Development of a new slot-weir-orifice combined fishway

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 multi-slot fishway (BMSF-8) and multi-slot 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 (but 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 twelve SWOF cases (i.e. SWOF-1~SWOF-12) manifest that SWOF-9 has the relatively lowest velocity and turbulence at Q=1000 L/s, contributing to the upstream migration of weak-swimming fish. Besides, when compared to VSF and MSWF-5, SWOF-9 always exhibits better hydrodynamic performance at Q=400~1000 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, 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 m/s, 0.80~0.91 m/s, 0.77~0.91 m/s and 0.85~1.00 m/s, respectively. Obviously, SWOF-9 serves as a better multi-species fishway in terms of hydrodynamic performance, but fish-passage experiments with live fish should be supplemented in the future.