The Hydro-Morphological Index of Diversity

Contemporary river engineering must guarantee effective long-term flood protection while also improving stream ecology. Nowadays, river engineering projects must aim at optimizing hydromorphological heterogeneity, as this is an acknowledged basic condition for maintaining stream biodiversity. In the present project, a new Hydro-Morphological Index of Diversity (HMID) was developed. The purpose of the HMID is to deliver a tool for the practitioner engaged in planning of integrated river engineering projects where habitat enhancement constitutes one of the project targets. By calculating the HMID, a quantitative statement of habitat heterogeneity enhancement for different project alternatives is possible, and therefore recommendations of which alternatives to prioritize from an ecomorphological perspective can be given. The HMID was developed within the framework of the "Integrated River Management" project, an interdisciplinary research program involving different University Institutes in Switzerland. During extensive field campaigns, hydraulic and geomorphic data were recorded at morphologically contrasting sites at three streams in Switzerland (Bünz, AG; Venoge, VD; Sense, FR/BE). By means of correlation analysis, relationships between the measured variables could be detected. Being significantly correlated to a number of hydraulic and geomorphic variables, the hydraulic variables flow velocity and water depth were found to accurately represent the hydromorphological template of a stream. A formula for the HMID could be proposed by comparing the variability of these two hydraulic variables between the study reaches. The developed formula used the coefficient of variation of flow velocity and water depth as a measure to describe hydromorphological variability. A good correlation of HMID scores with rankings obtained by means of a multimetric visual habitat assessment method supported the capability of the HMID to represent the hydromorphological state of a stream. Correlation between HMID scores and macroinvertebrate-based biotic indices, on the other hand, did not meet expectations for all tested stream reaches. Numerical modelling for the study reaches at the river Sense was conducted to examine the temporal variability of the hydraulic variables and the HMID. HMID scores were calculated for different discharges in river, and temporal variability was lower in natural than in channelized reaches. The increments of hydraulic variables for changing discharge are greater in channelized than in natural reaches. Thus, aquatic biota in channelized reaches must cope not only with a degraded habitat template but also with higher stress conditions. However, physical habitats in natural reaches lose stability when discharges with major bed reshaping processes occur. These high discharges correspond to intermediate disturbance events, which are important towards maintaining ecological functions. In a case study, the suitability of the HMID for application was demonstrated. After completion of a restoration project, a stream reach should be characterized by a high HMID and a stable temporal variability (unless discharges above a disturbance threshold occur). In this way, the HMID provides the necessary hydromorphological template to achieve a high ecological potential for a restored stream reach. However, it must be avoided that high hydromorphological heterogeneity does not become a primary aim in itself. For a sound restoration project, processes at the watershed scale also must be included. In particular, it is necessary to evaluate the sediment regime of the entire watershed (mainly of the upstream areas), to estimate the long-term geomorphic evolvement of the project reach and to verify whether a dynamic equilibrium for the reach can be obtained. Finally, the ecological success of habitat enhancement measures depends on the conditions of other potential stressors (e.g. sediment or excessive nutrients, chemical pollution, habitat fragmentation, strongly modified flow regime). An integrated vision of these factors is a primordial rule for ecologically successful river restoration projects.

The Hydro-Morphological Index of Diversity: a planning tool for river restoration projects

Walter Gostner

Flood protection and river engineering projects nowadays have to improve also the ecological condition of the river. Very often the space is not available for a full restoration of the river morphology. Therefore the hydro-morphological heterogeneity has to be optimized within certain space constraints. For such projects a tool for practitioners would be very helpful which allows to quantify the habitat heterogeneity enhancement for different project alternatives and to recommend the best alternative in view of eco-morphological perspective. In his research project Dr. Walter Gostner proposed a new Hydro-Morphological Index of Diversity (HMID), which allows a quantitative statement of the enhancement of habitat heterogeneity during the comparison of different project alternatives in the framework of river engineering projects. Compared to other existing habitat indices, which are mostly based on visual, qualitative assessment in the field and therefore influenced by the subjectivity of the observers, the new HMID is based on statistical parameters calculated by numerical 2D and 3D simulations during project planning and thus can be denoted fully objective. The HMID was developed on the basis of very extensive field campaigns by recording a large amount of hydraulic and geomorphic data as it has been done rarely before. In order to see clearly the hydro-morphological heterogeneity several very contrasting sites from fully natural to very channelized stretches have been analysed on three different gravel bed rivers in the Swiss Pre-alps (Bünz, Venoge, Sense). By comparing the variability of the numerous hydraulic and morphological parameters between the studied stretches a formula for the HMID could be proposed. Dr. Walter Gostner could show that the coefficients of variation of flow velocity and water depth alone are sufficient to obtain a reliable and predictive HMID. With the development of the HMID Dr. Walter Gostner made available a very useful predicting tool to evaluate the ecological potential of river engineering projects.

EPFL - LCH2012

Impact of Hydropeaking on Fish and their Habitat

Émilie Person

High-head storage hydropower plants are an important renewable source of energy in alpine areas. Kinetic energy released from water, which is stored in reservoir and diverted through turbines, produces electricity. During daily peaks of energy demand, the powerhouse outflow is released in the downstream river, creating artificial flow fluctuation, so-called hydropeaking. This alters the natural flow regime of rivers and has a negative effect on ecosystems and biodiversity. As a result, water discharge, temperature, fine particle load and other abiotic factors are changed. Consequently, river organisms and their habitat are impacted. Resulting from an increased pressure for atmospheric carbon mitigation, hydropower production is expected to increase in the future (e.g. from storage powerplants). In Switzerland this trend is further enhanced by the recent governmental decision to phase out nuclear power production. Thought, the revision of the Swiss water protection act shows the growing awareness to protect natural ecosystems downstream of hydropower facilities. However, there is a strong need for research in this field due to the lack of knowledge on the adverse impacts stemming from hydropower production. This study is part of the interdisciplinary research project “Sustainable use of hydropower – innovative measures to reduce hydropeaking problematic” and it focuses on the impact of hydropeaking on fish and their habitat. Brown trout is used as a target species and important steps in their life cycle are studied. Three target stages of brown trout development were selected: adults, spawning and young-of-the-year. Each different life stage has specific habitat requirements. The latter can be used for identifying potential landscape filters constraining fish population renewal. Landscape filters are determined by the joint influence of river morphology and discharge regimes, such as hydropeaking. In this work, two rivers, with different morphological characteristics, are studied, namely the Vorderrhein and the Hasliaare Rivers. Both rivers show a hydropeaking regime, are situated in alpine areas and have a comparable hydrological regime. The hydrology of the two rivers is characterized by low discharge in winter and high discharge in summer due to snowmelting. Fish species composition is similar and strongly dominated by brown trout. The Vorderrhein River is one of the few natural and morphologically intact rivers found in Switzerland, which allows to isolate the effect of hydropeaking from other potential human-induced stressors. In contrast, the Hasliaare River has been strongly channelized in the past century. Thus, the Hasliaare River system was chosen to investigate the joint effect of hydropeaking and river channelization. In the Vorderrhein River, the seasonal impact of hydropeaking on adult brown trout habitat was modeled using the CASiMiR fish module. Therefore, different critical seasons are defined. Furthermore, the natural reproduction success was assessed and brown trout reproduction and rearing habitat were modeled. Habitat preference of spawning and young-of-the-year are established with specific Habitat Suitability Curves. The habitat model was adapted to the hydropeaking problem and indices measuring habitat dynamics were developed. Moreover, the transferability of Habitat Suitability Curves in habitat models was discussed. In addition, young-of-the-year density as well as egg to hatch survival were monitored. The results show that hydropower operations have an effect on brown trout habitat, whereat spawning and young-of-the-year life stages are more impacted than adults. The impact is seasonal and aggravated in winter. The natural river morphology provides suitable habitat areas at both peak and off-peak discharges. Although these suitable habitat areas are dewatered almost entirely or displaced on a daily basis. In the Hasliaare River system, the joint effect of hydropeaking and channelization on young-of-the-year, lake and stream resident spawning brown trout were studied. Steady and dynamic habitat conditions were evaluated and the habitat was modeled for three different degraded morphologies. Specific preference curves for each investigated life stage were developed. Moreover, the reproduction success was monitored by egg to hatching survival experiments and young-of-the-year density surveys. The results show that channelization aggravates the impact of hydropeaking as no young-of-the-year or spawning habitat is present at peak flow. In addition, egg development was found to be impaired. Therefore, the density of young-of-the-year individuals was negligible in the hydropeaking section. The habitat model shows that in a channelized river such as the Hasliaare River, suitable habitat conditions for fish are restrained at peak flow by the riverbed width. Finally, a tool for evaluating scenarios for mitigating the impact of hydropeaking on the downstream ecosystem was developed. The novel economic-ecological diagnostic and intervention method takes into account financial as well as environmental outcomes of hydropeaking mitigation measures for fish habitat improvement. The approach comprises (1) a hydropower operation model of flow regime generation and cost estimates for different mitigation measures, (2) a 2D hydrodynamic model to simulate the flow conditions in representative river reaches, and (3) a dynamic fish habitat simulation tool to assess the sub-daily changes in fish habitat conditions. This modeling approach gives the possibility to estimate true benefits of rehabilitation measures. The intervention diagnostic method was tested on the Hasliaare River. The developed tools and knowledge will help implement scientifically-based solutions for a sustainable hydropower management. The study may help in supporting the application of river restoration projects at existing and newly developed hydropower facilities in alpine areas.

EPFL2013

Impact of hydropeaking on fish and their habitat

Émilie Person

EPFL - LCH2013

Impact of Hydropeaking on Fish and their Habitat

Émilie Person

EPFL2013

Impact of hydropeaking on fish and their habitat

Émilie Person

EPFL - LCH2013

The Hydro-Morphological Index of Diversity: a planning tool for river restoration projects

Walter Gostner

EPFL - LCH2012