# Development of Driftwood Capture Trellis for Capturing Driftwood in Agricultural Drainage Ditches
## 1 Introduction
In large-scale drainage systems which have high-frequency designations, driftwood capture trellis debris control facilities or retention ponds can be established, but this is not common for most smaller drainage systems located in agricultural and mountainous areas. The U.S. Department of Transportation Federal Highway Administration (FHWA [35]) and the Ministry of Land, Infrastructure, and Transport of Korea recommend the installation of debris control facilities to keep debris out of storm drains connected to the drainage system [35; 37]. Debris control structures are structures placed across well-defined channels to form basins which impede drainage flow. Practices that reduce the quantity of floating debris include directional felling uphill with a tree-pulling system and providing a buffer strip of undisturbed vegetation along the drains. Debris control structures are divided into six groups according to type of debris, as shown in Figure 1.  
Figure 1: Debris control structures: (**a**) deflector; (**b**) rack; (**c**) riser; (**d**) rib; (**e**) fin; (**f**) dam [35]. Debris can be grouped based on size into the following categories: light floating debris (LFD), medium floating debris (MFD), heavy floating debris (HFD), floating debris (FD1), fine detrits (FD2), coarse detritus (CD), and boulders (Table 1). Debris in the drainage from agricultural lands or plains is expected to include smaller twigs, dead leaves, grit, and sand; it is difficult to classify or define clear standards for the classification of such debris. According to the standards of the FHWA [35], LFD can be defined as debris found in drainage from plains and agricultural areas, while other types are found in mountainous areas and near streams [35]. The debris control structures suggested in the past were mostly for large-scale disaster mitigation facilities in mountainous areas and near streams. There is an urgent need for the development of debris driftwood capture trellises in small-scale drainage systems in plains and agricultural lands. Many researchers have studied large-scale facilities, including permeable driftwood control barriers or facilities, in an attempt to alleviate the damage produced by sediment-related disasters. However, driftwood reduction methods in large-scale facilities, which mostly deal with logs, not twigs, in drainage systems, are of limited applicability to smaller facilities. In general, too little attention has been paid to driftwood capture trellises for agricultural drainage ditches, both domestically and internationally. This study intends to develop a driftwood capture trellis that captures driftwood from agricultural drainage ditches. Using a hydraulic experiment, the study estimates driftwood capture efficiency under a variety of experimental conditions and establishes installation standards for agricultural drainage ditches. In addition, it aims to determine whether design discharge is installed and estimate the capture efficiency in various areas, by developing formulas that estimate discharge conditions and capture efficiency.