The Hydro-Morphological Index of Diversity:a Planning Tool for River Restoration Projects

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

Der hydromorphologische Index der Diversität

Im modernen Flussbau müssen nicht nur schutzwasserbauliche, sondern auch ökologische Anforderungen berücksichtigt werden. Durch entsprechende Gestallung ist eine möglichst grosser Strukturreichtum anzustreben, da dieser zweifelsfrei eine der Grundvoroussetzungen für eine hohe Biodiversität in einem Fliessgewässer darstellt

Indice hydromorphologique de la diversité

La diversité morphologique est nécessaire au fonctionnement des écosystèmes aquatiques. Cette fiche propose un nouvel indice – l’indice hydromorphologique de la diversité (IHMD) – pour calculer la diversité hydromorphologique. Cet outil permet d’évaluer quantitativement les projets d’aménagement des eaux en ce qui concerne l’amélioration de la diversité morphologique

The hydro-morphological index of diversity: a tool for describing habitat heterogeneity in river engineering projects

We present a new hydro-morphological index of diversity (HMID), a tool aimed for use in river engineering projects and firstly developed at gravel-bed streams in Switzerland, but intended for a broader use. We carried out field work with extensive hydraulic and geomorphic data collection, conducted correlation analysis with hydro-morphological variables, formulated the HMID, and analyzed the correlation between HMID and a visual habitat assessment method. The HMID is calculated by means of the coefficient of variation of the hydraulic variables flow velocity and water depth, which have been demonstrated to sufficiently represent the hydro-morphological heterogeneity of alpine gravel-bed stream reaches. Based on numerical modeling, the HMID can be calculated easily for a comparison of different alternatives in river engineering projects and thus achieves predictive power for design decisions. HMID can be applied at a reach-related scale in engineering programs involving geomorphic measures that aim at the enhancement of habitat heterogeneity of a stream. However, the application of HMID has to be integrated with evaluations of the long-term streambed evolvements that are considered at a catchment scale and strongly related to the sediment regime of the stream under stud

Index für hydro-morphologische Diversität

Strukturvielfalt ist eine Voraussetzung für die Funktionsfähigkeit von Gewässerökosystemen. Das vorliegende Merkblatt stellt einen neuen Index vor – den sogenannten hydro-morphologischen Index der Diversität (HMID), mit dem sich die hydro-morphologische Diversität berechnen lässt. Als Hilfsmittel für den Wasserbau ermöglicht er es, flussbauliche Projekte in Bezug auf die Verbesserung der Strukturvielfalt quantitativ zu beurteilen

Der hydraulisch-morphologische Index der Diversität: Ein Indikator für die ökologische Funktionsfähigkeit von Fliessgewässern

Es ist unbestritten, dass die Biodiversität und ökologische Funktionsfähigkeit eines Fließgewässers in direktem Zusammenhang mit dessen hydraulischen und morphologischen Parametern und deren Ausprägung steht. Wasserrahmenrichtlinien, Hochwasserschutz und vermehrte Bemühungen in der Flussrevitalisierung erfordern interdisziplinäre Forschung, um das Zusammenspiel abiotischer und biotischer Faktoren von Fließgewässern besser erfassen zu können. Vorliegender Artikel enthält den anhand von Fallstudien ausgearbeiteten Vorschlag für einen hydraulisch morphologischen Index der Diversität (HMID), welcher bei flussbaulichen Maßnahmen als Indikator für deren Wirksamkeit in Bezug auf die Verbesserung der Fließgewässerökologie herangezogen werden kann

The hydro-morphological index of diversity: a tool for describing habitat heterogeneity in river engineering projects

We present a new hydro-morphological index of diversity (HMID), a tool aimed for use in river engineering projects and firstly developed at gravel-bed streams in Switzerland, but intended for a broader use. We carried out field work with extensive hydraulic and geomorphic data collection, conducted correlation analysis with hydro-morphological variables, formulated the HMID, and analyzed the correlation between HMID and a visual habitat assessment method. The HMID is calculated by means of the coefficient of variation of the hydraulic variables flow velocity and water depth, which have been demonstrated to sufficiently represent the hydro-morphological heterogeneity of alpine gravel-bed stream reaches.Based on numerical modeling, the HMID can be calculated easily for a comparison of different alternatives in river engineering projects and thus achieves predictive power for design decisions. HMID can be applied at a reach-related scale in engineering programs involving geomorphic measures that aim at the enhancement of habitat heterogeneity of a stream. However, the application of HMID has to be integrated with evaluations of the long-term streambed evolvements that are considered at a catchment scale and strongly related to the sediment regime of the stream under study

Förderung der Dynamik bei Revitalisierungen

Naturnahe Fliessgewässer sind dynamische Systeme: Gewässersohle und Ufer werden regelmässig durch Hochwasser umgestaltet, wodurch neue Lebensräume entstehen. In den letzten Jahrzehnten wurde diese Dynamik vielerorts eingeschränkt, weil zahlreiche Fliessgewässer verbaut wurden. Ein wichtiges Ziel von Revitalisierungen ist, sie wiederherzustellen. Das vorliegende Merkblatt präsentiert Grundlagen für die Förderung der Dynamik

Amélioration de la dynamique

Les cours d’eau proches de l’état naturel sont des systèmes dynamiques: le lit et les rives sont régulièrement modi!és par des crues, entraînant la création de nouveaux habitats. Durant les dernières décennies, cette dynamique a souvent été restreinte suite à l’endiguement de nombreuses rivières. Son rétablissement est un objectif important des revitalisations. Cette fiche présente les bases nécessaires à l’amélioration de cette dynamique

Gravel bar inundation frequency: an important parameter for understanding riparian corridor dynamics

Riparian zones are some of the most valuable and at the same time endangered ecosystems in the world. Their progressive degradation caused by anthropogenic pressure calls for the adoption of effective, resilient restoration strategies. However, a full understanding of the complex mechanisms governing riparian ecosystems has not yet been achieved, and many assumptions are based on qualitative findings. We quantitatively investigated the habitat conditions of a key riparian plant, the German tamarisk (Myricaria germanica), using a two-dimensional hydrodynamic model that was created for a braided reach of the river Sense (Switzerland). The results demonstrate that the presence of this species in gravel bar habitats is strongly correlated with inundation frequency. The species was present on gravel bars near the main river channels, which are inundated every 4–5 years. Where the gravel bars are frequently flooded, seedlings do not survive the hydrodynamic perturbations, whereas elsewhere, where periodic flooding does not reach, M. germanica is replaced by stronger competitors. Our study contributes to an understanding of the dynamics of riparian corridors and provides a quantitative basis for developing effective restoration plans, which may involve the optimisation of hydropower regulation programmes