Roser Casas-Mulet

Survival of eggs of Atlantic salmon (Salmo salar) in a drawdown zone of a regulated river influenced by groundwater

Groundwater may create refuges for Atlantic salmon egg survival during low flows in regulated rivers and thus play an important role for survival during winter. To investigate the links between the survival of salmon embryos and hyporheic hydrological processes during permanent winter drawdown, a 100-m-long and 50-m-wide gravel area in a regulated river, the River Suldalslågen, was used for an experimental study. Surface and subsurface water levels were monitored with 2-min time resolution by means of water pressure sensors placed in pipes. Temperature, conductivity and dissolved oxygen were also measured. Eight cylindrical boxes, each with two compartments (at 10- and 30-cm depth, respectively) containing 50 Atlantic salmon eggs, were placed in the river bed substrate of both the drawdown zone and the permanently wetted area as a reference. They were regularly checked for survival during winter from January to May, coinciding with egg development period for this river. Survival rates in boxes in the dewatered river bed were between 8 and 78% during winter, compared to 80 to 99% in the reference wetted area. The main driver for egg survival in the dewatered area was groundwater with sufficient oxygen levels.

A cost-effective approach to predict dynamic variation of mesohabitats at the river scale in Norwegian systems

ABSTRACT This paper presents a cost-effective approach to predict dynamic variation of mesohabitat classes or hydromorphological units (HMUs) in the context of a peaking scenario. Predicting dynamic mesohabitats has been a challenge in the last 20 years. This is mainly due to the fact that mesohabitat changes do not show a simple relationship with varying discharges. The HMUs Simulation Method, by using a one-dimensional hydraulic model as a basis, proved to be a promising tool to simulate HMUs at four varying discharges in a Norwegian river. Low flows and surface pattern criteria were the most challenging to simulate and best modelling results were achieved for the higher flows. Further development on this approach should follow, but at present the method shows promising results towards the prediction of dynamic HMUs at the river scale.

Minimising biases in expert elicitations to inform environmental management: Case studies from environmental flows in Australia

Abstract Environmental managers often do not have sufficient empirical data to inform decisions, and instead must rely on expert predictions. However, the informal methods often used to gather expert opinions are prone to cognitive and motivational biases. We developed a structured elicitation protocol, where opinions are directly incorporated into Bayesian Network (BBN) models. The 4-stage protocol includes approaches to minimise biases during pre-elicitation, workshop facilitation and output analysis; and results in a fully functional BBN model. We illustrate our protocol using examples from environmental flow management in Australia, presenting models of vegetation responses to changes in riverine flow regimes. The reliance on expert opinion and the contested nature of many environmental management decisions mean that our structured elicitation protocol is potentially of great value for developing robust environmental recommendations. This method also lends itself to effective adaptive management, because the expert-populated ecological response models can be readily updated with field data.

Hydrological and thermal effects of hydropeaking on early life stages of salmonids: A modelling approach for implementing mitigation strategies

Alterations in hydrological and thermal regimes can potentially affect salmonid early life stages development and survival. The dewatering of salmon spawning redds due to hydropeaking can lead to mortality in early life stages, with higher impact on the alevins as they have lower tolerance to dewatering than the eggs. Flow-related mitigation measures can reduce early life stage mortality. We present a set of modelling tools to assess impacts and mitigation options to minimise the risk of mortality in early life stages in hydropeaking rivers. We successfully modelled long-term hydrological and thermal alterations and consequences for development rates. We estimated the risk of early life stages mortality and assessed the cost-effectiveness of implementing three release-related mitigation options (A,B,C). The economic cost of mitigation was low and ranged between 0.7% and 2.6% of the annual hydropower production. Options reducing the flow during spawning (B and C) in addition to only release minimum flows during development (A) were considered more effective for egg and alevin survival. Options B and C were however constraint by water availability in the system for certain years, and therefore only option A was always feasible. The set of modelling tools used in this study were satisfactory and their applications can be useful especially in systems where little field data is available. Targeted measures built on well-informed modelling tools can be tested on their effectiveness to mitigate dewatering effects vs. the hydropower system capacity to release or conserve water for power production. Environmental flow releases targeting specific ecological objectives can provide better cost-effective options than conventional operational rules complying with general legislation.

Two decades of ecohydraulics: trends of an emerging interdiscipline

ABSTRACT We assessed how the emerging field of ecohydraulics research has changed over two decades by examining the proceedings of the biennial International Symposium on Ecohydraulics. By using Natural Language Processing (NLP) in word usage, this paper provides a deep analysis of a longitudinal dataset and enables us to test more detailed questions than previous snapshots of the ecohydraulics literature. We formulated three main hypotheses related to the degree of multidisciplinarity, interdisciplinarity and transdisciplinarity within ecohydraulics. We investigated temporal changes in author affiliation patterns and identified dominant topics of research. The total number of proceeding papers has increased over time and the field is becoming increasingly global. This and the identification of 10 distinctive macro-topics suggest well-developed multidisciplinarity in ecohydraulics. There has been reasonable stability in individual topics across time, except for 11 (out of 51) significant trends within the macro-topics of Fish responses, Hydraulic modelling, Water quality, Physical habitat modelling and Social responses, suggesting some increase in interdisciplinarity. The proportion of practitioners collaborating with researchers has surprisingly not changed greatly over time, indicating ecohydraulics has been transdisciplinary to some extent from its inception. Our results arguably provide an opportunity to better integrate fundamental understanding into practical applications in water management.

Deficiencies in our understanding of the hydro-ecology of several native Australian fish: a rapid evidence synthesis

Environmental flows aim to mitigate the impacts of modification of riverine flow regimes by restoring components of the natural flow regime. Explicit evidence-based cause–effect relationships between flow regimes and fish responses are required for defensible flow recommendations. However, flow recommendations are typically based on expert opinion rather than a rigorous test of the available evidence. We used rapid evidence synthesis to systematically review the literature on responses of several native Australian fish to flow-related and other important environmental variables, and tested 13 explicit hypotheses. The hypotheses were related to the condition, reproduction and survival of pygmy perches, carp gudgeons, blackfish and flat-headed gudgeons. The evidence was insufficient to reach strong conclusions for all but three of our hypotheses. Late-spring high flows are associated with increased survival of pygmy perches and carp gudgeons, and exotic fish are associated with decreased survival of these fishes. The evidence that warmer spring water temperatures enhance their reproduction was inconsistent. The dearth of evidence to support or refute most hypotheses points to substantial gaps in our understanding of hydro-ecology of these native Australian fish, highlighting the need for targeted monitoring and research to further understand key flow relationships for these fish species.

Impacts of Hydrological Alterations on Water Quality

This chapter presents an overview of the response of water quality to hydrological alterations due to anthropogenic activities and how this drives the need for environmental water provisions. The chapter outlines the major driving processes of water quality change and highlights how interactions between water quantity and quality depend on the characteristics of individual catchments and anthropogenic influences. It also discusses management strategies to mitigate some water quality problems using environmental water releases. Salinity, water temperature, nutrient concentrations, and dissolved oxygen have been selected as both representative and important indicators of stream water quality. The flow-dependent processes, anthropogenic impacts, and management options have been discussed for each of these.

Early careers on ecohydraulics: challenges, opportunities and future directions

ABSTRACT Early career researchers (ECRs) play a critical role in our knowledge-based society, yet they are the most vulnerable group in the scientific community. As a young, interdisciplinary science, ecohydraulics is particularly reliant on ECRs for future progress. In 2014, the Early Careers on Ecohydraulics Network (ECoENet) was created to help the development of young researchers in this field. In this paper, we synthesize the outcomes of a workshop for ECRs organized by ECoENet in February 2016. We aim to show how the potential of ECRs can be maximized to drive progress in ecohydraulics. According to the most recent entrants to the field, major challenges lie in becoming more integrated as a discipline, developing a common vocabulary and a collective vision, engaging effectively with policy-makers, and encouraging public participation. ECRs need to develop their careers on an international scale in a way that crosses traditional disciplinary boundaries, including the social sciences, and allows them time to work at fundamental levels rather than focusing solely on individual applications. We propose a strategy to facilitate this by providing: a platform for disseminating research; an international support network; and a set of services for enhancing ECR training and experience.