Withdrawal Depth Research Articles

Managing cyanobacteria with a water quality control curtain in Iron Gate Reservoir, California

Mejica BN, Ebert DA, Tanaka SK, Deas ML. 2023. Managing cyanobacteria with a water quality control curtain in Iron Gate Reservoir, California. Lake Reserv Manage. 39:291–310.Iron Gate Reservoir, a eutrophic monomictic reservoir on the Klamath River, a Pacific coast river within the United States, stratifies thermally during summer and is subject to cyanobacteria blooms that produce microcystin toxins, causing public health concerns. An impermeable curtain was installed in Iron Gate Reservoir upstream of the powerhouse intake to control the withdrawal depth and improve water quality of releases to the downstream Klamath River. Thermal stratification minimizes vertical downward movement of cyanobacteria-laden near-surface waters, and the curtain was hypothesized to reduce cyanobacteria and toxin concentrations downstream of the curtain and dam. The Wedderburn number, which indicates unstable (mixed) or stratified conditions, was used to calculate mixed layer depths and define conditions under which the curtain would be likely to be effective. Changes in chlorophyll a, cyanobacteria gene, Microcystis spp. gene, and microcystin concentrations were used to quantify curtain effectiveness for different curtain depths and mixed layer depths. When curtain depth extended below the mixed layer, concentrations of total chlorophyll a, total cyanobacteria, total Microcystis spp., and total microcystin in waters downstream of the curtain were statistically significantly reduced by an average of 87, 90, 78, and 64%, respectively. Concentrations were not consistently reduced downstream of the curtain under other configurations. Findings indicate the curtain can be managed to take advantage of stratification within the epilimnion and address issues pertaining to downstream cyanobacteria and associated toxins, and should improve water quality and reduce public health notices for the 305.7 km of river downstream of Iron Gate Dam.

Decision support system for selective withdrawal in water supply reservoirs: an approach based on thermal stratification

Abstract We consider the problem of determining water withdrawal depth in water supply reservoirs with multilevel intakes in an effective and systematic manner. In the traditional way, operators decide which intake port to use based on their own experience and water samples taken from various depths. Our goal is to provide assistance to operators in the decision-making process and establish a systematic approach for determining the appropriate water withdrawal level in a stratified reservoir. To achieve this, we propose an algorithmic approach as a decision support system for estimating the water withdrawal level. We validate our approach using long-term data collected from a water supply reservoir and compare the results with those of the operator's decisions. The results reveal that when the depth tolerance is set to 10 m, the approach and operator's decisions match at an 80% rate. However, when the depth tolerance is increased to 15 m, the matching percentage improves to over 90%.

Energy, Exergy and Exergo-Economic Analysis of an OTEC Power Plant Utilizing Kalina Cycle

This study aims to analyse an Ocean Thermal Energy Conversion (OTEC) system through the use of a Kalina Cycle (KC), having a water-ammonia mixture as a working fluid. KC represents a technology capable of exploiting the thermal gap of ocean water. This system was then compared with OTEC systems, which exploit ammonia, R134A and butane-pentane mixture as working fluid. The comparison was carried on through energy analysis, exergetic analysis, and exergo-economic analysis using the EES (Engineering Equation Solver) software. For each case study, cost rates and auxiliary equations were evaluated for all components and the mass flow rate and unit exergy cost for each stream. The results showed that the KC with water-ammonia as working fluid achieves the best exergo-economic performance among the examined cycles. The cost of electricity produced through KC using water - ammonia mixture was found to be 26,66 c€/kWh. The thermal efficiency and the exergetic efficiency were calculated and the withdrawal depth of ocean water was considered. The efficiencies resulted to be 3.68% for the thermal efficiency and 95.96% for the exergetic efficiency.

Alarming carcinogenic and non-carcinogenic risk of heavy metals in Sabalan dam reservoir, Northwest of Iran

ABSTRACT This research aims to assess contamination status of water and sediment in Sabalan dam reservoir (SDR) and evaluate the impact of water withdrawal depths on the carcinogenic and non-carcinogenic risks of metals for exposed people. Results of metal pollution indices revealed some degree of pollution in water and sediment of the reservoir, especially associated with arsenic. Risk assessment of metals in water of the SDR for non-carcinogenic materials through different scenarios of water withdrawal depth revealed that consuming water from the depth of 10 m can be somewhat troublesome to human health. The carcinogenic risk of arsenic from depth of 10 m of the reservoir was about four times greater than that from water surface. Minimum carcinogenic risk of consuming water in the reservoir was found to be 1.69 × 10E-4, which is higher than the maximum limit proposed by the U.S. EPA, indicating the water consumption from the SDR can result in harmful effects on human health.

Experimental and Numerical Investigations of Hydraulics in Water Intake with Stop-Log Gate

A stop-log gate, installed in water intake of hydropower project, has become an effective facility in achieving selective withdrawal and temperature control for the sake of benefiting downstream ecosystems. Hence, it is of great importance to comprehensively explore the water intake hydraulics with the gate, not limited to some specific case studies. This study deals, through laboratory experiments and numerical simulations, with flow features of such a gate-functioned intake. The physical model test is used to validate the numerical simulation. Subsequently, a series of numerical cases considering different hydraulic and geometric conditions are performed to help look into the behaviors. Particular attention is paid to the flow regimes, head loss and flow velocity distributions. The results showcase the effect of the gate on the intake flow regime, and in terms of head loss and flow velocity distribution, the influences of the upstream water head, intake chamber width and withdrawal depth are revealed in detail. An empirical expression, with regard to the coefficient of head loss, is derived and validated by data from the available literature. Moreover, it is found that the maximum velocity at trash rack section is dependent exclusively on the relative withdrawal depth and always occurs at a certain height range above the gate. These results may provide a meaningful reference for the research of water intake with similar situations.

Managing climate change in drinking water reservoirs: potentials and limitations of dynamic withdrawal strategies

BackgroundClimate change induced a rise in surface water temperature and a prolongation of summer stratification in drinking water reservoirs. Stratification and temperature are important factors for drinking water production because they influence bio-geo-chemical processes and thus affect water quality. Most drinking water reservoirs have outlet structures that allow water to be withdrawn from different depths at variable rates. The thermal structure of these reservoirs can thus be managed actively by means of dynamic withdrawal schemes.ResultsWe employed the hydro-physical General Lake Model to simulate the effects of different withdrawal strategies on temperatures and stratification in three German reservoirs. In particular, we assessed the potential of depth- and time-variable withdrawal to mitigate the impacts of climate change. We found that deep water temperatures (25 m below surface) and the end of summer stagnation are strongly controlled by the withdrawal regime. Specifically, the simulated impact of the withdrawal scheme was of the same order of magnitude as the observed impact of climate change over the last 30 years. However, the end of ice cover, the onset of summer stagnation, and near-surface temperatures (3 m depth) were rather insensitive to altered withdrawal strategies.ConclusionsOur results suggest that an adaption of withdrawal depth and timing will partly compensate for the effects of climate change. Dynamic withdrawal should thus be considered as an integral part of future reservoir management strategies.

Impacts of Varying Dam Outflow Elevations on Water Temperature, Dissolved Oxygen, and Nutrient Distributions in a Large Prairie Reservoir

Dam operations are known to have significant impacts on reservoir hydrodynamics and solute transport processes. The Gardiner Dam, one of the structures that forms the Lake Diefenbaker reservoir located in the Canadian Prairies, is managed for hydropower generation and agricultural irrigation and is known to have widely altering temperature regimes and nutrient circulations. This study applies the hydrodynamic and nutrient CE-QUAL-W2 model to explore how various withdrawal depths (5, 15, 25, 35, 45, and 55 m) influence the concentrations and distribution of nutrients, temperature, and dissolved oxygen (DO) within the Lake Diefenbaker reservoir. As expected, the highest dissolved nutrient (phosphate, and nitrate, ) concentrations were associated with hypoxic depth horizons in both studied years. During summer high flow period spillway operations impact the distribution of nutrients, water temperatures, and DO as increased epilimnion flow velocities route the incoming water through the surface of the reservoir and reduce mixing and surface warming. This reduces reservoir concentrations but can lead to increased outflow nitrogen (N) and phosphorus (P) concentrations. Lower withdrawal elevations pull warmer surface water deeper within the reservoir and decrease reservoir DO during summer stratification. During fall turnover low outflow elevations increase water column mixing and draws warmer water deeper, leading to slightly higher temperatures and nutrient concentrations than shallow withdrawal elevations. The 15 m depth (540 m above sea level) outflow generally provided the best compromise for overall reservoir and outflow nutrient reduction.

Effects of Lake–Reservoir Pumped-Storage Operations on Temperature and Water Quality

Pumped-storage (PS) hydropower plants are expected to make an important contribution to energy storage in the next decades with growing market shares of new renewable electricity. PS operations affect the water quality of the connected water bodies by exchanging water between them but also by deep water withdrawal from the upper water body. Here, we assess the importance of these two processes in the context of recommissioning a PS hydropower plant by simulating different scenarios with the numerical hydrodynamic and water quality model CE-QUAL-W2. For extended PS operations, the results show significant impacts of the water exchange between the two water bodies on the seasonal dynamics of temperatures, stratification, nutrients, and ice cover, especially in the smaller upper reservoir. Deep water withdrawal was shown to strongly decrease the strength of summer stratification in the upper reservoir, shortening its duration by ~1.5 months, consequently improving oxygen availability, and reducing the accumulation of nutrients in the hypolimnion. These findings highlight the importance of assessing the effects of different options for water withdrawal depths in the design of PS hydropower plants, as well as the relevance of defining a reference state when a PS facility is to be recommissioned.

From End-of-Pipe to Nature Based Solutions: a Simple Statistical Tool for Maximizing the Ecosystem Services Provided by Reservoirs for Drinking Water Treatment

Despite the efforts to control, protect and improve freshwater resources, eutrophication is still one of the main causes for reservoir water quality deterioration. Low-quality raw water reaching water supply treatment plants (WTP) implies an increment of chemical reagents to meet safety requirements, which may also increase the potential of disinfection by-products formation. The objective of this paper was to study the relationship between raw water quality coming from a water supply reservoir and the use of reagents in the associated WTP, through a series of stepwise regression models, in order to develop a simple statistical tool to select the most adequate withdrawal depth for optimizing the treatment processes. The results showed that chlorides, ammonia and water color were the main subrogate parameters in the reservoir explaining the need of chlorine and ozone in the pre-treatment and alum sulphate consumption in the WTP. Therefore, by controlling the variation of these parameters in the water column it would be possible to select the most appropriate reservoir withdrawal depth for reducing costs and risk of by-products formation during treatment, making the most of the water purification service offered by the ecosystem.

Modeling of Turbidity Variation in Two Reservoirs Connected by a Water Transfer Tunnel in South Korea

The Andong and Imha reservoirs in South Korea are connected by a water transfer tunnel. The turbidity of the Imha reservoir is much higher than that of the Andong reservoir. Thus, it is necessary to examine the movement of turbidity between the two reservoirs via the water transfer tunnel. The aim of this study was to investigate the effect of the water transfer tunnel on the turbidity behavior of the two connecting reservoirs and to further understand the effect of reservoir turbidity distribution as a function of the selective withdrawal depth. This study applied the CE-QUAL-W2, a water quality and 2-dimensional hydrodynamic model, for simulating the hydrodynamic processes of the two reservoirs. Results indicate that, in the Andong reservoir, the turbidity of the released water with the water transfer tunnel was similar to that without the tunnel. However, in the Imha reservoir, the turbidity of the released water with the water transfer tunnel was lower than that without the tunnel. This can be attributed to the higher capacity of the Andong reservoir, which has double the storage of the Imha reservoir. Withdrawal turbidity in the Imha reservoir was investigated using the water transfer tunnel. This study applied three withdrawal selections as elevation (EL.) 141.0 m, 146.5 m, and 152.0 m. The highest withdrawal turbidity resulted in EL. 141.0 m, which indicates that the high turbidity current is located at a vertical depth of about 20–30 m because of the density difference. These results will be helpful for understanding the release and selective withdrawal turbidity behaviors for a water transfer tunnel between two reservoirs.

Recycling Irrigation Reservoir Stratification and Implications for Crop Health and Production

AbstractRecycling irrigation reservoirs (RIRs) are an emerging aquatic ecosystem and water resource of global significance. This study investigated the vertical distribution of water temperature, dissolved oxygen (DO), and pH in eight RIRs at two nurseries each in Virginia and Maryland from 2011 to 2014. Monomictic thermal stratification was observed from April to October in all RIRs, despite their shallow depths (0.75‐3.89 m). The strongest stratification had a top‐bottom temperature difference of 21.53°C. The top‐bottom temperature difference was positively correlated with water column depth, air temperature, and daily light integral (p < 0.05). Wind speed did not impact the thermal stratification, likely due to their relatively small surface areas. Thermal stratification affected the vertical distribution of DO and pH. The top‐bottom differences in DO and pH were greater during stratification periods than nonstratification periods. Water pH in all RIRs was higher at the top than at the bottom with the greatest difference of 4.16 units. Discovery and characterization of thermal stratification in RIRs helps understand water quality dynamics in this novel ecosystem and promote safe and productive water reuse for irrigation. Specifically, water withdrawal depths should be adjusted according to variations in temperature, DO, and pH during the stratification and nonstratification periods to mitigate pathogen risk and improve water treatment efficacy and crop production.

Colonoscopy: do operator motions and posture count?

Colonoscopy: do operator motions and posture count?

Caedichnus, a New Ichnogenus Representing Predatory Attack on the Gastropod Shell Aperture

Predatory traces, in which the tracemaker has damaged the prey animal's skeleton to kill and consume it, have a deep fossil history and have received much scientific attention. Several types of predatory traces have been assigned to ichnotaxa, but one of the most studied predatory traces, the wedge-shaped excision produced as a result of attacks mainly by crustaceans on the apertures of gastropod shells, has yet to be described as an ichnotaxon. We propose the ichnogenus Caedichnus to describe the shell damage produced by aperture peeling behavior. Caedichnus is produced by predators that are unable to crush their prey's shells outright. Depending on the predator's peeling ability and the prey's withdrawal depth within the shell, the trace can extend through several whorls of the shell. Aperture peel attacks may fail, allowing such damage to be repaired by surviving gastropods. Thus, the types of attacks that produce Caedichnus may exert selective pressure on prey to evolve better-defended shells (in the case of gastropods) or to inhabit better-defended shells (in the case of hermit crabs). The identification of these trace fossils will enhance our understanding of how predation influences the morphological, and even behavioral, evolution of prey organisms.

Diversion of Mississippi River Water Downstream of New Orleans, Louisiana, USA to Maximize Sediment Capture and Ameliorate Coastal Land Loss

Boat-based field data and monitoring station data from the tidal reach of the Mississippi River are utilized to examine the sediment capture of large (>1,400 cms) proposed water and sediment diversions from the channel to build and sustain wetlands in the Mississippi delta. The purpose herein is to suggest the importance of siting the diversion relative to river morphology and operating it to optimize sediment capture. At the site of a proposed diversion near Myrtle Grove, LA, water and sediment data suggest that the washload (fine) fraction is strongly weighted toward the rising limb of individual freshets (e.g., flows >16,990 cms, 1 to 5 events/y over the last 49 y) based on daily turbidity records. Significant variability in suspended fines exists between freshets depending on whether they are the first peak of the water year, and on their tributary source. Much of the sand fraction in suspended load, since it is derived from the underlying bed (e.g., bed material load), is strongly tied to water discharge in this reach, and can be accurately predicted by ratings curve. An analytical model is presented that is utilized to test efficiency of sand capture in a diversion based on ADCP backscatter data calibrated by isokinetic water samplers. Using observations from the diversion site, the model predicts a 30 % more efficient sand capture for a 1,416 cms diversion (0–10 m withdrawal depth) at a discharge of 27,250 cms (March 2011) on the proposed lateral bar diversion site, relative to a thalweg site on the opposite bank. This suggests that the proximity of large dunes, and the turbulence induced by them, is a primary control on sand resuspension in the water capture zone, which in turn plays a strong role in efficiency of diversion sand capture.

Stratification dynamics in a shallow reservoir under different hydro‐meteorological scenarios and operational strategies

Vertical mixing plays a major role in functioning of seasonally stratified aquatic systems. In this study, we employ a 1‐D stratification model and a 9 year forcing data set to simulate the thermal dynamics in a large, but shallow reservoir that regularly displays a polymictic character with complete mixing events during summer. Such mixing dynamics is typical for many water bodies in the temperate zone having an intermediate depth. In many cases summer‐mixing events were documented to induce severe water quality deteriorations (e.g., cyanobacterial blooms). We examined and quantified the response of summer‐mixing behavior to combinations of hydrological regimes, i.e., water level fluctuations and withdrawal depth, and changes in meteorological variables, i.e., air temperature and wind speed. According to our findings: (i) increasing summer air temperatures considerably increase the resistance of the water column against mixing; (ii) while the combination of maintenance of a high and constant water depth and implementation of epilimnetic discharge results in almost complete resistance to mixing, their individual effects are also substantial, being roughly comparable to the effects of 4–6 K increase in air temperatures; (iii) wind is a critical variable, 30% increase of which can compensate up to 5.5 K increase in air temperatures; and (iv) effects of changes in air temperature, wind speed, and water depth are inter‐dependent, as indicated by enhanced importance of wind and temperature in response to decreasing water depth, as well as reduced importance of depth in response to decreasing wind speed and increasing temperature.

Characterization of residence time variability in a managed monomictic reservoir

The average length of time land‐borne compounds remain within an aquatic system is one of the key parameters controlling its biochemical processes. This study explores the magnitude and sources of daily, seasonal, and interannual variability of river water residence time in the Sau Reservoir, a prototypical example of a Mediterranean water supply. Daily estimates of residence time from 1998 to 2005 were obtained from a series of tracer experiments simulated with a one‐dimensional physical model, based on actual observations and synthetic scenarios. Results highlight that multiple in situ factors, both natural and managed by humans, affect the residence time in reservoirs. Simulated residence times varied on average ∼30% on a daily basis, as a result of natural meteorological (17%) and river inflow temperature (11%) variability. The management of withdrawal depths largely controlled the seasonal variations: The practice of withdrawing water from the shallowest outlet, which was close to the intrusion level of summer inflows, promoted shorter residence times in summers than winters. Interannual variability was primarily associated with the natural variability of inflow volume (25%), and secondarily with surface meteorology (8%). Excessive withdrawals prior to and during long dry periods, however, drastically reduced the reservoir storage capacity and withdrawal options, leading to shorter residence times in dry years. The flushing time, calculated as the ratio of storage volume and flow rates, captured the trends in annual mean residence times reasonably well but not daily and seasonal residence times.

SIMULATIONS OF FLOW CIRCULATIONS AND ATRAZINE CONCENTRATIONS IN A MIDWEST U.S. RESERVOIR

Atrazine is the most commonly used herbicide in the spring for pre-emergent weed control in the corn cropping area in the Midwestern United States. A frequent high level of herbicide concentrations in reservoirs is a great concern for public health and aquatic ecosystems. In this study, a two-dimensional hydrodynamics and toxic contaminant transport model was applied to Saylorville Reservoir, Iowa, USA. The model simulates physical, chemical, and biological processes and predicts unsteady vertical and longitudinal distributions of a toxic chemical. Model results were validated by measured temperatures and atrazine concentrations. Simulated flow velocities, water temperatures, and chemical concentrations demonstrated that the spatial variation of atrazine concentrations was largely affected by seasonal flow circulation patterns in the reservoir. In particular, the simulated fate and transport of atrazine showed the effect of flow circulation on spatial distribution of atrazine during summer months as the river flow formed an underflow within the reservoir and resulted in greater concentrations near the surface of the reservoir. Atrazine concentrations in the reservoir peaked around the end of May and early June. A thorough understanding of the fate and transport of atrazine in the reservoir can assist in developing operation and pollution prevention strategies with respect to timing, amount, and depth of withdrawal. The responses of atrazine transport to various boundary conditions provide useful information in assessing environmental impact of alternative upstream watershed management practices on the quality of reservoir water.

Modeling Turbidity Intrusion Processes in Flooding Season of a Canyon-Shaped Reservoir, South China

Continual runoff events in flooding season affect hydraulic structure and nutrient circulation strongly in reservoirs. The phenomenon of turbid current intrusion and water clarity decreasing was observed in flooding season in Liuxihe reservoir, Guangdong, south China. Numerical simulation techniques are used to study the hydrodynamic processes of runoff events. According to 2 years’ monthly measurements, daily inflow turbidity is estimated by inflow volume and precipitation. Then, a 1-D hydrodynamic coupled with water quality model is applied to simulate the thermal stratification and vertical turbidity distribution during the period with high turbid runoff events. The results show good performance in reproducing the reservoir thermal structure, the magnitude and distribution of turbidity in the reservoir. Based on these, 4 simulation cases are introduced to examine the effects of different reservoir management measures (e.g. different outflow volume and withdrawal depth) on suspended matters’ concentration (turbidity) and distribution in water column. The results can be the basis of water quality management measures of the reservoir administration and local government.

Formation of a zoned magma chamber and its temporal evolution during the historic eruptive activity of Tarumai Volcano, Japan: Petrological implications for a long-term forecast of eruptive activity of an active volcano

Tarumai Volcano started a series of historic eruptive activity in AD 1667 after a dormancy of approximately 2000 years. The historic juvenile ejecta are mainly silicic andesite pumice associated with scoria, banded pumice and dome lava (SiO 2 = 55–63%), and are mixing products of two or three end-member magmas. In the initial largest plinian eruptions (AD 1667 period), simple mixing between two end-member magmas, silicic andesite (SA) and basalt, occurred. Large plinian eruptions (AD 1739 period) and the latest intermittent eruptions (AD 1804–AD 1909: latest period) also produced mixed magmas including both the SA, intermediate-SiO 2 andesite (IA), and basalt. Magmatic temperatures of the SA and IA magmas are 900–950 °C and approximately 1000 °C, respectively. The rocks of each period form linear trends in oxide–oxide diagrams, suggesting that mixing of two end-member magmas occurred in each period. Thus, it can be estimated that the IA magma was formed by mixing between the basaltic and SA magmas. These relations suggest that the injection of the basaltic magma into the SA magma occurred before the AD 1667 period, resulting in the formation of a zoned magma chamber. These two magmas were then withdrawn to mingle, during the AD 1667 period. After the period, the zoned chamber was composed of an upper SA magma and a lower mixed IA magma. Chemical compositions of the basaltic magma have been slightly different in each period since AD 1667. In addition, the phenocrystic minerals of the IA magma also have changed as a consequence of re-equilibration with the more mafic IA bulk magma compositions present from AD 1739 to AD 1909. Thus, distinct basaltic magma has repeatedly injected into the zoned chamber before each eruption. Although the scale of eruptions became much smaller after the plinian eruptions of AD 1739, the ratio of IA magma in the latest eruptive materials is much larger than that in AD 1739, suggesting that a larger amount of the lower part (IA magma) of the zoned magma chamber was effectively withdrawn in the latest period. However, withdrawal depth should be much shallower in the latest activity compared with the activities in AD 1667 and AD 1739 because the tapping depth from a chamber strongly depends on eruption rate. Thus, it is hypothesized that most of the SA magma in the upper part of the zoned magma chamber was consumed in the AD 1667 and AD 1739 periods. The temporal change of the magma system suggests that a large plinian eruption similar to what occurred in AD 1667 or AD 1739 is unlikely in the near future because most of the major magma (SA magma) has already erupted. Because it took considerable time (ca. 2000 yr) to accumulate a large volume of SA magma previously, we forecast that the volcano will enter a prolonged dormant period to accumulate voluminous SA magma for a next eruptive stage, or it will erupt only IA magma similar to the small eruptions that occurred during AD 1804–1909.

선택취수 수심에 따른 취수탑 유입유동 특성

Shallow water withdrawal systems have been replaced with a selected withdrawal system to keep stable raw water quality in spite of occurrence of algae and muddy inflow. Before reconstruction of the water intake tower in Yongdam reservoir supplying water to Gosan water treatment facility, we have predicted flow patterns of inflowing water into the water intake tower for various withdrawal conditions. It has been predicted that the water in the withdrawal layer is significantly inflowed from the front with fast velocity into the water intake tower irrespective of withdrawal depth, while the water away from the withdrawal layer is withdrawed a little from the side with slow velocity.