Outlet Elevation Research Articles

Release of suspension particles from a prismatic tank by multiple jet arrangements

The performance of circular and linear jet arrangements on the release of suspended sediment out of a prismatic tank has been investigated. Experiments conducted are (1) without any forced jet stirring (reference case), (2) four jets arranged in a horizontal circle and (3) aligned jets; they were all in a tank containing water with a known homogeneous initial suspended sediment concentration. The concentration of the suspended sediment inside the tank and released through the outlet is monitored over time, and the evacuated sediment ratio (ESR) is defined, computed, and used as a metric for comparison between the various configurations. The idealized suspended sediment release is also calculated and compared to measured quantity. In order to explain the significant differences in evacuated sediment ratio, the induced circulation is analyzed by measuring the flow field on two vertical planes using the ultrasonic Doppler method. The geometrical parameters of the jet arrangement, the outlet elevation as well as the discharge of the jets are varied. Thus, the optimal parameter combination regarding sediment release can be identified. Finally, recommendations regarding jet arrangement and jet discharge practice in conditions of high sediment release are given.

Modelling of lake level under climate change conditions: Lake Purrumbete in southeastern Australia

Lake Purrumbete is located in western Victoria, Australia, and is highly regarded for its ecological, social, economic and scientific values. Recently, many lakes in the region have been dry or at their lowest level in recorded history, due to a drought that broke in 2010. For this study, a modified difference water budget method was employed to estimate net groundwater flux through the difference between the level of the lake and the water table, along with the specific yield and area of the aquifer. This model successfully modelled the lake level fluctuations. In recent years, Lake Purrumbete has fallen below the outflow level; however, because of its large volume, changes in salinity to date are minor and do not affect its freshwater status. An understanding of how these systems will behave in the future and how they may be best managed in a drying climate is considered an important step to adapt to climate change. Postulated future climatic changes in the region of the lake were used to project the lake level fluctuations to 2030 using the water budget model, and showed that dry conditions would cause the lake level to remain below its outlet elevation, but wet conditions would result in a significant recovery in the lake level. If the level of Lake Purrumbete continues to fall, the main threat to its ecological status will be the potential loss of some significant areas of fringing wetland habitat. The lowering in lake level could cause a shift in the abundance of algal plankton and so influence the whole lake food web. This may reduce the invertebrate diversity of the lake.

Performance of drainage water management systems in Illinois, United States

Drainage water management (DWM) is the practice of varying the drainage intensity of a subsurface drainage system to ensure that no more water is transported from a field than is necessary for optimizing crop growth and for facilitating seedbed preparation and other agrotechnical practices. This variation is achieved by using stop logs in a control structure to adjust the outlet elevation of the drainage system. An experiment was set up to test the hypothesis that the implementation of this practice will reduce nitrate (NO₃) loads from subsurface drainage systems in Illinois, United States, without adversely affecting yields. This experiment consisted of instrumenting and collecting precipitation, flow, and water quality data from four pairs of fields on different soils in Illinois. Each pair consisted of one field with a conventional (free) drainage system and one field with a drainage system whose outlet was managed in accordance with the Illinois Practice Standard for DWM. Annual NO₃ load reductions from the managed fields ranged from 37% to 79%, with an average load reduction of 61%. However, because of difficulties in measuring flow under submerged outlet conditions and because water left the managed fields by pathways other than through the outlets of the drainage systems, the efficacy of the practice is likely less than these numbers would indicate. There were no consistent patterns to the relationship between DWM and yields. In some instances, yields increased on the managed fields, and in others, yields decreased. Because of confounding factors, such as weather and topography, studies of longer duration are required to determine the effect of DWM on yield.

Dealing With Uncertainty When Assessing Fish Passage Through Culvert Road Crossings

Assessing the passage of aquatic organisms through culvert road crossings has become increasingly common in efforts to restore stream habitat. Several federal and state agencies and local stakeholders have adopted assessment approaches based on literature-derived criteria for culvert impassability. However, criteria differ and are typically specific to larger-bodied fishes. In an analysis to prioritize culverts for remediation to benefit imperiled, small-bodied fishes in the Upper Coosa River system in the southeastern United States, we assessed the sensitivity of prioritization to the use of differing but plausible criteria for culvert impassability. Using measurements at 256 road crossings, we assessed culvert impassability using four alternative criteria sets represented in Bayesian belief networks. Two criteria sets scored culverts as either passable or impassable based on alternative thresholds of culvert characteristics (outlet elevation, baseflow water velocity). Two additional criteria sets incorporated uncertainty concerning ability of small-bodied fishes to pass through culverts and estimated a probability of culvert impassability. To prioritize culverts for remediation, we combined estimated culvert impassability with culvert position in the stream network relative to other barriers to compute prospective gain in connected stream habitat for the target fish species. Although four culverts ranked highly for remediation regardless of which criteria were used to assess impassability, other culverts differed widely in priority depending on criteria. Our results emphasize the value of explicitly incorporating uncertainty into criteria underlying remediation decisions. Comparing outcomes among alternative, plausible criteria may also help to identify research most needed to narrow management uncertainty.

Effects of Flood on Thermal Structure of a Stratified Reservoir

An important factor in aquatic environment is water temperature, which influence many important processes in an aquatic ecosystem. In this paper, a 3-D model of thermal-hydrodynamic was developed to simulate the thermal structure in stratified reservoir, taking YE reservoir, a typical canyon reservoir in south-west China as an example. The simulated results showed that YE reservoir is a stratified reservoir, and water column in reservoir have two overturning periods per year separated by periods of stratification. In this case, 7-days flood process (from Jul.17th to Jul.23th) during the normal flow year was taken as a inflow charge, the results showed if the temperature of flood is the same as that of the outflow from the reservoir, the thermal structure will maintain the former status, and if the temperature of flood is lower than that of the outflow, the flood will cause thermocline erosion to some extent. And in this case, the effect time can last two months. By changing the outlet location, simulations demonstrate that the outlet elevation is the main factor controlling the thermal structure in YE reservoir.

Valley network-fed, open-basin lakes on Mars: Distribution and implications for Noachian surface and subsurface hydrology

A new catalog of 210 open-basin lakes (lakes with outlet valleys) fed by valley networks shows that they are widely distributed in the Noachian uplands of Mars. In order for an outlet valley to form, water must have ponded in the basin to at least the level of the outlet. We use this relationship and the present topography to directly estimate the minimum amount of water necessary to flood these basins in the past. The volumes derived for the largest lakes ( ∼ 3 × 10 4 to ∼ 2 × 10 5 km 3 ) are comparable to the largest lakes and small seas on modern Earth, such as the Caspian Sea, Black Sea, and Lake Baikal. We determine a variety of other morphometric properties of these lakes and their catchments (lake area, mean depth, volume, shoreline development, outlet elevation, and watershed area). Most candidate lakes have volumes proportional to and commensurate with their watershed area, consistent with precipitation as their primary source. However, other lakes have volumes that are anomalously large relative to their watershed areas, implying that groundwater may have been important in their filling. Candidate groundwater-sourced lakes are generally concentrated in the Arabia Terra region but also include the Eridania basin [Irwin, R.P., Howard, A.D., Maxwell, T.A., 2004a. J. Geophys. Res. 109, doi: 10.1029/2004JE002287. E12009; Irwin, R.P., Watters, T.R., Howard, A.D. Zimbelman, J.R., 2004b. J. Geophys. Res. 109, doi: 10.1029/2004JE002248. E09011] and several lakes near the dichotomy boundary. This areal distribution is broadly consistent with where groundwater should have reached the surface as predicted by current models. Both surface runoff and groundwater flow appear to have been important sources for lakes and lake chains, suggesting a vertically integrated hydrological system, the absence of a global cryosphere, and direct communication between the surface and subsurface hydrosphere of early Mars.

Stratified flow through outlets

Experimental and theoretical studies of stratified flow through outlets are reviewed, focusing on limiting height of aspiration, withdrawal layer thickness, and outflow concentration. First, a new non-dimensional criterion for limiting height of aspiration is proposed. It is found that this non-dimensional criterion changes only slightly for different kinds of selective withdrawal, including two-layer flow and linearly stratified flow through outlets at different levels. Therefore, if the salinity of density current and the outflow discharge are known, the limiting height of aspiration or the withdrawal layer thickness can be estimated. Second, characteristics of the outflow concentration of turbid density currents through outlets are studied. Based on the field observations in Sanmenxia Reservoir and Guanting Reservoir in China, as well as a number of laboratory experimental data from outlets in vertical walls and bottom outlets, a simplified model is developed to analyze the empirical relationship between outflow concentration and several critical parameters including outflow discharge, inflow sediment concentration, interface elevation, and outlet elevation. These research findings are readily applicable for outlet design, especially in sediment-laden waters.

Evaluation of the reduction in the water storage capacity of Black Lake, AK

The paper provides a systematic evaluation of the causes that trigger reduction of a lake's water storage volume. This evaluation is demonstrated herein through combined numerical analysis and field work conducted on the south side of the Alaska Peninsula to address the reduction in the water storage volume of Black Lake. The contribution of this research was the development of an integrated approach that adequately quantifies the causes of reduction of water storage volume of lakes. For this purpose, a set of established routing, erosion, riverine, and lake models were integrated to identify quantitatively the causes of the Black Lake water storage reduction. Selection of the models was a compromise between their complexity, compatibility, capability, and available input data. The results of this study suggest that contrary to what has been long thought the lake receives sufficient water influx to maintain its maximum storage capacity. In addition, sedimentation was not found to the cause, because siltation since 1950 has reduced the storage capacity by only 1.0%. The reduction in the lake storage was mainly attributed to severe degradation at the lake outlet. The outlet elevation of the lake has decreased by at least 1.0 m over the past 55 years. This study recommended that a gated weir could be used as a control structure to maintain the elevation at the lake's outlet. In addition, an erosion model predicted that the lake may loose 80% of its current storage capacity within a 100‐year period causing a complete destruction of the ecosystem, if no action is taken.

An integrated framework of lake‐stream connectivity for a semi‐arid, subarctic environment

AbstractLake‐stream networks dominate the semi‐arid, subarctic Precambrian shield. Such a network consists of a number of lake basin elements linked to each other by surface channels. To investigate the processes causing seasonal severance of flow connection in the lake‐stream system, a chain of lakes in northern Canada was studied in 2004. Water balance shows that rapid and substantial runoff from the local basin slopes during the snowmelt period led to a rise of lake levels above their outlet elevations to generate outflow. Continued summer evaporation caused draw down of lake storage below the outflow thresholds, represented by the lake outlet elevations. Outflow ceased and the lakes became disconnected. Summer rainfall in a semi‐arid environment was insufficient to overcome storage deficit to re‐establish flow connectivity among all lakes. For the drainage system as a whole, streamflow interruption or continuity depends on the linkage of its lake‐stream sub‐units. The principle of fill and spill governs runoff generation and flow connection between the lake elements. This principle is applied to a conceptual model of flow along a chain of lakes, taking account of (1) antecedent storage in individual lakes, (2) their storage change calculated through water balance and (3) the thresholds to be exceeded for outflows to occur. Copyright © 2007 John Wiley & Sons, Ltd.

Glacial Lake Agassiz: A 5000 yr history of change and its relationship to the δ18O record of Greenland

Lake Agassiz was the largest lake in North America during the last period of deglaciation; the lake extended over a total of 1.5 × 10 6 km 2 before it drained at ca. 7.7 14 C ka (8.4 cal. [calendar] ka). New computer reconstructions—controlled by beaches, isostatic rebound data, the margin of the Laurentide Ice Sheet, outlet elevations, and a digital elevation model (DEM) of modern topographic data—show how variable the size and depth of this lake were during its 4000 14 C yr (5000 cal. yr) history. Abrupt reductions in lake level, ranging from 8 to 110 m, occurred on at least 18 occasions when new outlets were opened, reducing the extent of the lake and sending large outbursts of water to the oceans. Three of the largest outbursts correlate closely in time with the start of large δ 18 O excursions in the isotopic records of the Greenland ice cap, suggesting that those freshwaters may have had an impact on thermohaline circulation and, in turn, on climate.

The thermal structure of Sau Reservoir (NE: Spain): a simulation approach

In this study, a 1D model of reservoir hydrodynamics DYRESM has been applied to Sau Reservoir, a river valley reservoir in the North-Eastern Spain. Simulation is undertaken for 3 years (1995–1997). Meteorological input data measured at the dam are only available from May of 1997. In this case the simulation results fit measured temperatures very well. In the remaining periods, some meteorological data (radiation, wind and rainfall) were obtained from two nearby stations. Simulated temperature distribution in 1996 is close to the observed one. In 1995, however, the simulated result is far from the observed data. Inflows , outflow and local meteorological events such as storms and gusts of wind seem to be responsible for the differences. By changing some parameters, the effects of flow, light extinction coefficient and outlet elevation on thermal stratification are investigated. Simulations demonstrate that the inflow with high temperature is the main factor controlling the thermal structure in Sau Reservoir and demonstrate that the effect of residence time on thermal stratification is manifested mainly by the changes in the depth of thermocline.

Investigation of break location effects on thermal-hydraulics during intermediate break loss-of-coolant accident experiments at ROSA-III.

The rig of safety assessment (ROSA)-III facility is a volumetrically scaled (1/424) boiling water reactor (BWR/6) system with an electrically heated core designed for integral loss-of-coolant accident (LOCA) and emergency core cooling system (ECCS) tests. Break location effects on thermal-hydraulics during intermediate LOCAs were investigated by using four experiments at the ROSA-III, the 15 and 25% main recirculation pump suction line break (MRPS-B) experiments, the 21% single-ended jet pump drive line break (JPD-B) experiment and the 15% main steam line break (MSL-B) experiment. Water injection from the high pressure core spray (HPCS) was not used in any of the experiments. Failure of ECCS actuation by the high containment pressure was also assumed in the tests. In the MRPS-B experiments, the discharge flow turned from low quality fluid to high quality fluid when the downcomer water level dropped to the main recirculation line outlet elevation, which suppressed coolant loss from the vessel and the core. In the JPD-B experiment, the jet pump drive nozzle was covered with low quality fluid and low quality fluid discharge continued even after the downcomer water level reached the jet pump suction elevation. Low quality fluid discharge ceased after the ADS actuation. It suggestes that the JPD-B LOCA has the possibility of causing larger and more severe core dryout and cladding temperature excursion than the MRPS-B LOCA. The MSL-B LOCA was characterized by mixture level swell in the downcomer and the core. The core mixture level swell resulted in the much later core dryout initiation than that in the MRPS-B LOCA, however, ECCS actuation was also delayed because of slow downcomer water level drop.

An Open Ditch Surge Flow Furrow Irrigation System

AN automated rotating gate enabled an existing open channel furrow irrigation system to be adapted to surge flow. Equipment performance was quite reliable. System hydraulics were analyzed with respect to unequal outlet elevations, spatially varied flow within an irrigation bay, and unsteady flow due to the opening or closing of the automated gate. System design considerations are presented.