Specific sediment yield model for reservoirs with medium-sized basins in Spain: An empirical and statistical approach

Assessment of current reservoir sedimentation rate and storage capacity loss: An Italian overview

Sedimentation has a prominent impact on the functionality and lifetime of reservoirs and is a growing concern for stakeholders. Various parameters influence sedimentation caused by soil erosion. Here we have examined fifty Italian reservoirs to determine sedimentation rates and storage capacity loss. The reservoirs studied have an average age of 78 years as of 2021, with the highest loss of capacity observed, equal to 100%, for Ceppo Morelli. For the fifty Italian catchments covering north, south, central and islands of Italy, we found the mean annual sediment yield varying between 17-4000 m³/km². year. Six of fifty reservoirs studied (Quarto, Colombara, Ceppo Morelli, Fusino, Vodo and Valle di Cadore) are already in a very critical situation in terms of storage capacity loss. Out of the fifty reservoirs, half of them will reach their half-life year by 2050. For example, for the Fusino reservoir located in northern Italy, we observed a loss of 90% of the storage volume as of 2020 with respect to its operation year 1974, compared to 6% in 2015 as available in literature. Modelling the sediment delivery ratio (SDR) is an open question, due to the lack of adequate data and uncertainties about the variability in hydrological, geomorphological, climate and landcover parameters. Here, we addressed the issue with a simplified multiple regression approach based on sediment delivery ratio values retrieved by the RUSLE model. We found different multi regressions for reservoirs belonging to the Alpine and Apennine regions. This analysis offers a starting point for the management and prioritization of adaptation and remediation policies necessary to address reservoir sedimentation.

Expanding the Sediment Transport Tracking Possibilities in a River Basin through the Development of a Digital Platform—DNS/SWAT

Simulation of stochastic and variable sediment transport processes within models still poses a big challenge, especially in mountainous areas. Since sediment transport, including erosion and deposition, remains an unceasing problem in many areas, sediment modeling is perceived as a possible solution. This article combines a review of the selected sediment models with a presentation of the effects of several years of research using the DNS digital platform in the Western Carpathians. The review focuses on the main advantages and gaps in selected modeling tools with particular emphasis on one of the most popular: SWAT. The description of the digital platform—DNS is an example of how to answer these gaps by combining subsequent models, methods, and databases using their best features. To accentuate the benefits of such an approach, the effects of combining subsequent models (AdH/PTM) and methods (fingerprinting) on a common digital DNS space are presented, on the example of the Raba River (basin). In this way, both unique possibilities of estimating the amount of contamination carried with sediment particles and their sources, as well as sequencing of sedimentation in the reservoir, taking into account its subsequent zones, were obtained.

Nutrient deposition over the past 60 years in a reservoir within a medium-sized agricultural catchment

Widespread dam construction has reduced the hydrological connectivity of catchments of various sizes. Nutrients lost from upper catchments can be intercepted by dams and deposited in reservoir sediments, and this reduces downstream nutrient transportation. Few previous studies have assessed historical nutrient deposition rates (NDRs) in man-made reservoirs. Using ¹³⁷Cs and ²¹⁰Pb_ex deposition chronologies, this paper examines the total nitrogen (TN), total phosphate (TP), and organic matter (OM) concentrations in six sediment cores recovered from Xujiaya reservoir (catchment area 580 km²), provides estimates of historical NDRs by referencing the original capacity curve, and explores temporal changes to the NDR since dam construction. The results show that anthropogenic sources resulted in the increase in nutrient concentrations in the upper parts of the cores, whereas natural sources were the main contributors to nutrient deposition across the whole reservoir. In addition, sediment supply from the catchment was the main source of the nutrients deposited in the reservoir, and the changing patterns of NDRs were overall regulated by sediment yields. The TN, TP, and OM profiles in the six cores, together with the historical NDRs, reflect the pattern of nutrient deposition in the reservoir derived from this agricultural catchment over the past 60 years. The results provide new insight into the effect of dam construction on nutrient deposition at a medium-sized catchment scale against a background of recent environmental change influenced by human activity.

Forest fire effects on sediment connectivity in headwater sub-catchments: Evaluation of indices performance

Forest fires and post-fire practices influence the hydrological response of the soil in terms of runoff and sediment connectivity (SC). In this study, the ability of four indices (IC-Borselli, IC-Cavalli, IC-Persichillo and aggregated index of connectivity (AIC)) to assess SC was evaluated in three Mediterranean headwater sub-catchments (66, 143 and 194 ha) affected by an arson fire in 2012. Three temporal scenarios (before the fire, one year after the fire and two years after the fire including post-fire practices (salvage logging, skid trails and check dams)) and two computation targets (streams: hillslope-channel SC; and check-dams: hillslope-outlet SC) were considered, obtaining 66 maps of SC at fine spatial resolution (2 m of cell size). Burn severity classes were estimated using Landsat-7 imagery and the dNBR index. The indices' output analysis included geomorphic (landscape units), mathematic (significance, percentiles and frequency distribution), fire (burn severity classes and unburnt areas) and sedimentological (measured specific sediment yield - SSY) criteria. The IC-Borselli and AIC were the most responsive approaches to the effects of fire on SC at catchment scale, whereas the IC-Persichillo was the most sensitive index to the increasing burn severities. The overlay between the fire severities and the geomorphic features appeared as a key aspect to understand the hydrological response at both the stream-system and outlet targets. We found a good and positive agreement between the measured SSY in the three check-dams and the changes in the estimated SC_OUTLET due to the fire, especially with the IC-Borselli and AIC. For a better implementation of post-fire programs, we recommend SC_OUTLET maps -from AIC- to assess sediment transport in streams, which is dominated by the deposition process, and SC_STREAM maps -from IC-Borselli and AIC- to place sediment control measures at hillslopes for intense rainfall events when effective sediment transport happens.