Assessment of sediment exclusion efficiency for several modified labyrinth weirs
Tóm tắt
A trapezoidal labyrinth weir is a general transverse hydro-structure typically placed across rivers that causes longitudinal sediment discontinuity and affects riparian ecological system. A sediment exclusion labyrinth (SEL) weir is a modification designed to increase sediment exclusion from upstream to downstream over or through it. Hydraulic model experiments were carried out in straight rectangular cross-sectional open channel (15 m in length and 0.82 m in width). Four different shapes of weirs were examined. type 1 was a general labyrinth weir, whereas types 2–4 were SEL weirs with an inclined bottom slope (type 2), open slots (type 3), and reversed-wedge type holes (type 4). Standard sand (Jumunjin, Korea, d
50 = 0.56 mm, σ
g = 1.48, SG = 2.65) was uniformly supplied upstream using an in-house grooved drum, and sediment exclusion efficiency was calculated from the ratio of sediment amount to excluded sediment yield for each type of weir. Higher efficiencies were founded in all SEL weirs compared with the sediment exclusion efficiency of the type 1 weir. In particular, type 2 and type 4 weirs were easy to construct and their flow patterns and hydraulic performance were similar to those of type 1. Finally, their sediment exclusion efficiencies were higher under a normal water level (F
r ≤ 0.2), whereas the type 3 weir was the pattern favorable for a high water level (F
r > 0.2) because its discharge capacity was significantly higher. Sediment exclusion characteristics were analyzed in terms of flow rate based on the decomposition analysis of residual sediment particle size distribution. It is expected that the results from this study will be used to design SEL weirs as basic materials if more hydrodynamic parameters are studied and combined with field monitoring.
Tài liệu tham khảo
Bagnold RA (1966) An approach to the sediment transport problem from general physics. US Geol Surv Prof Paper 422(1):231–291
Bhuiyan F, Hey RD, Wormleaton PR (2007) Hydraulic evaluation of W-weir for river restoration. J Hydraul Eng 133(6):596–609
Bunt CM, Cooke SJ, McKinley RS (1998) Creation and maintenance of habitat downstream from a weir for the greenside darter, Etheostoma blennioides: a rare fish in Canada. Environ Biol Fishes 51(3):297–308
García MH (2008) Sedimentation engineering: processes, measurements, modeling, and practice, vol 110. ASCE Publications, Reston
Im, JH (2007) Estimation of discharge coefficient with shape of labyrinth weir. Dissertation, Hongik University
Saffman P (1965) The lift on a small sphere in a slow shear flow. J Fluid Mech 22(02):385–400
Shields FD Jr, Copeland RR, Klingeman PC, Doyle MW, Simon A (2003) Design for stream restoration. J Hydraul Eng 129(8):575–584
Shields FD Jr, Morin N, Cooper CM (2004) Large woody debris structures for sand-bed channels. J Hydraul Eng 130(3):208–217
Taylor G (1968) The performance of labyrinth weirs. Dissertation, University of Nottingham
Tullis JP, Amanian N, Waldron D (1995) Design of labyrinth spillways. J Hydraul Eng 121(3):247–255
Tullis JP, Willmore CM, Wolfhope JS (2005) Improving performance of low-head labyrinth weirs. In: Proceedings of the 2005 World Water and Environmental Resources Congress, May 15–19
Tullis BP, Young JC, Chandler MA (2007) Head-discharge relationships for submerged labyrinth weirs. J Hydraul Eng 133(3):248–254
Wormleaton PR, Soufiani E (1998) Aeration performance of triangular planform labyrinth weirs. J Environ Eng 124(8):709–719