Laura Nardi

A multi-scale hierarchical framework for developing understanding of river behaviour to support river management

This paper introduces this special issue of Aquatic Sciences. It outlines a multi-scale, hierarchical framework for developing process-based understanding of catchment to reach hydromorphology that can aid design and delivery of sustainable river management solutions. The framework was developed within the REFORM (REstoring rivers FOR effective catchment Management) project, funded by the European Union’s FP7 Programme. Specific aspects of this ‘REFORM framework’ and some applications are presented in other papers in this special issue. The REFORM framework is founded on previous hierarchical frameworks, sixteen examples of which are reviewed. However, the REFORM framework has some particular properties that reflect the European context for which it was developed. The framework delineates regional landscapes into nested spatial units at catchment, landscape unit, segment, reach, geomorphic unit and finer scales. Reaches, regardless of their ‘naturalness’, are assigned to a river type based on valley confinement, planform and bed material. Indicators are quantified at each spatial scale to feed three groups of assessments. First, contemporary indicators at reach and geomorphic unit scales investigate present processes, forms and human pressures within each reach. These feed assessments of present reach hydromorphological function/alteration, including whether the reach is functioning appropriately for its type; riparian corridor function and alteration; and hydromorphological adjustment. Second, indicators at catchment to segment scales investigate water and sediment production and delivery to reaches and how these are affected by human pressures now and in the past. These are used to construct an inventory of changes over space and time. Third, historical reach and geomorphic unit scale indicators are used to construct the trajectory of reach-scale changes. Contemporary reach-scale assessments, space–time inventory, and trajectory of changes are then combined to establish how river reaches of different type, subject to different human pressures, and located in different environmental contexts behave in response to changes at all considered spatial scales. These support forecasts of the likely responses of reaches to future scenarios (e.g., changes in climate, land cover, channel interventions).

New tools for the hydromorphological assessment and monitoring of European streams

Hydromorphological stream assessment has significantly expanded over the last years, but a need has emerged from recent reviews for more comprehensive, process-based methods that consider the character and dynamics of the river with greater accuracy. With this as a focus, a series of hydromorphological tools have been developed and/or further extended in Europe within the context of the REFORM (REstoring rivers FOR effective catchment Management) project. The aim of this paper is to present the set of REFORM hydromorphological assessment methods and, based on some examples of their application, to illustrate and discuss their synergic use, specific features, limitations and strengths. This assessment and monitoring includes three tools: the Morphological Quality Index (MQI), the Morphological Quality Index for monitoring (MQIm), and the Geomorphic Units survey and classification System (GUS). These tools constitute the assessment phase of an overall multi-scale, process-based hydromorphological framework developed in REFORM. The MQI is aimed at an assessment, classification and monitoring of the current morphological state; the MQIm aims at monitoring the tendency of morphological conditions (enhancement or deterioration); the GUS provides a characterization, classification and monitoring of geomorphic units. A series of examples are used to illustrate the potential range of application, including: (i) an assessment of morphological conditions; (ii) an assessment of the morphological effects of restoration projects; (iii) an evaluation of the geomorphic impacts of interventions for risk mitigation; and (iv) an integrated use of MQI and GUS to assess and characterise morphological conditions. Finally, some of the main features, strengths and peculiarities of the three hydromorphological tools are discussed with the support of examples of their application.

Diagnosing problems induced by past gravel mining and other disturbances in Southern European rivers: the Magra River, Italy

The multi-scale hierarchical framework developed within the REFORM project, for the study of the functioning of river reaches and their catchments, was applied to the Magra River catchment (Northern Tuscany, Italy). The Magra River is a quite dynamic gravel-bed river that has undergone severe channel adjustments over the last century (i.e. incision and narrowing). The REFORM framework was then applied in order to (1) explore the locations and causes of these adjustments, and (2) assess how different river reaches responded to specific human activities (i.e. land use changes, dams, gravel mining). The work aims at providing information to aid sustainable river management and restoration. In accordance with the framework, initially, all the relevant spatial units (i.e. from the catchment to the reach scale) were delineated and then characterised in further detail. Then, a summary of the trajectories of change following human impact was provided. Combined with an overview of the main human pressures still influencing the river system, this allowed us to define the current conditions at the river reach scale. Finally, the knowledge acquired in the previous parts was assembled to build a better understanding of current river conditions and controls on past changes, as well as to enable the formulation of some future scenarios. The latter analysis was focussed on a couple of reaches located in a sensitive and relatively low impacted segment, in order to better highlight the interpretative power of the hierarchical framework. The framework was applied by combining the knowledge derived from previous studies and the computation of additional and relevant indicators. This study demonstrated the helpfulness of the hierarchical framework in diagnosing problems and supporting management strategies for a medium-sized, gravel-bed river catchment.

IDRAIM: A Methodological Framework for Hydromorphological Analysis and Integrated River Management of Italian Streams

A methodological framework for hydromorphological assessment, analysis and monitoring (named IDRAIM) has been developed with the specific aim of supporting the management of river processes by integrating the objectives of both the Water Framework and Floods Directives. The framework builds on existing and up-to-date geomorphological concepts and approaches, but accounts for the specific Italian context in terms of channel adjustments and human pressures, and includes a component qualitatively addressing the hazards related to fluvial dynamics. The method was designed to be used by environmental or water agencies on a national level. The framework includes the following four phases: (1) catchment-wide characterization of the fluvial system; (2) evolutionary trajectory reconstruction and assessment of present river conditions; (3) prediction of channel evolution; (4) identification of management options.

Assessing Restoration Effects on River Hydromorphology Using the Process-based Morphological Quality Index in Eight European River Reaches

The Morphological Quality Index (MQI) and the Morphological Quality Index for monitoring (MQIm) have been applied to eight case studies across Europe with the objective of analyzing the hydromorphological response to various restoration measures and of comparing the results of the MQI and MQIm as a morphological assessment applied at the reach scale, with a conventional site scale physical-habitat assessment method. For each restored reach, the two indices were applied to the pre-restoration and post-restoration conditions. The restored reach was also compared to an adjacent, degraded reach. Results show that in all cases the restoration measures improved the morphological quality of the reach, but that the degree of improvement depends on many factors, including the initial morphological conditions, the length of the restored portion in relation to the reach length, and on the type of intervention. The comparison with a conventional site scale physical-habitat assessment method shows that the MQI and MQIm are best suited for the evaluation of restoration effects on river hydromorphology at the geomorphologically-relevant scale of the river reach.

Assessment of Morphodynamical Reactions on Redynamisation Measures - Case Study Upper Rhine

The paper reports on the methodology applied to assess the morphodynamical development of a river reach which is planned to be re-dynamised, according to the “INTERREG IVa - Redynamisation of the Old Rhine” project (2009-2012). The river reach is located at the Upper Rhine parallel to the Grand Canal d’Alsace. Most of the discharge is directed through the canal and only a minimum discharge is flowing through the River Rhine. In the ca. 40 km long section morphological features are nowadays absent due to limited sediment supply and transport. A dynamic river bed shall be supported by means of floodplain lowering, sediment deposition and removement of bank protection. The applied methodology combines 3D-numerical modelling of the flow field and stability approaches to assess morphological changes with particular reference to the sediment dynamics and stability of the main channel and the floodplain areas.

The Magra River (Italy): Effects of the 25th October 2011 Flood Event and a Preliminary Application of the IDRAIM Framework

The Magra River catchment experienced an extreme flood event on 25th October 2011, with return periods ranging from about 100–200 years along the Magra, and up to 500 years along some tributaries. This flood event resulted in morphological changes, flooding, damages and loss of human lives, and has further exacerbated existing conflicts in river management. Such conflicts stem from flood safety being the main management priority, but a growing recognition that preservation of channel forms and physical processes is also important for the aims of the Water Framework Directive. The objectives of this study are to: (1) document channel changes that occurred during this large flood, and analyse them in the context of the longer term (last 150 years) evolutionary trajectory of the river; (2) analyse potential conflicts between preservation of morphological functioning and dynamic mitigation of the channel resulting in increased hazards related to processes of erosion or aggradation.