Barasona Reservoir Research Articles

Synthetic Hydrographs Generation Downstream of a River Junction Using a Copula Approach for Hydrological Risk Assessment in Large Dams

Peak flows values (Q) and hydrograph volumes (V) are obtained from a selected family of historical flood events (period 1957–2017), for two neighboring mountain catchments located in the Ebro river basin, Spain: rivers Ésera and Isábena. Barasona dam is located downstream of the river junction. The peaks over threshold (POT) method is used for a univariate frequency analysis performed for both variables, Q and V, comparing several suitable distribution functions. Extreme value copulas families have been applied to model the bivariate distribution (Q, V) for each of the rivers. Several goodness-of-fit tests were used to assess the applicability of the selected copulas. A similar copula approach was carried out to model the dependence between peak flows of both rivers. Based on the above-mentioned statistical analysis, a Monte Carlo simulation of synthetic design flood hydrographs (DFH) downstream of the river junction is performed. A gamma-type theoretical pattern is assumed for partial hydrographs. The resulting synthetic hydrographs at the Barasona reservoir are finally obtained accounting for flow peak time lag, also described in statistical terms. A 50,000 hydrographs ensemble was generated, preserving statistical properties of marginal distributions as well as statistical dependence between variables. The proposed method provides an efficient and practical modeling framework for the hydrological risk assessment of the dam, improving the basis for the optimal management of such infrastructure.

Water and sediment fluxes in Mediterranean mountainous regions: comprehensive dataset for hydro-sedimentological analyses and modelling in a mesoscale catchment (River Isábena, NE Spain)

Abstract. A comprehensive hydro-sedimentological dataset for the Isábena catchment, northeastern (NE) Spain, for the period 2010–2018 is presented to analyse water and sediment fluxes in a Mediterranean mesoscale catchment. The dataset includes rainfall data from 12 rain gauges distributed within the study area complemented by meteorological data of 12 official meteo-stations. It comprises discharge data derived from water stage measurements as well as suspended sediment concentrations (SSCs) at six gauging stations of the River Isábena and its sub-catchments. Soil spectroscopic data from 351 suspended sediment samples and 152 soil samples were collected to characterize sediment source regions and sediment properties via fingerprinting analyses. The Isábena catchment (445 km2) is located in the southern central Pyrenees ranging from 450 m to 2720 m a.s.l.; together with a pronounced topography, this leads to distinct temperature and precipitation gradients. The River Isábena shows marked discharge variations and high sediment yields causing severe siltation problems in the downstream Barasona Reservoir. The main sediment source is badland areas located on Eocene marls that are well connected to the river network. The dataset features a comprehensive set of variables in a high spatial and temporal resolution suitable for the advanced process understanding of water and sediment fluxes, their origin and connectivity and sediment budgeting and for the evaluation and further development of hydro-sedimentological models in Mediterranean mesoscale mountainous catchments. The dataset is available at http://doi.org/10.5880/fidgeo.2018.011.

Case Study: Effect of Climatic Characterization on River Discharge in an Alpine-Prealpine Catchment of the Spanish Pyrenees Using the SWAT Model

The new challenges in assessment of water resources demand new approaches and tools, such as the use of hydrologic models, which could serve to assist managers in the prediction, planning and management of catchment water supplies in view of increased demand of water for irrigation and climatic change. Good characterization of the spatial patterns of climate variables is of paramount importance in hydrological modelling. This is especially so when modelling mountain environments which are characterized by strong altitudinal climate gradients. However, very often there is a poor distribution of climatic stations in these areas, which in many cases, results in under representation of high altitude areas with respect to climatic data. This results in the poor performance of the models. In the present study, the Soil and Water Assessment Tool (SWAT) model was applied to the Barasona reservoir catchment in the Central Spanish Pyrenees in order to assess the influence of different climatic characterizations in the monthly river discharges. Four simulations with different input data were assessed, using only the available climate data (A1); the former plus one synthetic dataset at a higher altitude (B1); and both plus the altitudinal climate gradient (A2 and B2). The model’s performance was evaluated against the river discharges for the representative periods of 2003–2005 and 1994–1996 by means of commonly used statistical measures. The best results were obtained using the altitudinal climate gradient alone (scenario A2). This study provided insight into the importance of taking into account the sources and the spatial distribution of weather data in modelling water resources in mountainous catchments.

Combining catchment modelling and sediment fingerprinting to assess sediment dynamics in a Spanish Pyrenean river system

The elevated supply and transfer of sediment in river systems can impact on water resource infrastructure, water quality and ecosystem health around the world. Moreover, the loss of reservoir capacity due to siltation is of particular concern in regions that experience water scarcity, such as the Mediterranean. Therefore, quantifying the sediment production from contributing catchments to reservoirs is of major interest to support the development of management plans for maintaining reservoir sustainability. Within this context, sediment production from a catchment in the central Spanish Pyrenees was investigated by combining the outputs of the Soil and Water Assessment Tool (SWAT) model with sediment source fingerprinting. The study examined the large alpine-prealpine catchment of the Barasona reservoir, which is an agroforest catchment supplying sediment to the reservoir at an annual rate of around 3.5tha−1. For the period 2003–2005 the simulated specific sediment yields for the catchment by SWAT model are mostly below 2tha−1year−1 with maximum values reaching 250tha−1year−1. Simulated sediment production is dependent on (i) land use/cover, (ii) precipitation amounts and (iii) slope gradients. The highest sediment yield was simulated for the badlands, in the wettest year and for the greatest slope gradients. The predicted catchment source contributions obtained for the reservoir sediments were low (<7%) for forest and scrubland sources, greater for agricultural sources and exceeded 50% for subsoil sources. Results from both procedures indicate that badlands are the main sediment source while agricultural land is of secondary importance. This combination of procedures allowed catchment sediment production and source contributions to be linked to reservoir infilling. It also demonstrates the benefits of combined modelling and sediment fingerprinting approaches in complex catchments where siltation threatens water and energy security.

Land use sediment production response under different climatic conditions in an alpine–prealpine catchment

Loss of soil and subsequent export of sediments to streamflows by water erosion constitute significant environmental threats because of the areal extent typically involved and the agricultural activities that they support. Climate change is expected to impact on the availability of water and therefore on soil resources. In this context, hydrological and soil erosion models allow for the mapping and quantifying of soil redistribution and sediment productions for different land uses and climatic scenarios that can be used for valuable projections for catchment management. A simulation experiment was achieved by using the Soil and Water Assessment Tool (SWAT) model in the mountainous catchment of the Barasona reservoir (1509km2, Central Spanish Pyrenees), which is characterized by a heterogeneous climate and topography, that brings it a varied mosaic of soil types and land uses. In order to investigate differences in sediment productions from the land uses under different climatic conditions the sediment produced from the land uses was assessed for two years. 2003 and 2005 were selected to represent contrasted precipitations and wet and dry conditions, respectively. Moreover, the distribution of land uses and climate in the catchment enabled the division of the catchment into two parts which allowed the assessment of the sediment productions in the northern alpine and the southern Mediterranean parts of the catchment. The specific sediment yield varied largely in relation with precipitation, seasons, land use types and catchment parts, from 0 to 243tha−1year−1. Furthermore, according to the prediction of the IPCC and climatic studies for the region an increase of 2°C was simulated to assess the impact on sediment yield. Different responses to the temperature increment were observed between wetter (2003 and northern part) and drier (2005 and southern part) conditions and also for the land use types. Great decreases in sediment production were observed for the 2°C increase scenario in wetter conditions, whereas low decreases with some increments occurred in the drier conditions. The proposed model proved useful for the assessment of the behaviour in sediment production from the land uses under different climatic conditions in large alpine–prealpine catchments at a regional level.

Suspended sediment, carbon and nitrogen transport in a regulated Pyrenean river

Regulation alters the characteristics of rivers by transforming parts of them into lakes, affecting their hydrology and also the physical, chemical, and biological characteristics and dynamics. Reservoirs have proven to be very effective retaining particulate materials, thereby avoiding the downstream transport of suspended sediment and the chemical substances associated with it (e.g. Carbon, C, or Nitrogen, N). The study of fluvial transport of C and N is of great interest since river load represents a major link to the global C and N cycles. Moreover, reservoirs are the most important sinks for organic carbon among inland waters and have a potential significance as nitrogen sinks. In this respect, this paper investigates the effects of a Pyrenean reservoir on the runoff, suspended sediment, C and N derived from the highly active Ésera and Isábena rivers. Key findings indicate that the reservoir causes a considerable impact on the Ésera–Isábena river fluxes, reducing them dramatically as almost all the inputs are retained within the reservoir. Despite the very dry study year (2011–2012), it can be calculated that almost 300,000t of suspended sediment were deposited into the Barasona Reservoir, from which more than 16,000 were C (i.e. 2200t as organic C) and 222t were N. These values may not be seen as remarkable in a wider global context but, assuming that around 30hm3 of sediment are currently stored in the reservoir, figures would increase up to ca. 2.6×106t of C (i.e. 360,000t of organic C) and 35,000t of N. Nevertheless, these values are indicative and should be treated with caution as there is incomplete understanding of all the processes which affect C and N. Further investigation to establish a more complete picture of C and N yields and budgets by monitoring the different processes involved is essential.

Sediment size distribution and composition in a reservoir affected by severe water level fluctuations

The reservoir sediments are important sinks for organic carbon (OC), the OC burial being dependent on two opposite processes, deposition and mineralization. Hence factors such as severe water level fluctuations are expected to influence the rate of OC accumulation as they may affect both deposition and mineralization. The Barasona Reservoir has been historically threatened by siltation, whilst the use of water for irrigation involves a drastic decrease of the water level. In this context, we have studied the physical and chemical characteristics (grain size, major and minor elemental compositions, organic and inorganic carbon, and nitrogen) of the recent sediments of the Barasona Reservoir and the relationships among them in order to: a) elucidate the main processes governing OC accumulation, b) evaluate the rate of OC mineralization and c) approach the effect of drought on the sediment characteristics in this system. Our results indicated that Barasona sediments were dominated by fine silts (>60%) and clays (>20%), the mean particle size decreasing from tail to dam. Desiccation increased particle sorting and size distribution became bimodal, but no effect on average size was observed. Attending to the composition, Barasona sediments were very homogeneous with low concentrations of nitrogen (TN) and phosphorus (<1.2gkg−1dw and <0.6gkg−1dw, respectively) and high concentration of OC (≈36gkg−1dw). TN was negatively related to dry weight. Sediment mixing due to drastic changes in water level may have favoured the observed homogeneity of Barasona sediments affecting carbon, major ions and grain size. The high amount of OC deposited in Barasona sediment suggested that the adsorption of OC onto fine particles was more important than in boreal lakes. The rate of oxygen consumption by wet sediment ranged from 2.26 to 3.15mgO2m−2day−1, values close to those compiled for Mediterranean running waters.

Identifying sediment sources by applying a fingerprinting mixing model in a Pyrenean drainage catchment

Spanish Pyrenean reservoirs are under pressure from high sediment yields in their contributing catchments. Sediment fingerprinting approaches offer the potential to quantify the contribution of different sediment sources, evaluate catchment erosion dynamics and develop management plans to tackle, among other problems, reservoir siltation. Within this context, the objective of this study was to assess catchment source contribution changes both over a longitudinal river reach and to a reservoir delta deposit to improve our understanding of sediment supply dynamics. The catchment of the Isábena River (445 km2), located in the central Spanish Pyrenees, is an agroforest catchment supplying sediments, together with the Ésera River, to the Barasona reservoir at an annual rate of ~350 t km2 with implications for reservoir longevity. The ability to discriminate between agricultural, forest, subsoil and scrubland sources based on geochemical, radionuclide and magnetic susceptibility fingerprint properties analysed in the <63-μm sediment fraction was investigated by conducting statistical tests to select an optimum composite fingerprint. The contributions of sediment sources for channel bed and delta sediments were assessed by applying a new data processing methodology which was written in the C programming language and designed to test the entire parameter space, providing a detailed description of the optimal solution by a Monte Carlo method. The solution for each sample was characterised by the mean value of the user-defined solutions (n = 100) and the lower goodness of fit value was applied. The solutions from the mixing model had goodness of fit values >82 %. The channel bed sediments in the upper reach were dominated by subsoil sources (>80 %), and the lower reaches had a higher proportion of sediment coming from the agricultural source (>55 %). Contributions for delta sediments were dominated by agricultural, forest and subsoil sources but in varying proportions within the deposit. The switch in the sources of sediment between the headwaters and the catchment outlet was due to differences in the distribution of the land uses/land covers in the contributing areas. Differences between channel bed sediment and delta sediment source contributions were related to local sediment deposition conditions. The new unmixing approach is able to provide the optimal solution by a robust and integral Monte Carlo method guaranteeing a broader interpretation of the optimal solution including its dispersion in all unmixing cases. The results support the use of sediment fingerprinting approaches in this Spanish Pyrenees mountain catchment, which will enable us to better understand catchment sediment delivery to an important water supply reservoir.

Modeling sediment sources and yields in a Pyrenean catchment draining to a large reservoir (Ésera River, Ebro Basin)

The study aimed to use the Soil and Water Assessment Tool (SWAT) model to simulate erosion processes in an alpine–prealpine catchment in order to provide data and information that may be relevant for managers so as to minimize reservoir siltation and water quality degradation. The main objective was to assess sediment production across the catchment and sediment supply to the main reservoir. The Barasona reservoir catchment (1,509 km2) is located in the Central Spanish Pyrenees, in the Ebro Basin. This catchment was selected for the case study given the regional significance of the Barasona reservoir and its siltation problems. The catchment has a mountain climate, with strong altitudinal and north–south gradients. The catchment is characterized by heterogeneous topography and lithology, resulting in a varied mosaic of slopes, soil types, and land covers. The Jueu karst system and two small headwater reservoirs were parameterized and calibrated in the model. The SWAT model sediment calibration for the catchment was based on a prior monthly hydrologic calibration, and the model validation was based on the sediment depositional history of the Barasona reservoir. The simulation period (2003–2006) and the validation period (1993–2002) produced average sediment yields to the reservoir of 643,000 and 575,000 t year−1, respectively. Large variations in sediment production were found between the subcatchments in the Barasona catchment due to differences in rock outcrops, land cover, and slope gradient. Sediment loss in the Jueu karst system was 15,500 t and the two small headwater reservoirs retained 31,200 and 50,300 t. Sediment production in relation to precipitation showed high temporal variability, with specific sediment yields to the Barasona reservoir ranging from 2.74 to 8.25 t ha−1 year−1. Strong lithological control was observed for sediment production in the subcatchments. The main sediment sources were located in the badlands developed on marls in the middle part of the catchment (internal depressions). The proposed model has proved useful for identifying areas where significant erosion processes take place in large alpine–prealpine catchments at a regional level and also for assessing discharge losses by the karst system and the sedimentary role of the small reservoirs. The information obtained through this research will be of interest in assessing the spatial distribution of sediment sources and areas of high sediment yield, which will be useful to establish criteria for remediation strategies.

Análisis del impacto del cambio climático en el ciclo de sedimentos de la cuenca del río Ésera (España) mediante un modelo hidrológico distribuido

In this study, the distributed hydrological and sedimentological model TETIS was applied in the Ésera River catchment (Spain). The aim of this study was to analyze the effect of Climate Change on the sediment dynamics in the catchment and the siltation of Barasona reservoir that drains it. The implementation of the sediment sub-model was performed using the volumes of sediment deposited in the reservoir and measured from three historical bathymetries as reference. To analyze the effects of Climate Change, the precipitation and temperature series obtained from the PRUDENCE project, for the current and future A2 and B2 climate scenarios have been used as model inputs. From the results of the simulations with TETIS, it can be concluded that the flow discharges tend to decrease in the future as a direct result of reduced precipitation, increased potential evapotranspiration and reduced soil moisture within the catchment. Despite the trend towards more torrential rainfall, model results indicate that floods will also tend to decrease, more markedly for the A2 scenario than for the B2 scenario, due to the large decrease in soil moisture already mentioned. Moreover, sediment transport tends to decrease for the A2 and increase for the B2 scenario. This situation is reflected in the siltation rates of Barasona reservoir, wherein for B2 no substantial changes are expected, as compared to the situation of the current climate condition, whereas for the A2 scenario a significantly longer service life is expected.

Modelización espacialmente distribuida de la erosión y el transporte de sedimento en cuencas de montaña del Pirineo aragonés: retos para la calibración y validación

Most erosion models applied at basin scale are based on spatially aggregated representation, for example, in a space subdivision of the surfaces to which behavior is assumed homogeneous (sub-basins, hydrological units, etc.). This approach leads to a desirable simplification of the calculations, but presents difficulties in addressing problems related to sediment transport and identification of sediment source areas, which should be treated by a continuous spatial representation. Spatially distributed models, however, allow a more accurate approach to this problem, at the cost of an increased computational complexity. The objective of this work is the calibration and validation of the model WATEM/SEDEM, an empirical-conceptual spatially distributed model, to predict erosion and sediment yield in two watersheds in the Central Spanish Pyrenees: i) the watershed of the Barasona Reservoir (1504 km2), which is drained by the Ésera and Isábena Rivers, the model calibration and validation was based on the depositional history of the Barasona Reservoir and suspended sediment records over 3 years (May 2005–May 2008) at the outlet of the Isábena River; ii) the experimental Arnás catchment (2.84 km2), the model calibration was performed based on a dataset of soil redistribution rates derived from point 137Cs inventories, allowing capture differences per land use in the main model parameters. The validation process was carried with the registration of six years of suspended sediment at the outlet of the Arnás catchment. The calibration process for watershed of the Barasona Reservoir showed the problem you have when trying to calibrate the parameters of transport capacity with a single variable (the export of sediment to the basin outlet), making impossible to find a single set of parameters that optimize the error function, making it necessary to adopt a compromise solution. For the experimental Arnás catchment the model calibration processes using spatially distributed sediment yield derived from 137Cs inventories allowed calibrating the empirical parameters of transport capacity in a satisfactory way, finding a single combination of values that optimizes the error function. These results show that the calibration parameters of transport capacity are a fundamental aspect of the model WATEM/SEDEM and other similar models. To obtain a reliable estimate of the spatial distribution of erosion and sediment transport requires a calibration and validation by means of spatially distributed data of soil loss, which in turn allows a calibration of spatially distributed parameters concerning transport capacity

Una aproximación sedimentológica al aterramiento de embalses y la erosión en cuencas de montaña : el embalse de Barasona y la cuenca de Esera-Isábera (Pirineos centrales, Huesca)

A sedimentologic study of the Barasona reservoir (Central Pyrenees, Huesca province) and its catchment basin illustrates the spatial and temporal evolution of depositional processes in mountain basins. We analyze the sediment composition, identify sedimentary facies, and reconstruct the tri-dimensional geometry of the reservoir based on 20 cores and 3 profiles. Most of the sediment load to the Barasona reservoir is transported during flood events, which underlines the importance of the hydrologic regime of the rivers. Changes in mineral composition inform of sediment provenance and transport processes in the catchment are a. A preliminary chronology based on the identification of floods in the sedimentary record (sandy silt layers) allow to investigate the interaccions reservoir-catchment and changes in sedimentation rates through the last four decades. Physical factors as topography, lithology and drainage patterns appear to be majar controllers on soil erodibility. However, our study stresses the importance of human activity through changes in the use of the land. A better understanding of these processes is needed for suitable management of limited resources of soil and water and to alíviate reservoir sedimentation problems

Regional scale modeling of hillslope sediment delivery: A case study in the Barasona Reservoir watershed (Spain) using WATEM/SEDEM

Soil erosion and sediment delivery to streams are important environmental problems and major concerns in sustainable development. In recent years several tools have been proposed for assessing the delivery of sediment from hillslopes to stream networks, but there are still few examples of their application to large basins, and studies include a discussion of calibration and validation issues. In this study a spatially distributed soil erosion and sediment delivery model (WATEM/SEDEM) was applied to the watershed of the Barasona Reservoir (1504 km 2 , Central Spanish Pyrenees), which is drained by the Ésera and Isábena Rivers. Model calibration and validation was based on the depositional history of the Barasona Reservoir and suspended sediment records over 3 years (May 2005–May 2008) at the outlet of the Isábena River. Despite interannual differences in precipitation and runoff, it was possible to establish an optimum value (7–23) for the ktc parameter. This enabled estimation of the long-term average annual sediment yield to the reservoir, as well as the relative contribution of each river. Large spatial variability in hillslope sediment delivery was found, and the major sediment sources were in the lower part of the watershed (agricultural fields) and in the badlands developed on Eocene marls in the middle part of the watershed (Pyrenean Inner Ranges). The relative importance of sediment source areas was assessed in relation to land use, and the relationship between the sediment delivery ratio and the catchment area was studied as a function of the geomorphological units. For the moment WATEM/SEDEM remains mainly as a researcher’s tool, until either the problem of the scarcity of soil erosion data or the need for calibration of the transport parameters will be solved.

Modelling sediment export, retention and reservoir sedimentation in drylands with the WASA-SED model

Abstract. Current soil erosion and reservoir sedimentation modelling at the meso-scale is still faced with intrinsic problems with regard to open scaling questions, data demand, computational efficiency and deficient implementations of retention and re-mobilisation processes for the river and reservoir networks. To overcome some limitations of current modelling approaches, the semi-process-based, spatially semi-distributed modelling framework WASA-SED (Vers. 1) was developed for water and sediment transport in large dryland catchments. The WASA-SED model simulates the runoff and erosion processes at the hillslope scale, the transport and retention processes of suspended and bedload fluxes in the river reaches and the retention and remobilisation processes of sediments in reservoirs. The modelling tool enables the evaluation of management options both for sustainable land-use change scenarios to reduce erosion in the headwater catchments as well as adequate reservoir management options to lessen sedimentation in large reservoirs and reservoir networks. The model concept, its spatial discretisation scheme and the numerical components of the hillslope, river and reservoir processes are described and a model application for the meso-scale dryland catchment Isábena in the Spanish Pre-Pyrenees (445 km2) is presented to demonstrate the capabilities, strengths and limits of the model framework. The example application showed that the model was able to reproduce runoff and sediment transport dynamics of highly erodible headwater badlands, the transient storage of sediments in the dryland river system, the bed elevation changes of the 93 hm3 Barasona reservoir due to sedimentation as well as the life expectancy of the reservoir under different management options.

Sediment sources and siltation in mountain reservoirs: a case study from the Central Spanish Pyrenees

Based on a 137 Cs -derived chronology, we reconstruct the depositional history of the Barasona reservoir in the Ésera–Isábena Basin, Central Pyrenees (Spain). Most of the sediments were delivered to the Barasona reservoir during flood events. Comparative mineralogical studies of the Ésera and Isábena river channels and the Barasona reservoir sediments help to identify sediment sources and areas of high sediment yield risk, and to establish erosion and sediment transport processes in the watershed. Changes in the mineralogical composition of the sediments can be used to discriminate the relative contribution of the Ésera and Isábena rivers during flood periods. Three main periods in the siltation history of the Barasona reservoir were distinguished: (1) From dam construction (1932) to the early 1950s, the reservoir was flushed every year using the lower gates, and average sediment accumulation was very low (1.5 cm/yr). (2) During the 1950s and 1960s, the sedimentation rate increased and reached the highest values: 15 cm/yr, 24.6 cm/yr and 18.2 cm/yr in the Ésera river mouth, the northern and the southern areas of the reservoir, respectively. Both changes in the exploitation regime (no annual flushes) and climate variability (increased flood frequency and river inflow) caused this increase in sediment delivery and accumulation. (3) The third period was initiated by the enlargement of the dam in 1972. The new sedimentary dynamics in the reservoir caused a general decrease in the sedimentation rate (11.6 cm/yr in the southern areas; 10 cm/yr in the Ésera mouth) that was especially noticeable in the northern areas, where the accumulation rate was reduced to 3.7 cm/yr. An increase in channel erosion processes during this period contributed to the transport of sediments to the inner areas of the reservoir.