Channel response to gravel mining activities in mountain rivers

Geomorphology, 2010

Historical information on river degradation was used in a case study on the Gállego River, a tributary of the Ebro River, in northeastern Spain. The Gállego drains about 4000 km 2 of the southern slopes of the Pyrenees. Good channel surveys since the 1940s allowed a comparison of longitudinal bed profiles over time. Over this period about 1 million m 3 of gravel was mined according to the archival records. The volume of alluvium lost due to incision in the same period was 2 million m 3. This imbalance is tentatively explained by a budget model based on a bedload equation and an algorithm to determine whether the effective bedload transport is controlled by the transport capacity or by the supply of sediment. It appears that the incision process has changed the magnitude of the shear stresses on channel bed. As the river became deeper, the channel could accommodate higher discharges without overbank flooding. The results obtained from a second model based on diffusion equation for the bed elevation compared well with the field data. This model is based on the hypotheses of steady uniform flow regarding water and sediment conservation.

2013

This paper presents a novel 2D-depth average model especially developed for gravel-bed rivers, named Lican-Leufu (Lican=pebble and Leufu=river, in Mapuche’s language, the native inhabitants of Central Patagonia, Argentina). The model consists of three components: a hydrodynamic, a sedimentological, and a morphological model. The flow of water is described by the depth-averaged Reynolds equations for unsteady, free-surface, shallow water flows. It includes the standard k-e model for turbulence closure. Sediment transport can be divided in different size classes (sand-gravel mixture) and the equilibrium approach is used for Exner’s equation. The amour layer is also included in the structure of the model and the surface grain size distribution is also allowed to evolve. The model simulates bank slides that enable channel widening. Models predictions were tested against a flume experiment where a static armour layer was developed under conditions of sediment starvations and general good...

Hydrological Processes, 2015

A 2D depth averaged model has been developed for simulating water flow, sediment transport and morphological changes in gravel bed rivers. The model was validated with a series of laboratory experiments and then applied to the Nove reach of the Brenta River (Northern Italy) to assess its bed material transport, interpret channel response to a series of intensive flood events (R.I.  10 years), and provide a possible evolutionary scenario for the medium term. The study reach is 1400 m long with a mean slope of 0.0039 m m -1 . High resolution digital terrain models were produced combining LiDAR data with colour bathymetry techniques. Extensive field sedimentological surveys were also conducted for surface and subsurface material. Data were uploaded in the model and the passage of two consecutive high intensity floods was simulated. The model was run under several hypotheses of sediment supply: one considering substantial equilibrium between sediment input and transport capacity, and the others reducing the sediment supply. The sediment supply was then calibrated comparing channel morphological changes as observed in the field and calculated by the model. Annual bed material transport was assessed and compared with other techniques. Low-frequency floods (R.I.  1.5 years) are expected to produce negligible changes in the channel while high floods may erode banks rather than further incising the channel bed. Location and distribution of erosion and deposition areas within the Nove reach were predicted with acceptable biases stemming from imperfections of the model and the specified initial, boundary and forcing conditions. A mediumterm evolutionary scenario simulation underlined the different response to and impact of a consecutive sequence of floods.

Proceedings of the International Conference on Fluvial Hydraulics, Lisbon, Portugal, 6-8 September 2006, 2006

A conceptual model for the morphological and textural evolution of gravel bed rivers is proposed. It is composed of conservation and closure equations. The former are drawn from the shallow-water theory, using a multiple layer framework and the continuum hypothesis for each transport layer. The latter specifies flow resistance and phenomena pertaining to the dynamics of gravel transport. Special attention is given to the theoretical formulation of the velocity of the bedload layer and to the experimental characterization of the grain and water velocities. For that purpose, new experimental gravel transport data is presented. The proposed formulation envisages the incorporation of sediment dynamics in the overall momentum conservation equation. The model is applied to a simple test case, strong overfeeding imposed at the upstream end of a mild-sloped mobile bed channel. The numerical results of the proposed model are compared with those of a classic de Vries-type model. It is argued that the inclusion of the dynamics of the transported particles represents a major change in the structure of the morphological models, thus justifying further research efforts.

Australian Geographer, 2014

Hydrological Processes, 2014

Downstream hydraulic geometry relationships describe the shape of alluvial channels in terms of bankfull width, flow depth, flow velocity, and channel slope. Recent investigations have stressed the difference in spatial scales associated with these variables and thus the time span required for their adjustment after a disturbance. The aim of this study is to explore the consequences in regime models considering the hypothesis that while channel width and depth adjust quickly to changes in water and sediment supply, reach slope requires a longer time span. Three theoretical models were applied. One model incorporates an extremal hypothesis . Theoretical regime equations for mobile gravel-bed rivers with stable banks. Geomorphology 64: 207-220), and the other two are fully physically based (Ikeda S, Parker G, Kimura Y. 1988. Stable width and depth of straight gravel rivers with heterogeneous bed materials. Water Resources Research 24: 713-722; Parker G, Wilcock PR, Paola C, Dietrich W, Pitlick J. 2007. Physical basis for quasi universal relations describing bankfull hydraulic geometry of single-thread gravel-bed rivers. ). In order to evaluate the performance of models introducing the slope as an independent variable, we propose two modifications to previous models. The performance of regime models was tested against published data from 142 river reaches and new hydraulic geometry data from gravel-bed rivers in Patagonia (Argentina) and north-eastern Italy. Models that assume slope as a control predict channel depth and width reasonably well. Parker et al.'s (2007) model improved predictions because it filters the scatter in slope data with a relation slope-discharge. The extremal hypothesis model of predicts comparably to the other physically based models. Millar's model was chosen to describe the recent changes in the Piave and Brenta rivers due to human interventionmainly in-channel gravel mining. The change in sediment supply and recovery was estimated for these rivers. This study supports the interpretation that sediment supply is the key factor guiding morphological changes in these rivers. H Ã ¼ 0:125Q Ã0:16 S À0:62 m 0 0:64 (5) Parker et al. (2007) proposed a physical-based model where the hydraulic geometry is described by means of three reach-averaged variables: width, mean depth, and 2349 REGIME THEORIES IN GRAVEL-BED RIVERS

Journal of agricultural engineering, 2013

A 2D depth average model has been used to simulate water and sediment flow in the Brenta River so as to interpret channel changes and to assess model predictive capabilities. The Brenta River is a gravel bed river located in Northern Italy. The study reach is 1400 long and has a mean slope of 0.0056. High resolution digital terrain models has been produced combining laser imaging detection and ranging data with colour bathymetry techniques. Extensive field sedimentological surveys have been also carried out for surface and subsurface material. The data were loaded in the model and the passage of a high intense flood (R.I. > 9 years) was simulated. The model was run under the hypothesis of a substantial equilibrium between sediment input and transport capacity. In this way, the model results were considered as a reference condition, and the potential trend of the reach was assessed. Low-frequency floods (R.I. » 1.5 years) are expected to produce negligible changes in the channel while high floods may focalize erosion on banks instead than on channel bed. Furthermore, the model predicts well the location of erosion and siltation areas and the results promote its application to other reaches of the Brenta River in order to assess their stability and medium-term evolution.

Engineering Geology for Society and Territory - Volume 3, 2014

Gravel mining may induce deep changes in river morphology including bank instabilities, downstream as well upstream bed incision. In the present work, morphological changes due to a large sediment mining in the Orco river (a tributary of the Po river, located in the Piemonte Region) are documented and modeled. The river mining occurred in 2003-2004, a volume of about 130,000 m 3 of sediment was extracted over a surface of about 70,000 m 2 at about 25 km upstream the confluence with the Po river. The mining and the response of the river to this intervention is well-documented through an experimental methodology developed by the CNR-IRPI and based on four distinct LIDAR surveys realized in the years 2003, 2004, 2006 and 2007. The observed morphological changes that occurred immediately after the gravel extraction in the time period 2004-2006 were then reproduced using the hydro-morphological 1D model BASEMENT developed by the ETH (www.basement.ethz.ch). Results indicate the model is able to capture not only the depositional and erosional areas, but it also provides a good estimate of the volume of sediment mobilized.

with 17 figures and 3 tables Summary. A first aim of this paper is to investigate the existence, if any, and the parameters defining the occurrence conditions of a continuum of rhythmic, transverse roughness elements of gravel-bed rivers such as transverse ribs, step-pools and riffle and pool sequences. The investigation is carried out by the analysis of a large data set consisting of almost all the data available in the literature and unpublished field data measured by the authors on a few rivers in the eastern Alps and the northern Apennines. Open questions about the origin of these bedforms are considered and tested against the data set available. A few equations relating the main geomorphic parameters are obtained. They can be used for river restoration and paleohydrological inference. The jamming factor (ratio between the size of the coarser particle and channel width) is found as a relevant parameter in the development of the bedforms considered. The conditions and the interplays between the jamming factors and others parameters such as bedform wavelength and streambed gradient are considered in order to discriminate the fields of existence of the larger roughness transverse, cyclic elements of gravel bed rivers and to show that transverse ribs, step-pools and riffle and pool sequences are part of a coarse grained bedform continuum.

Sustainability

In current river management, we very often use environment-friendly hydraulic structures when it is required for river bed or river bank protection due to erosion of a river channel. Block ramps are one of many methods used to stabilize river beds. They provide a semi-natural solution to certain river engineering problems in mountain streams. When building block ramps, one can use the dissipative behavior of large rock blocks or boulder elements randomly placed on the river bed to enhance fish migration in an upstream direction; thus, they can serve as fish passes. In this paper, we present the results of the numerical modelling of a bed load transport and the morphological changes of a river bed where a block ramp was designed and built. The main aim of the study was to investigate the difference of 2D modelling of a bed load transport along the mountain stream reach with boulder ramps in comparison to the classical methods of Hjulström, Shields, and Russian standard ST-24-2396. Th...