So far, only a small number of studies have focused on the combined fishway. This study aims to develop a new slot-weir-orifice combined fishway (SWOF-9) on the basis of the previous vertical-slot fishway (VSF), bilateral-symmetric multislot fishway (BMSF-8), and multislot pool-weir combined fishway (MSWF-5). Firstly, by installing vertical slots, oblique rectangular weirs, bottom orifices, and energy-dissipation piers in each pool, SWOF-9 possesses four fish-passage channels (compared with only one in VSF and two in both BMSF-8 and MSWF-5), provides more ample migration space for fish (being beneficial to enhancing fish-passing efficiency), and significantly decreases mainstreams’ velocity and turbulence by sharing flow rate and promoting the flow energy consumption. Secondly, the numerical results of VSF, BMSF-8, MSWF-5, and 12 SWOF cases (i.e., SWOF-1–SWOF-12) manifest that SWOF-9 has the relatively lowest velocity and turbulence at Q=1,000 L/s, contributing to the upstream migration of weak-swimming fish. Besides, when compared with VSF and MSWF-5, SWOF-9 always exhibits better hydrodynamic performance at Q=400–1,000 L/s. Thirdly, for large fishway size (pool width = 2.20 m, slot width = 0.59 m, and bed slope = 1.67%), VSF suits the burst swimming speed Uburst>1.92–2.04 m/s, BMSF-8 fits Uburst>1.36–1.42 m/s, and MSWF-5 fits Uburst>1.36–1.60 m/s, but the four fish-passage channels of SWOF-9 adapt to Uburst>1.08–1.15, 0.80–0.91, 0.77–0.91, and 0.85–1.00 m/s, respectively. Obviously, SWOF-9 serves as a better multispecies fishway in terms of hydrodynamic performance, but fish-passage experiments with live fish should be supplemented in the future.
Zhang et al. (Tue,) studied this question.