Most dams have a low-level outlet that consists of a closed conduit through the dam with a slide gate or valve to regulate flow. These outlets are used mainly for irrigational purposes but also for flushing the reservoir and controlling the reservoir elevation. When discharging through the low-level outlet works, negative pressures can develop on the downstream side of the gate creating a potential for cavitation damage and vibration. To minimize these effects, air vents (vented to the atmosphere) are installed on the downstream side of the gate to limit downstream pressure to something above vapor pressure (i.e., near atmospheric pressure). Previous air venting studies have been mostly limited to large dam outlet geometries, which typically feature a vertical gate in a flat-bottomed discharge tunnel. The large-dam air demand analysis has been based on the Froude number of the supercritical flow at the vena contract (located between the gate and the hydraulic jump) and the water flow rate. Small to medium-sized embankment dams typically utilize a slide gate installed on the sloped upstream face for flow control, followed by a vertical elbow connected to a sloping pipe. With this outlet geometry, there is no 1-D vena contracta flow, no classical hydraulic jump, and no representative Froude number. Additionally, no head-discharge characteristic data have been found for inclined slide gates (vented or non-vented) for small to medium-sized dams. Consequently, unless a flow measurement structure is installed in the discharge channel downstream of the dam, determining the water discharge rate based on gate opening and head on the gate, and consequently the air demand is problematic. This study focuses on quantifying air demand and air vent sizing for the small to medium-sized embankment dam low-level outlet geometries by providing: 1. Cd values as a function of gate openings and air demand; to better estimate flow rates from outlet works of similar geometries. 2. Flow conditions for varying operating conditions. 3. A new relationship for sizing air vents as a function of driving head and gate opening. 4. The magnitude of negative pressures for non-vented conduits. 5. A foundation for future studies and development of air demand research. This thesis presents the findings of this study.

The purpose of this research was to investigate the hydraulic performance of stepped spillways. A thorough investigation was made of all printed material on stepped spillways, and a summary of this material is presented in the text. Data from experiments in the laboratory were used to develop a design procedure for stepped spillways and hydraulic jump stilling basins. The experimental study was conducted at Utah State University - Utah Water Research Laboratory in Logan, Utah. Four models were built and tested in the laboratory under various flowrates. The crest of the model spillway was constructed in the shape of a standard USBR nappe-shaped crest. Small steps were fitted to the crest so that the envelope of their tips just intersected the crest profile. These small steps allowed a smooth transition of the flow from the nappe-shaped crest to the constant slope region. Two slopes were tested in the research: 0.7H:1.0V and 0.5H:1.0V. At each of these slopes two sizes of steps were tested. Steps did not very in size down the face of the model, although step sizes varied on the different models. The model height and steps tested were for a dam with a prototype height of over 67 feet and steps in the 1-2 foot range. Diagrams and pictures of the four models tested are included in the text and appendix. Findings from the research showed that given a ratio of step height over critical depth (0.1201.897, the energy dissipation will remain in the 90% region, although there might be problems with the flow leaping away from the structure. Data on the models were slightly scattered, but all of the data from the four models agree to one energy loss graph. Support for these data showed a nearly perfect correlation in the downstream conjugate depths on all four models at similar flowrates. By using data obtained from the models and literature, a design process with guidelines for designing a stepped spillway is presented. This process includes crest design and step displacement in the transition region, approximate step size, and approximate slope necessary for adequate operation of the stepped spillway. By taking data collected from the models, and data from USBR design manuals for smooth spillways, a spreadsheet design process was created that compared the size of stilling basins required using either a smooth spillway or a stepped one. Results showed that given a unit flowrate range of 15 cfs/ft to 140 cfs/ft and spillway height of approximately 100 ft, the stilling basin volume was reduced by 62% to 43% respectively. This size reduction can translate to a considerable cost savings in prototype construction. This study, along with data from other researchers, has proven that a stepped spillway can greatly increase the amount of energy dissipation over that achieved on a standard smooth face spillway. The stepped concept can be used as an excellent energy dissipator and in some cases can totally remove the need for any type of dissipator at the toe of the spillway.

The probable maximum flood (PMF) is used for the xxi assessment of maximum flood potentials in spillway sizing of new dams and in evaluating the adequacy of existing hydrologic structures. Determination of the PMF begins with the estimation of the probable maximum precipitation (PMP) for a particular dam site. Selecting hydrologic methods and assumptions for converting PMP to PMF, which are most appropriate for Utah conditions, is important to meet current inflow design flood (IDF) safety standards. The objectives of this study were (a) to demonstrate a maximization approach to PMF determination, (b) to evaluate effects of basin characteristics and isohyetal or uniform rainfall pattern on PMP and hence PMF, (c) to evaluate uncertainties due to hydrologic procedures through sensitivity studies, (d) to analyze historical events for indications of actual loss rates, (e) to analyze historical snowpack and melt conditions for critical snowmelt conditions, (f) to assess implications of this study for a degree of conservatism index, and (g) to evaluate the implications of the study for the selection of procedures for PMF determinations. A sensitivity study was conducted to evaluate the hydrologic methods and assumptions (e.g., loss rates, unit hydrographs, basin subdivision, temporal storm distribution, flood routing, and antecedent events) which may be used in northern Utah PMF studies. The maximization of local storm PMF produced a higher peak reservoir stage than using basin average PMP only. Evaluation of effects of basin characteristics on PMF showed that local storm PMP is critical for basins up to about 2,000 square miles in northern Utah. Estimation of maximum probable rain-on-snow flood conditions for Porcupine Basin for April, May, and June revealed that there are significant increases in peak flows and flood volumes due to the contribution of snowmelt in the months of May and June. The results from the degree of conservatism assessment performed on local storm PMF estimates for Porcupine Basin showed that the overall effect of assumptions made and procedures followed in a typical PMF determination is almost certainly a conservative estimate.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Civil Engineering, 1980. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Bibliography: leaves 121-123. / by Gary E.B. Choot. / M.S.

京都大学 / 0048 / 新制・論文博士 / 博士(地球環境学) / 乙第12901号 / 論地環博第11号 / 新制||地環||26(附属図書館) / 31655 / (主査)教授 渡邉 紹裕, 教授 宇佐美 誠, 准教授 小林 広英 / 学位規則第4条第2項該当 / Doctor of Global Environmental Studies / Kyoto University / DFAM

Student Number : 9612464Y - MSc dissertation - School of Mining Engineering - Faculty of Engineering and the Built Environment / This study was conducted at the West Rand Region, part of South African-based AngloGold operations. The study assesses the impacts of gold mining on the water quality and the change in landuse resulting from the mining activities on the West Rand Region. This was achieved by collecting historical data relating to the tailings dams and both surface and groundwater qualities between 1998 and 2003. The landuse information was gathered from the topographic map of Carltonville and remotely sensed data in the form of aerial photographs, landsat data and ASTER images. The data was analysed in a GIS ILWIS. The sizes of the tailings dams have not changed significantly during the study period. The size of the plantation also shows a decreasing trend due to pollution from the tailings dams. The area surrounding the Anglo Gold mining operations is sparsely-vegetated due to both poor soils and the impacts of mining activities. The surface water quality is poor and this water has negative impacts on the environment following accidental discharges and has potential negative impacts from seepage through the unlined dams. The quality of the groundwater is generally good with the exceptions of BH 18, MBH 8, MBH 5 and MBH 3 whose pollution arises from North mine tailings dams and North boundary dam. MBH 5 shows an improvement in water quality over time. The potential generation of AMD from the tailings dams is inhibited by the neutral pH of the tailings. In order to improve the environment in the West Rand Region and to prevent further pollution, planting of indigenous trees to make up for shrinking plantation and lining of the dams be undertaken. Stricter maintenance and monitoring of both the sewage plants and the dams be implemented to avoid accidental discharges of poor quality water into the environment. A study to accurately quantify the groundwater pollution arising from both the tailings dams and other surface water bodies should be undertaken.

No description available.

Many rivers can shape their path through the landscape with erosion and deposition where the riverbed and riverbanks both shape the direction and energy of the flow. The river flow can erode the riverbanks and create meanders which is when the river creates bends in its path that become increasingly curved. Meanders are affected by natural aspects of the landscape but also by anthropogenic structures like dams. The Rönne river is the largest river in the region of Skåne in southern Sweden and along it is three major dams that act as barriers for fish species. These dams are scheduled to be removed in 2024. To estimate how the Rönne river may react to the removal of these dams, the river’s erosion, deposition, and stream width was studied for the years 1926-1934, 1960, 1970 and 2018. By understanding how the dams have affected the river, it may be possible to argue how the river will change after the dams are removed. Erosion was greatest downstream of the dams but changes to deposition and stream width did not follow the pattern indicative with dams. The dams were not the determining factor and other factors such as land use and surficial geology are more impactful to the morphological changes in the river. Issues with the method and used materials affected and created uncertainty with the results. Improvements and changes are therefore needed for the method and the materials to better determine how the Rönne river is affected by the studied dams.

京都大学 / 新制・課程博士 / 博士(工学) / 甲第24888号 / 工博第5168号 / 新制||工||1987(附属図書館) / 京都大学大学院工学研究科都市社会工学専攻 / (主査)教授 角 哲也, 教授 田中 賢治, 准教授 竹林 洋史 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

The dynamic characteristics of pressurized cylindrical membranes used as dams are considered here. Single-anchored air-inflated membranes are predominantly studied. Load combinations are considered without any water, with impounding water, and with water overflow. The two major experimental variables are the dam's internal pressure and the stream's flow rate or the impounded water height. The existence of upstream water is shown to completely change the dynamic characteristics of the membrane-dam, now a structure-fluid system. Two aspect ratios are considered with the same height, at two separate open-channel facilities. The material used is modeled as an inextensible weightless membrane without any bending stiffness. It is shown that the ratio between the internal pressure head and the upstream water head, identified as the "pressure ratio", is the major controlling parameter. During overflow conditions, the pressure ratio is shown to have a critical value where the energy of vibration maximizes. In addition, the ratio of the upstream water head to the dam's height, identified as the "load ratio", is non-linearly proportional to the vibration's energy level. Both the pressure ratio and the load ratio are shown to be dependent on the model's aspect ratio. The pressure ratio is slightly non-linearly proportional to the natural frequencies of the system, while the load ratio is inversely proportional. Up-scaling of the results follows the Froude law. The source of vibrations either in the form of a driving force or a perturbation force is identified to be at the downstream base of the dam. / Ph. D.