Ian Maddock

The Effect of Flow Regulation on the Distribution and Dynamics of Channel Geomorphic Units (CGUs) and Implications for Marble Trout (Salmo marmoratus) Spawning Habitat in the Soča River, Slovenia.

A river channel survey was completed along three reaches (totalling 14.3km), i.e. an unregulated stretch and two regulated reaches (with reduced flows) of the Soca River to assess the spatial pattern of CGU type, size, hydraulics and distribution. In addition, one regulated reach was re-surveyed at different discharges to investigate the dynamics of CGUs and their relationship with flow. CGUs were classified and mapped using visual assessment and physical measurements of the hydraulic characteristics (velocity and depth) in each CGU. The effect of flow regulation on the hydraulic character of the river becomes apparent by highlighting differences in the types of CGUs present between the regulated and unregulated reaches. Reduced flows from river regulation also significantly reduces the size of CGUs, alters their hydraulic character, and affects the longitudinal distribution of types by creating greater habitat fragmentation. Hydraulic preferences for spawning habitat of marble trout (Salmo marmoratus) were obtained from previous research. The hydraulic character of CGUs were analysed at different discharges and combined with the hydraulic preferences of the species to evaluate the impact of flow regulation on habitat availability. Analysis shows that intermediate measured flow provides increased spawning habitat availability in the chosen reach for this target species.

Position choice and swimming costs of juvenile Atlantic salmon salmo salar in turbulent flow

ABSTRACT Swimming costs (SCs) for fish have been shown to be affected by turbulence. However, this idea has not yet been implemented in habitat models, which often represent hydraulics using water velocity averaged over time and space. In this study, we analysed the habitat selection of individual juvenile Atlantic salmon Salmo salar (L. 1758) in relation to predicted SC in the turbulent flow of a large outdoor flume. We used a previously published SC model parameterized using mean velocity, turbulence intensity, water temperature and fish mass. Results showed that 86% of fish chose locations with significantly lower predicted SC than expected at random. Position choice was negatively related to predicted SC, mean velocity, spatial velocity gradient, and Reynolds stresses. Based on the findings, a novel habitat suitability curve is recommended for juvenile Atlantic salmon. The results are expected to contribute towards the improvement of bioenergetics modelling to increase our understanding of the impacts of environmental changes and management activities.

Evaluation and Application of Environmental Flows for Running Waters in Slovenia

Water use invariably results in major impacts on river flows. Environmental Flows (EF) are defined as the quantity and quality of water that is needed to preserve the structure and the function of the river and riparian zone ecosystem and sufficient quantity of water to enable the survival and reproduction of aquatic organisms in different hydraulic habitats. This paper describes the criteria and methods used to determine EF and experiences with their application in Slovenia. The diversity of running waters of Slovenia demand special treatment and determination of EF for each individual section of the river system. Using hydrological, morphological and ecological criteria, two different approaches are used for the determination of EF in Slovenia, a rapid assessment method and a detailed assessment method. For both methods, data are then analyzed by an expert panel in order to determine an EF. Since 1994, more than 180 study sites have been examined for research and application of EF in Slovenia. Determination of EF for existing users has prioritized their water requirements so they can remain economically viable. Where new schemes are proposed, there has been much greater scope to prioritize ecosystem requirements. EF determination is receiving growing attention and will continue to increase in importance, driven by research that aids our understanding of flow-biota relationships and recent environmental policy and legislation at both the national and European level.