Reservoir Thermal Structure Research Articles

Aquatic photosynthetic carbon pump driven by periodic temperature variations affects dissolved inorganic carbon and hydrochemical characteristics in a groundwater-fed reservoir

Under the influence of periodic temperature variations, biogeochemical cycling in water bodies is markedly affected by the periodic thermal stratification processes in subtropical reservoirs or lakes. In current studies, there is insufficient research on the influence and mechanism of dissolved inorganic carbon (DIC) distribution in karst carbon-rich groundwater-fed reservoirs under the coupled effects of thermal structure stratification and the biological carbon pump (BCP) effect. To address this issue, the Dalongdong (DLD) reservoir in the subtropical region of southern China was chosen as the site for long-term monitoring and research on relevant physicochemical parameters of water, DIC, and its stable carbon isotope (δ13CDIC), CO2 emission flux, as well as the reservoir's thermal stratification index. The results show that: (1) the DLD reservoir is a typical warm monomictic reservoir, which exhibits regular variations of mixing period-stratification period-mixing period on a yearly scale due to thermal structure changes; (2) DIC was consumed by aquatic photosynthetic organisms in the epilimnion during the stratification period, leading to a decrease in DIC concentration, partial pressure of CO2 (pCO2) and CO2 emission flux, and an increase in stable carbon isotope (δ13CDIC). During the mixing period, the trend was reversed; (3) During the thermal stratification, aquatic photosynthesis and water temperature were the primary factors controlling DIC variations in both the epilimnion and thermocline. Regarding the hypolimnion, calcite dissolution, organic matter decomposition, and water temperature were the dominant controlling factors. These results indicate that although carbon-rich karst groundwater provides a plentiful supply of DIC in the DLD reservoir, its availability is still influenced by variations in the reservoir's thermal structure and the metabolic processes of aquatic photosynthetic organisms. Therefore, to better estimate the regional carbon budget in a reservoir or lake, future studies should especially consider the combined effects of BCP and thermal structure variations on carbon variations.

Combined effects of climatic change and hydrological conditions on thermal regimes in a deep channel-type reservoir

The thermal regime in large reservoirs plays a significant role in the water quality and ecosystem succession; however, little is known about the impacts of regional climate changes and hydrological conditions on a sizeable stratified reservoir with strong inflow conditions, i.e., the Xiangjiaba Reservoir. Using measured data from 2014 to 2018, the monthly and seasonal variations of the water temperature, thermal stability, and their influencing factors were addressed by using empirical models. The results showed substantial variability and seasonality in the reservoir water temperature, which correlated highly with the air temperature, inflow water temperature, and discharge. Correspondingly, there was a seasonal varying thermal stratification in the reservoir's yearly cycle, with its duration being up to 4 ~ 5months, the maximum surface-bottom water temperature difference being up to 7 ~ 10°C. There were significant positive correlations between Schmidt's stability index of the thermal structure and inflow-reservoir temperature difference and the surface-bottom temperature differences, while negative correlations with large discharge. Moreover, the inflow tends to influence thermal stability by retaining hypolimnion cold water, with its maximum bottom hysteresis residence time being up to ~ 4months. Research findings indicated that climate warming in the recent 30years (1988 ~ 2017) would cause a 0.213°C/decade and 0.153kJ/m2/decade increase in reservoir surface water temperature and Schmidt's stability index, respectively. Among these variations, the inflow temperature increase caused by climate change accounted for the largest proportion, i.e., 0.16°C/decade and 0.115kJ/m2/decade. Therefore, climate warming significantly affected the thermal regimes in this large reservoir, and the inflow water temperature increase due to warm air was the main factor altering the reservoir's thermal structure. Findings from the present study provide a fresh perspective on how to best optimize the deep channel-type reservoirs' water quality in the face of anticipated climate change.

Assessment of total evaporation rates and its surface distribution by tridimensional modelling and remote sensing

In arid and semiarid environments, evaporation is responsible for significant water losses from reservoirs. This condition is of special concern in the Brazilian Northeast region, as this is one of the most populous semiarid areas in the planet. The present study aims to assess the spatio-temporal variability of evaporation rates on the water surface of Pentecoste reservoir, located in the Brazilian semiarid region, by using both the hydrodynamic model Delft3D and a remote sensing technique (RS). While RS has already been used to evaluate the spatial distribution of evaporation rates in lakes, Delft3D was innovatively tested and applied for this purpose for the first time in this study. The calibration results showed an accurate reproduction of the water level variability (r2 of 0.997), along with a satisfactory calibration of the reservoir's thermal structure for the full water column (MAE of 0.539 °C, RMSE of 0.572 °C, and NMAE of 0.008). Curves relating monthly evaporation rates with air temperature and wind speed showed strong correlation between those variables (r2 of 0.817 for air temperature and 0.849 for wind speed). Also, the averaged evaporation rates modeled by Delft3D differed by less than 5% compared to RS. Regarding the spatial distribution results, for the wet period the evaporation patterns were similar to those of RS, while in the dry period RS provided a more stable evaporation pattern when compared to Delft3D. The innovative approach proposed in the present study can be used to better understand the evaporation dynamics in surface waters and optimize the location of damping evaporation structures, namely air diffusers, shading systems, and floating solar panels, which are important for improving water availability, not only in drylands.

Impact of Climate Change on Basin Hydrological Characteristics and Thermal Structure of Reservoirs

AbstractIn this study, a hydrodynamic model of water quality (CE‐QUAL‐W2) coupled with a hydrological model (SWAT) with emission scenarios predicted by general circulation models in the future were applied to examine the impact of climate change on the thermal structure of a reservoir. According to the results, the mean annual air temperature will increase from 1.47 to 1.80°C (B1) and from 2.00 to 2.11°C (A2). The average of the monthly precipitation total will also increase from 2.95 to 3.17 mm (A2) and from 5.32 to 9.67 mm (B1) in the future. The results of the hydrological model indicate river flow reduction (A2 scenario), no variation (ECHAM5‐OM B1) and increase (HadCM3 B1) in the future. Also, the occurrence time of maximum and minimum monthly discharges are projected to change. To determine the importance of upstream watershed hydrology on thermal structure modelling, the simulation was carried out twice, once with and then without the SWAT model. By comparing the results, it was concluded that by applying the coupled model, the climate change impact on upstream hydrology characteristics and temperature effect both in the surface and bottom layers, altered duration of the stratification cycle and its onset and termination, could be simulated successfully. Copyright © 2017 John Wiley & Sons, Ltd.

Thermal structure and Energy Budget for Alghadir reservoir, Iran

Knowing the rate of evaporation from surface water resources such as channels and reservoirs is essential for precise management of the water balance. Few detailed evaporation studies exist for small lakes or reservoirs in arid regions of the world. In this study, monthly evaporation was determined by Bowen Ratio Energy Budget technique (BREB) for Alghadir reservoir (Saveh, Iran) from 1995–2007 and compared with class-A pan. Daily data were obtained from IMO (Iran Meteorological Organization) weather station, located near the reservoir, for all of these years. Some variations have been observed on the estimated evaporation of the energy budget at different years, ranging from 151 cm for 1997 to 174 cm for 2006. There is no specific evaporation pattern for all the years, but evaporation rates were low in winter (January and February) and highest during the summer (July and August). However, the times and month of highest evaporation rates varied during the study period. Surveying of reservoir thermal structure showed that, inflow and outflow energy fluxes to this water volume have large variations. In addition, incoming solar shortwave radiation, incoming atmospheric longwave radiation, and longwave atmospheric radiation emitted from the water surface are largest energy fluxes for this small and deep reservoir. Results of this study could explain the importance and sensible contribution of the evaporation rates as a fundamental parameter in the hydrological cycle of reservoirs ecosystem in the arid regions of Iran.

Modelling potential effects of climate change on winter turbidity loading in the Ashokan Reservoir, NY

AbstractRecent studies have indicated that potential future climate change may lead to changes in the timing and quantity of snowpack accumulation and winter (November to April) streamflow patterns including increased streamflow and turbidity in early winter and a slight reduction in turbidity loads at the time of traditional early spring run‐off. In this study, we examine the potential effects of these predicted changes on reservoir turbidity levels. Our analysis focuses on Ashokan Reservoir, NY, which can at times receive significant watershed turbidity inputs mainly from stream channel erosion from the Esopus Creek. Both measured and simulated turbidity loads and climatology are input to CE‐QUAL‐W2 (W2), a reservoir turbidity transport model that can simulate reservoir turbidity and other water quality parameters. The W2 model is applied to estimate the effects of hydroclimatology on effective settling rates and turbidity transport as a result of differences in reservoir thermal structure during summer and winter events. Simulations suggest that the effective settling velocity is substantially lower at low temperatures during winter time. Winter average stream flow is simulated to increase by 12% and 20%, which leads to increases in reservoir turbidity by 11% and 17% for the future period 2046–2065 and 2081–2100, respectively. From a seasonal perspective, a change in timing of peak streamflow with increased flows during the winter and slightly reduced flows during early spring leads to increased average reservoir turbidity during winter and slightly decreased in‐reservoir turbidity during early spring and summer. Copyright © 2013 John Wiley & Sons, Ltd.

Impact of climate change on Cannonsville Reservoir thermal structure in the New York City water supply

Global Circulation Model values of mean daily air temperature, wind speed and solar radiation for the 2081–2100 period are used to produce change factors that are applied to a 39 year record of local meteorological data to produce future climate scenarios. These climate scenarios are used to drive two separate, but coupled models: the Generalized Watershed Loading Functions-Variable Source Area model in order to simulate reservoir tributary inflows, and a one-dimensional reservoir hydrothermal model used to evaluate changes in reservoir thermal structure in response to changes in meteorological forcing and changes in simulated inflow. Comparisons between simulations based on present-day climate data (baseline conditions) and future simulations (change-factor adjusted baseline conditions) are used to evaluate the development and breakdown of thermal stratification, as well as a number of metrics that describe reservoir thermal structure, stability and mixing. Both epilimnion and hypolimnion water temperatures are projected to increase. Indices of mixing and stability show changes that are consistent with the simulated changes in reservoir thermal structure. Simulations suggest that stratification will begin earlier and the reservoir will exhibit longer and more stable periods of thermal stratification under future climate conditions.

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.

Modelling the propagation of turbid density inflows into a stratified lake: Daecheong Reservoir, Korea

Many reservoirs and associated downstream ecosystems located in the Asian monsoon climate region are under increased pressure from the long-term negative effects of turbid flood runoff. Despite the ubiquitous use of turbidity ( C T) as a barometer of water quality and environmental “health”, C T modelling studies have been rare due to lack of detailed experimental data required for validation. This study explored the fate and transport of a turbid density flow entering a stratified reservoir (Daecheong Reservoir, Korea) through application of a coupled three-dimensional (3D) hydrodynamic and particle dynamics model and subsequent validation of the predictions against an extensive data-set collected during the flood season of 2004. The turbidity model simulated multiple size groups of suspended sediment (SS) and used site-specific SS –C T relationships to convert between field measurements ( C T) and model state variables (SS). The model showed good performance in reproducing the reservoir thermal structure, flood propagation dynamics and the magnitude and distribution of turbidity in the reservoir. The turbidity modelling framework developed in this study can be adopted within a real-time management system for forecasting of turbidity and to support adaptive control of withdrawal facilities in reservoirs that suffer from turbid flood runoff.

Effects of Climate and Dam Operations on Reservoir Thermal Structure

Recently, the United States Bureau of Reclamation agreed to increase spring releases from Upper Colorado River Basin reservoirs to create a more natural flow regime in the lower Gunnison River and Upper Colorado River. Fishery managers have expressed concern that new operations could change reservoir conditions and jeopardize popular and economically important reservoir sport fisheries. This study attempts to predict how one aspect of reservoir conditions, thermal structure, might respond to new dam operations at Blue Mesa Reservoir aimed at addressing downstream ecological concerns. A one-dimensional thermal model ~CE-THERM! is applied to simulating thermal effects of ''traditional'' and proposed ''new'' dam operation scenarios. To evaluate the relative importance of climate and dam operations a sensitivity analysis of hydrologic ~i.e., inflows and starting reservoir elevation ! and meteorologic ~i.e., air tempera- ture, cloud cover, and dew point temperature! inputs was conducted along with an ''extreme'' dam operation scenario. Results indicate that reservoir managers at Blue Mesa Reservoir have considerable latitude for new operations without negative thermal consequences. The natural variability of climate and hydrology appear to exert stronger control over reservoir thermal structure than reservoir operations at Blue Mesa.

Geothermal reservoir simulation

This paper is intended to be a state of the art review of geothermal reservoir simulation. Its recent application to the modelling of real geothermal reservoirs is described and put in the context of an emerging general approach to reservoir modelling. The use of computer simulation for geothermal well test analysis is described. One of the main recent uses of reservoir simulators has been for conducting numerical experiments aimed at improving the understanding of geothermal reservoir physics. Such studies on fractured reservoirs, the thermal structure of reservoirs and the effects of non-condensable gases and dissolved salts are outlined.