer insights into the study’s implications.