Investigation of Sand Trap and Bar Screen Mechanisms on Urban Drains (Case Study: Shahjalal Upashahar, Sylhet, Bangladesh)

Improper maintenance, inadequate drainage system design, and increasing non-porous surfaces due to urbanization result in waterlogging in urban areas. Shahjalal Upashahar is a prominent urban area in Sylhet city which faces waterlogging conditions due to sediment deposition, leading to the loss of original drainage channel capacity. This study focused on reducing the sediment accumulation in the drainage channel by implementing a sand trap and bar screen mechanism. To design the sand trap for a 100-year return period, the study area was divided into five sub-watersheds using the ArcGIS tool. Rainfall data (2000-2023) were collected from the nearby meteorological station. Based on the determined slope and length of all sub-catchments, the concentration times range from 10.995 to 13.8707 minutes. Using the concentration time, the rainfall intensity was calculated from the Intensity Duration Frequency curve (IDF). The highest runoff was calculated for all sub-watersheds using the rational equation. The peak discharge for catchments 1 through 5 were 1.263, 1.784, 0.254, 1.183 and 1.326 m3/sec, respectively. The required cross-section of the rectangular sand trap was determined using the equation of continuity Q = AV. The bar screen was designed based on the size of solid waste and the prevailing velocity of flow. In this study, the designed cross-sectional areas of sand traps ranging from 0.38 to 2.26 m2 for five sub-watersheds were expected to reduce sediment accumulation by maintaining full drainage channel capacity.