Large Water Level Research Articles

SU‐GG‐T‐294: A New Cone‐Beam CT Daily QA Phantom for Stereotactic Radiosurgery

Purpose: In Stereotactic Radiosurgery (SRS), sub‐milimeter accuracy for patient setup is necessary. We developed a phantom for SRS using CBCT for patient alignment. Method and Materials: The phantom is a semi‐spherical shaped acrylic with the dimension of 11 cm diameter and 12 cm height. It consists of four sections: hollow cone‐shaped top, house‐made large water level, metal target supporter with 15 mm diameter stainless steel ball target and hollow cone offset between radiation and mechanical axis of the CT canner. The bottom of the phantom is attached to a frame that can be placed on treatment table of the linear accelerator. The phantom was scanned by using diagnose CT and exported to the ADAC Pinnacle planning computer. The phantom is then aligned by using lasers and CBCT images are taken. The image correlation was carried by comparing external contours of the phantom itself and two contours of the chamber in the phantom. Results: The geometrical accuracy of the stereotactic radiosurgery system using the CBCT as secondary double check was investigated over 8 different gantry angles and table rotations, and their average uncertainty is approximately 0.5 mm in three major orientations with maximum 0.8mm errors. Four physicists were asked to do image fusion, intra‐user variations were less than 0.25mm. The dosimetric uncertainties of 75% isodose volumes were also evaluated. Between planning computer and film irradiation, the uncertainties were less than 1 mm in three major axis. Conclusion: The CT and CBCT images can be correlated with 0.5mm steps. The daily QA phantom was very effective to investigate any systematic errors including CT images, planning procedure, geometrical uncertainty of CBCT, and gantry flex of the linear accelerator. The unique geometrical features of the phantom provide minimum intra‐user variations with 0.5mm uncertainty, which is comparable to the setup uncertainty of the laser.

Plant-associated invertebrates and hydrological balance in the large volcanic Lake Bracciano (Central Italy) during two years with different water levels

Lakes in the Mediterranean region experience an altered hydrological balance with large water level reductions and/or fluctuations within and between years. To date, little is known about the reaction of invertebrate assemblages inhabiting the littoral zone to water level changes in natural lakes. Here, we present the case of the volcanic Lake Bracciano, one of the largest and deepest Italian lakes. We compared the numerical composition and taxonomic richness of plant-associated invertebrate assemblages sampled from three sites and three depth ranges (0–4 m, 4–8 m and 8–15 m) between years with different water levels. Using historical data, we built a hydrological balance model to assess the role of different water budget components on the water levels. The hydrological balance showed that the volume of water currently abstracted for human use exceeds the potential changes caused by the projected warming of climate and decreasing amount of precipitation by nearly an order of magnitude. In a low water level year, littoral macrophytes and invertebrate assemblages exhibited qualitative and quantitative differences at all sampling sites and depths. The invertebrate assemblage showed a reduced taxonomic richness and lower numerical abundance of the more sessile forms (water mites, gastropods, nematodes, naidid oligochaetes), which feed directly on living plants or epiphytic algae, and an increase of more mobile and/or detritivore taxa.

Mediterranean Sea level variations during the Messinian salinity crisis

The Mediterranean Basin has not always been connected to the Atlantic Ocean. During the Messinian salinity crisis (MSC), the Mediterranean Sea became progressively isolated by a complex combination of tectonic and glacio‐eustatic processes. When isolated, the Mediterranean water level depends on the hydrological flux and is expected to vary significantly. The amplitude and number of large water level fluctuations in the isolated Mediterranean is still controversial, despite numerous geological investigations. The observation of 3–5 surfaces of erosion in the Nile delta (Eastern Basin) provides new elements for understanding the dynamics of the MSC. Our model demonstrates that numerous water level falls of short duration may explain the preservation of a discontinuous river profile at ∼−500 m and ∼−1500 m in the Western Basin, as well as the existence of deep surfaces of erosion in the Eastern Basin.

The Environmental Bank Protection Plan in a Drainage Pump Station with Large and Frequent Water Level Changes

The Environmental Bank Protection Plan in a Drainage Pump Station with Large and Frequent Water Level Changes

OSL chronology for a sediment core from the southern Baltic Sea: A continuous sedimentation record since deglaciation

A chronology based on optically stimulated luminescence (OSL) dating is presented for the late- and post-glacial evolution of the southern Baltic Sea (∼15 ka to present). During this period, large water level and salinity changes occurred in the Baltic Basin due to opening and closing of connections to the North Atlantic. Previous attempts to establish a chronology for these palaeoenvironmental changes have mainly been conducted in coastal settings where organic material for 14C dating is abundant. Many of these records are, however, discontinuous due to the large water level fluctuations. In contrast, in the relatively deep water of the Arkona Basin, the sediment record is expected to be more or less continuous. The single aliquot regenerative dose (SAR) procedure was used to date 32 samples of fine quartz sand from a 10.86 m long sediment core from the centre of this basin (45 m water depth). Tests of luminescence characteristics confirmed the suitability of the material for OSL dating and the ages agree well with the available AMS 14C ages on shells. The Baltic Ice Lake drainage to the North Atlantic appears to occur ∼11.6 ka, agreeing with other published evidence. However, we suggest that the main marine Littorina transgression appears in the Arkona Basin at about 6.5 ka, rather than at 8.5 ka, as previously thought.

Understanding and managing the stressed Mexico-USA transboundary Hueco bolson aquifer in the El Paso del Norte region as a complex system

As the latest drought has swept over the southwestern United States, most local and regional water providers have had to rely on ground water to meet their water demands as surface water supplies have diminished. In areas near major population centers this situation has continued to put strain and stress on already over-drafted regional aquifers. Metropolitan centers throughout the southwestern United States, as exemplified by Las Vegas, Nevada; Phoenix and Tucson, Arizona; and El Paso, Texas, have a history of over drafting their available ground water resources. How these stressed aquifers should be managed is an urgent issue. In El Paso, Texas long-term groundwater mining in the transboundary Hueco bolson aquifer has resulted in large water level drawdowns within the basin, particularly in several well fields. This situation has promoted the intrusion of brackish water into fresh water zones, and consequently reduced the volume of fresh water stored in the aquifer. Management of this aquifer is made more complex as the water resources of the region are shared across the United States/Mexico boundary and the transboundary region continues to grow rapidly. This paper describes the current situation within the Hueco bolson due to over drafting and continued reliance on the fresh water in storage and describes how understanding the dynamics of the aquifer as a complex system can offer managerial perspectives that can be used to establish operational procedures and programs for bringing drawdowns into equilibrium, increasing the longevity of the aquifer, gradually restoring water quality, and offering the hope of utilization of the resource in a sustainable manner.

Short Term Storm Surge Forecasting

This paper discusses storm surge water levels along with exploratory data analysis, development of event magnitudes for characteristic surge return periods, and sort term forecasting potential of surge water levels using localized linear techniques. The area considered is a location in the New York-Long Island (N.Y.-L.I.) area. The short term local linear forecasting of storm surge water level is found to be meaningful for time periods on the order of 1–2 hours using only water level information without additional meteorological information. Characteristics of the historically large surge events for both Northeasters and Hurricanes are also discussed in the paper along with potential of local linear forecasting to provide useful information for various types of large water level events. The limited forecasting study is a first step in a planned broader assessment of forecasting future storm water levels for emergency management knowledge and planning.

COMPARATIVE STUDY IN WATER RESOURCES DEVELOPMENT OF WESTERN REGIONS IN THE U.S. AND CHINA

This article identifies some challenges and opportunities in water resources development that the U.S. hasexperienced and that China is experiencing during the development of its western regions. Due to lack of long-term regionalwater resources planning and management policies, many aquifers in the western region of the U.S., such as in Arizona,California, Colorado, Nevada, New Mexico, and Texas, have been experiencing large water level drawdowns, reduction ofstream flow, land subsidence, earth fissures, and deterioration of water quality caused by overdraft of groundwater. To addressthese challenges, measures such as the conjunctive use of surface water and groundwater to reduce pumping stresses ofaquifers, aquifer storage and recovery (ASR) systems to replenish stressed aquifers, and regulatory changes to enhancelong-term resources planning and management have been taken. By comparing water resources conditions in the westernregion of China with those in the U.S., it is clear that China will face challenges in water resources development similar towhat the U.S. has already experienced. By examining this experience, water development in western China may better sustaingrowth and reduce negative impacts. For example, conjunctive uses of surface water and groundwater can reduce stresseson regional aquifers. With the enforcement of new water laws in China, institutions in charge of water resources distributioncan play more active roles in water planning and management. Further, more comprehensive comparative studies of waterresources development in the U.S. and China are recommended so that both nations can benefit by sharing experience andknowledge as both nations tackle this critical issue.

ボスポラス海峡横断鉄道トンネル建設工事の施工支援ツールとしての３次元流動シミュレーション

The immersed tunnel crossing the Bosphorus Strait located in Istanbul, Turkey, is under construction. It is known that the current field of the Bosphorus Strait is complicated. It has two-layer flow of surface southward and bottom northward. In this paper, the numerical hydrodynamic simulation, which is carried out to clarify the current structure, is described. This simulation results are used for construction assistance system.For the simulation, the salinity and temperature boundary conditions of both northern and southern ends of the strait are vertically given as step function. The simulation results agree with monitoring results well. Through the simulation, following results are found out. Large water level difference between both ends of the strait causes the increase of the current speed of both surface and bottom layers. However, in one range of the water level difference, the maximum current speed of the surface layer reaches a constant value of 1.8 m/s approximately. The current structure is mainly ruled by the shape of the density interface.

Dual porosity mechanism for transient groundwater and gas anomalies induced by external forcing

The geochemical response of groundwater to external forcing is studied in a tunnel hosted in fractured gneiss near and above an artificial lake having large water level variations. Dripping waters have been monitored in two zones characterized by highly different flow rates representing different contributions of water from matrix porosity and fractures. Transient increases of sulfate and magnesium concentrations, observed in both zones, are not related to meteorology but associated with radon bursts into the tunnel air. This indicates that transient enhancement of conductance, with discharges of saline water and radon from the matrix porosity to the fractures, is a mechanism able to produce both groundwater and gas anomalies, in response to hydrogeological or mechanical processes such as increases in pore pressure or changes in crack geometry. Besides its applications to environmental issues, the proposed discharge mechanism may be relevant for the understanding of geochemical precursors of earthquakes, as an alternative to aquifer mixing.

Over twenty years trend of chloride ion concentration in Lake Biwa

Recent increase of chloride ion concentration in Lake Biwa was considered. Over the past 20 years' data at the North Basin of Lake Biwa showed that chloride ion concentration has been continuously increasing from 7.4 to 9.9 mg l-1 at 0.5 m depth from lake surface and from 7.3 to 9.9 mg l-1 above the bottom (depth of over 80 m from lake surface). This low level salinity indicated, however, about 35% increase through 20 years. In this paper, we reported the trend and the tendency of chloride ion concentration at some locations and the change of climatic data through 20 years in Lake Biwa. In a short period within one year, chloride ion concentration clearly fluctuated in the upper water layer. This fluctuation was mostly influenced by precipitation. Similar trend of chloride ion concentration could be seen in the South Basin of Lake Biwa with much higher concentration than that in the North Basin. We also discussed the long-term changes of chloride concentrations in 5 major rivers with large catchment area, water level and precipitation. The data of river discharge indicated that some rivers in the southern part of the North Basin in Lake Biwa contain a relatively high chloride concentration compared with others. Furthermore, we proposed a simple conceptual model with variable outflow and inflow fluxes. This conceptual model expressed an amount of chloride budget. We estimated the average chloride flux flowing from the watershed into Lake Biwa using the data of chloride ion concentration in the lake and the data of water discharge from the lake. Comparing the results of the model analysis with the data of 12 major rivers contributing large flux to Lake Biwa, we suggested that river inflow is one of the major sources to induce the increase of chloride ion concentration in the lake, and the inflow from non-point source can be also important sources.

Dynamic Model for Monitoring Landslides with Emphasis on Underground Water in Trabzon Province, Northeastern Turkey

The aim of this study is to form a dynamic deformation model for landslides. Static and kinematic models used in practice in determining movements do not deal with the mechanical characteristics of the object and the deformation mechanism. They may yield misleading results in interpreting movements. In contrast, dynamic deformation models determine movements regarding the mechanical characteristics of the object and the deformation mechanism. In this study, a dynamic model reflecting the effect of the cause of movement for landslides was used for determining movements. For this purpose, the modeling of the effect of heavy rainfall and large underground water level changes in activating landslides was investigated. A test network was established in a slide area in Macka County in the province of Trabzon in the northeast of Turkey. The coordinates of network points were computed with geodetic measurements. Underground water levels of the network points were determined with geological and geophysical measurements. Using these data, movements were determined with both kinematic and dynamic models. Results of both models were compared to each other. It was concluded that determining movements with the dynamic model was more suitable than using the kinematic model in landslide studies. It was also concluded that, regarding the difficulties in its construction, the dynamic model should be preferred in cases where human life is in serious danger. As another result of this study, it is shown that before interpreting movements of network points, it is necessary to detect slip surfaces on the study area and then perform the interpretation according to these slip surfaces.

Phytoplankton response to changed nutrient level in Lake Peipsi (Estonia) in 1992–2001

In the 1990s, the nutrient load from the catchment area, carried into the large shallow eutrophic Lake Peipsi (area 3555 km 2 ), diminished in comparison with the 1980s. The aim of the investigation was to analyse statistically biotic response to alterations in nutrient level in the lake following the reduction in external loading. In-lake changes of the relationship between phosphorus and nitrogen compounds and phytoplankton were analysed for 10 years (1992–2001). The content of biogenic elements (total phosphorus, orthophosphate, total nitrogen and ammonia) indicated a decrease and thereafter a stabilization of the parameter values during the observation period. An opposite trend was observed for the nitrite and nitrate ions. The lowest Ntot:Ptot ratio (about 11–13) was registered in 1995–96. However, despite a definite decrease of the nutrient level, the biomass of phytoplankton (particularly cyanobacteria) displayed an increasing trend. Strong and long-lasting (up to October–November) algal blooms were noted in recent years. The structure of the phytoplankton community changed considerably: the share of cyanobacteria (particularly, heterocystous forms) demanding less nutrients increased while the contribution of chlorophytes decreased. The amount of nutrients per biomass unit of different phytoplankton groups decreased. Water level appears to be a significant factor affecting the content of dissolved inorganic nutrients. In particular, NO3N increased and PO4P decreased at higher water level. Large inter-annual water level fluctuations will decrease stability of the ecosystem.

Moving Boundary Level Model for Flow with Large Water Level Change

Moving Boundary Level Model for Flow with Large Water Level Change

The Effects of Frozen Soils on Groundwater Recharge and Discharge in Granitic Rock Terrane of the Canadian Shield

Hydrologic measurements on groundwater flow systems of the Canadian Shield during the winter period provide insight into groundwater dynamics and can support conclusions based on measurements of the more “active” spring-to-fall, open-water period. To illustrate this, we present the results of detailed and continuous year-round measurements of parameters such as groundwater levels, air/soil temperatures, soil heat flux and soil moisture content which were made in upland recharge and wetland discharge areas of a local groundwater flow system in granitic terrane of the Canadian Shield. Recharge to the groundwater flow system in the rocks of the study area occurs as rain or snowmelt waters infiltrate exposed vertical and/or sub-horizontal soil-infilled fractures in outcrops of the upland area. During winter, soils in the fractures of the recharge area do not normally freeze below 0.5 m depth and shallow (5-20 cm depth) soil temperatures are most often only 1-2°C below freezing. During the spring melt period the temperature of these frozen soils remains near 0°C for several weeks as the pore ice absorbs thermal energy necessary for the phase transition from ice to water. However, despite these soils being completely or partially frozen, infiltration and recharge to the groundwater flow system in the rock occurs as shown by large and rapid rises in watertable and piezometric levels. In the groundwater discharge area of this flow system, near-surface soil temperatures (5 cm depth) reached minimums of about -12°C during the 1996 winter and freezing soils extended downward to more than 75 cm depth. During the spring melt period, as meltwaters add heat to the substrate, these shallow soil temperatures also, rise to near 0°C and remain frozen for several weeks as latent heat of fusion of ice becomes a factor. However, during the spring melt period, while ice covers ithe surface and soils are still frozen in the discharge area, groundwater level rises are recorded in both the overburden and bedrock of the discharge area. This is attributed to hydraulic pressure being rapidly transmitted to the discharge area through the low storativity groundwater flow system in the rock from the large waterlevel increases occurring in the rock of the adjacent upland recharge area.

Continental lake level variations from Topex/Poseidon (1993–1996)

The water level of continental lakes fluctuates due to variations in evaporation and precipitation within their catchment basin in response to regional climatic changes. With satellite altimetry, lake level variations can now he monitored almost continuously with a precision of a few centimeters. In this note, we present water level changes of three American Great Lakes (Superior, Michigan and Huron) and three African lakes (Tanganyika. Malawi and Turkana) based on 4 years (1993–1996) of altimetry data of the Topex/Poseidon (T/P) satellite. The levels of these lakes show a dominant annual cycle highly correlated with precipitations. American Great Lakes are regulated, hence present little interannual variations. This is unlike African lakes which markedly respond to regional (possibly global) climatic changes. A large water level decrease of lakes Tanganyika and Malawi (≥ 20 cm.yr −1) is observed by T/P for 1993–1996. This trend is associated with recurrent droughts recorded in East and South Africa since the early 1990s, as a result of the series of recent ENSO events.

Numerical experiments on low-frequency fluctuations on a submerged coastal reef

Low-frequency fluctuations on a reef coast are studied through a numerical model based on nonlinear conservation equations of mass and momentum. The model is used to investigate the long wave generation and propagation phenomena under both breaking and non-breaking incident short wave groups. The effects of incident wave characteristics and reef topography on the long wave phenomena are discussed. The results show that the long wave elevations on reef coasts are substantial, which explains the large water level fluctuations observed at certain occasions.

Numerical simulation of overbank flood discharges

AbstractA full computer based investigation of the factors influencing the modelling of overbank flood discharges has been carried out. Several floods of differing magnitudes and peak curvatures were routed down regular channels using an implicit finite difference scheme and the influence of time and distance steps used for the numerical solution of the flow equations were investigated.Spillage over sharp crested weirs was assumed to satisfactorily simulate the overbank flood discharge; the importance of a correct estimation of the coefficient of discharge was also checked. It was shown that sensibly chosen values of the time step had little effect on the simulations. This was also true for the value of the coefficient of discharge when the sideweir flow was predominately drowned, but not for free flow conditions. It was also shown that close spacing of computational nodes was required at the onset of overbank flow to accurately simulate the overflow and also model the occurrence of large water level gradients.

Large amplitude water level oscillations in throttled surge tanks

After a theoretical analysis of system singularities, and normalized equations describing the water-level motion in the throttled surge tank of a hydropower plant are solved on a digital computer. The critical stability conditions for large amplitude oscillations are obtained by finding the conditions under which the initial state point of the system is, in the terminology of the phase plane method, on the limit cycle. The paper demonstrates the possibility of the existence of 2 limit cycles around the singularity representing the steady operating point and the feasibility of the adoption of surge tanks with a section smaller than Thoma critical value.

Automatic filling and emptying of a water evaporation pan

The class A pan is used universally to estimate water evaporation for large reservoir water level control, for irrigation purposes, for predicting field drying of agricultural crops or simply for water budget calculations. Water level can be monitored automatically with a floating-type water level gage. However, it is important to re-establish the water level at a standard height each day. A control module with inflow and outflow solenoid valves was designed and adapted to a class A pan to correct the water level at a fixed time interval defined by the user. The water level was brought back to the standard level within 5 or 6 min after typical daily rainfall or evaporation. The system was stable provided the error tolerance was above the accuracy of the water level gage (±0.2 mm in the present system).