The SCS-CN method is a globally known procedure used primarily for direct-runoff estimates. It also is integrated in many modelling applications. However, the method was developed in specific ...geographical conditions, often making its universal applicability problematic. This study aims to determine appropriate values of initial abstraction coefficients λ and curve numbers (CNs), based on measured data in five experimental catchments in the Czech Republic, well representing the physiographic conditions in Central Europe, to improve direct-runoff estimates. Captured rainfall-runoff events were split into calibration and validation datasets. The calibration dataset was analysed by applying three approaches: (1) Modifying λ, both discrete and interpolated, using the tabulated CN values; (2) event analysis based on accumulated rainfall depth at the moment runoff starts to form; and (3) model fitting, an iterative procedure, to search for a pair of λ, S (CN, respectively). To assess individual rainfall characteristics’ possible influence, a principal component analysis and cluster analysis were conducted. The results indicate that the CN method in its traditional arrangement is not very applicable in the five experimental catchments and demands corresponding modifications to determine λ and CN (or S, respectively). Both λ and CN should be viewed as flexible, catchment-dependent (regional) parameters, rather than fixed values. The acquired findings show the need for a systematic yet site-specific revision of the traditional CN method, which may help to improve the accuracy of CN-based rainfall-runoff modelling.
Riparian zones are dynamic ecosystems that form at the interface between the aquatic and terrestrial components of a landscape. They are shaped by complex interactions between the biophysical ...components of river systems, including hydrology, geomorphology, and vegetation. Remote sensing technology is a powerful tool useful for understanding riparian form, function, and change over time, as it allows for the continuous collection of geospatial data over large areas. This paper provides an overview of studies published from 1991 to 2021 that have used remote sensing techniques to map and understand the processes that shape riparian habitats and their ecological functions. In total, 257 articles were reviewed and organised into six main categories (physical channel properties; morphology and vegetation or field survey; canopy detection; application of vegetation and water indices; riparian vegetation; and fauna habitat assessment). The majority of studies used aerial RGB imagery for river reaches up to 100 km in length and Landsat satellite imagery for river reaches from 100 to 1000 km in length. During the recent decade, UAVs (unmanned aerial vehicles) have been widely used for low-cost monitoring and mapping of riverine and riparian environments. However, the transfer of RS data to managers and stakeholders for systematic monitoring as a source of decision making for and successful management of riparian zones remains one of the main challenges.
Summary
Over the past few decades, numerous floodplain restoration projects have attempted to re‐establish complex and diverse river floodplains. They often aim to restore lateral connectivity (i.e. ...interactions between the main river channel and floodplain channels) and rejuvenate floodplain habitats which are no longer maintained or created by fluvial processes. Nonetheless, results of these experiences in terms of hydromorphological conditions and adjustments are rarely shared.
The Rhône River is a large, highly regulated system where lateral connectivity has been greatly reduced. We investigated habitat dynamics (using sedimentological indicators as proxies) in 18 floodplain channels that were restored between 1999 and 2006. Environmental data (bathymetry and grain size of surficial fine sediments) were acquired on 3–5 surveys for each channel covering 6–12 years after restoration. In addition, a pre‐restoration survey was made in 12 of the 18 channels.
Using pressure sensors in the floodplain channels and rating curves in the main channel, we quantified the upstream overflow frequency and magnitude (i.e. maximum shear stress) in the channels and tested how these variables explain observed sedimentological patterns.
Between‐channel diversity accounted for 81% of the sedimentological variability observed after restoration. Time‐averaged sedimentological conditions were robust and well predicted from overflow frequency and magnitude. Similarly, an indirect index of lateral connectivity used by hydrobiologists was also predictable from overflow frequency and magnitude.
The remaining 19% of the sedimentological variability was attributed to temporal variation within channels and was mainly related to changes in longitudinal grain size gradient. This emphasises that grain size patterns are periodically reworked as a result of the flooding regime (backflow versus overflow) without significantly affecting average grain sizes. However, trajectories of grain size changes were stochastic and not always related to the hydrological regime. Accordingly, the partial pre‐restoration data suggest that post‐restoration sedimentological conditions were often similar to those observed before restoration, except in a few channels where major restoration works were performed.
Our results quantify how changes in upstream overflow frequency and magnitude can modify physical conditions in the floodplain channels. They can be used to design habitats that are infrequent or missing at the floodplain scale. These results also suggest that changes in upstream plug morphology are a primary habitat driver. Such changes could be more frequently implemented in the Rhône and elsewhere to maximise the diversity of physical conditions in floodplains.
Abstract
Steep mountain environments are typically characterized by high sediment production. In the case of high hillslope–channel connectivity, high production and intensive transport of sediments ...are problematic and can cause damage in inhabited areas. At the end of the 19th century, due to flood events, large‐scale torrent control measures were inappropriately applied, disrupting the natural processes, and riparian and water ecosystems in watersheds. Connectivity in watersheds affects the course and magnitude of hazards that threaten human society. This is also why the topic of connectivity should be considered in the management of watercourses. Our study links the issue of sediment connectivity (lateral/longitudinal) and the sediment transport‐related risk in unmeasured forested watersheds Hučivá Desná and Upper Moravice. We applied a methodology for sediment transport‐related risk assessment and the well‐established effective catchment area (ECA) approach and connectivity index (IC) to two headwater streams. The results showed the parts of the streams with the highest degree of hazard related to sediment transport and sediment contribution areas connected to them. Based on the field survey, it was found that the best suitable threshold for ECA delineation for Hučivá Desná catchments is 8° and for Upper Moravice is 10°. Area of sediment contribution areas for Hučivá Desná is four times bigger than for Upper Moravice. The Hučiva Desná, therefore, has a higher potential sediment supply from the slopes, which also increases the possibility of occurrence of hazards associated with the sediment transport regime. All three applied methods confirmed that the parallel roads along channels decrease slope–channel connectivity, especially in the Upper Moravice catchment. The combination of methodologies created a suitable tool to identify the most problematic stretches of streams in terms of sediment connectivity and risk related to sediment transport, which can be useful for water and sediment management in unmeasured forested watersheds.
Delineation of flood extents is an important task in various disciplines. Traditional sophisticated hydrodynamic or alternative non-hydrodynamic approaches can be used depending on the availability ...and quality of input data and, in particular, the purpose of the delineation. This work focuses on testing the accuracy of flooded areas computed by GIS-based non-hydrodynamic AIZM tool, which is undemanding in terms of input data and technological requirements. The flood delineation is carried out on the basis of flood height at a single point and its spreading along a stream line over a digital elevation model (DEM). In order to assess the tool's performance, flood inundations have been computed along 60 river reaches in the Czech Republic and compared with benchmarks inundations: (1) real flood events that occurred in 1997, 2002 and 2006, as mapped from aerial and satellite imagery and (2) flood hazard maps designed for flood events of 5-, 20- and 100-year return periods. The accuracy of the outputs is examined and interpreted in the context of the river reaches' specificities to identify generally favourable conditions as well as the key limitations of the model. The results outline that under certain conditions, the AIZM tool can be used as a reliable tool for flood extent delineation in data scarce areas (e.g. lacking hydrodynamic constants and channel bathymetry), for reconstruction of past flood events or for preliminary estimation of flooded areas.
•A non-hydraulic GIS-based approach “AIZM” for delineating flood inundations is presented.•The accuracy of outputs has been tested using 60 river reaches of different types.•The comparison is based on both real and modelled benchmark inundation extents.•The AIZM tool can easily provide data on the extent of missing inundations.•The AIZM tool can be employed for reconstructing inundations based on flood marks.
The testing of a model performance is important and is also a challenging part of scientific work. In this paper, the results of the physically-based EROSION-3D (Jürgen Schmidt, Berlin, Germany) ...model were compared with trapped sediments in a small reservoir. The model was applied to simulate runoff-erosion processes in the Svacenický Creek catchment in the western part of the Slovak Republic. The model is sufficient to identify the areas vulnerable to erosion and deposition within the catchment. The volume of sediments was measured by a bathymetric field survey during three terrain journeys (in 2015, 2016, and 2017). The results of the model point to an underestimation of the actual processes by 30% to 80%. The initial soil moisture played an important role, and the results also revealed that rainfall events are able to erode and contribute to a significant part of sediments.
Headwater streams play an essential role in catchment hydrogeomorphology while supplying water and sediment to downstream reaches along the channel network. Adaptive management strategies which ...require ecological rehabilitation and natural hazards prevention methods are increasingly needed to sustain ecological services provided by headwater streams. However, environmentally sound and economically effective stream management techniques depend on relevant information on boundary conditions, operating processes and evolutionary trajectories of a river system, which are often unavailable. Therefore, it is desirable to provide river managers with scientifically rigorous, yet easy to apply tools (methods) to assess channel and catchment conditions. The present paper focuses specifically on the sediment supply and transport (SST) regime, a crucial component of the fluvial system and a source of significant hazard to people and infrastructures. The SST hazard and risk assessment procedure was developed for small headwater streams with a catchment area of up to ca. 50 km
2
. The method comprises two core modules.
Module 1
is designed to rapidly evaluate susceptibility to SST hazard based on four catchment variables (relief, lithology, erosion-prone surfaces, and connectivity).
Module 1
is intended primarily for river managers to differentiate between catchments and identify those with the highest probability of SST hazard.
Module 2
comprises a detailed evaluation of channel and catchment variables; thus, it is to be conducted applying basic training in fluvial geomorphology and GIS skills.
Module 2
includes five successive steps: channel network segmentation, identification of segments with vulnerable and hazardous anthropic elements, determination of the dominant mode of sediment transport, determination of SST hazard category, and calculation of SST risk score. The method was designed to balance the present-day understanding of sediment flux in the catchment-scale sediment cascades and applicability for target end-users, mostly technically educated professionals and research scientists in river mechanics and erosion and sedimentation.
The quasi-natural meandering type of alluvial rivers is quite unusual in Central European watersheds. The lack of extensive regulation allows such rivers to shift along their floodplain and cause ...erosion of natural and agricultural lands. Description of channel morphometric parameters over decadal timescales allows a better understanding of such river systems like Sajó River (Slovakia-Hungary) where no preliminary work is available regarding channel dynamics. In addition, to just describing the geomorphic processes, the environmental management implications of these meandering rivers need to be investigated as well. Thus, this study represents a bend-scale morphological analysis on the 124 km long section of the Sajó River in the Hungarian territory in eight different periods between 1952 and 2011. Archive aerial imagery, orthophotographs and topographical maps were organized into a database, then GIS-based analyses were performed to quantify the rate and extent of channel shifts, bend development and the area of erosion/accretion. On the bend scale, we have calculated several morphometric parameters (bend length, chord, amplitude, the radius of curvature) to quantify the evolutionary trajectory of reaches. Hydrological time series data were evaluated to reveal its possible role in the processes. Based on the available GIS-data of natural elements and anthropogenic intervention, we delineated 12 different reaches showing similar characteristics, from which six reaches were defined as natural. According to the morphometric parameters of the natural reaches, channel widths became narrower and the planform became more concentrated spatially in most of the reaches while the overall sinuosity of almost all natural reaches increased. Although artificial cutoffs mainly reduced the reach complexity, in some cases, they have accelerated the bend development downstream in the following few years. Erosion and accretion activity were higher in the periods when the discharge was higher than the effective discharge but its effect became less apparent in the second half of the investigated time period. By 1980, major artificial cutoffs and bank protection works were carried out that could have an impact in reducing the potential channel shifting. Based on our results, we propose a possible preservation and some modifications along the Hungarian part of the Sajó River reaches to be carried out by the local river management authorities. We conclude that this study provides a detailed demonstration of the Sajó River morphodymanics which can be used for further land planning to avoid harmful consequences of recent bank erosion processes not only along the Sajó River, but other similar rivers in Europe.
•We determine evolution of channel dynamics by detailed morphometric analysis.•Segmentation of total reach resulted 12 sub-reaches showing similar characteristics.•Bank protection reduces bend complexity but accelerates erosion downstream.•Discharge plays a key role in of bank erosion but it decreased through time.•Statistical difference exists between ‘natural’ and ‘anthropogenic’ reaches.
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