Search Results (15)

The Ma’anshan section of the lower Yangtze River features a complex multi-anabranching system, where the river divides into several branches around mid-channel sandbars, with distinct point bars alternately developing along both banks. Within this morphologically active system, Zhengpu Harbor suffered severe operational disruptions by accelerated siltation at its approach channel, primarily due to its vulnerable location downstream of the expanding Niutun River point-bar on the left bank. To systematically diagnose the mechanisms of siltation, this study integrates multi-method investigations: decadal-scale morphodynamic analysis using long-term bathymetric surveys, numerical modeling to quantify engineering impacts on flow dynamics, and multiple linear regression analysis for the contributions of key influencing factors. The result identifies three primary drivers of siltation, collectively responsible for 70% of the sediment accumulation, including the rightward shift of the thalweg in the Ma’anshan left branch, reduced flow diversion of the left Branch of Central bar, and the expansion of the Niutun River point bar. River engineering structures, such as bridges, contribute approximately 12%, while changes in upstream flow-sediment supply account for approximately 18%. To mitigate siltation at Zhengpu Harbor’s approach channel, this study proposes targeted engineering interventions to enhance local hydrodynamic conditions. The spur dikes were designed to enhance the morphological stabilization of the Central bar head to regulate flow distribution. A diversion channel could also be excavated at the tail of the Niutun River shoal, and emergency dredging was recommended at the harbor front. Numerical modeling indicates that these measures will increase flow velocity by over 0.1 m/s at the harbor front, mitigating the siltation situation. The study concludes that the proposed engineering measures can reduce annual siltation by approximately 30% under normal-year hydrological conditions, demonstrating their feasibility in mitigating siltation trends in multi-anabranching river systems. This research provides a reference for addressing siltation issues in harbors within complex anabranching river systems. Full article

Soil erosion poses a significant global environmental challenge, causing land degradation, deforestation, river siltation, and reduced agricultural productivity. Although the Revised Universal Soil Loss Equation (RUSLE) has been widely applied in Brazil, its use in the tropical river basins of the Amazon remains limited. This study aimed to apply a GIS-integrated RUSLE model and compare its soil loss estimates with multiple linear regression (MLR) models based on terrain attributes, aiming to identify priority areas and key geomorphometric drivers of soil erosion in a tropical Amazonian river basin. A digital elevation model based on Shuttle Radar Topography Mission (SRTM) data, land use and land cover (LULC) maps, and rainfall and soil data were applied to the GIS-integrated RUSLE model; we then defined six risk classes—slight (0–2.5 t ha⁻¹ yr⁻¹), slight–moderate (2.5–5), moderate (5–10), moderate–high (10–15), high (15–25), and very high (>25)—and identified priority zones as those in the top two risk classes. The Caeté River Basin (CRB) was classified into six erosion risk categories: low (81.14%), low to moderate (2.97%), moderate (11.88%), moderate to high (0.93%), high (0.03%), and very high (3.05%). The CRB predominantly exhibited a low erosion risk, with higher erosion rates linked to intense rainfall, gentle slopes covered by Arenosols, and human activities. The average annual soil loss was estimated at 2.0 t ha⁻¹ yr⁻¹, with a total loss of 1005.44 t ha⁻¹ yr⁻¹. Additionally, geomorphological and multiple linear regression (MLR) analyses identified seven key variables influencing soil erosion: the convergence index, closed depressions, the topographic wetness index, the channel network distance, and the local curvature, upslope curvature, and local downslope curvature. These variables collectively explained 26% of the variability in soil loss (R² = 0.26), highlighting the significant role of terrain characteristics in erosion processes. These findings indicate that soil erosion control efforts should focus primarily on areas with Arenosols and regions experiencing increased anthropogenic activity, where the erosion risks are higher. The identification of priority erosion areas enables the development of targeted conservation strategies, particularly for Arenosols and regions under anthropogenic pressure, where the soil losses exceed the tolerance threshold of 10.48 t ha⁻¹ yr⁻¹. These findings directly support the formulation of local environmental policies aimed at mitigating soil degradation by stabilizing vulnerable soils, regulating high-impact land uses, and promoting sustainable practices in critical zones. The GIS-RUSLE framework is supported by consistent rainfall data, as verified by a double mass curve analysis (R² ranging from 0.64 to 0.77), and offers a replicable methodology for soil conservation planning in tropical basins with similar erosion drivers. This approach offers a science-based foundation to guide soil conservation planning in tropical basins. While effective in identifying erosion-prone areas, it should be complemented in future studies by dynamic models and temporal analyses to better capture the complex erosion processes and land use change impacts in the Amazon. Full article

This study examines the effectiveness of torrential erosion control structures (concrete check dams) to mitigate post-fire sediment transport within the Seich Sou Forest in Thessaloniki, Greece. Four years after the fire of 1997, which burned 68% of the forest, check dams were constructed (in 2001) to control erosion and sediment transport in the catchments of Eleonas and Panteleimon. In 2022, our team conducted field surveys, in which the size, effective storage capacity, and siltation of 40 check dams were recorded. The results revealed that the dams stored 14.36% and 18.81% of their total effective capacity in the Eleonas and Panteleimon catchments, respectively, with average annual erosion levels of 0.33 t/ha/year and 0.21 t/ha/year. These low rates of erosion could be attributed to the shallow, rocky soils and rapid post-fire vegetation recovery. However, this study highlights that timely construction of check dams immediately after the fire could have significantly increased their effectiveness. The results showed that if the dams were constructed immediately after the fire, they would retain 6.17 t/ha/year (Eleonas) and 7.08 t/ha/year (Panteleimon), during the first three post-fire years. These values of erosion are in agreement with previously published studies in Mediterranean ecosystems. This study highlighted the importance of the timely construction of post-fire erosion control structures to increase sediment storage and reduce soil transportation. Full article

The role of trees in watershed hydrology is governed by many environmental factors along with their inherent characteristics and not surprisingly has generated diverse debates in the literature. Herein, this conceptual meta-analysis provides an opportunity to propose a conceptual model for understanding the role of trees in watershed hydrology and examine the conditions under which they can be an element that increases or decreases water supply in a watershed. To achieve this goal, this conceptual meta-analysis addressed the interaction of forest cover with climatic conditions, soil types, infiltration, siltation and erosion, water availability, and the diversity of ecological features. The novelty of the proposed conceptual model highlights that tree species and densities, climate, precipitation, type of aquifer, and topography are important factors affecting the relationships between trees and water availability. This suggests that forests can be used as a nature-based solution for conserving and managing natural resources, including water, soil, and air. To sum up, forests can reduce people’s footprint, thanks to their role in improving water and air quality, conserving soil, and other ecosystem services. The outcomes of this study should be valuable for decision-makers in understanding the types of forests that can be used in an area, following an approach of environmental sustainability and conservation aiming at restoring hydrological services, mitigating the costs of environmental services, promoting sustainable land use, managing water resources, and preserving and restoring soil water availability (SWA) when investing in reforestation for watershed hydrology, which is important for the human population and other activities. Full article

This study comprehensively explores the intricate hydrodynamic and geomorphological processes that affect the Sulina Channel and bar area. It employs advanced hydrodynamic, wave, and sediment transport models to simulate the influence of marine currents, waves, and shipping traffic on sediment transport and deposition patterns, providing valuable insights for maintaining navigable conditions in the Sulina Channel. It is shown that sediment deposition is highly dynamic, particularly in the Sulina bar area, where rapid sediment recolonization occurs within one to two months after dredging. The simulation indicates that vessels with drafts of 11.5 m cause notable erosion. In comparison, drafts of 7 m have a minimal impact on sediment transport, emphasizing the importance of managing vessel drafts to mitigate sediment disturbances. This research highlights and quantifies the siltation phenomenon from the Black Sea to the mouth of the Sulina Channel, effectively addressing the challenges posed by natural and anthropogenic factors to ensure the Channel’s sustainability and operational efficiency. Full article

Reservoirs overflow during flood season because of sedimentation cycles, which severely affects their effectiveness. Siltation is a major problem in dams constructed in waterways in arid and semi-arid areas. Therefore, the reservoirs in wadis lose their capacity due to sedimentation. This study determines an optimal design of the trapping basin on steep slope areas for Wadi Bishah in the Asir region of southwestern Saudi Arabia. The empirical design criteria of the sediment-trapping basin is used to mitigate the effects of sedimentation in the King Fahd Dam. The empirical design of the trapping basin constructed upstream of the dam located in the wadi is presented. Moreover, the annual suspended and bed sediment load (Q_s and Q_b) techniques for estimating the volume of sediments are used, and the relationship between the sediment trapping efficiency and size is determined. The sediment trapping in Wadi Bishah upstream sediment-trapping basins is selected to reduce the amount of sediment. One of the important results of this study tries to create a new concept to trap sediment in wadis, which are located in arid and semi-arid areas. The results obtained were evaluated using theoretical and empirical equations to determine the appropriate size of the basin. The results demonstrate that the optimal dimensions for the sediment confinement basin are L_b × W_b × h_s = 3500 × 500 × 1.5 m. Also, for these dimensions, the basin efficiency was assumed to be in the range of 60–70%. The trap basin should be constructed at open check dams upstream (U/S) of the proposed basin to enhance its efficiency. Further investigation is required to understand the transport and deposition of sediments, particularly fine sediments in the basin. Additionally, the effects of sediment traps in Wadi Bishah should be assessed during the construction of these structures to aid water resource management and mitigate flood disasters. Full article

In this study, a quasi-stumps group structure was proposed and placed upstream of the bridge piers to mitigate the scour of the waterflow on the riverbed. Both experiment and numerical simulations using FLOW 3D were employed to study the protective effect of this structure. The numerical results were in good agreement with the experimental findings. It was found that the quasi-stumps group can effectively reduce the flow velocities around the bridge piers, thereby promoting the deposition of suspended sediment. As a result, there was no erosion around the piers, and instead, siltation was formed, which contributed to the stability of the piers. The deposition height around the piers increased as the L (the horizontal distance between the quasi-stumps group and the piers) decreased and both the P (the height of the quasi-stumps group) and S (the ratio of the area of a single leaf on the quasi-stumps group to the cross-sectional area of a single pier) increased. As the L, P, and S increased, the quantity of suspended sediment deposition over the entire riverbed increased. The optimal combination of the quasi-stumps group’s protective effect was determined to be L = D (pier diameter), P = H (water depth), and S = 0.148. Full article

Urban drainage infrastructures are facing critical challenges due to a lack of integrated asset management, periodic maintenance, improper design, and construction methodologies. The objective of this study is to understand the urban drainage challenges and assess the failure causes and their impacts to recommend possible mitigation measures. Drainage failure causes and impacts are analyzed using the analytical hierarchy process (AHP) qualitative multicriteria decision model after conducting technical group discussions, interviews, and technical field surveys. The assessment was performed by taking representative samples from both cross- and longitudinal drainage infrastructures. The AHP analysis results showed that approximately 35.5% and 28.6% of failure causes are debris and various solid wastes for cross- and longitudinal drainage structures with correlation coefficients of 0.93 and 0.95, respectively. The result showed that design and construction defects are the second major failure causes. The research results showed that urbanization has a direct relationship with major drainage failure causes, resulting from man-made debris and solid waste clogging. On the other hand, drainage failure caused by siltation, drifts, and vegetation is higher in newly developing semi-urban and agricultural areas. The number of barrels in cross-drainage structures also contribute significantly to cross-drainage failure by creating a flow barrier due to the intermediate columns. The drainage failure impact assessment result showed that both cross- and longitudinal drainage failures primarily impact road pavement following transport disruption and traffic accidents, accounting for 38.5%, 18%, and 16%, respectively. Our research recommended that the mitigation measures for drainage failure are proper asset management and maintenance, appropriate construction supervision, and awareness creation, with weights of 36.3%, 15.5%, and 15.3%, respectively. As a drainage problem mitigation measure, the longitudinal drainage analysis results showed that the provision of a combination of cross-fall slopes, gutter slopes, and local depressions at the inlets can contribute to an increase in the trapping efficiency of the drainage system by 50%, which can reduce surface flooding substantially. Full article

Pengpeng Beach, near Niaoyu Fishing Harbor, is an offshore sandbar that formed on the west side of Niaoyu Island in Penghu County, Taiwan, in 1995. Due to siltation, Pengpeng Beach also forms a sandbar tail that stretches toward the Niaoyu Fishing Harbor, meaning the Niaoyu Fishing Harbor and its navigation channel are facing serious siltation problems. This study aimed to find a solution for the siltation problem of the area by utilizing geotextile tubes, which are an economical material in terms of their material and construction cost, as well as being ecologically friendly in terms of their carbon emissions during production and transportation. Based on numerical simulations, location candidates for placing silt trap facilities were tested, selected, and modified to develop alternative mitigation plans. Evaluation of the mitigation plans was based on (1) the silt mitigation effect; (2) engineering cost; (3) public acceptance; and (4) impact on the surrounding landscape. The results showed that the proposed silt mitigation plan would be effective, and the plan was accepted by the local residents and government. Full article

Reliable quantitative information regarding sediment sources is essential for target mitigation, particularly in settings with a large number of loose provenances caused by earth disasters. The lakes in the Jiuzhaigou World Natural Heritage Site (WNHS) are facing serious environmental problems of silting and swamping, which threaten the sustainability of the area, especially after the earthquake on 8 August 2017 (the “8.8 earthquake”). Therefore, a field investigation was conducted after the “8.8 earthquake” (June 2020), and the Arrow Bamboo and Rhino Lakes, which were affected by the earthquakes to different degrees, were selected as the research objects. Based on the data of 27 environmental indicators from 31 surface sediment and soil samples in and around the lakes, the spatial distribution characteristics of the lake sediment sources were quantified using composite fingerprint recognition technology. Furthermore, a high protection standard of a WHNS and a process treatment scheme for reducing the siltation of the Jiuzhaigou lakes were proposed. The results showed that the contribution ratio of loose matter sources entering the lake on the road-side of the Arrow Bamboo and Rhino Lakes (16.5% and 21.8%, respectively) was lower than that on the forest-side (83.5% and 78.2%, respectively), indicating that physical barriers such as roads can effectively reduce the sediment input, while the lake forest side contributes a large number of loose matter sources, which has not attracted attention in the past and requires protection. High protection standards for the Jiuzhaigou WHNS are suggested. Accordingly, the entire control scheme of Jiuzhaigou lake sediment reduction including “monitoring–control–interception–buffer–cleaning” is provided. Source erosion monitoring is the first step in blocking the sediment source. Vegetation restoration and surface coverage should be conducted in areas where water and soil losses have occurred. Necessary engineering measures should be implemented to intercept loose material sources at points where geological disasters occur frequently. A buffer zone should be established between the lake and the mountain to intercept the sediment. Sediment caused by geological disasters with low interference must also be cleaned from the lake. The level of nutrients in the lake must be controlled by the regular cleaning of plant debris from the lake and lakeside. Full article

Existing evidence about climate change in Zimbabwe has tended to focus more on elements and events of the climate system, marginalizing changes in the hydrological and ecological system. To contribute to the improved understanding of climate change, this study captured the observations of climate change in Malipati, a remote agrarian dryland area in the Chiredzi District, Zimbabwe. The aim of the study was to gather detailed insights about perceived environmental changes using the evidence drawn from local and indigenous populations who have close interactions with their natural environment. A household questionnaire-based survey with randomly chosen farmers (n = 116) revealed that participants’ observations of changes in hydrological and ecological system were consistent with available evidence of increasing temperatures and little rainfall recorded in the district. Results also showed high sensitivity of the area to climate change that manifest in various indicators: hydrological changes in rivers, streams, swamps, and ground water; and ecological changes through the behaviour of trees, insects, birds, and wild animals. Sex and age of the participants did not influence the way they perceived most of these changes (p > 0.05). However, education and the period of stay in the area were related to the respondents’ perceived changes in river flows and siltation, and the conditions of swamps (p < 0.05). Our study also revealed deeper insights about the human-biodiversity interactions in the face of climate change in unique areas where communities live alongside wildlife. The evidence drawn from local and indigenous populations can be used to inform local-based solutions to the growing problems of climate change and biodiversity loss. Future studies would need to further examine such areas to understand the mitigation and adaptation practices that would promote the sustainable co-existence of humans and wildlife. Full article

Siltation is the biggest environmental challenge associated with nickel laterite mining in the Philippines. The amount of silt generated is huge and one mitigation strategy currently employed by the mining companies is the construction of siltation ponds where the bulk of the clayey- and silt-sized surface runoffs is collected. However, this poses several serious environmental hazards such as landslides due to heavy rainfall and the potential release of hazardous heavy metals. A promising approach to reduce the risks associated with long-term storage of nickel mine waste (NMW) is to employ circular economy by repurposing it for ceramic applications. While generating useful materials with economic value out of a mine waste, it will result in a reduction in volume of waste for disposal. In this study, the method employed to produce NMW-based ceramic wall and floor tiles is slip casting as it is the most appropriate method in forming tiles with complex surface features. Five formulations of NMW-based slips were made for the casting of ceramic tiles and each slip was characterized for its suitability as raw material. The results of NMW characterization show that NMW could be utilized as raw materials for both ceramic wall and floor tiles and the addition of feldspar can enhance casting and physical properties. Full article

Soil loss is one of the most important causes of land degradation. It is an inevitable environmental and socio-economic problem that exists in many physiographic regions of the world, which, besides other impacts, has a direct bearing on agricultural productivity. A reliable estimate of soil loss is critical for designing and implementing any mitigation measures. We applied the widely used Revised Universal Soil Loss Equation (RUSLE) in the Khabur River Basin (KhRB) within the NW part of the Zagros Fold and Thrust Belt (ZFTB). The areas such as the NW Zagros range, characterized by rugged topography, steep slope, high rainfall, and sparse vegetation, are most susceptible to soil erosion. We used the Digital Elevation Model (DEM) of the Shuttle Radar Topography Mission (SRTM), Tropical Rainfall Measuring Mission (TRMM), Harmonized World Soil Database (HWSD), and Landsat imagery to estimate annual soil loss using the RUSLE model. In addition, we estimated sediment yield (SY) at sub-basin scale, in the KhRB where a number of dams are planned, and where basic studies on soil erosion are lacking. Estimation of SY will be useful in mitigation of excessive sedimentation affecting dam performance and watershed management in this region. We determined the average annual soil loss and the SY in the KhRB to be 11.16 t.ha⁻¹.y⁻¹ and 57.79 t.ha⁻¹.y⁻¹, respectively. The rainfall and runoff erosivity (R factor), slope length (L factor), and slope steepness (S factor), are the three main factors controlling soil loss in the region. This is the first study to determine soil loss at the sub-basin scale along with identifying suitable locations for check dams to trap the sediment before it enters downstream reservoirs. The study provides valuable input data for design of the dams to prevent excessive siltation. This study also aims at offering a new approach in relating potential soil erosion to the actual erosion and hypsometric integrals. Full article

The recent and continuous development of unmanned aerial vehicles (UAV) and small cameras with different spectral resolutions and imaging systems promotes new remote sensing platforms that can supply ultra-high spatial and temporal resolution, filling the gap between ground-based surveys and orbital sensors. This work aimed to monitor siltation in two large rural and urban reservoirs by recording water color variations within a savanna biome in the central region of Brazil using a low cost and very light unmanned platform. Airborne surveys were conducted using a Parrot Sequoia camera (~0.15 kg) onboard a DJI Phantom 4 UAV (~1.4 kg) during dry and rainy seasons over inlet areas of both reservoirs. Field measurements of total suspended solids (TSS) and water clarity were made jointly with the airborne survey campaigns. Field hyperspectral radiometry data were also collected during two field surveys. Bio-optical models for TSS were tested for all spectral bands of the Sequoia camera. The near-infrared single band was found to perform the best (R²: 0.94; RMSE: 7.8 mg L⁻¹) for a 0–180 mg L⁻¹ TSS range and was used to produce time series of TSS concentration maps of the study areas. This flexible platform enabled monitoring of the increase of TSS concentration at a ~13 cm spatial resolution in urban and rural drainages in the rainy season. Aerial surveys allowed us to map TSS load fluctuations in a 1 week period during which no satellite images were available due to continuous cloud coverage in the rainy season. This work demonstrates that a low-cost configuration allows dense TSS monitoring at the inlet areas of reservoirs and thus enables mapping of the sources of sediment inputs, supporting the definition of mitigation plans to limit the siltation process. Full article

Flooding and overflow are recurring problems in several Brazilian cities, which usually face disorderly development. The causes vary, and include increased impervious surface areas, deficiency/inefficiency of drainage structures and lack of maintenance, siltation of rivers, channel obstructions, and climatic factors. In this paper, we present an analysis of mitigation measures to minimize flooding in a watershed located in the core of the city of São Paulo, the biggest city with the highest gross domestic product (GDP) in Brazil. Observed rainfall records and existing intensity duration frequency (IDF) curves for the region are used to obtain design storms. To account for climate change, the equidistance quantile matching method for updating IDF curves under climate change, a well-known procedure, was applied to the existing historical data. Several different global climate models (GCMs) and one regional model were applied to obtain and update rainfall design storms. The GCMs and future scenarios used were from Intergovernmental Panel on Climate Change—IPCC Assessment Report 5 (AR5) and two future projections—representative concentration pathway (RCP) 4.5 and 8.5. Spatially distributed reservoirs combined with low-impact development (LID) measures were used to evaluate different design storm scenarios combined with return periods of 25 and 100 years as well as the updated IDF under climate change for RCP 4.5 and RCP 8.5. Results show that the proposed changes to the drainage system can help reduce the risk and damage of flooding. The climate change scenarios, however, impose a significant threat and need immediate attention from city planners and stakeholders. Full article