ABSTRACT Anthropogenic barriers in aquatic habitats have led to fragmentation and decreased fish diversity worldwide. Road crossing barriers such as culverts are a significant source of fragmentation and can impede aquatic organism passage (AOP). Many large extent efforts to inventory road crossing barriers and prioritize restoration efforts do not consider temporal variation in flow. One of the greatest predictors of whether a road‐stream crossing acts as a barrier to AOP is the presence of an outlet drop—the distance between the bottom of a culvert and the water's surface. Increased velocity caused by precipitation events can increase tailwater elevation, decreasing outlet drop height and changing barrier severity during precipitation events. However, little is known about how this change in outlet drop height impacts AOP and what factors drive these changes. We used cameras to gain continuous water level monitoring data to quantify the relationship between precipitation events and outlet drop height. In the spring of 2024, we selected 25 culvert sites in upstate South Carolina and set up cameras to take a photo every 10 min at the outlet of all sites. Out of the 25 sites, we observed connection events at 15 sites. We observed between 1 and 16 unique connection events throughout the study period, and 10 culverts had no connection events. A hurdle model revealed that outlet drop height was negatively associated with the length of connection events and that daily precipitation was positively associated with the length of connection. Cameras can be used as a low‐cost and low‐effort method to monitor barrier severity over time and examine how temporal variation in stream flow impacts AOP at culverts. However, more detailed information on changes in water velocity, depth, and species swimming abilities is necessary to fully evaluate changes in AOP at culverts during storm events.
Twiner et al. (Wed,) studied this question.