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This study is a broad and critical review of the transdisciplinary literature on the construction of culverts and their impacts on stream hydrology and geomorphology as well as on stream habitats and biota. For engineers, a culvert is a structure, usually of the tunnel type, that transfers a stream or open drain under a road, railway line, or other obstacle from one side to the other. In fact, culverts are complex hydraulic structures whose impacts on stream ecosystems must be evaluated and understood before they are designed. The objective of this paper is to analyse and discuss recent knowledge about culvert functioning in terms of their negative effects on the passage of freshwater biota, particularly fish, and on entire stream ecosystems. We present the results of many studies showing that improperly designed culverts are barriers for migrating animals and usually have serious ecological consequences (mainly disturbances to fish life history). We also pay attention to different culvert modification methods that increase their passability for organisms and mitigate the impacts of culverts on the surrounding environment. The other purpose of this review is therefore to emphasize that the integration of the knowledge and professional experience of biologists and ecologists with those of river managers, river engineers, hydraulic engineers, hydrologists, and geomorphologists is necessary to design culverts that preserve the natural properties of streams.

Hydraulic structures disrupt fish migration thereby contributing to declines in fish populations around the world. Methods for piping fish upstream over dams can offer much steeper lift than conventional fishways. We describe the lifting mechanism of a tube fishway, demonstrated using numerical modelling, verified by a physical model. Efficacy is demonstrated by safely lifting two species of Australian native fish over 8 m up an embankment. Significant volumes of water can be transported from a chamber at the foot of a dam over its crest using simple conduits and two valves. Unsteady flow contributes entirely or significantly to the volume of water lifted. We explore how this piped system could be scaled up, while controlling turbulence impacts on fish. We propose new methods of characterising hydraulic efficiency for fishways that recognise the energy used and the value of the water discharged.

Rainfall-runoff modeling is necessary for many hydrological studies, such as estimating peak discharges and designing hydraulic structures. The intensity and frequency of extreme climatic events necessitate the use of advanced approaches that incorporate different climatic and landscape parameters for rainfall-runoff modeling. The majority of small basins around the world lack hydrometric data. This study applied an artificial neural network (ANN) to simulate the rainfall-runoff process using data from field sampling plots in conjunction with rainfall and hydrometric data. For this purpose, similarly sized field plots were established among different land uses to determine the amounts of initial loss and infiltration during rainfall occurrences at the Talar basin in the north of Iran. The modeling process was carried out using a multi-layer perceptron network where the network inputs were rainfall time series, initial loss, soil antecedent moisture condition (A.M.C), and the time to peak of the basin, and the output was runoff time series. The data from rain gauge and hydrometric stations and field plots were collected for three consecutive months. The threefold exercises of training (R-sqr = 0.96, MSE = 0.005), cross-validation (R-sqr = 0.95, MSE = 0.006), and test (R-sqr = 0.81, MSE = 0.05) have yielded favorable results. The modeling results also indicated the significance of the cumulative rainfall data and initial loss in the modeling process. Results show that runoff time series and flood hydrograph can be simulated using the optimal inputs and an appropriate neural network structure for the basins without active hydrometric stations.

The paper presents research findings on the production potential of phyto-fouling occurring on onshore hydraulic structures (HS) along with characteristics of the vertical and horizontal distribution of phytomass along groins in various regions of the Black Sea. A minimum average level of fouling phytomass was more frequently observed in the western waters of Crimea, while the maximum occurred in the south and southeast. Many phyto-fouling characteristics occurring on hydraulic structures increase from the coast towards the sea, along with the Shannon index and diversity of dominant species. The maximum of most production performance associated with cenosis and each sector near the water surface is a characteristic of the vertical distribution of phyto-fouling. Observed horizontal changes in periphyton phytomass are moderate, while vertical changes exceed the biological “norm.”

The proposed research sets the task of conducting monitoring aimed at determining the horizontal displacements of the channel of the Stryi River the largest right-bank tributary of the Dniester River. For this purpose, the river was zoned according to morphometric and hydrological characteristics. Three parts were identified, namely highland, piedmont and lowland ones, which radically vary in the nature of the flow and the amount of the displacement. The main research purpose consists in analyzing the impact of anthropogenic factors on the hydrological regime of the Stryi River, as well as studying the effect of the Ukrainian Carpathian Foredeep (UCF) and the Stryi Deep on the mode of horizontal displacements. The research object is processes occurring within the Stryi River channel. Considering main natural factors affecting the channel’s horizontal displacements, special attention is paid to the geological and sedimentological structures located in the region where the Stryi River and its tributaries flow; among the anthropogenic factors, deforestation and the extraction of building materials from the river channel are highlighted. Topographic, geological, soil maps and satellite images of various periods uploaded into ArcGIS software allowed us to monitor displacements observed for as long as 140 years ago. To monitoring the Stryi River channel displacements, such materials as topographic maps scaled 1: 75000 (Austrian period – 1874), 1: 100000 (Polish period – 1933, Soviet period – 1990); satellite images of Sentinel-2 (2019 and 2020 (after the flood)); a map of Quaternary sediments and a soil map scaled 1: 200000 were used. The Stryi River flows between two structures, i.e. the Skybovi Carpathians and the UCF. The right-bank tributaries (Bystrytsia, Limnitsia, Stryi, etc.), which begin in the Carpathians, cross the outer and inner boundaries of the UCF and are characterized by the stable river channel in its mountainous part, multi-braided in its piedmont part, as well as perennial and significant meandering within the Pre-Carpathian region. Lithological deposits have a significant impact at the mouth of the Stryi River. According to the research study results, displacements of up to 1,350m are measured in this area. The research includes an analysis of the influence of geological and sedimentological structures on the Stryi River displacement and the nature of its flow. It has been established that deforestation in the river basin, as well as unauthorized extraction of gravel materials, creates a significant environmental problem in this region. The results of monitoring of the channel deformation processes should be taken into account when solving problems related to river channel processes, namely the construction of hydraulic structures, the design of power transmission networks crossing rivers, the development of gas pipelines, the identification of hazardous flooding zones, the determination of consequences of destruction after floods, the establishment of boundaries of water protection zones, the management of recreational activities, monitoring of border lands and the establishment of an interstate border along rivers.

Many areas of the world are particularly vulnerable to sedimentation. Determining the amount of soil erosion and sediment rate from watersheds would be the first step in reducing sedimentation. Soi...

Soil erosion has serious threats to agricultural production, hydraulic structures, and the world’s ecosystem. The objective of this study is the delineation of soil erosion susceptibility zones in the Chitral district using spatial analyst tool in conjunction with Analytical Hierarchy Process (AHP). This district is highly vulnerable to soil erosion due to the mountainous topography. For the sustainability of agricultural land use as well as regional and local development, it is necessary to find out soil erosion probability zones and soil loss at the watershed scale. Eleven different factors; lithology, slope, elevation, plain curvature, lineaments, land cover, aspect, rainfall, drainage density, NDVI (Normalized Difference Vegetation Index) and NDWI (Normalized Difference Water Index) are considered in this study. Weights have been assigned to each factor, and maps have been generated through GIS (Geographic Information System) tools. The final map from the combination of all maps shows intensities of soil erosion in five different classes including very high, high, medium, low and very low. Very high and high erosion is observed in 13% and 18% of the total study area respectively, which shows that area is under serious danger of soil erosion. Elevation, slope, curvature, NDWI, and rainfall are found to be the dominant factors influencing soil erosion process. This study highlighted areas at risk of severe erosion which will be helpful for researchers and planners to plan for control of soil erosion.

A model of the water balance of Torey Lakes is proposed. The model is based on the integration of satellite data for 1989-2020 and ground-based observation data for the period of 1965- 2018. The analysis of long-term changes in the water level in the lakes revealed its cyclicity. A possible change in the level of Torey Lakes is estimated taking into account the impact of the construction of a hydraulic structure on the transboundary Ul’dza River. Variants of the planned development of water use in the Mongolian part of the catchment area in the form of the water inflow reduction by 10 and 20% are considered. The water balance model is used to demonstrate a possible negative impact of inflow variations on the hydrological regime of the lakes.

In estimating the discharge of the ungauged watershed, we tried to estimate the discharge by applying the weight of the watershed characteristics without using a numerical model. To calculate the discharge of the ungauged watershed considering the watershed characteristics, applied the weight of the watershed characteristics to the existing drainage area ratio method. The watershed development degree and hydraulic structures in the watershed for watershed characteristics were applied as weights. As a result of scenario A, it was analyzed that 2 out of 6 observation stations were underestimated, two were overestimated. As a result of scenarios B, C, and D, the ratio of the calculated discharge to the observed discharge was analyzed to be relatively closer to 1.0 than that of scenario A but still analyzed that the error was significant. In the future, to more accurately calculate the discharge in the ungauged watershed considering the characteristics of the watershed, it will be necessary to develop a quantitative evaluation method.

The role of streamflow is very important in any type of hydrologic. For very effective flood routing and hydraulic structure design, it is important to have a large dataset of past years. We now have a conceptual rainfall-runoff model that can predict streamflow based on pre-existing datasets. Because there is no or very little observed data in un-gauged basins, calibrating these models to predict daily streamflow becomes difficult. Nowadays, parameters for example river width can be observed using satellite images, and some studies show a promising associated relation between discharge and river width. The suggested study demonstrates a method for calculating streamflow from river width extracted with the help of satellite imagery. To predict streamflow, hydrological models are calibrated using river width instead of in site observed streamflow, and for estimating uncertainty Generalized Likelihood Uncertainty Estimation (GLUE) is used. For validation, the suggested method is implemented in the Kharun river basin situated in the Chhattisgarh state of India. The obtained Nash-Sutcliffe efficiency is 92.6 % for simulated river discharge in 2019-2020 at the 50% quantile, which is promising.

Rivers carry suspended sediments along with their flow. These sediments deposit at different places depending on the discharge and course of the river. However, the deposition of these sediments impacts environmental health, agricultural activities, and portable water sources. Deposition of suspended sediments reduces the flow area, thus affecting the movement of aquatic lives and ultimately leading to the change of river course. Thus, the data of suspended sediments and their variation is crucial information for various authorities. Various authorities require the forecasted data of suspended sediments in the river to operate various hydraulic structures properly. Usually, the prediction of suspended sediment concentration (SSC) is challenging due to various factors, including site-related data, site-related modelling, lack of multiple observed factors used for prediction, and pattern complexity.Therefore, to address previous problems, this study proposes a Long Short Term Memory model to predict suspended sediments in Malaysia's Johor River utilizing only one observed factor, including discharge data. The data was collected for the period of 1988–1998. Four different models were tested, in this study, for the prediction of suspended sediments, which are: ElasticNet Linear Regression (L.R.), Multi-Layer Perceptron (MLP) neural network, Extreme Gradient Boosting, and Long Short-Term Memory. Predictions were analysed based on four different scenarios such as daily, weekly, 10-daily, and monthly. Performance evaluation stated that Long Short-Term Memory outperformed other models with the regression values of 92.01%, 96.56%, 96.71%, and 99.45% daily, weekly, 10-days, and monthly scenarios, respectively.

Hydraulic structures are man-made waterworks interacting with the rainfall run-off to store and convey water, or mitigate the impact of run-off. Current approaches in hydraulic structure design ten...

Many hydraulic structures are constructed in an open channel according to the purposes and the nature of the region. Weir is one of these structures which is used for discharge measurements as well as rising water depth in irrigation channels. According to the crest, there are two different shapes: sharp and broad crested weir. A stepped weir is constructed to reduce scour that happened downstream. There are different studies dealt with discharge coefficient, energy dissipation, and other hydraulic characteristics for flow over the weir. In this study, the coefficient of discharge for the Al-Shalalat stepped weir on the Al-Khusr River has been evaluated. The discharge coefficient equation is predicted, and the result values are compared with previous studies. The percentage error for the predicted discharge equation presented in this study compared with previous studies does not exceed 10%.

In recent years, the Cavally River has been subject to multiple activities, including the construction of diversion channels and a bridge that makes it vulnerable to flooding. In order to assess the impact of these hydraulic structures on the river hydrodynamic functioning, a 1D-2D model was realized. The implementation of the 1D-2D model consisted of first running the 1D model, then the 2D model, and finally in coupling them. The 1D-2D model was designed with the 1988 flood hydrograph, a Manning’s coefficient of 0.052 m1/3/s for the minor bed and 0.06 m1/3/s for the major bed. The results of the hydraulic model show that the velocities are almost identical to those of the Cavally in natural operation. The values of the velocities are included between 0.4 m/s and 1.3 m/s at the level of the minor bed of the river and between 0.06 m/s and 0.71 m/s at the level of the floodplains. The average water level for flood propagation is 262.37 ± 0.44 m before construction of the structures and 262.23 ± 0.85 m after construction of the structures. The 0.41 m reduction in water level due to the diversion canal and bridge is negligible compared to the total fluctuations of the Cavally River, which vary from 6 to 7 m over the year.

Sediment material transported by the Indus River has two origins, the catchment and its wetted perimeter, whereas the amount of materials transported from the river itself depends on variables such as the flow type and the sediment load. The annual sediment load transported in the Indus River ranged from 270 to 600 million tons (MT) before the building of dams and barrages. The average sediment load is 0.715 MT/day or approximately 260 MT/ year after the construction of hydraulic structures. The average particle size, D50, of the bedload is approximately 0.125mm at the Sukkur barrage [1]. In this study, research was conducted to evaluate sediment problems in the Nara Canal, take-off from the left pocket of the Sukkur Barrage on the Indus River. The collected data from the left pocket, the bed, and suspended material in upper Nara and its off-taking canals were analyzed to assess sediment transport dynamics of upper Nara canal at various locations and its off-taking canals. The bed material at RD 553+600 shows a minimum size of 0.07 and a maximum of 0.7mm with 54% fine-sand mixed with 46% medium-sand in 2003. Fine-sand increased to an average of 75% while medium sand diminished to 25% at RD 553+600 in Nara canal and at RD 595+000 in Jamrao complex in 2013. The suspended load with low and high flows during 2012 exhibits that in all the cases the sand proportion was increasing in the Upper Nara canal system flowing to the Jamrao complex. The sediment concentration value indicates that there is the deposition of sand at the upper Nara canal and the Jamrao complex causing a discharge reduction in the Nara Canal system.

Methodological approaches and results of estimation of peak flow characteristics of the Iya River taking into account the extreme rainfall flood in the town of 2019, that led to the catastrophic flood in Tulun (the Irkutsk region), are considered. A hydrodynamic model considering the impact of hydraulic structures is proposed to determine the peak flow and to calculate flooding levels. The characteristics of peak flow are determined by various methods, including those considering several floods per year. It is recommended to obtain design values by generalizing the results of several methods of hydrological calculations.

Design flood discharge is one of the important parameters in the management of water resources, especially water resources utilization structures and water damage control structures. This parameter serves to determine the dimensions and capacity of the planned water structures. As an important reference, this design flood discharge must be carefully determined so that the planned building is effective and financially functional and economically efficient. This study aims to determine the design flood discharge using rainfall data which will be recommended as a reference for the design of a micro-hydro power plant building in Kaliwadas River, Pekalongan Regency, Central Java Province. The results of the analysis based on rainfall data are compared with estimates using discharge data to determine deviations resulting from the use of rainfall data. Frequency analysis is applied to both types of rainfall and maximum daily discharge data. Chi-Square and Kolmogorov-Smirnov tests were performed to test four distribution methods: Normal, Normal Log, Pearson Log III and Gumbel. Transformation of design rainfall into design discharge is done using the Snyder Synthetic Unit Hydrograph Method, by first optimizing the hydrograph parameter. The analysis shows that the design flood discharge using rainfall data is relatively lower than using discharge data with an average deviation of more than 15%. This deviation is expected to occur when the transformation of rainfall into discharge is influenced by various very complex parameters, especially changes in land cover and rainfall distribution that have not been fully accommodated. However, for watersheds with very limited discharge data, the use of rain data can be an option for establishing a design flood discharge.

In Punjab (Pakistan), the increasing population and expansion of land use for agriculture have severely exploited the regional groundwater resources. Intensive pumping has resulted in a rapid decline in the level of the water table as well as its quality. Better management practices and artificial recharge are needed for the development of sustainable groundwater resources. This study proposes a methodology to delineate favorable groundwater potential recharge zones (FPRI) by integrating maps of groundwater potential recharge index (PRI) with the DRASTIC-based groundwater vulnerability index (VI). In order to evaluate both indexes, different thematic layers corresponding to each index were overlaid in ArcGIS. In the overlay analysis, the weights (for various thematic layers) and rating values (for sub-classes) were allocated based on a review of published literature. Both were then normalized and modified using the analytical hierarchical process (AHP) and a frequency ratio model respectively. After evaluating PRI and FPRI, these maps were validated using the area under the curve (AUC) method. The PRI map indicates that 53% of the area assessed exists in very low to low recharge zones, 22% in moderate, and 25% in high to excellent potential recharge zones. The VI map indicates that 38% of the area assessed exists in very low to low vulnerability, 33% in moderate, and 29% in high to very high vulnerability zones. The FPRI map shows that the central region of Punjab is moderately-to-highly favorable for recharge due to its low vulnerability and high recharge potential. During the validation process, it was found that the AUC estimated with modified weights and rating values was 79% and 67%, for PRI and VI indexes, respectively. The AUC was less when evaluated using original weights and rating values taken from published literature. Maps of favorable groundwater potential recharge zones are helpful for planning and implementation of wells and hydraulic structures in this region.

The modeling of peak flood discharges and flood frequency analysis at various sites on a river is essential for planning, design, and management of hydraulic structures. The first and the foremost aim of this study is to choose the best-fit flood model among Log Pearson type 3 (LP3), Generalized Extreme Value (GEV), and Gumble (EV1) for each of the eight sites on the Jhelum River and for the same purpose goodness-of-fit tests like Anderson–Darling (A–D) and Kolmogorov–Smirnow (K–S) and distribution graphs (P–P plot and Probability difference graph) were used. The parameters of these models were determined by L-moments. The outcomes of the study reveal that the LP3 model is best-fit for Khanabal, Sangam, Awantipora, Padshahi Bagh, Ram Munshi Bagh, and Asham, and GEV is the best fit for Sopore, and Baramullah sites. Furthermore, peak discharges for 2-, 5-, 10-, 25-, 50-, 100-, 200-, and 500-year return periods were estimated and the analysis depicts that the discharge rate determined by distribution models at a return period of 5 years or more would surpass the safe carrying capacity (990.85 cumecs) of the Jhelum river. The study further shows that there exists a high positive correlation (R2 = 0.99) between observed and predicted peak discharges of LP3 and GEV models. Thus, indicating LP3 and GEV as best-fit models for modeling and flood frequency analysis of annual peak discharges on the Jhelum River.

Flood frequency analysis (FFA) considering the confluence of interconnected rivers is important for hydraulic structures (such as dams or diversions) design, but it has received little attention. This study develops a copula-based method for FFA and quantile estimation considering the confluence of two interconnected rivers, along with the uncertainty estimation by a nonparametric bootstrapping algorithm. Flood probability distribution and return periods are estimated for the two rivers by mapping from bivariate to univariate peak flow quantile estimation. The methodology is applied to the case study of Qezel Ozan and Shahrud Rivers which merge to one of the largest reservoir dams in Iran: Sefidrud (Manjil) dam. According to the results from Peak flow records from Gilvan station (GPF) at Qezel Ozan River and from Loshan station (LCF) at Shahrud River, Gaussian copula with Weibull and gamma margins fits best. Also, it shows that some peak flow quantiles with the same magnitudes have a different probability of occurrences at the confluence of the rivers, and the bivariate estimation uncertainty usually plays an important role in FFA. These findings suggest the use of bivariate instead of univariate distributions to the peak flows at the confluence of interconnected rivers, in which the sampling uncertainty should be considered.

Culverts are important hydraulic structures for delivering a range of valuable socioeconomic services; however, they are also known to have negative impacts on freshwater and estuarine river system...

The study was intended to find out the catchment characteristics of an area and the IDF (Intensity-Duration-Frequency) analysis of rainfall of that area using Gumbel method and Log Pearson type III method. In different studies, the IDF equations are generated for an area without acknowledging the catchment, stream length of the catchment and the time of concentration. In our study the Digital Elevation Map (DEM) of Dhaka was used. The DEM was analyzed using QGIS to find out different catchments, catchment area, catchment slope, stream length etc. The rainfall data of 18 years was collected from BMD (Bangladesh Meteorological Department) at 24 hours’ interval. This rainfall data was analyzed using Gumbel method and Log Pearson Type III method because these methods give accurate prediction for return period more than the range of the acquired data. The return period was taken as 2 years,5 years,10 years,25 years,50 years and 100 years. Finally, the intensity for different return period was plotted against the duration of the rainfall to find out the IDF curve. For any kind of rainfall analysis to find the peak discharge for designing storm sewage lines, small hydraulic structures or calculating surface runoff, infiltration, sub-surface runoff, discharge at rivers or water bodies, the derived IDF equations can be used. Even to find out peak discharge with a return period more than 18 years these set of equation can be used. This method can also be used in other sub urban or urban areas to find out the time of concentration of that catchment and IDF relationships for short duration rainfalls.

An important aspect in the restoration of longitudinal connectivity in rivers and streams is the implementation of fish migration systems at the upstream of the functional hydraulic structures (weirs, drop structures or river sills). The diversity of these existing structures as well as the different locations of these weirs within the river, watershed and riparian zone challenge the design engineers to find new holistic solutions for fish migration systems. The Azuga River study area requires a new synergistic fish migration design system. Being a mountain area, rapid increase in water level is quite frequent, especially after heavy or prolonged rainfalls and during spring snow melt. Therefore, it is necessary to design a specific system for fish migration to meet this locations requirements. Due to the characteristics in this location of the Azuga river, the classic fish migration systems would not be functional. The indigenous/mountain trout is considered as the target species in this paper. Although this is a good swimming species, the use of classical systems could, due to exhaustion, prevent and/or reduce the movement of fish upstream of the two weirs (also known as river sills). This new, comprehensive solution, presented in this paper includes: (i) the restoration and stabilization works of the right bank in the weir study area by using biotechnical measures and (ii) the upstream migration system itself - for supporting the migration of fish on the Azuga River.

Reservoir sedimentation is significant for the efficiency and life of a dam. Flushing orifices have been used in many small dams and other hydraulic structures to remove deposited sediments. Tempor...

Curtain Weirs (CWs) are hydraulic structures that act as a barrier to the flow and diffusion of heat across the width of a water body. Algal blooms occur frequently in Xiangxi Bay (XXB), which is one of the largest tributaries of the Three Gorges Reservoir (TGR). Numerical modeling has become a widely accepted tool for predicting and diagnosing hydrodynamic problems. A laterally averaged two-dimensional hydrodynamic and water quality model (CE-QUAL-W2) was used to simulate the CWs and the hydrodynamics, temperature and chlorophyll-a concentrations for XXB. The developed model was calibrated using data collected in XXB from January to December in 2010. The results indicated that the maximum chlorophyll-a concentrations was observed 154 mg/m3 at sampling sites XX09, XX06 and XX01. The CWs led to a marked reduction of the overall chlorophyll-a concentrations 30–85% because of the CWs height and locations. Therefore, the proposed CWs represent a potential method of reducing algal blooms and improving water quality in XXB of the TGR. Keywords: Curtain weirs (CW), Xiangxi Bay (XXB), CE-QUAL-W2, Algal blooms, Three Gorges Reservoir (TGR)

Flood data on a high temporal scale are required for the design of hydraulic structures, flood risk assessment, flood protection, and reservoir operations. Such flood data are typically generated using rainfall-runoff models through an accurate calibration process. The data also can be estimated using a simple relationship between the daily and the sub-daily flow records as an alternative to rainfall&ndash, runoff modelling. In this study, we propose an approach combining an artificial neural network (ANN) model for peak flow estimation and the steepness index unit volume flood hydrograph (SIUVFH) method for sub-daily flow disaggregation to generate hydrographs on an hourly time scale. The SIUVFH method is based on the strong relationship between the flood peak and the steepness index, which is defined as the difference between the daily flood peak and daily flow several days before the peak, it is also used for selecting a reference unit volume flood hydrograph to be scaled to obtain the sub-daily flood hydrograph. In this study, to improve the applicability of the SIUVFH method for locations with a weak relationship between the flood peak and steepness index, the ANN-based flood peak estimation was used as an additional indicator to determine a reference unit volume flood hydrograph. To apply the proposed method, ANN models for estimating the peak flows from the mean daily flows during peak and adjacent days were constructed for the studied dam sites. The optimal ANN structures were determined through Monte Carlo cross-validation. The results showed a good performance with statistical measurements of relative root mean square errors of 0.155&ndash, 0.224, 0.208&ndash, 0.301, and 0.244&ndash, 0.382 for the training, validation, and testing datasets, respectively. An application of the combined use of the ANN-based peak estimation and the SIUVFH-based flow disaggregation revealed that the disaggregated hourly flows satisfactorily matched the observed flood hydrograph.

Manholes in combined sewers may become surcharged during storm events, resulting in complex mixing conditions. Although manhole hydrodynamics are reasonably well understood, predicting mixing across a surcharged manhole remains a challenge. An analytical compartmental mixing model for manholes, based on jet theory, has been further developed and applied to generate cumulative residence time distributions (CRTDs), which describe mixing. The modeled CRTDs were compared with the experimentally derived CRTDs of over 850 manhole configurations to evaluate how well the new compartmental model represents physical processes. The model underpredicts short-circuiting in manholes with manhole diameter to pipe diameter ratios greater than 4.4 and consequently overestimates mixing. Otherwise, the modeled CRTDs show good agreement with the experimental CRTDs. The new compartmental model represents key manhole hydrodynamics that are not represented in current software modeling packages, which assume manholes are instantaneously well-mixed. The compartmental model provides good predictions of the experimental downstream concentration profiles, although with reduced peak concentrations in those manhole configurations where short-circuiting is not well-predicted. Despite this, the compartmental model still predicts concentrations downstream of a manhole in closer agreement with the recorded data than the complete instantaneously well-mixed assumption. As an analytical model requiring no inputs other than manhole geometry, the new compartmental model applies to a wide range of manhole configurations, is robust, and is useful for predicting manhole mixing in practical applications.

In this study, the flow trends on either side of the Manantali dam, in the upper Senegal River basin, were assessed. The assessment was carried out for the period 1970 to 2019 using the Sen slope and the Mann-Kendall test. The Mann-Kendall trend test was used to indicate the direction of the trends, while the Sen slope was used to assess the magnitude of the change. The results of the study showed that there was an upward trend in the flow of the Senegal River both annually and for every month upstream (Bafing-Makana station) and downstream (Bakel station) from the barrage. The strongest upward trend is noted in October on the upstream station with 4.12 m3/month and in September on the downstream station with 10.99 m3/month. In return, the weakest upward trend is observed in May on the upstream station with 0.07 m3/month and in August on the downstream station with 0.67 m3/month. The annual flow also showed a significant increase upstream (with a rate of 0.35 m3/year) and downstream (with a rate of 4.53 m3/year) with a confidence level of 99 %. The results of the study also showed that an increase in precipitation causes an increase in runoff, despite the construction of hydraulic structures.

Yoo, H.J.; Kim, D.H.; Park, M.H., and Lee, S.O., 2021. Economic sediment transport control with sediment flushing curves for sea dike gate operation: Case study in Saemangeum Basin, Korea. In: Lee, J.L.; Suh, K.-S.; Lee, B.; Shin, S., and Lee, J. (eds.), Crisis and Integrated Management for Coastal and Marine Safety. Journal of Coastal Research, Special Issue No. 114, pp. 161–165. Coconut Creek (Florida), ISSN 0749-0208. As the major reclamation works in Korea, the sea dikes have been installed for preventing the saltwater intrusion in Saemangeum Basin connected with Mangyeonggang and Dongjingang River, Korea since 2010. Recently, the sedimentation issues near the gates due to change of flow velocity might induce serious problems such as water pollution, local scour, stability of hydraulic structures linked with dike. We focused that the gate operation rule was changed to alleviate the sediment transport problem by altering the management water surface elevation in this study. The 3D numerical model, SCHISM, was used to simulate the sediment transport under the gate operation rule which was embedded after modifying the hydraulics structure module in SCHISM. The numerical model was verified by comparing with the measured data in the literature. It was found that the phenomenon induced by gate operation was accurately simulated to compare with the field measurements from Korea Rural Community Corporation (KRCC). Based on the results of SCHISM, the Best Management Practices on gate operation were examined and suggested the optimal solution in terms of structural stability and water use including water quality.

BACKGROUND Tip-to-base conduit widening is considered a key mechanism that enables vascular plants to grow tall by decreasing the hydraulic resistance imposed by increasing height. Widening of hydraulic anatomy (larger conducting elements towards the base of the vascular system) minimizes gradients in leaf-specific hydraulic conductance with plant height, allowing uniform photosynthesis across the crown of trees. Tip-to-base conduit widening has also been associated with changes in conduit number. However, in bryophytes, despite having representatives with internal water conducting tissue, conduit widening has been scarcely investigated. METHODS Here, we examined the changes in hydroid diameter and number with distance from plant tip in Dawsonia superba Grev. and D. polytrichoides R.Br., two representatives of the genus containing the tallest extant bryophytes. KEY RESULTS We found that the position of these moss species on the global scale of conduit size and plant size was consistent with a general scaling among plants with internal water transport. Within plants we found similar patterns of conduit widening and number with distance from plant tip in endohydric mosses to those observed in vascular plants. CONCLUSIONS Thus, this study demonstrates that land plants growing upwards in the atmosphere show analogous conduit widening of hydraulic structures, suggesting efficient internal water transport is a convergent adaptation for photosynthesis on land. This article is protected by copyright. All rights reserved.

Labyrinth weirs are often a favorable design option for regulating the water surface level in irrigation channels and increasing the spillway discharge capacity of dams. Sedimentation in irrigation channels and around related hydraulic structures such as weirs and turnouts is a common problem that causes disruption in operation. In this research, the effects of upstream sedimentation levels (non-sedimentation, S= 30, 60 and 90% of P=weirs’ height) and downstream bed levels on hydraulic performance of trapezoidal labyrinth weirs with various cycle’s geometries were investigated experimentally. The result showed that increase of S up to 60%P did not have a significant effect on the discharge coefficients and related total upstream head labyrinth weirs but further increase of S to 90%P reduced the discharge coefficient of weirs 15% approximately. Comparison of results indicated that for S up to 60%P, reduction of cycle number and its length in flow direction decreased the weirs’ discharge coefficients. However, by increasing S to 90%P, reduction of the apex angle of cycles and increase of the length of weirs in flow direction decreased the discharge coefficients of weirs. Analysis of results indicated that increase of tailwater level to two-thirds of P changed the flow pattern of falling nappe and the discharge coefficients of weirs changed significantly especially at high flow discharges. Finally, statistical equations were developed for estimation of the discharge coefficient of the trapezoidal labyrinth weirs for different upstream sedimentation levels and tailwater levels.

Dam is a hydraulic structure constructed across the river to impound water. Generally dams are used for multipurpose, thus dam stability is essential. Floods resulting from the failure have caused some of the most destructive catastrophes in the past decades (George and Nair Aquat Procedia 4:853–860, 2015). The current study was undertaken to understand the Hydrological Review and Dam Break Analysis (DBA) of Suvarnavathi dam constructed across Suvarnavathi River. An unsteady flow simulation is done using HEC-RAS (Hydrological Engineering Center River Analysis System) model to determine, probable maximum flood, flood travel time and the affected villages. From hydrological review, it is clear that existing spillway capacity is inadequate. Hence dam height must be raised further to a height of 10.1 m. The results obtained from Dam break analysis under overtopping and piping criteria furnished proof to give statement that, 46 villages and a city will be under submergence and rehabilitation cost turns out to be 3440.64 crores under overtopping failure. 23 villages and a city will be under submergence and rehabilitation cost turns out to be 1802.73 crores under piping failure.

Stratified flows and the resulting density-driven currents occur in the natural environment and commonly in saline lakes. In the Great Salt Lake, Utah, USA, the northern and southern portions of the lake are divided by an east-to-west railroad causeway that disrupts natural lake currents and significantly increases salt concentrations in the northern section. To support management efforts focused on addressing rising environmental and economic concerns associated with varied saltwater densities throughout the lake, the causeway was recently modified to include a new breach. The purpose of this new breach is to enhance salt exchange between the northern and southern sections of the lake. Since construction, it typically exhibits a strong density-driven bidirectional flow pattern, but estimating flows and salt exchange has proven to be difficult. To obtain much needed insights into the ability of this hydraulic structure to exchange water and salt between the two sections of the lake, a field campaign coupled with CFD modeling was undertaken. Results from this study indicate that the vertical velocity profile in the breach is sensitive to density differences between flow layers along with breach geometry and water surface elevations. The CFD model was able to accurately represent the bidirectional flows through the breach and provides for improved estimates of water and salt exchanges between the north and south sections of the lake.

Rivers have been subject to the construction of numerous small-scale anthropogenic structures, causing the alteration and fragmentation of habitats. Despite their impact on fish habitat selection, migration, and swimming performance, more hydraulic structures are being added to riverine systems. These mainly have the purpose of harnessing renewable energy or mitigating the impact of flooding, as in the case of leaky barriers that are widely used for natural flood management. By providing a sustainable and cost-effective supplement to traditional hard engineering flood risk management methods, these channel-spanning wooden barriers are constructed using sustainable, local materials, intended to slow down surface water and groundwater flow, reduce flood peaks, and attenuate the flow reaching downstream communities. Despite their increasing popularity, little is known about the design implications on fish movement or hydrodynamics. Using scaled laboratory flume experiments we investigate how the physical design of four leaky barriers varying in porosity, length, provision of overhead cover, and color, impact on fish movement and spatial usage, and the channel hydrodynamics. Our fish behavioral analysis reveals that juvenile rainbow trout (Oncorhynchus mykiss) movement reduces with barrier presence. Upstream passage increases with barrier color but not cover, for shorter rather than longer leaky barriers, and for a non-porous barrier compared to its porous counterpart. Barrier-specific flow alterations appear to play a secondary role compared to barrier color. Our study showed that physical barrier design and leaky barrier presence alter fish movement, and therefore care needs to be taken during the design of such natural flood management structures.

In addition to soil losses on hillslopes, unpaved rural roads, especially when poorly designed and maintained, can be a significant contributor to the erosive processes seen at the catchment scale. In areas with deep soils, the solutions primarily focus on channeling excess surface runoff into settling ponds or terraces. However, few studies have addressed runoff control from roads on steep slopes in areas of shallow soil. Modeling hydrological processes at the catchment scale is a useful strategy for choosing the most effective and least costly conservation practices to control surface runoff. This study applies a mathematical model to a monitored catchment in southern Brazil to better understand the effects of conservation practices on unpaved roads and their impact on the hydrological and erosive dynamics of a small rural catchment. We calibrated the LISEM model using data from eight stormwater events and evaluated how three different road conservation scenarios—low (LI), medium (MI), and high intensity (HI)—contributed to sediment yield (SY), surface runoff volume (Qe), and peak flow (Qp) reduction. The LI and MI scenarios involved installation of hydraulic structures to control the road surface runoff (i.e. road ditch graveling, diversion weirs and grass waterways) while the HI scenario added surface runoff control practices (grass strips) to surrounding crop fields, in addition to the practices included in the MI scenario. Based on these scenarios, the results showed a Qe reduction at the catchment outlet from − 3.5% (LI) to − 22.5% (HI). The Qp and SY varied from + 6.0% (LI) to − 292.5% (HI) and from + 20.0% (LI) to − 963.9% (HI), respectively. These results show that the low- and medium-intensity practices were not effective in controlling surface runoff from roads, based on the Qe, Qb, and SY observed at the catchment’s outlet. On the other hand, when MI scenarios were complemented with practices to control surface runoff in the cultivated areas, a significant reduction in surface runoff (Qe and Qp) and SY was verified.

In forested mountain catchment areas, both bedload and large wood (LW) can be transported during ordinary flows. Retention structures such as sediment traps or racks are built to mitigate potential hazards downstream. Up to now, the design of these retention structures focuses on either LW or bedload. In addition, the majority of LW retention racks tend to retain both LW and bedload, while bedload transport continuity during ordinary flows is an important aspect to be considered in the design. Therefore, a series of flume experiments was conducted to study the effect of LW accumulations at an inclined bar screen with a bottom clearance on backwater rise and bedload transport. The main focus was put on testing different LW characteristics such as LW size, density, fine material, and shape (branches and rootwads), as well as a sequenced flood. The results demonstrated that a few logs (wood volume of ≈ 7 m3 prototype scale with a model scale factor of 30) are sufficient to reduce the bedload transport capacity to below 75% compared to the condition without LW. Fine material and smaller wood sizes further reduced bedload transport and increased backwater rise. In contrast, LW density and LW shape had a negligible effect. The test focusing on a sequenced flood highlighted the need for maintenance measures to avoid self-flushing of the bed material. The results of this study further indicate that an inclined bar screen may need to be adapted by considering LW characteristics in the design of the bottom clearance to enable bedload continuity during ordinary flows., Water, 13 (16), ISSN:2073-4441

A number of hydraulic structures have been installed along the Yeongsan River, including an estuary dam and two weirs (Seungchon and Juksan). While these structures aid in regional water security and use and reduce flooding, they reduce water flow in the summer, thereby frequently causing algal blooms. This study simulated algal bloom and water quality characteristics of sections of the Yeongsan River in South Korea under different weir and estuary dam operating conditions using the Environmental Fluid Dynamics Code—National Institute of Environment Research (EFDC-NIER) model. Results showed that when the management levels of the Juksan Weir and estuary dam were maintained, simulated water levels were EL. 3.7 m in the weir section and EL. −1.2 m (below average water level of the Yellow Sea) in the dam section. When both the weir and dam were open, the water levels varied with the tide, in contrast, when the Juksan Weir alone was open, the water level was between EL. −1.2 and −0.9 m, in line with the management level of the estuary dam. Opening the weir alone reduced algal blooms by 72–84% in the weir region, and opening the estuary dam alone reduced the algal blooms by 83% in the dam region. This improvement was attributed to the reduced water retention time and dilution due to seawater inflows.

Water flow direction and velocity affect and controls erosion, transport and deposi- tion of sediment in rivers, reservoirs and different hydraulic structures. One of the main structures affected is pumping stations within the dams wherein the velocity distribution near the station intake is disturbed. The two-dimensional (2-D) HEC-RAS 5.01 model was utilized to study, analyse and evaluate the effects of pumping rates and flow depth on the flow velocity distribution, flow stream power and their effects in the Mosul Dam reservoir. The pumping station was considered as a case study. The station is suffering from sediment accumulation around, and in, its intake and suction pipes. The main inflow sources to the reservoir are the Tigris River and run-off from the valleys within its basin. The reservoir was divided into two parts for the present study, including the upper part near the pumping station (analysed as a two-dimen- sional zone), while the lower part was analysed as a one-dimensional flow to reduce the simulation period computation time (1986–2011). Different operation plans (i.e. pumping rate and water depth) were considered. The results of the depth-averaged velocity model indicated that when the pumping station was working at a range from the designed full capacity (100% to 25% of its full capacity), the maximum flow ve- locity increased from 75 to 4 times the normal velocity when there is no pumping dependent on pumping rate and flow depth. For the same operation plans, the flow stream power varied from around zero values to 400 times at full pumping capacity and low flow depth. For sediment routing along the reservoir, the considered statisti- cal criteria indicated the model performance in estimating the total sediment load deposition and invert bed level is much better than in the case of erosion and deposition areas for different considered bed sections of the reservoir. Validerad;2020;Nivå 1;2020-03-30 (alebob)

Euphrates River extends about 125 km within the study area located in Annassiriyah City, Dhi Qar Governorate, Iraq. The impact of the seven hydraulic structures on the discharge capacity of the Euphrates River needs to be considered. The main objectives of this research are to increase the discharge capacity of Euphrates River within Annassiriyah City during flood seasons and study the impact of these hydraulic structures on the river capacity by using HEC-RAS 5.0.3 software. Five scenarios were simulated to study the different current condition of Euphrates River within Annassiriyah City. Other additional four scenarios were implemented through river training to increase the river capacity to 1300 m³/s; it is the flood of 100 year return period. The results of the current condition showed that the maximum discharge capacity of Euphrates River within Annassiriyah City is just 300 m³/s. The results of applied improvements show that the capacity can reach 1300 m³/s when Al Chibayish Weir was hypothetically removed from the river system. Additionally, the river capacity will be reduced to 600 m³/s when Al Chibayish Weir is considered. It was concluded that the 100-year flood discharge cannot be achieved without removing Al Chibayish Weir from the river system.

Wood is recognized as a key element of river ecosystem for a large number of positive feedbacks with biotic and abiotic components, both when it is present as large wood deposit or as live vegetation on the riparian zone. Despite the positive impacts of wood, when considering the high flow events, the presence of woody riparian vegetation within the channel can increase the potential risk related to local wood accumulation, bridge clogging or damages at hydraulic structures. Both the effects given by the riparian vegetation and in-channel dead wood need to be considered when evaluating the large wood-related hazards in rivers. For these reasons, we need to increase the knowledge on the relative importance of floodplains in recruiting large wood. An analysis was conducted on the base of a post event field survey on the Ombrone Grossetano River (Italy) which helped to identify the main variables controlling the uprooting process of riparian vegetation. The implementation of a conceptual model for plant stability helped to predict the tree uprooting that occurred during that flood event. The proposed approach can be extended to any other gravel-bed rivers, such that the evaluation of the vulnerability of woody riparian vegetation can give practical advices for maintenance strategies about vegetation cutting.

Knowledge of sediment transport has been used to determine whether erosion or deposition will occur beneath the hydraulic structures, especially the magnitude of this erosion or deposition, and the time and distance over which it will occur. This paper, utilizes the stream gauging by wading method in estimating the bed load transport and scour depth in Kwadna Basin. The estimate of bed load transport enhances the understanding and design of the hydraulic structures overlying water bodies. The current meter was used in measuring stream flow velocity in three critical points along the Kwanda stream. The measurement was used to derive an equation for depth of scour and the rate of erosion after a period of time. Laboratory tests such as sieve analysis and specific gravity were carried out on the samples obtained from the field which showed that the sediment is poorly graded gravelly sand material. The results of the laboratory tests as well as the stream flow parameters of the stream were used to compute the expected volumetric total sediment load transported daily as 889.33 m3/day with annual value of 338347.158 m3/year. Kwadna stream bed material had a geometric mean particle size, D50, of 0.993 mm and consequently, the river transported bed material of larger diameter which explains why there are more deposits of sediments in the basin. The depth of scour for points 1, 2 and 3 after 365 days of high peak rainfall were estimated to be 1.0238, 1.7753 and 1.7019 m, respectively. The findings of this work will help in selecting suitable cross sections for the river structures having observed problems arising from sediment transport and deposition so as to reduce the sediments negative impacts on such structures. Key words: Kwadna Basin, river sediment, stream gauging, bed load transport, scour depth.

Accurate assessment of stage–discharge relationships in open channel flows is important to the design and management of hydraulic structures and engineering. Flow junctions commonly occur at the co...

A railway drainage system gives vital role for effective, efficient operation of rail track. This study worked on an assessment of railway drainage system problem along the Addis Ababa- Mieso railway line, specifically on Akaki rives crossing. It was done to check adequacy of hydraulic structure provided on Akaki River crossing by undertaking hydrologic and hydraulic analysis. Hydrologic modeling of the Akaki catchment area was developed by HEC-GeoHMS program with the help of Arc-GIS and hydrologic analysis was computed by HEC-HMS program. The catchment land use, soil type, rainfall data, Akaki river stream flow data, etc were used to develop hydrological model. SCS unit hydrograph and flood frequency analysis methods were used to estimate instantaneous peak design discharge for 50 and 100 year return period. Model input parameters were calibrated and verified with observed flow data of the river at Akaki gauging station. Hydraulic models were developed by HEC-RAS step-backwater to determine water-surface profiles for the bridge. Cross-sectional elevation data, hydraulic-structure geometries, roughness coefficients along with peak-discharge esti¬mated were used as input for the model. Finally, adequacy of the bridge was evaluated where the bridge was hydraulically efficient over its design period.

Determination of the characteristics of maximum runoff of rain floods and spring water is widely used, but their calculation in the conditions of limited output data should be attributed to insufficiently studied both in theoretical and practical terms. For the normal functioning of hydraulic structures, as well as to avoid catastrophic consequences for settlements, it is necessary to calculate and predict the maximum runoff precisely. The insufficient degree of studying the peculiarities of forming the maximum runoff of rivers in Ukraine requires further development of the research. Unlike modern normative documents, the authors of the article are proposed a generalized structure for rain floods and spring water. Different methods are only parameters that are individually for floods and spring water. The current normative documents in force in Ukraine use the base-years experience in the field of the theory and practice of hydrological calculations, accumulated by scientific research institutes and project water management institutions as of 1975. In particular, in the absence of observation data for the maximum drainage of spring water, the structure of the empirical type is recommended, using the dependence on the estimated layers of the runoff and the coefficients that characterize the watercourse's friendliness, calculated from the materials of the analogue rivers. In order to take into account the reduction of the reduction of maximum drainage modules in the area of small catchment areas (with an area less than 10 km2), the parameter “b” is introduced into the structure of the formula. The maximum drainage of rain floods is determined taking into account the size of the catchments (at F 200 km2 – the reduction structure). The method of calculation and forecasts is brought to the level of their use. The relevance of the past period is due to the need to study the processes of forming the characteristics of the maximum runoff of rain floods and spring water.

Because river flooding and urban inundation due to extreme rainfall cause the severe damages on the infrastructure, it is necessary to develop an accurate prediction technique and to overcome the disasters. In this study, numerical simulation method was applied to predict urban inundation area with appropriate assumptions and hydrological data in the Lower Var valley region in France. The application site is located in the southeast of France and also geometrically complex with several hydraulic structures, such as weir and bridge piers from the mainstream of a river to the Mediterranean Sea. With complex geometrical consideration, numerical modelling of inundation was conducted separately with two steps. Firstly, the whole area of river reach with the urban area was simulated and analyzed. From the results, the smaller urbanized area was specified with consideration of the capacity of inundation. Two-dimensional hydrodynamic model, MIKE 21 FM (flow model) is applicable to simulations of river hydraulics and flood inundation including the urbanized properties. Upstream discharges for the boundary conditions were set up with based on the Gumbel distribution and SCHADEX method. From the numerical simulation, inundation area and river flow variation were analyzed and compared with respect to the upstream discharge scenarios. Furthermore, the effect of computational mesh resolution was analyzed with the urban model. Calculated flooded areas from the simulation results of the whole area model and urbanized models were compared and verified as a newly proposed and applied procedure of inundation analysis in the riverine area.

A spillway is a hydraulic structure used to provide the controlled release of surplus waters and floods from a dam into a downstream area. A side weir is a multipurpose hydraulic structure which is constructed in water conveyance systems with a height lower than that of the canal wall. When the water surface level goes up, the side weir regulates the discharge and controls the water surface in the main canal. Besides, the side weir controls and diverts floods in dam reservoirs, diverts the flow and protects the structure against the river inundations. In this research, a laboratory investigation is performed with 16 Type-A piano key weirs and three different pier heights of 10, 15 and 20cm. These weirs are studied for two cases of 1 and 2. The results show that the weirs with 15cm and 20cm heights in both cases 1 and 2 have the highest discharge coefficient in dimensionless ratios of 0.2> H/P> 0.4 and H/P>0.5 respectively. Having reviewed previous studies, it could be concluded that the trapezoidal piano key side weir is capable of releasing a flow 1.2 times more than that of the linear trapezoidal labyrinth weir with 12 degrees angle and 1.87 times more than the one with 6 degrees angle, and 1.5 times more than that of the triangular labyrinth weir.

In the past, water quality management was regulated on the basis of pollutant concentrations in rivers. However, the recent implementation of total maximum daily load (TMDL) in the Nakdong River, Korea, has achieved preservation of water quality with balanced watershed development based on a scientific approach. However, eight large weirs have been installed as part of the extensive river regulation works, in which the river geometry has also changed dramatically due to dredging. Consequently, the river environment has been changed, including the hydraulic characteristics, such as the residence time, longitudinal and transverse section, water depth, energy gradient, and flow rate. The water quality characteristics experienced the greatest impact from changes in the hydraulic characteristics of the river. Due to considerable difficulty in the actual implementation of the water quality management plan with respect to the changes, it was considered important to predict the water quality change likely to result from hydraulic characteristic changes in the river. In this study, the hydraulic coefficients reflecting the hydraulic characteristics were calculated and implemented in the water quality model according to the changes in the river environment. The estimated pollutant loads in subwatersheds were applied in the water quality model according to the TMDL of the Nakdong River. The hydraulic coefficients, indicating the hydraulic characteristics before and after the changes to the river environment, were applied in the water quality model with complete calibration and verification. The model simulation results were compared for analysis of the effect of an abrupt river environment change. The simulation results show that the river flow rate was reduced after the change to the river environment due to the effect of the hydraulic structures. As a result of the water stagnation, the BOD5 and Chl-a concentrations increased by 9.4% and 12.2%, respectively, whereas the T-N and T-P decreased by 6.1% and 5.0%, respectively. The impact of a drastic topography change on water quality and its improvement can be quantitatively evaluated by water quality modeling. In particular, BOD has proven to be the most effective for improving water quality when a river is in its natural state rather than when the pollution discharge loads are reduced or when the water quality, discharged from the water-treatment facility, is improved. This study analyzes the relationship between the improvement in water quality and the recovery of running water in each section of the Nakdong River. The current study also proposes a scientific alternative for river rehabilitation, which can improve the quality of stagnant water sections and enable a river to recover to its natural state.

A bottom curtain weir (BCW) is a hydraulic structure that acts as a barrier to the flow and diffusion of heat across the width of a water body. Algal blooms occur frequently in the largest tributary of Xiangxi Bay (XXB) of the Three Gorges Reservoir (TGR). A laterally averaged two-dimensional hydrodynamic and water quality model was used to simulate BCWs, including water temperature, hydrodynamics and chlorophyll-a concentrations, for XXB. The numerical models show that BCWs are a much more attractive, much less expensive and time-saving algal bloom controlling technique for subtropical reservoirs. The developed model was calibrated using data collected in XXB from January to December 2010. The maximum chlorophyll-a concentrations observed were 125-154 mg/m3 according to sampling sites such as XX09, XX06 and XX01. Overall chlorophyll-a concentrations were markedly reduced by 4-44% as a function of BCWs height and location. A seasonal algal bloom reduction rate of more than 37% was observed in summer. In some periods, such as May 27-31, June 2-4, June 16-18, August 16-18 and August 23-24, BCWs with heights of 3 m, 5 m and 7 m reduced algal blooms by up to 99% at XX09 and XX06 in XXB. Therefore, the proposed BCWs can reduce algal blooms and improve water quality to save domestic water and aquatic ecosystems in XXB of TGR.