The relation between rainfall, runoff, erosion and sediment transport is highly variable in Mediterranean catchments. Their relation can be modified by land use changes and climate oscillations that, ...ultimately, will control water and sediment yields. This paper analyses rainfall, runoff and sediment transport relations in a meso-scale Mediterranean mountain catchment, the Ribera Salada (NE Iberian Peninsula). A total of 73 floods recorded between November 2005 and November 2008 at the Inglabaga Sediment Transport Station (114.5km2) have been analysed. Suspended sediment transport and flow discharge were measured continuously. Rainfall data was obtained by means of direct rain gauges and daily rainfall reconstructions from radar information. Results indicate that the annual sediment yield (2.3tkm−1y−1 on average) and the flood-based runoff coefficients (4.1% on average) are low. The Ribera Salada presents a low geomorphological and hydrological activity compared with other Mediterranean mountain catchments. Pearson correlations between rainfall, runoff and sediment transport variables were obtained. The hydrological response of the catchment is controlled by the base flows. The magnitude of suspended sediment concentrations is largely correlated with flood magnitude, while sediment load is correlated with the amount of direct runoff. Multivariate analysis shows that total suspended load can be predicted by integrating rainfall and runoff variables. The total direct runoff is the variable with more weight in the equation. Finally, three main hydro-sedimentary phases within the hydrological year are defined in this catchment: (a) Winter, where the catchment produces only water and very little sediment; (b) Spring, where the majority of water and sediment is produced; and (c) Summer–Autumn, when little runoff is produced but significant amount of sediments is exported out of the catchment. Results show as land use and climate change may have an important role in modifying the cycles of water and sediment yields in Mediterranean mountain catchments.
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•Total suspended load is predicted from rainfall and runoff variables.•Suspended sediment concentrations are largely correlated with flood magnitude.•Sediment load is highly dependent on direct runoff.•Sediment load is not uniform through time but mostly concentrated in spring.•Rainfall distribution from radar images are used and compared to field data.
Hydropeaked rivers need attention Batalla, R J; Gibbins, C N; Alcázar, J ...
Environmental research letters,
02/2021, Letnik:
16, Številka:
2
Journal Article
Recenzirano
Odprti dostop
Hydropower is considered a renewable form of energy production, but generating electricity from rivers is not always environmentally benign. The global demand for renewables is increasing rapidly as ...fossil fuels are gradually phased out, so rivers will continue to be subjected to the pressures imposed by hydropower for decades to come. Finding ways of operating hydropower plants that limit impacts on downstream river ecosystems is therefore a pressing global concern. Usually, these plants cause marked and rapid fluctuations in flow in downstream river reaches, termed 'hydropeaking'. Hydropeaks result in a variety of ecological changes in the dynamic mountain rivers they typically affect; declines in fish and insect populations are evident, especially in reaches immediately downstream from the plant. While these changes are often acute and readily apparent, the underlying causal mechanisms remain unclear. We argue here that riverbed sediments are a critical but neglected causal link between hydropeaking flow regimes and ecological changes. We outline how a variety of tools from different branches of river science can now be brought together to understand precisely why hydropeaking alters sediment dynamics; these tools provide a mechanistic explanation for changes in bed sedimentary conditions and channel form across multiple scales and, consequently, a better understanding of ecological changes. By allowing us to simulate the effects of flow fluctuations on sediment dynamics and channel form, these tools also allow us to develop ways of releasing water from hydropeaking dams that limit impacts on aquatic habitat and species.
Mountain regions have a key role in the generation of runoff, and in the production and transfer of sediments to fluvial networks, especially in Mediterranean catchments where these processes are ...affected by marked changes in climate and land use (i.e. global change). This paper presents the water and the sediment budgets of the Ribera Salada (224 km2), a meso-scale Mediterranean forested catchment located in the Southern Pyrenees. Field monitoring follows an integrated basins scheme (five nested sub-catchments), where hydrological and sediment transport data were collected continuously over a two-year period (2012–2013). Precipitation was obtained using radar images, which allowed the elaboration of rainfall maps used to characterize the spatial distribution of rainfall across multiple scales. Results indicate that the catchment is hydrologically divided in two areas which show contrasting fluvial regimes: the upper part of the catchment is considered wet and has a constant flow regime, supplying the majority of the water, while the lower part is drier, with ephemeral tributaries and water losses into the alluvial aquifer of the main river channel. In contrast to water yield, most of the suspended sediment load (i.e. 80%) is supplied by the driest part of the catchment where sediment availability was greater and where there is a greater connectivity between sediment sources and the channel network. The sediment yield of the whole catchment and the respective sub-catchments sits in the lower bounds of values reported for the Mediterranean region, indicating the generally low intensity of hydrological and geomorphic processes in the area. Once more the sediment budget approach matched to sound hydrological data proves efficient to characterize sediment dynamics in river basins, with special interest in areas such as the Mediterranean mountain catchments, where the effects of global change appear to be more acute.
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•Two sub-catchments with contrasting hydrosedimentary regimes are identified.•The wet sub-catchment supplies the majority of the water.•Interactions river-aquifer controls water yield in the dry sub-catchment.•The dry sub-catchment supplies the majority of the sediment.•Results emphasise the importance of sediment sources and availability.
River regulation by dams modifies flow regimes, interrupts the transfer of sediment through channel networks, and alters downstream bed dynamics, altogether affecting channel form and processes. So ...far, most studies on the geomorphic impacts of dams are restricted to single rivers, or even single river stretches. In this paper we analyse the geomorphic status of 74 river sites distributed across four large basins in the Iberian Peninsula (i.e. 47 sites located downstream of dams). For this purpose, we combine field data with hydrological data available from water agencies, and analyse historical (1970) and current aerial photographs. In particular, we have developed a Geomorphic Status (GS) index that allows us to assess the physical structure of a given channel reach and its change through time. The GS encompasses a determination of changes in sedimentary units, sediment availability, bar stability and channel flow capacity. Sites are statistically grouped in four clusters based on contrasted physical and climate characteristics. Results emphasise that regulation changes river's flow regime with a generalized reduction of the magnitude and frequency of floods (thus flow competence). This, in addition to the decrease downstream sediment supply, results in the loss of active bars as they are encroached by vegetation, to the point that only reaches with little or no regulation maintain exposed sedimentary deposits. The GS of regulated river reaches is negatively correlated with magnitude of the impoundment (regulation). Heavily impacted reaches present channel stabilization and, in contrast to the hydrological response, the distance and number of tributaries do not reverse the geomorphic impact of the dams. Stabilization limits river dynamics and may contribute to the environmental degradation of the fluvial ecosystem. Overall, results describe the degree of geomorphological alteration experienced by representative Iberian rivers mostly because of regulation, challenging the successful long-term implementation of river basin management programmes.
This paper assesses annual and seasonal trends in runoff and sediment load resulting from climate variability and afforestation in an upland Mediterranean basin, the Ribera Salada (NE Iberian ...Peninsula). We implemented a hydrological and sediment transport distributed model (TETIS) with a daily time-step, using continuous discharge and sediment transport data collected at a monitoring station during the period 2009–2013. Once calibrated and validated, the model was used to simulate the hydrosedimentary response of the basin for the period 1971–2014 using historical climate and land use data. Simulated series were further used to (i) detect sediment transport and hydrologic trends at different temporal scales (annual, seasonal); (ii) assess changes in the contribution of extreme events (i.e. low and high flows) and (ii) assess the relative effect of forest expansion and climate variability on trends observed by applying a scenario of constant land use. The non-parametric Mann–Kendall test indicated upward trends for temperature and decreasing trends (although non-significant) for precipitation. Downward trends occurred for annual runoff, and less significantly for sediment yield. Reductions in runoff were less intense when afforestation was not considered in the model, while trends in sediment yield were reversed. Results also indicated that an increase in the river's torrential behaviour may have occurred throughout the studied period, with low and high flow events gaining importance with respect to the annual contribution, although its magnitude was reduced over time.
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•We applied a distributed hydrological model to reconstruct runoff and sediment yield.•Decreasing trends were detected for both variables at the annual and seasonal time scales.•Afforestation seemed to be the main factor driving the trends observed.•An increase in the torrential behaviour and reduction of peak flows was detected.
The paper presents the sediment budget of the Isábena basin, a highly dynamic 445-km
2 catchment located in the Central Pyrenees that is patched by highly erodible areas (i.e., badlands). The budget ...for the period 2007–2009 is constructed following a methodology that allows the interpolation of intermittent measurements of suspended sediment concentrations and enables a subsequent calculation of sediment loads. Data allow specification of the contribution of each subbasin to the water and sediment yield in the catchment outlet. Mean annual sediment load was 235,000
t
y
−
1
. Specific sediment yield reached 2000
t
km
−
2
y
−
1
, a value that indicates very high sedimentary activity, especially in the case of Villacarli and Lascuarre subcatchments, were most badlands are located. The specific sediment yield obtained for the entire Isábena is 527
t
km
−
2
y
−
1
, a high value for such a mesoscale basin. Results show that a small part of the area (i.e., 1%) controls most of the catchment's gross sediment contribution. Sediment delivery ratio (ratio between sediment input from primary sources and basin export) has been estimated at around 90%, while in-channel storage represents the 5% of the annual load on average. The high connectivity between sediment sources (i.e., badlands) and transfer paths (i.e., streamcourses) exacerbates the influence of the local sediment production on the catchment's sediment yield, a quite unusual fact for a basin of this scale.
► The paper presents the sediment budget of the River Isábena. ► Mean annual sediment load was 235,000
t
y
−
1
; the specific sediment yield, 572
t
km
−
2
y
−
1
. ► Sediment delivery ratio has been estimated at around 90%. ► In-channel storage represents the 5% of the annual load. ► High connectivity exacerbates the influence of sediment production on sediment yield.
Understanding and quantifying sediment load is important in catchments draining highly erodible materials that eventually contribute to siltation of downstream reservoirs. Within this context, the ...suspended sediment transport and its temporal dynamics have been studied in the River Isábena (445 km
2, south-central Pyrenees, Ebro basin) by means of direct sampling and turbidity recording during a 3-year dry period. The average flood-suspended sediment concentration was 8 g l
−
1
, with maximum instantaneous values above 350 g l
−
1
. The high scatter between discharge and suspended sediment concentrations (up to five orders of magnitude) has not permitted the use of rating curve methods to estimate the total load. Interpolation techniques yielded a mean annual sediment load of 184,253 t y
−
1
for the study period, with a specific yield of 414 t km
−
2
y
−
1
. This value resembles those reported for small torrents in nearby mountainous environments and is the result of the high connectivity between the badland source areas and stream courses, a fact that maximises sediment conveyance through the catchment. Floods dominated the sediment transport and yield. However, sediment transport was more constant through time than that observed in Mediterranean counterparts; this can be attributed to the role of base flows that entrain fine sediment temporarily stored in the channel and force the river to carry high sediment concentrations (i.e., generally in the order of 0.5 g l
−
1
), even under minimum flow conditions.
The number of studies assessing soil erosion and sediment transport has increased with the aim of achieving sustainable land and water management. Mediterranean rivers have been the object of many of ...these studies due to their naturally high values of sediment fluxes and a higher vulnerability under future climate scenarios. In this context, we attempt to use empirical relationships to (i) further assess the relation between sediment yield and basin scale and (ii) provide an update on the main drivers controlling sediment yield in these particular river systems. For this purpose, sediment yield data (from reservoir sedimentation surveys and sediment transport records) was collected from >100 locations distributed across the western Mediterranean area, with basin areas ranging from 1 to 100,000km2. Quantile Regression analysis was used to assess the correlation between basin area and sediment yield, while additional basin-scale descriptors were related to sediment yield by means of multiple regression analysis. Results showed the complexity in the relationship between basin scale and sediment yield, with changes in supply conditions with increasing area introducing uncertainties in the correlation. Despite the large scatter, analysis pointed towards the same direction and area appeared to be the main constrain for the maximum value of sediment yield that can be found at a specific basin scale. Results from the multiple regression indicated that variables representing basin's physiography, climate and land use were highly correlated with the basins' sediment yield. Also, a better model performance was obtained when using total sediment yield instead of specific values (per unit area). Validation showed model instability, potentially due to data limitations and the use of catchments with varying characteristics. Overall, despite providing some insights on the correlation between sediment yield and basin-scale characteristics, validation prevented direct extrapolation of the model to other catchments.
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•We used data on sediment yield and basin characteristics on the western Mediterranean.•Area proved to be a limiting factor in the upper range of sediment yield values.•Multiple regression using basin-scale variables analysis indicated model instability.•Uncertainties prevent the use of the model in other regions.
The Ebro River and its tributaries (North-Eastern Spain) are regulated by over 187 dams, with a total capacity equivalent to 57% of the total mean annual runoff. We analysed 38 gauging records from ...22 rivers that, by virtue of location within the drainage network and period of record, would reflect reservoir-induced hydrological changes. Most showed reduction in flood magnitude, with
Q
2 and
Q
10 reduced over 30% on average, more in rivers with higher values of the impounded runoff index, (calculated as reservoir capacity divided by mean annual runoff). Annual runoff did not show strong trends, but the variability of mean daily flows was reduced in most cases due to storing of winter floods and increased baseflows in summer for irrigation. Monthly flows ranged from virtually no change post-dam to complete inversion in seasonal pattern, the latter due to releases for irrigation in the summer, formerly the season of lowest flows.
This paper presents a comprehensive assessment of the suspended sediment load for the period (1998–2008) in the lower river Ebro (NE Iberian Peninsula), one of the most regulated large rivers in ...Europe. Sediment load estimates are based on continuous discharge and turbidity records, calibrated with direct suspended sediment samples covering a wide range of river's hydraulic conditions. The temporal variability of the sediment load and the role of the effective discharge at different temporal scales are specifically examined. At the log-term, the study period can be considered as dry. Mean annual load is estimated at around 0.092
×
10
6
t, a value that represents less than the 1% of what was transported at the beginning of the twentieth century in the absence of dams and under different land uses. In general, sediment concentrations observed between 1998 and 2008 are low (mean was 9
mg
l
−
1
and maximum was 240
mg
l
−
1
). Specific sediment yield was in the order of 1
t km
2 y
−
1
, also much lower than values reported in other western European rivers of the same scale and impact. At the annual scale, large floods were responsible for most of the transported suspended sediment (up to 80%). Nevertheless, when the effective discharge is calculated for the whole study period, floods of moderate magnitude and high frequency are responsible for the largest amount of sediment transport. The temporal scale used to calculate the effective discharge thus determines the final results. Load estimates derived from continuous suspended sediment and discharge data and from the flow duration method yielded similar values. This suggests that the latter method is also appropriate when sediment samples cover a large proportion of the observed discharges and statistical significant relations can be obtained and applied to long periods of record. This study provides further insights into the sedimentary status of one of the largest rivers in Europe. Results corroborate previous studies highlighting sediment deficit downstream from large dams. This type of information constitutes a key element to inform and improve current management and restoration actions.
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