Sediment Transport Monitoring Research Articles

Island Water Management Cyprus Facts Finding Mission and Gap Identifications

Water management on islands faces unique challenges due to limited size, isolation, climate change impacts, and economic development needs. These factors intensify water scarcity, highlighting the need for sustainable resource development through multidisciplinary approaches. Cyprus, the third-largest Mediterranean island, exemplifies these challenges, with the lowest water availability per capita in the region and severe water scarcity exacerbated by climate change. Addressing these issues requires a comprehensive master plan that integrates technical, environmental, social, and economic factors, focusing on climate change impacts on the water cycle. The Energy, Environment, and Water Research Center (EEWRC) plays a pivotal role in global resource management, emphasizing sustainable development goals and Integrated Water Resources Management Policy. EEWRC’s key initiatives include hydrodiplomacy and WEF Nexus and Integrated Water Resource Management IWRM, monitoring sediment transport pollution, water quality monitoring of basins and aquifers, smart water management of conventional and non-conventional water, and nature-based solutions for water and land management integration. To improve water management in Cyprus, establishing a National Commission for Water Experts is recommended. This commission would provide a detailed roadmap for water management, aligning with Sustainable Development Goals (SDGs) and the Climate Change Initiative coordinated by the Cyprus Institute. Additionally, organizing a conference focused on “Cyprus Island Water Management” would help launch this concept. In conclusion, it is crucial to develop a long-term strategy for optimal water resource management in Cyprus, addressing water issues, promoting conservation, launching climate-resilient initiatives, and fostering collaboration with national and international entities for success.

Applicability of sediment rating curves: analysis in the state of Rio Grande do Sul

The transport of sediments is present in all watercourses, occurring naturally, however, in different ways and characteristics. Its quantification in watersheds becomes extremely important for the planning and management of water resources. The sediment rating curve, which empirically describes the relationship between stream flow and suspended sediment concentration (Css), is an alternative tool to the lack of continuous monitoring of sediment transport. The aim of this research was to evaluate the use of rating curves in sedimentometric stations in Rio Grande do Sul, Brazil. Three Css data handling scenarios were tested for the analytical fitting of sediment rating curves considering a power function as follows: complete data sets, data sets subdivided into 10-year periods and subdivided into stream flow ranges. The approaches adopted in the present study were evaluated taking as reference 58 sedimentometric stations in the state. The goodness-of-fit tests used in this study - coefficient of determination, Relative Average Percentage Error and Nash Sutcliffe coefficient, indicated that the best results of the estimation of sediment transport were observed when the sediment rating curve was fitted to the 10-year period data set.

Field monitoring and modelling of sediment transport, hydraulics and hydroabrasion at Sediment Bypass Tunnels

Sediment Bypass Tunnels (SBTs) are proven to be an effective measure to reduce or even stop reservoir sedimentation by bypassing sediment laden flows around reservoir dams to the downstream river reach. They are mostly used in Switzerland, Japan, and Taiwan. However, hydraulic and sedimentological operating conditions and the resistance of the invert materials against hydroabrasive erosion affect their cost-effectiveness. Hydroabrasion is a pressing issue at SBTs, other hydraulic structures and steep bedrock rivers exposed to high sediment transport rates under supercritical flow conditions. The present study was therefore conducted to address this issue by aiming at improving knowledge on abrasion mechanics and calibrating a mechanistic saltation abrasion model enhanced by Demiral-Yüzügüllü (2021). To this end, the abrasion resistance of fourteen different invert materials installed at Solis, Pfaffensprung and Runcahez SBTs in Switzerland was quantified by annual 3D laser scanning and the hydraulic conditions and sediment transport rates were regularly monitored between 2017 and 2021. The analysis of invert scans and hydraulic conditions revealed that Prandtl’s first and second kinds of secondary currents occurring in the bends and straight sections of the SBTs, respectively, and the observed abrasion patterns were strongly interrelated. The tested potassium aluminate cement and steel fibre concretes, granite, cast basalt and steel plates had better abrasion resistance against impact of sediment-laden flows compared to other materials. Sediment mineralogical composition i.e., bulk hardness relative to the invert material properties significantly affected hydroabrasion. The enhanced abrasion prediction model was calibrated with the present data and a quasi-constant abrasion coefficient of kv = (4.8 ± 2.2) × 104 was obtained. The enhanced model is well-suited for both laboratory and field scales. The present findings will contribute to the sustainable utilization and operational safety of hydraulic structures, optimization of SBT and reservoir operations regarding bypassing efficiency and reservoir lifetime and modelling of bedrock river erosion.

ADCP suspended sediment transport monitoring using acoustic particle radius

Monitoring suspended sediment concentration (SSC) can be challenging as direct sampling methods are labour intensive and indirect measurements based on optical or acoustic backscatter are sensitive to changes in particle properties. Regardless, using ADCP backscatter to predict SSC is promising because of the possibility to capture suspended sediment transport by combining with flow measurements. To reduce sensitivity of established backscatter-SSC relations to changing particle size, a methodology is proposed where acoustic particle radius is derived using multi-frequency backscatter measurements obtained with a Nortek Signature1000 ADCP equipped with a vertical beam echosounder. Considering acoustic particle radii in an adapted backscatter-SSC model shows promising improvement in correlations with water sample reference measurements compared to the traditional single frequency approach based on a field test. Follow-up assessment is required to overcome limitations in dataset sample size and to investigate further improvements of the method. Still, application of the method can significantly enhance capability of ADCPs predicting SSC and – since backscatter is recorded over depth in conjunction with flow measurements – the ability to monitor suspended sediment transport using a single instrument.

Sentinel-2 MSI image time series reveal hydrological and geomorphological control of the sedimentation processes in an Amazonian hydropower dam

Monitoring sediment transport in a run-of-river hydropower dam was investigated to detect and quantify the siltation processes using Sentinel-2/MSI satellite images. We developed a method allowing us to assess the fate of sediment discharge in reservoirs and to map the locations of eroding and silting stream cross sections. This monitoring was achieved by retrieving the seasonal and interannual variation in suspended sediment concentration (SPM) longitudinally and by developing indices to detect local deviations from the overall SPM trend. A comparison between Sentinel-2 reflectance, processed for atmospheric and glint correction, and field measurements showed fine accuracy for the b8a/b4 band ratio (RMSE = 0.23 sr-1, N = 50) as well as a very good SPM retrieval performance for a wide range of concentrations [10–926 mg/L] with an RMSLE of 0.23 mg/L. SPM trend analysis demonstrated that significant (p < 0.001) sedimentation processes (i.e., decreases in SPM concentration upstream to downstream) occur for most parts of the hydrological cycle except during peak flooding when there was no significant SPM siltation. The overall rate of SPM decrease is −0.52 mg/L/km, varying from +0.11 mg/L/km down to −1.10 mg/L/km. We developed a deviation index to detect local anomalies from the overall upstream–downstream satellite-derived SPM trend. A satellite-derived map of eroding and silting reaches is produced evidencing the control of the sediment transport pattern by geomorphological features, such as rapids. Using independent bathymetric surveys, we showed that satellite data allow the locations of eroding and silting river reaches to be correctly mapped.

Monitoring Suspended Sediment Transport in the Lower Yellow River using Landsat Observations

The spatiotemporal variations in suspended sediment concentration (SSC) in the lower reaches of the Yellow River exhibit significant variability and are influenced by reservoir operations. Understanding the spatiotemporal distribution characteristics of SSC in water holds crucial implications for environmental protection and reservoir operation management. Based on daily-scale SSC monitoring data from four hydrological stations in the lower Yellow River, this study established an SSC remote sensing model applicable to Landsat series satellite data. The independent variable of the model, Rrs(NIR)/(Rrs(G) + Rrs(R) + Rrs(SWIR)), demonstrated sensitivity to water bodies with different SSC values. Distinctive spatiotemporal characteristics in sediment transport were observed across the lower Yellow River. Spatially, the SSC values in the Sanmenxia and Xiaolangdi reservoirs were notably lower than those in other river sections, averaging 1008.42 ± 602.83 mg/L and 1177.89 ± 627.95 mg/L, respectively. Over time, the majority of the river sections (96%) exhibited decreasing trends in SSC during 1984–2022, particularly in the downstream Xiaolangdi reservoir, with average SSC values of 4265.58 ± 1101.77 mg/L in the 1980s and 1840.80 ± 2255.15 mg/L in the 2020s. Seasonal variations in SSC were prominent, with higher summer concentrations, averaging 5536.43 ± 2188.77 mg/L (2020s summer) and 814.11 ± 158.27 mg/L (2020s winter). Reductions in SSC during 1984–2022 primarily occurred in summer, weakening its seasonal variability in the lower Yellow River. Water discharge emerged as a critical factor influencing suspended sediment transport, with SSC increasing in high-water-flow months. Following the construction of the Xiaolangdi reservoir, the relationship between SSC and water discharge at different stations underwent notable alterations. This study enhances our understanding of the spatiotemporal dynamics of suspended sediment transport in the lower Yellow River, providing valuable insights for utilizing long-term Landsat series data in the dynamic monitoring of river sediment transport.

An experimental study on monitoring of marine sediment transport by using a 3D sediment trap

The observation and analysis of sediment transport in oceans is an important means for the protection of the marine environment, resource development, construction engineering, and element cycling. However, traditional methods of observing sediment transport are either limited by the range of the instruments used or their own observational attributes, such that they cannot be used to accurately detect and analyze the process of transport of marine sediment. A 3D sediment trap has been proposed to compensate for the shortcomings of the various monitoring tools in our team, but no mature method for the analytical inversion of the data obtained from this device has been developed to date. In this paper, we developed analytical methods to invert sediment transport processes using corrected capture efficiency, sample inversion, and transport flux analysis. Through an annular flume test, we measured the turbidity, pressure, and particle size of the water stream and substituted them into the proposed analytical equations, thus verifying the applicability of the analytical methods. We used the slice experiment of the time series of the sediment samples, to determine the validity of the sample inversion, and establish the relationship between the particle size and concentration of the captured samples. We performed restoration tests on the process of sediment transport to establish a set of methods of flux analysis based on the velocity and turbidity of flow. And finally corrected for capture efficiency by particle size. The combination of analytical methods and 3D sediment trap could provide technological support for investigating the evolution of the sea, ecological cycle, and marine engineering.

Monitoring Sediment Transport in Certain Harbor Launches in the Southeastern Black Sea

The problem of shoaling on coastal structures is the result of an event that occurs as part of the natural cycle. In cases where shoaling cannot be detected or prevented, various economic and operational problems may arise and may cause disruptions. In this study, the complex coastal dynamic impact of shoaling on three sequential fishery coastal structures located within the borders of Rize province in the Eastern Black Sea region of Türkiye was examined in terms of bathymetric changes and sediment transport under the influence of the incident wave climate. The effects of these structures on each other were also investigated. With this aim, bathymetric measurements were carried out to examine the impact of waves on seabed erosion and deposition. A serious shoaling problem was identified at one of the harbor launches under investigation, where approximately 13,200 m3 of deposition occurs annually in a relatively small harbor launch area. Such physical problems are thought to be the result of shoaling, the selection of sites that are not viable for fishery-related coastal structures, or the wrong positioning of the breakwater.

Monitoring sediment transport pathways from an artificial nearshore berm, South Padre Island, Texas, USA, August 2018 to November 2019—Implications for coastal management

During August 2018 – November 2019, the transport pathways of dredge material from a specially constructed nearshore feeder berm were investigated as part of a collaborative study by the City of South Padre Island, U.S. Army Corps of Engineers–Galveston District, U.S. Geological Survey, Partrac GeoMarine Inc., and Texas A&M University, into the efficacy of beneficial use dredge material (BUDM) as a method of replenishing the beach profile and shoreface at South Padre Island, Texas with sediment. Dual-signature (fluorescent and ferrimagnetic) tracer particles, designed to be hydraulically equivalent to the dredge material, were placed on the berm, and a sampling program was initiated to monitor the spatiotemporal movement of tracer particles under the influence of the prevailing hydrodynamic regime. Wave and current data were collected and were used together with available metocean data to identify the forcing mechanisms of sediment transport; improved understanding garnered from the consideration of multiple datasets can be used to inform future coastal management decisions.Tracer analysis results indicated low magnitude, shoreward transport of dredge material from the berm and along shore transport in both northerly and southerly directions. Small amounts of tracer detected in beach face samples demonstrated connectivity between the constructed feeder berm and the shoreface. However, the generally low tracer concentration within beach face samples indicated low rates of sediment transport for berm sediments, and a low magnitude sediment transport pathway from the berm directly to the beach face, with possible storage of sediment in the nearshore bar system.Given that the berm was at or beyond the closure depth and considering the relatively weak prevailing near bottom hydrodynamic conditions, the potential for sediment to be mobilized and transported during the study period was generally low. Periods of higher energy waves, driven by north-northwest winds, were identified as a key driver of sediment transport but due to the infrequent nature of these events the sediment transport regime across the area of interest was temporally limited. Longshore movement of sediment was both north and south, mainly dependent on prevailing wind directions and resulting longshore currents.We discuss implications for coastal zone management and the use of feeder berms as an artificial beach nourishment mechanism to replenish sediments lost by coastal erosional processes. The insight into nearshore emplacement of material can be used by local governments and coastal managers to optimize the efficacy of berm emplacement and implement such schemes as a cost-effective nourishment option, or when onshore placement of material is not feasible.

Seismic signature of a river flooding in La Réunion Island during the tropical cyclone Dumazile (March 2018)

Monitoring of sediment transport during extreme flood events is difficult and often impossible. Fluvial seismology can provide constraints on the mechanisms of this transport and on the seismic sources but few cases of application in context of extreme events such as tropical cyclones were realized. Recordings from three seismic stations temporarily installed along a river (the Rivière du Mât) located in La Réunion Island (Indian Ocean) are analysed to characterize high-frequency (> 1 Hz) seismic noise induced by the extreme flood generated by the tropical cyclone Dumazile (March 2018). We evidence a good correlation (r2 = 0.94) between the amplitude of the seismic signal and the water level at lower frequencies (2–7 Hz), particularly during the rising limb of the river flood. The relationship between seismic amplitude and water level measurements tested at multiple frequency ranges are consistent with a signal dominated by water flow at lower frequencies and by sediment transport at higher frequencies (15–45 Hz). We show that the use of seismic measurement, particularly at stations located very close to the riverbed can provide comprehensive information on the mechanisms involved during sediment transport associated with extreme flood events when direct measurements are not possible.

Acoustic based assessment of cross-sectional concentration inhomogeneity at a suspended sediment monitoring station in a large river

Establishing and operating a harmonized sediment monitoring system along large rivers such as the Danube River is a challenging international task. As an element of such a system, a new monitoring site with state-of-the-art instrumentation is currently under development in the Upper-Hungarian section of the Danube River. The monitoring station will consist of a near-bank optical backscatter sensor and a horizontal acoustic Doppler current profiler (H-ADCP). As previous studies showed, the suspended sediment concentration (SSC) that is continuously measured with near-bank sensors can significantly enhance the temporal resolution of sediment transport monitoring. However, sediment plumes from tributary inflows upstream of the monitoring station can alter the detected near-bank concentrations, eventually biasing the sediment load estimation. Such an influence is likely in the cross-section of the planned monitoring station, therefore, a thorough preliminary analysis of the cross-sectional variation of the SSC was performed, based on expeditionary sediment measurement campaigns. Between 2018 and 2021 24 campaigns were carried out at different hydrological regimes, where physical sediment samplings together with fixed and moving boat ADCP measurements were performed. The cross-sectional variability of SSC and its influence on the sediment load estimations were assessed based on the moving boat ADCP measurements, after calibrating the backscatter signal with more than 500 physical samples. Based on the results, we identified different cross-sectional patterns of the SSC which is apparently governed by: (i) the actual hydrological situation considering both the main river and the tributary, and (ii) the local river morphology. Based on our findings, we suggested a correction method that accounts for the above effects, using which the near-bank SSC can be reliably converted into total suspended sediment load.

Joint probability analysis of water and sediment and predicting sediment load based on copula function

The Jinsha River comprises the upper reaches of the Yangtze River, which is the river section with the highest sediment content. Monitoring of sediment transport in the Jinsha River is done to the guarantee for the normal operation of the Three Gorges Reservoir. In the current study, a copula function was used to do a joint probability analysis of the water and sediment in the Jinsha River Basin (JRB), further a sediment load prediction model based on the copula function also was constructed. The results show that the average annual flow from 2001 to 2018 at the outlet of the Jinsha River (Yibin station) is about 60.43 billion m3, and the average annual sediment load is about 58.82 million t. The linear correlation coefficient between annual flow and annual sediment load is 0.28. The best marginal distribution for annual flow and sediment load is Pearson Type Three (PE3) and Generalized Normal (GNO), respectively, and the best fit for the combined distribution of the two variables is the Frank copula function. The synchronous probability of water and sediment occurrence is 0.459, and the asynchronous probability is 0.541. Based on the copula prediction model, the sediment load can be effectively simulated, and the correlation coefficient between the simulated sequence and the measured sequence reached 0.93. The current study provides important significance for the analysis of water and sediment in the JRB, which is beneficial to the management of Three Gorges Reservoir sediment discharge in the upstream and downstream.

Study on the Koshibu Dam sediment bypass tunnel operation based on sediment transport monitoring in upstream reaches

SBTs (sediment bypass tunnels) are a leading technique to mitigate reservoir sedimentation. SBTs consist of a tunnel connecting the upstream and downstream reaches of a dam and diverts sediment-laden flood directly during flood events. A difficulty in operating SBTs is to reduce sediment inflow into the reservoir effectively, and simultaneously sustaining dam functions such as flood mitigation and hydropower generation. To optimize the problem in controlling the timings required in opening and closing the gates in the SBTs, which are governed by the hydrograph and inflow sediment data. Despite many studies on SBT operations considering hydrograph, there are few of those on the temporal change of sediment inflow. Ultimately, this study aims at improving SBT operations by understanding sediment inflow from upstream reaches using an indirect bedload monitoring system called an impact sensor. For this study, the Koshibu River basin was chosen because impact sensors are already placed in several locations around the basin including inside of the SBT. This observation has revealed the amount of transported sediment during each season in a year, are shown with relations between hydrograph and sediment inflow, and the spatial transient of sediment transport peak levels. According to these observations, desirable rules for SBT operations are suggested.

Comparative study of multilayer perceptron-stochastic gradient descent and gradient boosted trees for predicting daily suspended sediment load: The case study of the Mississippi River, U.S.

Monitoring sediment transport is essential for managing and maintaining rivers. Estimation of the sediment load in rivers is fundamental for the study of sediment movement, erosion, and flood control. In the current study, three machine learning models—multi-layer perceptron (MLP), multi-layer perceptron-stochastic gradient descent (MLP-SGD), and gradient boosted tree (GBT)—were utilized to estimate the suspended sediment load (SSL) at the St. Louis (SL) and Chester (CH) stations on the Mississippi River, U.S. Four evaluation criteria including the Correlation Coefficient (CC), Nash Sutcliffe Efficiency (NSE), Scatter Index (SI), and Willmott's Index (WI) were utilized to evaluate the performance of the used models. A sensitivity analysis of the models to the input variables revealed that the current day discharge variable had the most effect on the SSL at both stations, but in the absence of current-day discharge data (Qt), a combination of input parameters including SSLt−3,SSLt−2,SSLt−1,Qt−3,Qt−2,Qt−1 can be used to estimate the SSL. The comparative outcomes indicated the high accuracy of MLP-SGD-5 model with a CC of 0.983, SI of 0.254, WI of 0.991, and NSE of 0.967 at station CH and the MLP-SGD-6 model with a CC of 0.933, SI of 0.576, WI of 0.961, and NSE of 0.867, respectively, at station SL. The results of MLP models were improved by SGD optimization. Therefore, the MLP-SGD method is recommended as the most accurate model for SSL estimation.

Monitoring of suspended sediment load and transport in an agroforestry watershed on a karst plateau, Southwest China

The timing and distribution of soil erosion in agroforestry landscapes in karst regions remains poorly understood at the watershed scale, despite the recognized deleterious impacts of soil erosion. The aim of the research presented here is to understand multi-scale soil erosion and its relationship with agricultural activities in an agroforestry catchment developed on limestone bedrock in southwest China. Soil erosion monitoring was carried out for runoff plots on the hillside of the basin, and high-frequency suspended sediment and discharge monitoring was carried out for the surface and underground rivers at the outlet of the basin. The results show that the annual sediment transport modulus in this catchment is extremely low (5.1 Mg km−2 a-1). Sediment fluxes in the underground and surface rivers account for 19.7 % and 80.3 % of the total flux, respectively. Soil leakage is an important way but not the main way of soil erosion in this typical karst watershed. There is no obvious soil erosion on the hillsides (less than 1 Mg km−2 a-1), and the annual soil erosion modulus in the paddy field is about 53.7 Mg km−2 a-1. Agricultural activities dominate the distribution of soil erosion. Rainfall that generates surface runoff in the watershed is the key factor affecting soil erosion. This kind of rainfall often occurs in the summer (June to August) during crop cultivation. This study reveals that preventing soil loss from lowland farmland during heavy rainfall events should be prioritized in karst watersheds where agroforestry is practiced.

Comparative Assessment of Fluvial Suspended Sediment Concentration Analysis Methods

The monitoring of fluvial suspended sediment transport plays an important role in the assessment of morphological processes, river habitats, or many social activities associated with river management. However, establishing and operating a well-functioning sediment monitoring system requires the involvement of advanced indirect methods. This study investigates the advantages and limitations of optical and acoustic devices, to quantify the uncertainties and provide a comprehensive comparative assessment of the investigated indirect methods. The novelty of this study, compared to previous ones, is that four different indirect techniques are parallel tested, i.e., the laser diffraction based LISST-Portable|XR, an infrared based optical instrument, the VELP TB1 turbidimeter, the acoustic based LISST-ABS (Acoustical Backscatter Sensor) sensor, and a 1200 kHz Teledyne RD Instruments Acoustic Doppler Current Profiler (ADCP). The calibration of all the indirect methods was performed based on more than 1000 samples taken from the Hungarian section of the Danube River within a wide suspended sediment concentration range. Implementing a comparative assessment of the different sediment analysis methods, a qualitative and quantitative characterisation of the applicability is provided. Furthermore, a proposal for an optimised sediment monitoring methodology is also suggested.

Impact of the Aral Sea Syndrome - the Aralkum as a Man-Made Dust Source

Ground based dust monitoring is an important tool for the long-term monitoring of aeolian sediment transport in Central Asia as it provides valuable insights into the spatial and temporal dynamics of dust deposition as well as grants access to the transported material for further analyses. Between 2006 and 2012 such a monitoring was carried out in the Turan lowland to analyze the effects of the newly formed Aralkum. The detected spatial and temporal dust deposition variability was significant and encourages further studies. The dust deposition increased over time, which correlates with a decreasing trend in precipitation, increasing wind speeds and a shift towards northern winds. More than 50% of all dust samples collected exceed the health based deposition threshold and the most intense dust storm events reached ground level deposition rates of up to 150 g/m2 per hour. This study showed the impact of the Aralkum, but also that the Kyzylkum is a far more active dust source. With regard to climate change and an increasing aridity in the region it can be expected that the aeolian dust transport will continue to increase, making a wide-spread monitoring program even more important.

Ascidian spicules of Quaternary sediments from the lower slope of the Campos Basin (Brazil)

Piston core GL-77 was collected in the lower slope of the northern Campos Basin, Brazil, and consists essentially of muds that have been deposited in turbiditic currents over the last 130 ka, at least, which corresponds to the Upper Pleistocene-Holocene interval. The identified ascidian spicules belong to the Didemnidae Family and are represented by species Micrascidites vulgaris, Bonetia brevis, Rigaudia multiradiata and Monniotia fasciculata. These species have irregular abundance and distribution, with Micrascidites vulgaris being the most common. Their occurrence is interpreted as resulting from transport to the depositional site in response to climate fluctuations (glacial and interglacial periods). The transport of ascidian spicules from a shallow-water sea is supported by the presence of terrestrial organic matter, mainly phytoclasts, sporomorphs and microphytoplankton, which were transported to the slope by the river systems. The results found in this study show that the relative frequency distribution pattern of didemnid spicules is a useful tool for monitoring sediment transport in the slope.

Current and Future Study Topics on Reservoir Sediment Management by Bypass Tunnels

Herein, we summarized the current and future study topics of sediment management using bypass tunnels based on the discussions at the Second International Workshop on Sediment Bypass Tunnels (SBTs) at Kyoto in May 2017. Although reservoir sediment management using bypass tunnels has appeared since the beginning of the 20th century in Kobe, the number of SBTs worldwide is still limited. To promote the installation of SBTs as an effective sediment management measure, it is essential to appropriately evaluate their long-term advantages economically and for the restoration of the aquatic ecosystem. An abrasion model has been developed to predict the abrasion rate of tunnels from the volume of sediment transport. Further, methods to monitor sediment transport in tunnels have advanced. With a significant amount of sediment supply by SBTs, the ecosystems in the downstream reaches of dams can be restored within a few years. A precise rainfall and runoff model for predicting the inflow hydrograph and sediment is essential for the efficient operation of dam gates and SBT (e.g., diverting minimum amount of water for sediment transport). Further studies are needed to clarify the suitable grain size for transportation through SBTs in terms of both the mitigation of tunnel abrasion and promotion of the restoration of downstream ecosystems.

Application of geophysical methods in a dam project: Life cycle perspective and Taiwan experience

There is a growing demand for using non-destructive geophysical techniques to internally image dam condition and facilitate the early detection of anomalous phenomena. Near surface geophysical techniques have advanced significantly in the last few decades, and can play a significant role in the siting, construction, and operational safety and sustainable management of dams. Application of engineering geophysics in site characterization during feasibility investigation phase is already part of the standard of practice. This paper introduces newer applications of engineering geophysics during construction phase, dam safety assessment, and sustainable management, including quality control of compacted soils, investigation of abnormal leakage in an earth dam, evaluation of an aged concrete dam, geophysical health monitoring for a newly-constructed dam, and monitoring of sediment transport for sediment management. The applications were presented with more emphases on the needs of dam engineering and adapting appropriate geophysical methods to make assessment more effective and consequential. The collage of these case studies is to broaden the view of how geophysical methods can be applied to a dam project throughout a dam's life cycle and strengthen the linkage between geophysical surveillance and engineering significance at all stages.