Search Results (4)

The scouring of cohesive and non-cohesive materials downstream of sluice gates is primarily based on high-velocity flow. The present study considered an experimental hydraulic model of submerged water flow issuing from a sluice gate installed on an apron that leads to the scour hole and dune in a downstream mixture of sand and clay bed. The purpose was to achieve a suitable efficiency of the weight ratio of clay in the sand–clay mixture (c) for the sediment bed. Scour parameters, including maximum scour depth (d_se) and its longitudinal location (x_se), and maximum dune height (h_d) and its location (x_d), were measured and compared for three variations, c = 0.1, 0.2, and 0.3, under five hydraulic conditions. Results revealed that all scour parameters were reduced by adding clay to the sand soil, and the maximum reduction was for d_se with the maximum value of 27.66%. The observed data were analyzed by multiple nonlinear regression analyses for each scour parameter to present new prediction equations for practical uses. The computed statistical parameters of correlation coefficient (R²), root mean square error (RMSE), mean absolute percentage error (MAPE), Nash–Sutcliffe efficiency (NSE), and scatter index (SI) present good accuracy for the predicted equations in the ranges of experimental data. Full article

River bridge engineering alters the hydraulic characteristics of rivers, impacting fluvial morphological stability. To investigate issues concerning flood conveyance capacity within the river reach hosting a new bridge and the safe operation of existing bridges, comparative physical model tests employing both mobile-bed and fixed-bed configurations were conducted. A 1:60 scale model was used to test flood peak discharges corresponding to 30-year and 100-year return periods and investigate pier spacings of 30 m and 40 m. These tests evaluated the relative advantages and limitations of each model type in simulating flow patterns, sediment transport, and riverbed evolution. Specifically, mobile-bed models more effectively capture the interaction between water flow and sediment dynamics, while fixed-bed experiments enable more precise measurement of hydraulic parameters. Pier spacing is recognized as one of the most critical factors influencing river flow regimes. Larger pier spacing (40 m) was found to reduce upstream backwater and local scour depth compared to smaller spacing (30 m), particularly under the 30-year flood scenario. Consequently, this study investigated the effects of pier spacing on flow patterns, obtained flood conveyance characteristics under various flood frequencies, and analyzed the underlying mechanisms governing flow fields, velocity variations, and local scour around piers. The research outcomes not only elucidate multiscale coupling mechanisms between water flow and sediment but also quantify the relationship between the extent of pier-induced flow disturbance and subsequent channel morphological adjustments. This quantification provides a dynamic criterion for risk mitigation of river-crossing structures and establishes a hydrodynamic foundation for studying flood hazards in complex river reaches. Full article

This work presents the chronology of the Holocene filling of the Guadalentín Tectonic Depression (Murcia, SE Spain) combining ¹⁴C and OSL age data. This work studies the sediments and paleosols interbedded in the sedimentary sequence between Totana and Librilla, using as reference the Espuña Karting section (Alhama de Murcia), which has been fully sampled for its geochronological analysis. The entire dated sequences record the last c. 20–19 ka BP, although local basal travertine beds extend back to the Late Pleistocene (30–33 ka). Soil morphology and properties from dated paleosols record different environmental crises in SE Spain, but also a progressive aridification throughout the Holocene. The Chalcolithic Paleosol develops soon after c. 4.6–4.0 BP, nearly coinciding with the start of the Meghalayan stage, evidencing a drastic change from relatively humid to arid conditions, coincident with the crisis of the Copper Age civilizations in Spain. The Bronze Age paleosol also developed under arid but relatively more humid conditions, indicating a more important and longer gap in the sedimentary sequence soon after c. 2.5–2.7 ka BP. This stop in the sedimentation are correlative to the first stages of fluvial incision at basin center locations and the desiccation and fragmentation of the ancient wetlands coinciding with the collapse of the Bronze Age civilizations in SE Spain (Argaric Culture). During the Ibero-Roman Humid Period (IRHP), c. 2.6–1.6 ka BP, the last pedogenic cycle occurred under relatively humid conditions. This preluded the progressive establishment of exorheic fluvial environments as well as a period of paleoseismic activity in the area around 2.0–1.8 ka BP. Full article

Anthropogenic activities, and in particular land use/land cover (LULC) changes, have a considerable effect on rivers’ flow rates and their morphologies. A representative example of those changes and resulting impacts on the fluvial environment is the Reno Mountain Basin (RMB), located in Northern Italy. Characterized by forest exploitation and agricultural production until World War II, today the RMB consists predominantly of meadows, forests and uncultivated land, as a result of agricultural land abandonment. This study focuses on the changes of the Reno river’s morphology since the 1950s, with an objective of analyzing the factors that caused and influenced those changes. The factors considered were LULC changes, the Reno river flow rate and suspended sediment yield, and local climate data (precipitation and temperature). It was concluded that LUCL changes caused some important modifications in the riparian corridor, riverbed size, and river flow rate. A 40–80% reduction in the river bed area was observed, vegetation developed in the riparian buffer strips, and the river channel changed from braided to a single channel. The main causes identified are reductions in the river flow rate and suspended sediment yield (−36% and −38%, respectively), while climate change did not have a significant effect. Full article