Abstract
Check dams are one of representative structural measures to reduce sediment disaster at a forest watershed. Therefore, it is essential to assess the structural vulnerability and functionality of check dams in the management of sediment disaster risk at watersheds. This study examined the main types of damages and deterioration characteristics in concrete and stone check dams, which comprise more than 80.0% of Korea’s check dam stock. This was based on the 4-step condition assessment, which is the modified version of condition assessment methodology for embankment dams to meet the characteristics of check dams. As a result, the damages and deterioration of concrete check dams were classified into ten representative types. And representative damage types of stone check dams were classified into nine types. The condition assessment results demonstrated that the spillway part frequently contacted with water and debris flows was deteriorated approximately 1.2 times faster than the wing parts for both concrete and stone check dams, and the maintenance demands of both types of check dams increased 15–20 years after construction. Thus, these deterioration characteristics of concrete and stone check dams should be considered in decision-making to determine maintenance priorities among the check dams stock. Furturemore, we analyzed the relationship between condition index and service time in the examined concrete and stone check dams. The degree of deterioration in concrete and stone check dams increased significantly as the service time increased. Based on the relationship between condition index and service time, we classified deterioration characteristics of check dams into two groups: 1) those that follow the average deterioration trends of their facility group (Group II) and 2) those that undergo an unexpected end-of-service life because of exceptional incidents or severe defects (Group I). We hope that our work will form a useful resource for engineers and decision-makers involved in planning, designing, constructing, and maintaining check dams.
Highlights
Mountain streams and rivers are main passages of sediments generated from slopes and floodplains
A total of 235 instances of deterioration were observed on the 30 reviewed concrete check dams (Figure 6 and Figure 7). These were classified into ten representative types: through crack (TC), surface crack (SC), joint deterioration (JD), abrasion/erosion (AE), leakage (L), TABLE 5 | Use of the check-dam condition grade and the maintenance measures, which are based on KISC’s (2019a) condition index (CI)
Sixteen instances were found on dam crests, and three of these were Grade C damage, which occurred at the shrinkage joints and extended to the downstream face
Summary
Mountain streams and rivers (hereinafter “Mountain Stream”) are main passages of sediments generated from slopes and floodplains This sediment transport process from a forest watershed sometimes causes debris flows and large-scale fluvial transport, resulting in great damage to developed areas on a downstream alluvial fans and flood plains (Rickenmann and Koschi, 2010). Its superannuation due to the deterioration of structure and the reduction of debris storage capacity sometimes causes the phenomenon of large sediment yield that results in great damage to downstream areas (Hueble and Fiebiger, 2005; Suda et al, 2009; Dell’Agnese et al, 2013; Mazzorana et al, 2014) It is important in the management of sediment disaster risk at forest watersheds to assess the durability, performance, and sustainability of check dams constructed on mountain streams to inform management and maintenance decision-making and policy. The method is helpful to identify objects to need repair, but its application is limited in the analysis that requires differentiation within the individual structures (e.g., service life analysis and prioritizing maintenance work orders)
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