Trade‐offs among road–stream crossing upgrade prioritizations based on connectivity restoration and erosion risk control

Abstract

Prioritizing projects to improve cost‐effectiveness has become a common practice in natural resources management, especially in selecting sites for river restoration work. Previous studies for prioritizing road–stream crossing upgrade projects focused on either restoring river connectivity or reducing sedimentation, even though crossings can affect connectivity and sedimentation simultaneously. In this study, we simulated site selection to maximize the improvement of connectivity restoration and sedimentation reduction of three prioritization schemes targeting (a) river connectivity, (b) erosion risk, or (c) both objectives concurrently and compared the results. Furthermore, we examined the relationships between the cost‐effectiveness of prioritizations and watershed characteristics. We found significant differences among the effectiveness of prioritization objectives; thus, trade‐offs should be taken into consideration when prioritizing crossings. The incorporation of spatial interdependency among crossings and weighting objectives could significantly change the cost‐effectiveness. We also found that splitting the budget and using a portion to individually prioritize each objective could be more cost‐effective than using the whole budget to achieve concurrent objectives. Watershed characteristics like size and connectivity‐ and sedimentation‐related factors could be used to help identify effective management for both connectivity restoration and sedimentation control.

Response of Sediment Connectivity to Altered Convergence Processes Induced by Forest Roads in Mountainous Watershed

“…As one common way of transmitting runoff and sediment downstream of the road, the road drainage outlet will significantly increase the runoff and sediment content in the downhill direction [17,51]. As a result, the existence of the road not only affects the length of the confluence path, but also the confluence accumulation between the transport path and the stream, thereby changing the spatial distribution of the confluence accumulation in the catchment [26,28]. This phenomenon was further confirmed in this study.…”

“…At the same time, the drainage networks will be extended to places previously not reached which will increase the possibility of runoff and sediment reaching the stream [23], ultimately increasing the sediment connectivity of the watershed [24,25]. In addition, a road-stream crossing affects the confluence characteristics by changing the natural properties of a stream network within a watershed [26], which has been shown to be the main way that sediment-loaded runoff is transferred from roads to streams through a direct path with the highest transmission efficiency [27,28].…”

A Review of the Sediment Production and Transport Processes of Forest Road Erosion

“…These factors encompass the length, slope, and surface area of roads, vegetation coverage, and soil texture. Among these factors, the catchment area defines the upper and lower bounds of runoff and sediment yield in each erosion unit, while slope and length govern the variability within these bounds [53]. Generally, the larger the catchment area or the greater the road slope, the higher the eroded sediment yield.…”

All Fish, All the Time: A Good General Objective for Fish Passage Projects?

“…The extent of “passability”—a term that commonly incorporates both the species and lifestages under consideration and the range of streamflows that allow their passage—is an important issue in frameworks for prioritizing passage projects (Kemp and O’Hanley 2010). Upstream movement by juvenile fishes has received considerable attention (e.g., Forty et al 2016) and many prioritization schemes simply use passability ranging from 0 to 1 as a multiplier in quantitative methods of prioritization (e.g., Lin et al 2020). However, alternative approaches seek to link degrees of passability to their population‐ and community‐level consequences (Kemp and O’Hanley 2010).…”