Fish Upstream Passage Through Gauging Stations. Experiences With Iberian Barbel in Flat-V Weirs

Abstract

The monitoring of river discharge is vital for the correct management of water resources. A worldwide facility used for measuring discharge are flat-V gauging weirs. These structures consist of a small weir, with a triangular cross-section and a flat “V”-shaped notch. Their extensive use is a consequence of their utility in the measurement of both low and high flow conditions. However, depending on their size, local morphology and river discharge can act as full or partial hydraulic barriers to fish migration. To give answer to this question, the present work studies fish passage performance over flat-V weirs considering their hydraulic performance. For this, radio-tracking and video monitoring observations were combined with computational fluid dynamics (CFD) models in two flat-V weirs, using Iberian barbel (Luciobarbus bocagei) as target species. Results show that fish passage is conditioned by both hydraulic and behavioral processes, providing evidences about the scenarios where flat-V weirs may act as full or partial barriers to upstream movements. For the studied flat-V weirs, a discharge range of 0.27-8 m3/s, with a water drop difference between upstream and downstream water levels lower than 0.7 m and a depth downstream the weir higher than 0.30 m can be considered as an effective passage situation for barbels. These findings are of interest to quantify flat-V weir impacts, for engineering applications and to establish managing or retrofitting actions when required.

Effect of thermo‐velocity barriers on fish: influence of water temperature, flow velocity and body size on the volitional swimming capacity of northern straight‐mouth nase (Pseudochondrostoma duriense)

“…Therefore, variations in water temperature and flow regimes (i.e., changes in discharge rates translated into water depth and flow velocity variations) can affect the fish's endurance to transverse an obstacle, which may limit the obstacle passage and may constitute thermal or velocity barriers for the fish migration (Haro et al, 2004;Langford, 1990). Furthermore, as both water temperature and discharge act as timers or triggers for the onset and maintenance of fish migration (García-Vega et al, 2022;Lucas et al, 2001), changes in these factors may affect not only the ability to surpass a barrier but also the motivation to traverse it (Bayse et al, 2019;Goerig et al, 2017;Sanz-Ronda et al, 2021). The expected effects of climate change could aggravate this situation, particularly in southern Mediterranean regions (Cramer et al, 2018), where most favourable scenarios predict for this century an increase in water temperature greater than 2.6 C for the spring-summer period (Senent-Aparicio et al, 2017;Solomon et al, 2007), just coinciding with the spawning migration of cyprinids (Doadrio, 2002;Kottelat & Freyhof, 2007), and a reduction in winter and spring discharge, which is already taking place (Ceballos-Barbancho et al, 2008;Sánchez-Hernández & Nunn, 2016).…”