Retrofitting pool-and-weir fishways to improve passage performance of benthic fishes: Effect of boulder density and fishway discharge José Maria Santos a, *, Paulo Branco a, b , Christos Katopodis c , Teresa Ferreira a , António Pinheiro b a Centro de Estudos Florestais, Universidade de Lisboa, Tapada da Ajuda, Lisboa 1349-017, Portugal b Centro de Estudos de Hidrossistemas, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, Lisboa 1049-001, Portugal c Katopodis Ecohydraulics Ltd., 122 Valence Avenue, Winnipeg, MB R3T 3W7, Canada A R T I C L E I N F O Article history: Received 27 April 2014 Received in revised form 19 August 2014 Accepted 13 September 2014 Available online xxx Keywords: Technical fishways Bottom substrate Upstream passage Acoustic Doppler Velocimeter A B S T R A C T Retrofitting, or the addition of features to existing fishways to make them more suitable for upstream fish passage, is an issue of increasing interest in fishway science. Despite its potential for aiding fish passage, few studies are available on retrofitting of pool-and-weir fishways by adding boulders at the bottom of each pool of these facilities. The aim of this study was to assess the performance of a full-scale retrofitted pool-and-weir fishway model with boulders placed at the bottom of each pool, to enhance passage of a cyprinid species, the Iberian barbel (Luciobarbus bocagei), which was considered as a representative of medium-sized benthic potamodromous cyprinids in Iberia and Western Europe. Particular attention was given to testing the effects of boulder density and fishway discharge on passage success and fish transit time, both of which affect fish passage efficiency. Although no significant difference in passage success was detected between boulder spacings (mean proportion for high density: 35% success; mean proportion for low density: 40% success), increased flows (62.7 l/s) induced a higher mean proportion (P < 0.05) of successful negotiations (50%), relative to low flows (38.5 l/s, 25%). With regard to fish transit time, under higher flows, fish took significantly less time (P < 0.05) to ascend the fishway with the higher (5.3  4.2 min) vs the lower boulder density (12.1  6.5 min). This study showed that fish passage success was discharge-related and independent of boulder density. However, a high density boulder configuration combined with higher fishway discharge can be beneficial as it reduced fish transit time. Such information could be used to retrofit ill-functioning fishways in order to improve fish passage efficiency and negotiation of fishways for benthic potamodromous cyprinids. ã 2014 Elsevier B.V. All rights reserved. 1. Introduction Pool-and-weir fishways are the most common type of fish passage devices worldwide (Hatry et al., 2013; Larinier, 2008; Pompeu et al., 2012). These facilities are predominantly installed at low head barriers built for small-scale hydropower and other water diversion structures and consist of a rectangular flume divided by cross-walls that create a series of consecutive pools arranged in a stepped pattern, with each one higher than the one immediately downstream (Katopodis et al., 2001). These pools divide the obstacle height into smaller steps to be negotiated by fish, which move from one pool to the next through openings in the cross-walls that are situated at the top (notches) and/or at the bottom (submerged orifices) (FAO/DVWK, 2002). Despite their worldwide popularity, the performance of these facilities, mea- sured as the proportion of fish successful negotiations with minimum delay, is relatively low in many parts of the world, such as in southern European countries (Santos et al., 2012), because their design was biased by salmonid-based guidelines. Salmonids are typically strong swimmers with great leaping abilities, while the most abundant fish species in southern European countries are potamodromous and resident cyprinids that have weaker swim- ming abilities (Katopodis Ecohydraulics Ltd., 2013). Therefore, incorporating additional provisions for fish passage in pool-and- weir fishways could facilitate upstream movement of these species. Retrofitting, or adding features to existing fishways to make them more suitable for upstream fish passage, is an issue of increasing interest in fishway science (Gough et al., 2012). The * Corresponding author. Tel.: +351 213 653 489. E-mail addresses: jmsantos@isa.ulisboa.pt (J.M. Santos), pjbranco@isa.ulisboa.pt (P. Branco), katopodisecohydraulics@live.ca (C. Katopodis), terferreira@isa.ulisboa.pt (T. Ferreira), antonio.pinheiro@tecnico.ulisboa.pt (A. Pinheiro). http://dx.doi.org/10.1016/j.ecoleng.2014.09.065 0925-8574/ ã 2014 Elsevier B.V. All rights reserved. Ecological Engineering 73 (2014) 335–344 Contents lists available at ScienceDirect Ecological Engineering journal homepage: www.else vie r.com/locat e/e coleng