Ecohydraulics of pool-type fishways: Getting past the barriers

The construction of pool-type fishways has greatly increased in recent years in response to widespread river fragmentation by man-made structures. However, the performance of such facilities has often been questioned, particularly for non-salmonid fish fauna, which are frequently the predominant group of species found in rivers. This study presents the main findings from field and experimental research conducted over the last 10 years on pool-type fishways in Portugal. Specific goals were: (i) to catalogue and evaluate the effectiveness of pool-type fishways built at small hydropower plants (SHP); (ii) to assess passage patterns of migrant fish populations through a “highly suitable” facility; (iii) to assess fish use for submerged orifices and surface notches under different flow regimes in experimental conditions and (iv) to determine the effect of hydraulic parameters on upstream movements of fish within these fishways. More than half (n = 19, 51%) of the visited fishways were considered to be unsuitable for the target potamodromous species. Seasonal movements peaked in the spring (>70%) and occurred independently of time of day. Laboratory experiments showed a significantly greater proportion of movements occurring through submerged orifices rather than surface notches. Of all the analyzed hydraulic parameters, the Reynolds shear stress was the one that most influenced fish movements within the fishways investigated. The results of this study provide new information and insights that could have important implications on the design of future fishways, particularly for larger potamodromous cyprinids.