Experimental study of the influence of sills on vertical slot fishway flow.

Aurélien Ballu, Gérard Pineau, Damien Calluaud, Laurent David

Tuesday 30 june 2015

16:30 - 16:45h at Amazon (level 1)

Themes: (T) Hydro-environment, (ST) Ecohydraulics and ecohydrology

Parallel session: 7G. Environment - Ecosystem

This paper presents results of an experimental study of the topology, kinematic quantities, turbulence and quantification of hydraulic parameters of flow inside vertical slot fishway (VSF). A VSF is a device used to facilitate the passage of fish through many obstacles, such as dams and weirs that can be found across streams, and obstruct their natural migration. The design of a VSF uses global criteria to accommodate the swimming capabilities of the species of fish that will pass through it. Notably, the head between pools, the volumetric dissipated power and the discharge coefficient are required. In practice, those design criteria are calculated without taking into account the possible presence of sills (an insert that functions like a wier) inside slots. However, existing VSFs often have sills introduced in the slots to restore the balance of water depth in the pools. In this context, experiments were carried out to estimate the influence of sills on the commonly used design criteria. Water depth measurements were taken by acoustic sensors in the middle of each pool of a VSF. Additionally, velocities were acquired by an Acoustic Doppler Velocimeter in several positions of the central pool. A map of the discharge coefficients and a cartograph of flow topologies were produced over 180 independent experiments, investigating five inclinations from 5% to 15%, three pool widths, four flow discharges and three sill heights. The results show that the presence of sills increases the three-dimensionality of the flow and tend to significantly change the flow topology (Wang et al., 2010). The sill height was found to have an effect on the discharge coefficient. The presence of sills changes the main design criteria values and could potentially make the passage of migrating fish through VSFs more difficult. Finally, a sensitivity analysis of the parameters used to estimate the commonly used criteria is proposed. This was undertaken in order to define predictive laws, which can help designers to develop systems that are as efficient as possible with the presence of sills.