Showing papers on "Siltation published in 2021"

Assessment of soil erosion rate and hotspot areas using RUSLE and multi-criteria evaluation technique at Jedeb watershed, Upper Blue Nile, Amhara Region, Ethiopia

Abstract: Soil erosion is a difficult forceful practice by which useful surface soil is removed, conveyed, and stored at a detached place causing the exposure of subsurface soil and siltation in reservoirs and natural streams. It also degraded different agricultural areas at different rates and different locations as well as created gulleys, but these degraded areas, degradation rates, and gulley locations were not well identified and quantified. Therefore; the core objective of this study is to evaluate soil erosion rate and to identify soil erosion hotspot areas as well as to identify gulley locations using Revised Universal Soil Loss Equation (RUSLE), Multi-criteria Evaluation Analysis Techniques, and Geographic Information System (GIS). Land Use/Land Cover (LU/LC) map, slope map, rainfall map, and Digital Elevation Model (DEM) were the necessary inputs used for this study. The results of this study indicated that the potential annual soil loss of the watershed ranged from 0.0 to 706.7 tons per hectare per year with an average annual soil loss rate of 27.7 tons per hectare per year. From the total area of the watershed (859.2 km2), the potential area for gully expansion is 63km2. The overall analysis indicated that 4.8% of the total watershed is highly sensitive; 54.24% is moderately sensitive; 17.69% is marginally sensitive while, 23.28% is currently not sensitive and the remaining 0.06% is a /constraint to erosion. Hence, the Areas which were categorized under highly and moderately sensitive classes needed direct mediation for better conservation planning. It is concluded that Gulley, LU/LC, Topographical wetness index, and soil types are factors that enable soil erosion from high to low, respectively. It is recommended that the concerned bodies should have to take care of the area from further soil erosion through creating awareness among the society about the sustainable use of natural resources and conservation methods.

Morphological evolution of estuarine channels influenced by multiple anthropogenic stresses: A case study of the North Channel, Yangtze estuary, China

Abstract: The Construction of mega-dams has attracted worldwide attention due to their impacts on channel scouring from downstream regions to estuaries. However, the impacts of dams and near-end engineering on the evolution of large alluvial estuarine channels are unknown. In this study, the morphological evolutionary process and response regime of the North Channel (NC) in the Yangtze estuary was examined between 1986 and 2016 by using hydrology, multibeam echo sounding and historical bathymetry datasets. The results showed that the NC exhibited overall erosion with a total volume of 9.09 × 108 m3 over the past 30 years. We concluded that sediment load reduction in the river basin was the main reason for channel scouring. However, the short-term influence of near-end engineering on the local channel evolution process could not be ignored. For example, the construction of the north-south channel bifurcation project resulted in slight siltation of the NC with a total volume of 0.12 × 108 m3 from 2002 to 2007 despite the sediment load decreasing from 3.4 × 108 t to 1.8 × 108 t since the closure of the Three Gorges Dam (TGD). Furthermore, after construction (2007–2016) of the Qingcaosha Reservoir, the largest reservoir in the Yangtze estuary, the NC experienced extensive scouring near the reservoir and limited morphologic changes to the margin channel far from the reservoir. The maximum scouring depth near the reservoir reached ~13.5 m. In terms of the scour rate, the value of the average annual scour depth was 23–24 times the riverbed erosion rate caused by sediment load reduction. Therefore, a re-evaluation of the unexpected impacts of near-end engineering on the local Yangtze estuarine channels is urgently needed.

Reduce the intensity of siltation of bulk reservoirs for irrigation and hydropower purposes

Abstract: The results of field studies to study the siltation of a reservoir and the dynamics of their siltation are presented. The article presents designs that allow reducing the amount of sediment entering the reservoir bowl. The structure will contain spillways located perpendicular to the bed of the supply channel, elements of connecting structures, a sediment storage facility, and a lateral water outlet to the sediment storage facility. The reservoir sediment has a mark below the bottom of the supply channel and above the maximum water level in the reservoir and a wall of large pebbles that act as a filter for residual turbid water in the channel. In the basin of the deposit storage, a road is provided for trucks and equipment to carry out its seasonal cleaning.

New Insight on Soil Loss Estimation in the Northwestern Region of the Zagros Fold and Thrust Belt

Abstract: 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.

The intensity of siltation of a small reservoir in Poland and its relationship to environmental changes

Abstract: Siltation of reservoirs is an indicator of the intensity of erosion processes and sediment yields of river catchments. An estimation of sediment yield is significant for hydroengineering practices, environmental prediction and modelling. It also reflects environmental changes in the form of climate and land use. The present study aimed to compare the amount of sediment deposited in a small reservoir in Poland, with the estimate of sediment yield from its catchment, using the Universal Soil Loss Equation coupled with a sediment delivery ratio (USLE-SDR) and an estimate of annual bed load transport, provided by a regional bed load formula. The estimate of the annual amount of bed load was based on the flow frequency graph and bed load rating curve of Skibinski. The dam of the reservoir was constructed in 1976. The first reservoir survey was carried out between 1979 and 1980, when the reservoir volume was estimated to be 252,000 m3. Subsequent surveys were carried out in 1991, 2003, 2009 and in the Spring of 2020. These surveys enabled the amount of sediment, deposited in the reservoir, to be measured across four different periods: 1980–1991, 1992–2003, 2004–2009 and 2010–2019. For the same periods, the USLE with a constant SDR (calculated using the approach provided by Vanoni) were used to estimate the quantity (mass) of suspended sediment yield from the contributing area of the catchment. The volume of suspended sediment, deposited in the reservoir, was obtained, taking into account the reservoir trap efficiency and assuming a density of suspended sediment deposits. Hydrological investigations of the Plachty gauging station on the Zagozdzonka River, the left tributary of the Vistula River, have been carried out by the Department of River Engineering at Warsaw University of Life Sciences since 1962. The catchment area at the Plachty gauging station, located just upstream of the reservoir, is 82.4 km2, whereas the catchment area above the dam of the Staw Gorny reservoir, is 91.4 km2. The estimated annual sediment yields for the catchment, based on reservoir surveys across four periods between 1980 and 2020, suggest a general decrease over time. This study was also undertaken to examine long-term variability in sediment yield, both in suspended sediment and bed load, related to rainfall-runoff erosivity, river discharge and land use changes, which could influence changes in catchment sediment yield. An analysis of local temperature and catchment runoff revealed a long-term increase in the mean annual temperature and a corresponding decrease in annual discharge. The annual values of total sediment input to the reservoir (suspended and bed load), estimated using the USLE-SDR and a bed load formula with sediment trap efficiency, are very close to the measured amounts of deposits in the reservoir. Annual deposits in the reservoir are decreasing with time. This is presumably caused by the decrease in arable land in the catchment. From the mean annual deposits in the reservoir, around 35% is bed load and 65% is suspended load. The average annual specific suspended sediment yield in the catchment, is ca. 9 Mg/km2.

Influence of check dams on flood hydrology across varying stages of their lifespan in a highly erodible Catchment, Loess Plateau of China

Abstract: Check dams are applied worldwide as an effective approach for soil conservation. Its effect on hydrology, however, has not been fully understood. As a critical step towards revealing the lumped effect of check dams at the regional scale, this study explored the modified flood hydrology induced by check dams in a representative highly erodible catchment in the Loess Plateau, China. A coupled hydrological and hydraulic modeling approach was applied to simulate the flooding process in different stages of deposition and topographic changes in a check dam reservoir. The results suggest a paradigm shift of the dam effect on flood attributes, which transits from a total interception in the early stage of the dam to peak reduction and flood detention, rather than a complete loss of flood control functions, when it approaches the maximum capacity of sedimentation. Under the same level of deposition, the reduction of a minor flood by a check dam was higher than that of a major flood. The topographic changes contributed to the reduction of flood peak appreciably by reducing the flow velocity and retarding the flood propagation. Noticeably, this reduction was augmented with the advancement of siltation and topographic changes, indicating the persistence of the hydrologic effects of check dams in the long run. As a result of these hydrological changes, the reduction in the flood flow velocity induced by check dams suggests substantial reductions in sediment transport and channel erosion during floods. In addition, a dam system containing multiple, cascading check dams exhibits much more significant effect in modifying both hydrologic and hydraulic properties of flood than individual dams. The current research provides a mechanistic understanding of the effects of check dams on catchment hydrology under heavy rainstorm conditions in small catchments.

To What Extent Can a Sediment Yield Model Be Trusted? A Case Study from the Passaúna Catchment, Brazil

Abstract: Soil degradation and reservoir siltation are two of the major actual environmental, scientific, and engineering challenges. With the actual trend of world population increase, further pressure is expected on both water and soil systems around the world. Soil degradation and reservoir siltation are, however, strongly interlinked with the erosion processes that take place in the hydrological catchments, as both are consequences of these processes. Due to the spatial scale and duration of erosion events, the installation and operation of monitoring systems are rather cost- and time-consuming. Modeling is a feasible alternative for assessing the soil loss adequately. In this study, the possibility of adopting reservoir sediment stock as a validation measure for a monthly time-step sediment input model was investigated. For the assessment of sediment stock in the reservoir, the commercial free-fall penetrometer GraviProbe (GP) was used, while the calculation of sediment yield was calculated by combining a revised universal soil loss equation (RUSLE)-based model with a sediment delivery ratio model based on the connectivity approach. For the RUSLE factors, a combination of remote sensing, literature review, and conventional sampling was used. For calculation of the C Factor, satellite imagery from the Sentinel-2 platform was used. The C Factor was derived from an empirical approach by combining the normalized difference vegetation index (NDVI), the degree of soil sealing, and land-use/land-cover data. The key research objective of this study was to examine to what extent a reservoir can be used to validate a long-term erosion model, and to find out the limiting factors in this regard. Another focus was to assess the potential improvements in erosion modeling from the use of Sentinel-2 data. The use of such data showed good potential to improve the overall spatial and temporal performance of the model and also dictated further opportunities for using such types of model as reliable decision support systems for sustainable catchment management and reservoir protection measures.

Anthropogenic and climate induced trace element contamination in a water reservoir in northwestern Mexico

Abstract: Water reservoirs are essential for regional economic development, as populations depend on them for agriculture irrigation, flood control, hydroelectric power generation, water supply for human consumption, and subsistence fishing activities. However, the reservoir environmental quality can be disturbed by enhanced sediment input and trace metal contamination, affecting human health as a consequence of contaminated water and fish consumption. With the purpose to understand the trends and extent of sediment accumulation and trace element contamination in the Oviachic reservoir (OV, northwestern Mexico) since its construction, the temporal variations of sediment accumulation, and As, Cr, Cu, Hg, Ni, Pb, and Zn concentrations, enrichment, and fluxes, were evaluated through the study of two 210Pb-dated sediment cores. We assumed that siltation and trace element contamination were driven by the development of anthropogenic activities in the region within the past ~ 70 years. Elemental concentrations accounted from null to minor enrichment for most elements, but moderate to significant enrichment by Hg. Mercury, As, and Cu fluxes have notably increased since the past decade, most likely because of a combination of anthropogenic and natural processes, including catchment erosion, artisanal gold mining, and recent drought conditions in the region. Arsenic and Hg concentrations may pose deleterious risks to biota in the reservoir, and consequently to humans through fish consumption, for which further biological and toxicological tests are advisable. This study highlights the importance of using sediment dating to assess historical trends of metal contamination and identify possible sources, to support decision-making in programs addressed to reduce environmental and health risks in aquatic ecosystems.

Impact of sedimentation by check dam on the hydrodynamics in the channel on the Loess Plateau of China

Abstract: The sedimentation by check dam in the channel affects hydrological process In this study, the effects of the sedimentation on the dynamic process of runoff and erosion power were investigated by dynamic coupling models (MIKE SHE model and MIKE 11 model) The study area was located in Wangmaogou watershed in the Loess Plateau of China Four scenarios including no check dam and check dam with siltation depths of 0, 4 and 8 m were designed to study the reduction effectiveness of check dam on the hydrodynamic processes The research showed that the silt dam not only reduced the total volume flow rate of floods but also increased the flood duration and delayed the occurrence of flood peaks The siltation depths of the dam influenced the flow velocity and runoff shear stress With deposition, the channel was longer in 8 m siltation compared with 0 and 4 m siltation The shear force and unit runoff power were remarkably reduced in the scenario of 8 m siltation, followed by 4 m, and lastly by 0 m The dam system can still vastly reduce the flow velocity along the channel in the full state and decrease the maximum flow velocity along the channel by more than 50% The decrease in flow velocity was the main reason for the decrease in the sediment-carrying capacity of the runoff, which directly reduced the runoff erosion intensity This study provides the scientific basis for understanding the regulation of check dam and sedimentation on hydrological process

Investigation of on-site implications of tea plantations on soil erosion in Iran using 137Cs method and RUSLE

Abstract: Tea plantations cover an area of ca. 31,000 ha in the Central North of Iran. This area, after clearing the original forests more than 50 years ago, became exposed to severe soil erosion. The objective of this study was to assess long-term soil erosion rates in tea farms and to evaluate their soil conservation effect at a whole-of-catchment scale. No previous information on direct measurements of soil erosion in this mountainous tea agro-ecosystem of Northern Iran is available. Point-based estimates of net erosion have been obtained using the 137Cs technique and these results were compared with estimates using the RUSLE model. Calculations of soil erosion rates from 137Cs inventories, based on the Mass Balance Model II, revealed that 1.3 mm year−1 and 1.45 mm year−1 of soils were lost from the two sub-catchments A1 and A2, into which the catchment can be divided. The annual net erosion rate of the entire catchment was 17.06 t ha−1 year−1 which is consistent with the rate of 20.4 t ha−1 year−1 obtained by the RUSLE model of at the same scale. This study suggests adopting soil conservation practices to control soil erosion, especially after deforestation and periodic pruning of tea bushes. Sustainable land-use plans are then necessary for tea farms of Iran to protect soil resources and to reduce the off-site impacts of land degradation (mainly siltation) on the reservoirs and coastal area.

Sustained growth of the largest uninhabited alluvial island in the Changjiang Estuary under the drastic reduction of river discharged sediment

Abstract: The evolution of the Changjiang Delta is obviously affected by current rapidly rising sea level and drastically declining river discharge, and it is also vital for the sustainable development of Shanghai and the Changjiang River Economic Belt, which represent China’s economic development leader and major national strategic area, respectively. In this paper, the growth pattern of Jiuduansha Island, the largest uninhabited alluvial island in the Changjiang Estuary, is studied in terms of the change in elevation, position and area over the past 50 years through using satellite-derived instantaneous shoreline positions and high/low tide exposure areas based on 497 satellite images from 1974 to 2020; and the influencing factors and future development patterns are further discussed by comparison with other alluvial islands or sandbars in the estuary The results show that Jiuduansha Island has maintained a rapid or even accelerated area growth rate, although the sediment discharge of the Changjiang River has sharply decreased in recent decades This sustained growth is mainly attributed to the existence of the estuarine turbidity maximum zone, coarsening fluvial sediment, onshore sediment replenishment by tide, cone-like geomorphology of Jiuduansha Island, and siltation promotion effect of vegetation The growth rate of the low tide exposure area of Jiuduansha Island increased from 1.9 km2 a−1 in 1974–1990 to 3.0 km2 a−1 in 1990–2020, and the growth rate of the high tide exposure area reached as high as 3.7 km2 a−1 in 1994–2020. The implementation of the Deep-Water Channel Project has significantly affected the evolution of Jiuduansha Island, including shifting the heads of Shangsha and Zhongxiasha from severe retreat to rapid accretion, and promoting tidal flat progradation seaward of the Jiangyanansha and Zhongxiasha, but restricting the growth of the low tide exposure area of Jiuduansha Island.

Impact of Wind on the Spatio-Temporal Variation in Concentration of Suspended Solids in Tonle Sap Lake, Cambodia

Abstract: Even though wind, water depth, and shear stress are important factors governing sediment resuspension in lakes, their actual relations to total suspended solids (TSS) distribution in natural environments have not been well elucidated. This study aims to elucidate the impact of the wind on the spatio-temporal variation of TSS in Tonle Sap Lake, Cambodia, during low-water (March and June, 50 mg/L) than that in the high-water season. The TSS concentration during the low-water season was empirically described by wind speed (W), water depth (D), and shear stress (τ_wave) with a function of W3, W3/D, and exp(W/D) or exp(τ_wave), depending on the location in the lake. The critical shear stress due to wind-induced waves at most of the places in the lake was higher than the total shear stress indicated. Sedimentation was predominant in December and June, and erosion (siltation) was dominant in March. Most of the siltation in March was dominant in the southern part of the lake.

Climate Change and Anthropogenic Interferences for the Morphological Changes of the Padma River in Bangladesh

Abstract: This research aims to identify the morphological changes of the Padma River due to the effects of anthropogenic climate change. The morphological changes were measured by aerial satellite images and their historical comparison, terrestrial survey, sedimentation in the riverbed, water flow, water discharge, siltation, and erosion along the river, etc. The Padma River has been analyzed over the period from 1971 to 2020 using multi-temporal Landsat images and long-term water flow data. The climatic parameters data related to temperature and rainfall were collected from 21 metrological stations distributed throughout Bangladesh over a 50-year period (1965-2015) to evaluate the magnitude of these changes statistically and spatially. The Padma, traditionally considered as a dominantly meandering river, is switching over into a braided river due to its highly susceptible nature of erosion and deposition. Results reveal that the tidal range is high during the dry season and increases from upstream to downstream of the river. Climate change may bring changes upstream by changing rainfall intensity, flood severity, and extreme temperature. More inundation can occur due to sedimentation, and more bank erosion can occur at the same time. An exponential increase of morphological activity with increased river flow, water discharge, bank erosion might substantially increase in the future. The changes in the flow introduced by climate change would impact the morphology of the Padma River of Bangladesh during the monsoon. A major change has been observed in the location of the bank and channel, as well as bars, along with their geometry and morphology over time. It is also observed that the bank line is not stable and migrated continuously. The overall width of the Padma River is varied significantly during the last 50 years. Maps and Landsat images represented that the river channel is shifting abnormally. Both climatic parameters and anthropogenic activity play an important role in fish biology and production. From this study, it is hypothesized that this assessment’s findings might help understand the overall hydrodynamic and morphological nature of the Padma River. It will suggest possible future developmental works that might be implemented on this river.

The scope for a system-based approach to determine fine sediment targets for chalk streams

Abstract: Fine sediment has a critical role in river ecosystems and is essential for habitat heterogeneity, ecosystem structure and function. Expansion and intensification of specific land uses, including agriculture, have increased fine sediment inputs into river networks. The detrimental impacts of excessive fine sediment on river ecosystems have been well documented and numerous sediment targets have been proposed or adopted to assess the gap between target and current levels of fine sediment. Where sediment targets exist, these are often over-simplified and applied across a wide range of river environments irrespective of the processes of fine sediment deposition and the tolerance or sensitivity of river biota to fine sediment. Thus, targets often fail to provide a reliable basis for identifying the need for management interventions to restore ecosystem health. This review adopts a system-based approach to the impacts of fine sediment after reviewing the suitability of existing targets for guiding management in chalk stream catchments specifically. Chalk streams are groundwater-dominated systems characterised by stable hydrological, ecological and thermal regimes and thus respond differently to excessive fine sediment compared with other fluvial systems. Chalk streams are often subject to high levels of sedimentation and siltation despite their low suspended sediment loads. In this paper, we review the characteristic processes and dynamics of chalk streams and how these influence fine sediment accumulation. The impacts of excessive fine sediment on chalk stream habitats and biota and the role ecosystem engineers play in the processes of fine sediment dynamics are discussed. Finally, we discuss the application of fine sediment targets for chalk streams in relation to the implementation of both source and process-based techniques for meeting the requirement for improved ecosystem management.

Discharge Characteristics of Piano Key Weirs with and Without Upstream Siltation

Abstract: The application of a piano key (PK) weir in a channel may lead to changes in the flow characteristics, upstream siltation conditions, and bed elevation. In this study, laboratory-based Type-A PK weir models with noses below the upstream apexes were studied under different flow and siltation conditions. A total of 342 datasets were collected from the three models. Upstream siltation had no impact on the discharge efficiency of submerged PK weirs, but under the free-flow condition, there was a maximum reduction of 4% in the coefficient of discharge. Planners and designers must consider such variations in channels with a high sediment load. However, at high H/P (where H is the head over the weir crest and P is the weir height), the siltation effect starts to decrease, possibly due to the alternation in the flow condition caused by tailwater submergence. The modular submergence was found to be approximately 0.5, which is close to the values available in the literature. The proposed equations for free-flowing PK weirs performed very well with a maximum error of approximately 7% and a mean absolute percentage error (MAPE) of approximately 2.5%. Furthermore, approximately 60% of the data lie within the ± 3% error bands, and almost all data lie within the ± 6% error bands. The equations proposed for submerged PK weirs also efficiently estimated the coefficient of discharge with a maximum error ranging from 9.0 to 11.32% and an MAPE varying from 2.94 to 4.27%.

Impacts of fine sediment input on river macroinvertebrates: the role of the abiotic characteristics at mesohabitat scale

Abstract: Instream hydraulics and riverbed substrate allow for the identification of mesohabitats, and contribute in shaping benthic macroinvertebrate assemblages. However, the role of different depositional conditions between mesohabitats in determining macroinvertebrate response to large sediment input still needs investigation. We studied the evolution of sediment deposits and benthic assemblages in two mesohabitats (a riffle and a glide) of an Alpine river affected by an extreme sediment input. Substrate and hydraulic characteristics were measured in each mesohabitat for 18 months after the sedimentation event. Benthic macroinvertebrates were sampled concurrently, and available pre-event data allowed for before/after comparison. We found evidence of a different response of benthic communities to siltation, associated to the physical structure of the mesohabitat they inhabit. Both substrate and macroinvertebrates were less impacted and recovered faster in the riffle than in the glide. Assemblages in the glide adjusted to the modified habitat through strong proliferation of sand tolerant and preferring families, resulting in higher density and lower diversity compared to the riffle. Our results could support the improvement of the impact assessment of sediment input events. This is particularly relevant given the current global warming, inducing the increase in frequency and intensity of severe rainfall events, and subsequent landslides.

Hydraulic calculation of irrigation settling tanks of Amu Darya irrigation systems

Abstract: The Amu Darya river carries a large amount of up to 15 kg/m3 of suspended matter containing up to 85-90% suspended and 10-15% bottom sediments, which pose a serious threat to the hydroelectric power station and irrigation systems operating in its basin. In case of dam water intake, head sump tanks are provided in the composition of waterworks. So, in the composition of Right-Bank and Left-Bank, sedimentation tanks with mechanical cleaning to protect the channels were built at the Takhiatash hydroelectric complex Kaskelenskaya and Selinsky irrigation system. It is established that the hydraulic and alluvial modes of operation of these settling tanks depend on the water, alluvial, and backwater modes of operation Takhiatash waterworks. It is noted that due to low water conditions, this hydroelectric power plant operated for a significant part of the year with fully closed gates in all spans, producing intensive siltation of the upper stream. These processes led to a change in the alluvial mode of operation of the settling tanks. At the same time, due to low water and excessive design dimensions, in the first years of operation, these settling tanks were heavily silted up, the bottom mark rose to 17.2 m (above the design 165 m). Properly designed settling tanks should prevent siltation of main and distribution channels while respecting the transport capacity of the channels located below. It is proved that some well-known methods for calculating settling tanks, due to their complexity and bulkiness, cannot be used in calculating siltation modes of settling tanks under operational conditions that require simplification or finding a simpler relationship. A simple method is developed for calculating the dynamics of sediment deposition in irrigation sump tanks based on the probability of turbulent pulsation motion. Recommended: for normal operation of irrigation septic tanks, it is necessary to carry out systematic monitoring of the output turbidity and intensity of treatment, as well as water supply according to the water consumption schedule.

A device for reducing the siltation of the front chamber of the pumping station in irrigation systems

Abstract: It has been determined that the reduction of siltation of the front chamber is necessary because the deposited sediments seriously violate the planned hydraulic structure of the flow when water is sucked up by pumps, as a result of which their efficiency decreases. The method of calculating the pipeline system of a new device designed to significantly reduce the siltation of the front chamber of irrigation pumping stations by artificially creating turbulence in the water flow in the bottom layer of the structure is presented. This calculation methodology is based on the use of the theory of flooded water jets, which makes it possible to determine the main characteristics of the jet. The latter allows calculating the design parameters of the pipeline system. The results of experimental studies are presented to compare the calculated data with the results of experiments, as well as to determine the effectiveness of the proposed device for a significant reduction in siltation of the front chamber of irrigation pumping stations.

Reservoir sedimentation and estimating dam storage capacity using bathymetry survey: a case study of Abrajit Dam, Upper Blue Nile basin, Ethiopia

Abstract: This specific study was conducted on the Abrajit reservoir in east Gojjam, Amhara region, Ethiopia. The general objective of the study was to investigate reservoir siltation and determination of the remaining valuable life span of the reservoir using ArcGIS 10.5 version and Golden surfer 16 latest version. A bathymetric survey using echo-sounding equipment (Garmin GPSMAP421s) was conducted and a topo map of reservoir data was used for assessment of the sediment volume. The accumulated sediment volume was estimated by subtracting the triangular interconnected network (TIN) map of the initial bed level from the currently measured bed level. The result of the research revealed that to date, 343,700.1 m3 bulk of sediment was accumulated in the reservoir that reduces 20% of the total reservoir capacity. In the results from the bathymetric investigation and software analysis, annually 28,641.675 m3 year−1 amount of sediment is coming from the catchments to the reservoir that contributed 1.66% of annual reservoir volume reduction. The measured recent storing capacity for the Abrajit Dam was 1,388,870 m3. From a comparison of remaining reservoir storage and annual sediment load, the reservoir will not serve more than 12 years. The estimated specific sediment yield (SSy) was found to be 4733.387 ton km−2 year−1. Therefore, to improve the estimated life span of the reservoir, watershed management is very important and further study is required to identify the area where watershed conservation will focus in the future. Upon the findings, the reservoir volume is running to reduce and it cannot serve all the demand what it designed for during the dry season. As a result, operation curves should be mandatory to give water service for the critical water needs, and regular monitoring of sediment accumulation in the reservoir is recommended.