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Positive effects of reservoir sedimentation management on reservoir life: Examples from Japan
(2016)
The effectiveness of different strategies against reservoir sedimentation is demonstrated herein using data sets of Asahi, Nunobiki and Dashidaira reservoirs in Japan. The applied strategies encompass
sediment routing with a bypass tunnel, drawdown flushing during floods and sabo dam construction in the catchment. It is shown that bypassing and flushing are very efficient strategies enlarging reservoir life by 3 to 21 times up to many hundreds of years. Furthermore, it is revealed that also efforts in the catchment, e.g. sabo dam construction, is effective enlarging reservoir life by 2.4 times.
Potential and risks of water reuse in Brandenburg (Germany) – an interdisciplinary case study
(2024)
For Brandenburg, a region in Germany with increasing water shortage and drought events, water reuse can counteract competition scenarios between drinking water supply, agricultural irrigation, and industrial use. Centralized and decentralized sources for reclaimed water are found to potentially substitute 245 or 28% of irrigation water, respectively, in agriculture production in Brandenburg. For such a reuse scenario, the
fate of organic micropollutants is examined for diatrizoate (DZA) and carbamazepine (CBZ). Retention in local sandy soil and transfer into roots and leaves of arugula are analyzed in lysimeter studies and greenhouse pot experiments. Vertical transport was found for DZA and accumulation in or on arugula roots with a root concentration factor of 1,925+34% but a low bioconcentration factor due to intrinsic molecule properties. CBZ was not found to be mobile in the sandy soil but accumulates in arugula roots and leaves by factors of 70+7% and 155+12%, respectively. Further research on potential plant uptake and groundwater enrichment for more substances is highly recommended as well as tertiary wastewater treatment prior to water reuse.
From 2023, new minimum standards for the reuse of treated wastewater will apply in the EU. Internationally, water reuse has already been a relevant issue for some time. Rising water demand worldwide, also as a result of global climate change, is increasing the scarity of freshwater resources in some areas. Reclaimed water is increasingly considered as a valuable substitute for natural water resources. Even before the new EU regulation came into force, DWA has published an extensive report covering a variety of aspects to be considered within the scope of non-potable water reuse. This article provides an overview of that DWA Topics issue “Non-Potable Water Reuse – Development, Technologies and International Framework Conditions for Agricultural, Urban and Industrial Uses”.
Sediment, which deposits and damages the function of reservoirs, is an essential element of aquatic habitats in downstream ecosystems. We reviewed ecosystem features of degraded channels associated with sediment deficiency below dams and ecosystem responses to changes in sediment conditions after management practices in Japan. Sediment bypass tunnel (SBT) is an effective way to transport sufficient amount of sediment to downstream ecosystems. Based on a concept of suitable mass and size of sediment for ecosystem, some effects and limitations of SBT on downstream ecosystems were discussed.
The Gaulwerk hydropower plant (HPP) has a design discharge of 3.5 m3/s and generates about 6.5 GWh per year. The HPP has been in operation since 1963 and uses the flow of two alpine streams. The HPP impounds a 300 m long reservoir with a 6.50 m high weir. The storage is completely filled with sediments and is classified as a valuable habitat for fauna and flora. Due to the sedimentation, the area upstream of the reservoir head inundates about two to three times per year during small flood events, leading to complaints from affected landowners and adjacent municipalities. To investigate sustainable solutions, a study of alternatives has been carried out in which three alternatives to im-prove both the sediment and flood situation are being investigated. In addition, the residual flow release will be adjusted and fish facilities realized in all alternatives. The paper will summarize the analysis of the alternatives encompassing the (1)
flood situation, (2) sediment management, (3) reha-bilitation measures of the hydraulic structures and their costs and (4) the environmental impact.
This paper describes the design of the new tunnel invert lining of the 9-foot tunnel at Mud Mountain Dam, Washington, USA. The tunnel diverts all bed load sediments into the tailwater. Major invert abrasion has been observed in the existing steel lining. The new invert design consists of 0.59 m2 and 0.79 m2 granite blocks that are 0.25 m thick and placed tightly together along the tunnel. Stability analysis showed factors of safety ranging from 1.2 to 2.6 against uplift. This will be achieved with strip drains placed in the bedding material along the tunnel. A service-design-life analysis was performed using abrasion prediction modelling.
This model was based on abrasion measurement data acquired from granite field tests at Pfaffensprung sediment bypass tunnel, Switzerland. The estimated annual abrasion depths for the granite were approximately 0.50 mm/year for average sediment transport conditions.
The derivation of an abrasion prediction model for concrete hydraulic structures valid in supercritical flows is presented herein. The state of the art saltation-abrasion model from Sklar and Dietrich (2004) is modified using the findings of a recent research pro-ject on the design and layout of sediment bypass tunnels. The model correlates the im-pacting parameters with the invert material properties by an abrasion coefficient kv. The value of this coefficient is verified by a similarity analysis to bedrock abrasion in river systems applying a correlation between the abrasion rate and the bed material strength. A sensitivity analysis reveals that the saltation-abrasion model is highly dependent on an adequate estimation of kv. However, as a first order estimate the proposed model en-ables the practical engineer to estimate abrasion at hydraulic structures prone to super-critical flows.
Reservoir sedimentation, a serious problem affecting the majority of reservoirs worldwide, was not systematically accounted for in the past. After 50 years of operation, a constantly decreasing reservoir volume becomes currently a serious challenge for reservoir owners, against which countermeasures have to be developed. This research focuses on sediment routing using a bypass tunnel to convey sediments past a dam.
By transporting sediments into the tailwater past a dam, their accumulation in the reservoir is reduced significantly. However, the global number of sediment bypass tunnels is limited primarily due to high investment and maintenance cost. The main problem of all bypass tunnels is the massive invert abrasion due to high flow velocities combined with high sediment transport rates. Therefore, VAW started two research projects to counter this problem. The main goal of the first project Layout and design of sediment bypass tunnels is to investigate the invert abrasion process by conducting hydraulic laboratory tests and to establish general design criteria for optimal flow conditions in which both sediment depositions in the tunnel are avoided and the resulting abrasion damages are kept at a minimum. The second project Optimizing hydroabrasive-resistant materials at sediment bypass tunnels and hydraulic structures investigates the hydraulic resistance of different tunnel invert materials, such as high performance concrete or cast basalt plates in prototype tests at the Solis bypass tunnel. The sediment transport measurement technique used in this project was optimized during preliminary model tests.
Reservoir sedimentation is increasingly affecting the majority of reservoirs all over the world. As many dams are more than 50 years of age, this problem is becoming more and more seriou403s nowadays. Reservoir sedimentation leads to various severe problems such as a decisive decrease of the active reservoir volume leading to both loss of energy production and water available for water supply and irrigation. These problems will intensify in the very next future, because sediment supply tends to increase due to climate change. Therefore coun-termeasures have to be developed. They can be divided into the three main categories sediment yield reduction, sediment routing and sediment removal. This paper focuses on sediment routing by means of sediment bypass tunnels. Sediment bypass tunnels are an effective measure to stop or at least decrease the reservoir sedimentation process. By routing the sediments around the reservoir into the tailwater in case of flood events sediment accumulation of both bed load and suspended load is reduced significantly. However, the number of sediment bypass tunnels in the world is limited primarily due to high investment and above all maintenance costs. The state-of-the-art design criteria of constructing bypass tunnels are summarized herein; major problems such as tunnel invert abrasion are discussed. The need for further research regarding sediment transport in bypass tunnels and invert abrasion is highlighted.
Worldwide, a large number of reservoirs impounded by dams are rapidly filling up with sediments. As on a global level the loss of reservoir volume due to sedimentation increases faster than the creation of new storage volume, the sustainability of reservoirs may be questioned if no countermeasures are taken. This paper gives an overview of the amount and the processes of reservoir sedimentation and its impact on dams and reservoirs. Furthermore, sediment bypass tunnels as a countermeasure for small to medium sized reservoirs are discussed with their pros and cons. The issue of hydroabrasion is highlighted, and the main design features to be applied for sediment bypass tunnels are given.
In this paper typical bypass efficiencies of sediment bypass tunnels (SBTs) used to counter reservoir sedimentation are described, distinguishing between two layouts of the tunnel intake. It results that SBTs are an effective measure to reduce the sedimentation of dam reservoirs, particularly of type (A) with intake at the reservoir head. The hydroabrasive wear of tunnel inverts is significant and
has to be mitigated by using adequate invert liners. The invert abrasion can be estimated based on an abrasion model where a correct input value of the bed material resistance coefficient is paramount to limit model uncertainties. Based on abrasion measurements at prototype SBTs typical values of the material resistance coefficient are recommended for high-strength concrete, natural stones and steel liners. The field experiences gathered so far and the comparison of various invert materials suggest granite pavers as a promising lining material for severe abrasion conditions.
Without adequate measures, reservoirs are not sustainable, neither the
reservoir itself due to continuous sedimentation, nor the downstream ecosystem due to altered sediment continuity. Appropriate actions are inevitable and require a systematic sedimentation management. Sediment bypassing constitutes one effective strategy that routes sediment load around reservoirs during floods. A sediment bypass system has the advantage that only newly entrained sediment is diverted from the upstream to the downstream reach thereby re-establishing sediment connectivity. Hence, such a system contributes to a sustainable water resources management while taking the downstream environment into consideration. This paper gives a state-of-the-art overview
encompassing design, bypass efficiency, hydraulics, challenges due to abrasion, positive effects on both downstream morphology and ecology, and makes design recommendations.
The Solis reservoir is located in the Alps in Grisons, Switzerland and is operated by the electric power company of Zurich (ewz). Since its construction in 1986, high sediment input during flood events has led to major aggradations in the reservoir. Up to date, nearly half of the original reservoir volume has been filled with sediments from upstream mountain torrents. The deltaic deposition starts extending into the active water volume. Therefore, ewz plans a sediment bypass tunnel to flush the incoming bedload around the dam to the downstream reach. In a first step the reservoir level during flood events is lowered to the minimum operation level. The delta is subjected to free surface flow and the bedload is transported over the delta and deposited further downstream. This sediment relocation decreases the delta volume within the active storage. During further flood events, the incoming sediment is led to the bypass tunnel intake using a guiding structure and flushed through the tunnel. If the flood exceeds the capacity of the bypass tunnel, the surplus flow passes the tunnel intake towards the bottom outlets with the bedload still being flushed through the tunnel. A skimming wall located upstream from the tunnel intake prevents driftwood blocking by leading it to the reservoir front where it can be safely removed. Both the sediment relocation due to water level drawdown and the flushing through the bypass tunnel are investigated and optimized in a hydraulic model at the Laboratory of Hydraulics, Hydrology and Glaciology (VAW) of ETH Zurich. Additionally, the sediment relocation process in the model is compared with a relocation test in the prototype.
Particle dynamics are investigated experimentally in supercritical high-speed open channel flow over a fixed planar bed of low relative roughness height simulating flows in high-gradient non-alluvial mountain streams and hydraulic structures. Non-dimensional equations were developed for transport mode, particle velocity, hop length and hop height accounting for a wide range of literature data encompassing sub- and supercritical flow conditions as well as planar and alluvial bed configurations. Particles were dominantly transported in saltation and particle trajectories on planar beds were rather flat and long compared with alluvial bed data due to (1) increased lift forces by spinning motion, (2) strongly downward directed secondary currents, and (3) a planar flume bed where variation in particle reflection and damping effects were minor. The analysis of particle saltation trajectories revealed that the rising and falling limbs were almost symmetrical contradicting alluvial bed data. Furthermore, no or negligible effect of particle size and shape on particle dynamics were found. Implications of experimental findings for mechanistic saltation-abrasion models are briefly discussed.
Sediment transport in high-speed flows over a fixed bed. 2: Particle impacts and abrasion prediction
(2017)
Single bed load particle impacts were experimentally investigated in supercritical open channel flow over a fixed planar bed of low relative roughness height simulating high-gradient non-alluvial mountain streams as well as hydraulic structures. Particle impact characteristics (impact velocity, impact angle, Stokes number, restitution and dynamic friction coefficients) were determined for a wide range of hydraulic parameters and particle properties. Particle impact velocity scaled with the particle velocity, and the vertical particle impact velocity increased with excess transport stage. Particle impact and rebound angles were low and decreased with transport stage. Analysis of the particle impacts with the bed revealed almost no viscous damping effects with high normal restitution coefficients exceeding unity. The normal and resultant Stokes numbers were high and above critical thresholds for viscous damping. These results are attributed to the coherent turbulent structures near the wall region, i.e. bursting motion with ejection and sweep events responsible for turbulence generation and particle transport. The tangential restitution coefficients were slightly below unity and the dynamic friction coefficients were lower than for alluvial bed data, revealing that only a small amount of horizontal energy was transferred to the bed. The abrasion prediction model formed by Sklar and Dietrich in 2004 was revised based on the new equations on vertical impact velocity and hop length covering various bed configurations. The abrasion coefficient kv was found to be vary around kv ~ 105 for hard materials (tensile strength ft > 1 MPa), one order of magnitude lower than the value assumed so far for Sklar and Dietrich's model.
The Solis dam was built in 1986 by the Electric Power Company of Zurich (ewz). Ever since the construction, large amounts of sediments accumulated in the reservoir and led to severe sediment aggradation. As a consequence, the storage volume was reduced by about 50% till 2012 causing loss of energy production. Additionally, in the near future sediments may have caused severe damage at the dam due to blockage of the bottom outlets. Therefore, in 2011 and 2012 a sediment bypass tunnel was realized in order to redirect the incoming sediments into the tailwater to inhibit sediment aggradation. Since its inauguration, the tunnel was operated four times including a 100-year flood event in August 2014. First operational experiences are described herein.
Results from a long-term stormwater quality monitoring program were used to derive total suspended solids (TSS) event load distributions at four small urban environments (flat roof, parking lot, residential catchment, high traffic street). Theoretical distribution functions were fitted to the empirical distribution functions obtained. Parameters of the theoretical distribution functions were optimized with respect to a likelihood function to get both optimized parameters and standard errors. Kolmogorov-Smirnov and Anderson-Darling test statistics were applied to assess the goodness-of-fit between empirical and theoretical distribution. The lognormal distribution function was found to be most expressive to approximate empirical TSS event load distributions at all sites. However, the goodness-of-fit of the statistical model strongly depends on the number of events available. Based on the results of a Monte-Carlo-based resampling strategy, around 40 events should be considered.
Stormwater pollutant process analysis with long-term on-line monitoring data at micro scale sites
(2016)
Stormwater Pollutant Process Analysis with Long-Term Online Monitoring Data at Micro-Scale Sites
(2016)
Stormwater Pollutant Process Analysis with Long-Term Online Monitoring Data at Micro-Scale Sites
(2016)
Struktural design of linings
(2001)
The German Worksheet ATV-M 127-2 published in January 2000 after a seven years period of preparation and discussion is now well accepted in design practice for lining systems made of different materials and installed in various methods. The concept based on stress, deformation and stability analyses supports simple formula and diagram usage in standard cases like circular pipes up to ND 600 and more elaborate analyses for non-circular cross sections. Beside a short description of the design code the theoretical background is presented. Experimental test configurations are discussed regarding restrictions such as test specimen length, friction and load distribution. There is need of further research projects in co-operation with other universities to solve the problems left in theory and in practical use.
The Tigray and Afar Water Initiative (TAWI) is a collaboration between the Mekelle University (Ethiopia), the Muenster University of Applied Sciences (Germany) and the Westfalian Wilhelms-University Muenster (Germany). This special initiative is concerned with the rural water supply for the particularly water-scarce regional states of Tigray and Afar in the semi-arid north of Ethiopia. This paper describes a pilot project near the village of Koraro, Hawzen county in the Tigray region and deals with river reaches or creeks which carry water for short periods and only after the longer of two rainy seasons. When these waters run dry, water is still often to be found under the dry beds and is used casually by local people for agricultural purposes. An impermeable wall constructed as a subsurface dam to retain water in the ensuing subsurface micro-reservoir under the bed of such rivers could enable this usage to be intensified and hence enhance the water supply of small local user-groups, while at the same time positively influencing the landscape water balance. Here, the word micro refers to the fact that only the pores of the granular soil of an alluvial river bed are used to store water. Furthermore, storing water underground also avoids the danger of increasing the incidence of diseases such as malaria, a consequence of open water ponds.
This paper deals with an experimental investigation of the mean and turbulence characteristics of supercritical quasi-uniform and gradually varied open-channel flows over a transitional rough bed. These conditions are typical for sediment bypass tunnels. The results show that the log-law holds well in the inner region across the channel. The roughness shifts the velocity profiles downward by an amount of ΔU+. The velocity-dip phenomenon and strong secondary currents exist in the channel for narrow open-channel flow. These currents cause the Reynolds shear stress distributions to deviate from the linear distribution and an undulation on the transversal distribution of the bed shear stress, which matches with the bed abrasion pattern. The streamwise turbulence intensity profiles deviate from the semi-empirical universal function whereas the vertical turbulence intensity profiles fit well with it only at the centerline of the channel. A strong wall effect exists on the turbulence intensities in the outer region.
Reservoir sedimentation is an increasing problem affecting the majority of reservoirs both in Switzerland and worldwide. As many dams are more than 50 years of age, this problem is becoming more and more serious nowadays. Res-ervoir sedimentation leads to various severe problems such as a decisive de-crease of the active reservoir volume leading to both loss of energy production and water available for water supply and irrigation. These problems will intensify in the near future, because sediment supply tends to increase due to climate change. Therefore, countermeasures have to be developed. They can be divided into the three main categories sediment yield reduction, sediment routing and sediment removal. This paper focuses on the sediment routing using sediment bypass tunnels. Sediment bypass tunnels are an effective means to decrease the reservoir sedimentation process. By routing the sediments around the reservoir into the tailwater, sediment accumulation is reduced significantly. However, the number of sediment bypass tunnels in the world is limited primarily due to high investment and maintenance costs. The main problem of all bypass tunnels is the invert abrasion due to high velocities in combination with high sediment transport. Three Swiss bypass tunnel examples suffering invert abrasion are presented in this paper. Furthermore, VAW started a research project to investigate the invert abrasion process by conducting hydraulic scale tests in the laboratory. The goal of this research project is to establish general design criteria for optimal flow con-ditions where both sediment depositions in the tunnel are avoided and the result-ing abrasion damages are kept at a minimum.
The stormwater management model SWMM of the US EPA is widely used to analyse, design or optimise urban drainage systems. To perform advanced analysis and visualisations of model data this technical note introduces the R package swmmr. It contains functions to read and write SWMM files, initiate simulations from the R console and to convert SWMM model files to and from GIS data. Additionally, model data can be transformed to produce high quality visualisations. In accordance with SWMM’s open source policy the package can be obtained through github.com or the Comprehensive R Archive Network (CRAN).
An experimental investigation of supercritical uniform and gradually varied open channel flows is presented for a wide range of Froude numbers and flume width-to-flow depth aspect ratios. The instantaneous streamwise and vertical flow velocities were measured in a laboratory flume over the entire width using a two dimensional–laser Doppler anemometry (2D-LDA) system to determine turbulence intensities, and bed and Reynolds shear stresses. The mean velocity patterns show undulation across the flume, indicating the presence of counterrotating secondary current cells. These currents redistribute turbulence intensities and bed and Reynolds shear stresses across the flume. For aspect ratios ≤ 4−5, i.e., narrow open channel flow, the velocity-dip phenomenon is identified both in the streamwise velocity and the Reynolds shear stress distributions. For high aspect ratios, i.e., wide open channel flow, the strength of secondary currents diminish toward the flume center, resulting in a 2D flow farther away from the walls and no velocity-dip phenomenon. Froude number effects on the flow characteristics are less pronounced compared to the aspect ratio effects. At high Froude numbers, the results for narrow and wide open channel flows agree well with literature data. The log-law holds in the inner region across the entire flume width for all investigated Froude numbers and aspect ratios. The Reynolds shear stress distribution agrees well with the computed spanwise bed shear stress distribution. At the flume side walls, the bed shear stresses are 20–50 % higher than the mean values. These results are verified with an engineering example in which high sediment transport and corresponding deep abrasion patterns at the side walls were observed.
Wastewater Generation Model to Predict Impacts of Urine Separation on Wastewater Treatment Plants
(2023)
Wastewater treatment plants are under increasing pressure to enhance resource efficiency and reduce emissions into water bodies. Separation of urine within the catchment area may be an alternative to mitigate the need for costly expansions of central wastewater treatment plant. While previous investigations assumed a spatially uniform implementation of urine separation across the catchment area, the present study introduces a modelling framework which allows to determine the influence of targeted urine separation on the operation and emissions of central wastewater treatment plants. The framework includes an adapted stochastic wastewater generation model, the Stormwater Management Model, and Activated Sludge Model No. 3 with Bio-P module (SIMBA#). The entire application is embedded in the R programming language. The model is validated by an extensive sampling and measurement campaign. Preliminary results based on observed and simulated wastewater generation and transport for a catchment area of 436 residents indicate the suitability of the model for wastewater generation and transport modelling, but also show further need for calibration.
Wastewater generation model to predict impacts of urine separation on wastewater treatment plants
(2024)
Wastewater treatment plants (WWTPs) are under increasing pressure to enhance resource efficiency and reduce emissions into water bodies. The separation of urine within the catchment area may be an alternative to mitigate the need for costly expansions of central WWTPs. While previous investigations assumed a spatially uniform implementation of urine separation across the catchment area, the present study focuses on an adapted stochastic wastewater generation model, which allows the simulation of various wastewater streams (e.g., urine) on a household level. This enables the non-uniform separation of urine across a catchment area. The model is part of a holistic modelling framework to determine the influence of targeted urine separation in catchments on the operation and emissions of central WWTPs, which will be briefly introduced. The wastewater generation model is validated through an extensive sampling and measurement series.
Results based on observed and simulated wastewater quantity and quality for a catchment area of 366 residents for two dry weather days indicate the suitability of the model for wastewater generation and transport modelling. Based on this, four scenarios for urine separation were defined. The results indicate a potential influence of spatial distribution on the peaks of total nitrogen and total phosphorus.