No abstract

The floods of 2015 and 2018 in the Middle Ebro River have led to a rethinking and updating of the forecasting and management systems. The improvements in the flow measurement systems applied in this type of extreme phenomena have led to questioning the values that were recorded in the past, officially changing the maximum flow rates of some historical floods. This has called for the need to update the knowledge/information of those recorded in the middle Ebro River, for example changing the return periods and making previous scientific studies obsolete. Updated data are applied, trying to re-characterize the floods of Ebro River since 1950, date in which the beginning of the “Anthropocene” is evident in the river management of the mainstream and its basin. At the same time, in the proposed risk management plans compliant with 2007/60/EC Directive, the structural measures are being replaced by more respectful and better adapted prevention systems for the river. The two processes interact and are essential for educating the population on risk, adopting preventive measures that are sustainable and consistent with the authentic (corrected) characteristics of the river and its floods. Thus, scientific knowledge has been consolidated as a tool to display corrected data, or, the river’s updated reality, and also to make the affected inhabitants aware of the need to follow new management protocols, focused on river resilience and social strategies.

El diagnóstico y evaluación hidromorfológica fluvial es un procedimiento necesario con el objetivo de la mejora del estado ecológico de los ríos afectados por notables impactos antrópicos. El índice hidrogeomorfológico IHG fue diseñado hace 15 años para ese objetivo. Se presenta la versión más actualizada del mismo y de su modalidad para cursos efímeros (IHG-E). Se localizan todas las aplicaciones del índice llevadas a cabo hasta el momento, un total de 60 tanto en Europa como en América. La versatilidad del índice ha quedado demostrada por la gran variedad de cursos fluviales en los que se ha aplicado. Se reflexiona sobre la empleabilidad del índice, la adecuación de los indicadores que analiza, sus criterios y las dificultades de aplicación. Se concluye que, además de permitir una evaluación hidromorfológica al uso, resulta especialmente útil para la identificación y valoración de los impactos en el espacio fluvial y, por tanto, para definir propuestas de restauración y para evaluar la eficacia de las mismas mediante una aplicación progresiva del índice a lo largo del seguimiento, identificando en qué aspectos va mejorando el río analizado.

How should the success of river and floodplain restoration be assessed? What should we be restoring? We contend that the benchmark for restoration should be the river in its “natural,” that is, quasi‐equilibrium condition prior to deliberate modification. The pre‐modification condition of the river represents a quasi‐equilibrium state in which the river accommodates and adjusts to catchment water and sediment fluxes, whether in a pristine or modified catchment. The resulting assemblage of river landforms (e.g., bars, channels, backwaters) is in balance with the prevailing flood and sediment regime. Furthermore, equilibrium channel forms can adjust to changes in, for example, flood magnitude and frequency via for example, channel expansion or contraction. A restored river system is one that once was anthropogenically restricted, but now has regained capacity to adjust its form. River restoration needs understanding of the history and trajectory of pre‐modification channels, so that the “right” river type can be restored. To assess the scope and success of restoration, we propose using a natural character index (NCI). The NCI is the ratio between a parameter which describes the form and function of a river now (observed) and the same parameter measured at a point or points in time past (expected). Exemplar parameters include sinuosity, floodplain width, active channel width, bar area (at a given flow) and riparian vegetation. Measurement of these parameters utilizes a combination of aerial photos, archive maps and LiDAR‐derived terrain models, the availability of which necessarily limits and determines what parameters can be used in NCI assessment. LiDAR is a useful tool providing an opportunity to comprehend pre‐modification river and floodplain character. We illustrate the NCI concept and its potential for use in assessing restoration effects using examples from New Zealand, Spain and Croatia. The result is an index of use as a “first cut” preliminary assessment for river practitioners.

RESUMEN.