Bottom Seals Research Articles

The hydrodynamics of fields in the Macedon, Pyrenees, and Barrow Sands, Exmouth Sub-basin, Northwest Shelf Australia: identifying seals and compartments

The Barrow Group strata (Macedon Member, Pyrenees Member, and Barrow Group sandstones) of the Exmouth Sub-basin host significant accumulations of gas and liquid hydrocarbons. There is currently oil production from the Macedon sandstone at the Enfield Field and ongoing development drilling at the Stybarrow Field. Active appraisal and exploration is underway, including the multi-field Pyrenees Development. In the course of assessing these discoveries, BHP Billiton and its joint-venture partners have undertaken a hydrodynamic study in order to better understand the sealing mechanisms, the position of free-water levels (FWLs), and the likelihood of compartmentalisation within the discoveries.Whilst the region is faulted with a predominant south-west-north-east grain, the potentiometric gradient is surprisingly flat indicating that the individual sands are hydraulically well connected. Other than the Macedon Gas Field, there is no pressure data that indicate intra-formational seals have been breached. Thus, top and bottom seal capacity is probably not limiting the pool sizes. Rather, structural spill points and fault seal capacity appear the significant factors in determining pool geometry, with the underlying aquifer being regionally connected around fault tips.On the field-scale, the flat hydraulic gradient allows for the calculated FWLs to have a high confidence. Pressure data from the hydrocarbon phases indicate that in some cases, fault zones may compartmentalise a field into multiple pools. These areas are then targeted for additional focused geological analysis to reduce uncertainty in field compartmentalisation. The Macedon Gas Field, on the eastern edge of the play fairway, marks a change in the trapping character with intra-formational and fault seals having been breached resulting in a single continuous gas pool despite internal structural complexity. Stybarrow and Laverda-Skiddaw clearly occur as separate accumulations and the Stybarrow data define a single oil column in contrast to the potentially compartmentalized Laverda-Skiddaw field. Stybarrow represents an anomalously large oil column relative to other fields in the area and it is located on the low hydraulic head side of a sealing fault.

The Hydrodynamics of Fields in the Macedon, Pyrenees and Barrow Sands, Exmouth Sub-Basin: Identifying Seals and Compartments.

The Barrow Group strata (Macedon, Pyrenees and Barrow sands) of the Exmouth Sub-Basin host significant accumulations of gas and liquid hydrocarbons. There is currently production from the Macedon sands at Enfield and ongoing development drilling at Stybarrow. Active appraisal and exploration is underway, including the mutli-field Pyrenees Development. In the course of assessing these discoveries, BHP Billiton and its joint venture partners have undertaken a hydrodynamic study in order to better understand the sealing mechanisms, the position of free-water- levels (FWL?s), and the likelihood of compartmentalisation within the discoveries. Whilst the region is faulted with a predominant southwest-northeast grain, the potentiometric gradient is surprisingly flat indicating that the individual sands are hydraulically well connected. Other than the Macedon Gas Field, there is no pressure data that indicate intraformational seals have been breached. Thus, top and bottom seal capacity is likely not limiting pool size. Rather, structural spill points and fault seal capacity appear the significant factors in determining pool geometry, with the underlying aquifer being regionally connected around fault tips. On the field-scale, the flat hydraulic gradient allows for the calculated FWL?s to have a high confidence. Pressure data from the hydrocarbon phases indicate that in some cases, fault zones effectively compartmentalize a field into multiple pools. The Macedon Gas Field, on the eastern edge of the play fairway, marks a change in the trapping character with intraformational and fault seals having been breached resulting in a single continuous gas pool despite internal structural complexity.

PRODUCT NEWS

PTFE wire (poly-tetra-fluoroethylene) is used in many applications, where wire, catheters, and cannulas interact with each other and the body, to reduce friction and provide easier movement. The new, high quality, lubrication coating for Sandvik Bioline wire can be applied in thicknesses from 0.00005″ (0.00127mm) to 0.0005″ (0.0127mm), to wires from 0.001″ (0.025mm) up to 0.030″ (0.762mm) diameter. It can also be applied to wires in any medical grade material including all the stainless alloys and super alloys used in the medical device industry.For more information, go to www.sandvik.com/bioline.Fluke Biomedical has released the DPM2 Plus Digital Universal Pressure Meter, a pressure meter designed to measure the positive and negative pressures of medical devices in either liquid or gaseous form to assist in repair and quality control. When coupled with the optional Parabolic Flow Adapter accessory, the displayed pressure can be interpreted using the look-up-table supplied with the parabolic flow adapter to determine flow from medical devices.For more information, go to www.flukebiomedical.com.The Value Engineering Alliance announces the availability of AVIA, inspection software specifically developed to provide reliable detection of subtle defects even when they reside in extremely large (~10 gigapixels) images. The software detects defects by comparing images of items or scenes of interest to their respective stored reference images. It optimizes its accuracy and repeatability by relaxing assumptions about image registration and employing proprietary image processing techniques. All differences that AVIA identifies as exceeding user-specified size and contrast thresholds are located, marked, ranked, and tabulated.For more information, go to www.The-V-E-A.com.Respironics, Inc. introduces its REMstar Pro M Series, a line of sleep therapy systems that provides patient comfort and ease of use in a sleek, modern design. Comfort features such as a ramp feature and integrated humidification are incorporated into the design. The optional ramp feature reduces the air pressure when a patient is trying to fall asleep and then gradually increases (or ramps) the pressure until the device reaches the patient's prescription setting.For more information, go to www.respironics.com.Processing hazardous fluids can be potentially dangerous with poor connections in analytical instruments. Diba Industries' Flared Tubing Assemblies ensure tight fluid connections for consistent, leak-free processing. Using a proprietary thermal forming technique, the guards flare the end of its tubing assemblies, backing it with a washer and threaded bottom seal fitting to create a leak tight seal. By eliminating the need for a ferrule, compressed tip or flanged insert, flow path diameter and consistent volume are maintained in sample, reagent, wash, waste and other types of lines.For more information, go to www.dibaind.com.TT Electronics OPTEK Technology has developed a silicon phototransistor in a miniature surface mount package with a variety of lead options. Designated the OP570 Series, the NPN phototransistors feature an integral lens that enables the devices to operate with higher performance at lower cost. Electrical performance of the OP570 Series NPN phototransistors is characterized at collector-emitter breakdown voltages of 30V, emitter-collector breakdown voltage of 5V, collector current of 20mA and power dissipation of 130mW.For more information, go to www.mts.com.

TOWARDS AN EFFICIENT EXPLORATION FRONTIER: CONSTRUCTING A PORTFOLIO OF STRATIGRAPHIC TRAPS IN FLUVIAL-LACUSTRINE SUCCESSIONS, COOPER-EROMANGA BASIN

In the Cooper-Eromanga Basin, the future of exploration lies in identifying an appropriate exploration portfolio consisting of stratigraphic traps in structurally low or flank areas. A variety of stratigraphic trap prospects in the Moorari and Pondrinie 3D seismic survey areas are identified in the Patchawarra, Epsilon, Toolachee and Poolowanna formations. To identify the stratigraphic traps, an integration of sequence stratigraphic concepts applied to non-marine basins and advanced 3D seismic data visualisation was employed. This paper focusses on estimating the chance of geologic success and the probabilistic reserves size for each prospect within its sequence stratigraphic context (lowstand, transgressive or highstand systems tracts). The geologic chance factors for an effective stratigraphic trap include reservoir, top seal, lateral seal and bottom seal within each depositional systems tract, the seal effectiveness of the adjacent depositional systems tracts and the appropriate spatial arrangement of these factors. The confidence values for the existence of geologic chance factors were estimated according to the distributions of the possible reservoir and seal rocks within each genetic-stratigraphic interval and the chance of geologic success of each prospect was calculated. For probabilistic reserves estimation, geologically reasonable ranges were estimated for each parameter employing Monte Carlo simulation to calculate the reserves distribution. When a series of possible exploration portfolios, including single or multiple prospects from the prospect inventory are plotted in terms of the chance of geologic success vs. the mean value of the reserves estimate, an efficient exploration frontier emerges. The portfolio candidates on the efficient exploration frontier were assessed with regard to chance of economic success and expected net present value (ENPV) using a simple cash flow model. The results indicate that appropriate portfolios include multiple prospect exploration especially with lowstand systems tract plays using single or multiple exploration wells. The portfolio construction approach for stratigraphic trap exploration should ultimately be made consistent with conventional play types, to enable an assessment of all exploration opportunities.

Concentration by Time Product and Gas Penetration after Marine Container Fumigation of Table Grapes with Reduced Doses of Sulfur Dioxide

Reduced doses of sulfur dioxide (SO2) were evaluated for the fumigation of marine containers with respect to the concentration × time (CT) product and gas penetration. Two commercial export containers were loaded at 32 °F (0 °C) with 20 metric pallets [40 × 48 inches (102.5 × 123.1 cm)] comprised of 72 expanded polystyrene foam boxes (12 tiers, 6 boxes/tier) of table grapes (Vitis vinifera) and fumigated with 1.0 and 0.5 lb (0.454 and 0.227 kg) SO2, respectively. A third marine container was loaded with 20 metric pallets comprised of 84 plastic boxes of table grapes (14 tiers, 6 boxes/tier) and fumigated with 0.25 lb (0.113 kg) SO2. The boxes contained 16 lb (7.3 kg) of table grapes distributed in nine polyethylene cluster bagsenclosed in a perforated polyethylene box liner. Fumigations were performed through the bottom seal of the rear door from pre-weighed compressed SO2 cylinders. CT product was calculated after taking samples of the atmosphere in the container every 5 to 10 min and measuring the ambient SO2 concentration with a gas sampling pump and colorimetric dosimeter tubes. Pallet and box penetration of the gas was assessed by placing passive colorimetric SO2 dosimeters inside the cluster bags in boxes located in both the third and ninth center boxes from the top of pallets located in the front, center, and rear of the load. Fumigations with 1.0, 0.5, and 0.25 lb SO2, with calculated CT products at 32 °F of 925, 360, and 40 ppm-h (μL·L-1·h-1) respectively, were found to provide excessive, adequate, and insufficient SO2 doses.

Evaluation of Jaw Profile on Heat Sealing Performance of Metallised Flexible Packages

Different profiles of jaws are used in the Brazilian market for heat sealing flexible materials used in food packaging by heated bar. The objective of this study was to evaluate the influence of the jaw profile on the quality of the top and bottom heat seals of pouches made of biaxially metallized polypropylene/biaxially co-extruded polypropylene (BOPPmet/BOPPcoex) amd biaxially metallized polypropylene/low density polyethylene (BOPPmet/LDPE). These materials are traditionally used for snacks and ground coffee packages. Five jaw profiles were evaluated: one flat and four grooved, using lengthwise, crosswise at profiles 120 and 90° and inclined. The heat sealing temperature and time were optimized for the two packaging materials for all profiles. The sealing pressure was fixed at 40 lbf/in 2 . Heat sealing quality was evaluated through visual examination, integrity, tensile strength and drop testing. All the tests were done before and after transport simulation on the packages. BOPPmet/BOPP-coex 100 g snack packages and BOPPmet/LDPE 250g ground coffee packages were prepared under laboratory conditions. The transport simulation was done on these packages by placing them into paperboard boxes (for snacks) or kraft paper sacks (for ground coffee). The BOPPmet/BOPPcoex packages presented integrity problems for all the profiles tested. The best heat sealing, tensile strength, drop impact resistance and appearance were obtained with the crosswise 90 and 120° and inclined grooved profiles, therefore these profiles are the recommended ones for top and bottom heat sealing of snacks MOPP/met/ BOPPcoex packages. The flat profile had the worst performance among the ones that were studied. Heat sealing quality was not affected by the transport simulation, for all profiles. The BOPPmet/LDPE packages did not show integrity problems. However, the transport simulation reduced the heat sealing quality for all profiles. The crosswise 120 and 90° grooved profiles showed similar performance and they are the recommended ones for BOPPmet/LDPE packaging of ground coffee or any product of similar appearance and density. The inclined, lengthwise and flat profiles are not recommended for these applications.

Use of Variograms to Quantify Distribution of Barriers to Flow in Incised Valley-Fill Newcastle Sandstone, Wyoming: ABSTRACT

Abstract The objective of this paper is to quantify the distribution of potential flow units within valley-fill outcrop deposits by utilizing geostatistical parameters, especially variograms. The Newcastle (Muddy) Sandstone, which is a prolific producer in the Powder River Basin of Wyoming, is the subject of our outcrop reservoir characterization analysis which compares the relationships of detailed geological (sedimentological) interpretations of facies, detailed in situ permeability measurements, and outcrop gamma-ray log surveys. Much of the Newcastle (Muddy) Sandstone, which crops out near Newcastle, Wyoming was deposited by tidal currents backfilling valleys formed during a Lower Cretaceous sea level drop. The Skull Creek Shales which underlies and is lateral to the Newcastle sandstone forms lateral and bottom seals. We concurrently measured the permeabilities and gamma-ray responses of beds on three vertical transects with a grid extending normal to the bedding and three lateral grids which are as nearly parallel to the bedding as possible. We generated geostatistical parameters from these data sets. In all cases, Dykstra-Parsons coefficients are in the neighborhood of 0.35 for the single-unit data and above 0.8 for the multi-unit measurements. Coefficients of variation are below 0.5 for single units and above 0.8 for multi-unit data sets. Multi-unit variograms show hole effect and often strong trend, while single unit variograms always indicate nugget effect with a weak trend. The correlation between the plots generated from measured permeability and gamma-ray responses are impressive. Permeability and gamma-ray variograms are similar. The variograms in the vertical and horizontal directions are quite different. Therefore, they cannot substitute one for another. We also concluded that relative semi-variograms are a better way of presenting formation heterogeneities. We observed that abrupt variations in outcrop gamma-ray values are also excellent indicators of bed contacts. We used the generated geostatistical parameters in a simulated annealing program to predict permeabilities of lateral profile A, and concluded that variogram, mean and standard deviation are required but not sufficient parameters to predict the distribution of reservoir heterogeneity.

Compartmentation in the Anadarko Basin: Implications for Exploration and Production: ABSTRACT

Abstract Integrated pressure, potentiometric, and geologic data demonstrate the existence of a basin-wide, completely sealed overpressured compartment in the Anadarko basin. All reservoirs within this complex exhibit pressure gradients ranging from 0.6 to 0.98 psi/ft, which exceed the normal gradient of 0.465 psi/ft. These reservoirs have produced large quantities of natural gas, particularly from the Pennsylvanian Red Fork and Morrowan sandstones. This mega compartment complex is enclosed by top, bottom, and lateral seals. The top seal, which is located between 8500 and 11,000 ft below the surface, is relatively horizontal, dips slightly to the southwest, and appears to cut across stratigraphy. However, the basal seal is stratigraphically controlled and seems to coincide with the Devonian Woodford Shale. The complex is laterally sealed to the south by an intense cementation zone associated with the Wichita uplift frontal fault zone and by the convergence of the top and basal seals along the eastern, northern, and western boundaries. Nested within this complex is a myriad of smaller compartments with their own distinct pressure gradients. In addition, local overpressured compartments are present outside the mega compartment complex in normal and near-normal pressured regions. Due to their hydraulically isolated nature, nested pressure compartments may provide drilling prospects that are not constrained by structural position or proximity to existing reservoirs. Predicting the compartment and seal geometries and internal reservoir quality should improve drilling success ratios and diminish hazards associated with drilling abnormally pressured rock sequences.

The Search for Subtle Stratigraphic Traps with High Resolution Seismic Data: Examples from the Powder River Basin, NE Wyoming, U.S.A.

Optimizing the temporal resolution of seismic data in both the acquisition and processing stages increases the detection rate of subtle, multiple stratigraphic traps in complex lithologic sequences. Field sizes ranging from 1 MMBO to 40 MMBO are found in the coastal facies of eolian sandstone reservoirs of the Permian Minnelusa Formation in northeast Wyoming, U.S.A. Generally, three main trap styles exist: (1) an erosional unconformity providing the top and lateral seals with a shoreline marine carbonate acting as the bottom seal; (2) marine carbonates providing both the top and bottom seals; and (3) topographic relief at the top of dune complexes that lack a bottom seal but are overlain by marine carbonates. Usable frequencies in excess of 100 Hz from depths greater than 3300 m allow resolution of 10 m sandstone reservoirs with 15?20% porosity. With this frequency it is possible to distinguish not only porous sandstone reservoir signatures, but also the trapping mechanisms involved. High resolution seismic data acquired prior to a recent oil discovery is shown here to demonstrate a successful methodology used to discover and develop Minnelusa oil in subtle stratigraphic traps. Successful exploration in coastal deposits such as the Minnelusa Formation requires an integrated approach to exploration. This includes broad band, high frequency seismic data acquisition and processing with a combined geological and geophysical interpretation. Using these techniques, discoveries are possible even in mature basins at exploratory drilling success rates well above the U.S. onshore industry average of 8?12%.

Methoden zur Immobilisierung von Bodenkontaminationen

AbstractMethods of immobilizing soil contamination. A number of remedial measures can bei applied to contain or immobilize contaminants which threat to pollute groundwater, soil or air. Some are still conceptional in character, others are in practical use. So far, bentonite/cement‐based slurry walls have often been constructed to regulate the groundwater flow in contaminated areas. In general, clay layers are used as bottom seal whenever available. Investigations, however, have shown that conventional and many natural materials do not exhibit the resistance to aggressive leachates which is necessary to retain the contamination over extended periods of time. In the proposed concept a partial or complete encapsulation of the contamination is recommended using barriers resistent to aggressive leachates, thus containing the contamination. This can be achieved by new silica gel containing materials and in some cases by suitable geotextiles. Extensive tests of such materials are presently under way at various abandoned waste sites in the F. R. Germany. Remedial action can then be planned and executed to decontaminate the site in ample time and without the risk of further contamination. New results are reported obtained during a one year test period with water glass of low alkalinity and high SiO2/Na2O ratio. Their resistance to leachates, low syneresis, and high hardness was accomplished by the two‐component system Dynagrout PPN, developed by Dynamit Nobel.

Chin Coulee Field--a Stratigraphic Trap in Lower Cretaceous Fluvial Valley-Fill Sandstones: ABSTRACT

Hydrocarbons, stratigraphically trapped in fluvial valley-fill sandstones, constitute some of the more important oil fields in North America. The Chin Coulee field in southeastern Alberta, Canada, has produced over 4.4 million bbl of oil since its discovery in 1960, with an estimated 1 million bbl still to be produced via secondary recovery. The field covers approximately 80 km2 with an average net pay thickness of 3 m. The hydrocarbons are stratigraphically trapped in the fluvial Sunburst Sandstone, which records the Early Cretaceous transgression of the Boreal Sea. These lower Mannville aggradational sequences accumulated in an incised drainage system in Jurassic marine shales, which provide the bottom seal for the reservoir sandstones. Following deposition of the Sunburst Sandstone, an accelerated rise in base level led to the accumulation of argillaceous limestones and calcareous shales commonly referred to as the ostracod zone. These fine-grained strata provide an effective seal above the porous sandstones. Postdepositional tilting of the strata to the west, due to subsidence in the foreland basin east of a rising orogene (Nelson uplift), resulted in migration of hydrocarbons in an easterly updip direction. Stratigraphic trapping of these hydrocarbons occurred in sandstones pinching out in the upper reaches of tributary valleys to the east of the main drainage system (Chin Coulee and Taber Southeast fields). Regional paleoenvironmental reconstructions suggest that the Sunburst Sandstone is equivalent to the Cut Bank Sandstone of the Cut Bank field area in northwestern Montana. The Cut Bank field lies along the same Late Jurassic drainage system (Fox Creek escarpment), and similar tributary valleys situated east of the escarpment may exist between these two producing field areas. This suggests the presence of additional untested hydrocarbon reservoirs exhibiting stratigraphic characteristics similar to those described in the Chin Coulee field. End_of_Article - Last_Page 300------------

Manure Effects on Model Lagoons Treated with Residue for Bottom Sealing

ABSTRACT AS part of a lagoon sealing study, two crop residues-cotton gin trash and ground corn cobsalong with a control soil, were subjected to a low constant hydraulic head percolation by deionized water for 13 days. On day 14, hydraulic heads were raised to 180 cm and manure additions at the rate of 160 mg/L volatile solids (based on full volume) were initiated. After Day 14, the units were allowed to operate as falling head permeameters between the thrice weekly (MWF) loadings. Total solids, carbon, nitrogen and results of microbial counts are reported for the influent and percolant before and after manure addition was begun. Effects of wastes on previously synthesized microbial gums are also reported. The results of this study were helpful in understanding processes in the bottom of a model waste lagoon that had been treated with a crop residue in an attempt to develop a bottom seal.

Overview of Seals for Hydrocarbons: ABSTRACT

Seals for hydrocarbons need to be analyzed and described at two differing scales. A micro view of the rock matrix, pore structure, and fluid content of the seal surface provides quantitative information about the capacity of the seal to impede hydrocarbon movement at a specific measured point. Such micro information often can be accurately measured, but can rarely be extrapolated to describe the overall (mega) sealing capacity of a large hydrocarbon trap. Efforts have been made over the years to describe the lateral variability of seals for hydrocarbon accumulations. One of the best features of the simple anticlinal structure is that it generally provides sequential sealing surfaces. Top-seal surfaces may be expected to have relatively little lateral variability (at least on the scale of an individual anticline). Faulted structures, in contrast, require not only a top seal, stable in lithology over the trap area, but require juxtaposition of the hydrocarbon-bearing interval against a sealing lithology at the fault plane surface. Large hydrocarbon columns become almost impossible to seal if the trapping configuration requires multiple faults with throws that vary along the individual faults. Stratigraphic traps for hydrocarbons typically require a top seal, bottom seal, and an updip lateral seal. In addition, the transition from reservoir to seal must be very rapid or the hydrocarbon accumulation will largely occupy a waste-zone--not quite a reservoir, hardly a seal. Regionally, it can be shown that hydrocarbons are preferentially distributed under major roofing seals. These major sealing units are characterized by broad extent, by laterally stable character, and commonly by ductile lithologies. Where these regional seals are above significant source rocks and reservoirs, they largely control the emplacement of hydrocarbon accumulations. End_of_Article - Last_Page 921------------

Geology and Hydrocarbon Accumulation in Mississippian Midale Beds, Benson Oil Field, Southeastern Saskatchewan: ABSTRACT

End_Page 841------------------------------In southeastern Saskatchewan the Mississippian strata dip south-southwest and are progressively truncated northward against the post-Mississippian erosion surface. Impermeable red beds of the Watrous Formation unconformably overlie the Mississippian carbonate sequence. The Benson field is a structural and stratigraphic trap in which oil has accumulated in dolomite layers of the Midale Beds beneath the erosion surface. The dolomite rocks which are microsucrosic and commonly burrowed have good to excellent intercrystalline and moldic porosity. Dolomite layers are present at several stratigraphic positions within the lagoonal carbonate rocks of the Midale Beds and range from 0.1 to 3.2 m in thickness. Either limestones (wackestones and micritic packstones), highly calcareous dolomites (microsucrosic), or anhydritic dolomites (cryptocrystalline) provide the caprocks and the bottom seals for the porous layers. Laterally, the dolomites grade into highly calcareous dolomites and/or wackestones. The porous layers result from selective dolomitization of carb nate sediments. Close to the erosional edge, porosity in the dolomites has been reduced or obliterated by secondary anhydrite. End_of_Article - Last_Page 842------------

Hydrocarbon Accumulation in Meramec-Osage"(Mississippian) Rocks, Sooner Trend, Northwest-Central Oklahoma"

Two trapping mechanisms operating together: discontinuous lateral permeability in joint system, top and bottom shale seals in productive area

Spillway Gate Vibration on Arkansas River Dams

Spillway tainter gates are susceptible to flow induced vibrations particularly when the gate lips are submerged by tailwater levels. Vibrations experienced on the spillway gates of the Arkansas River Navigation Project were severe enough to cause cracks in the structural members and welded connections of the gates. The nature, patterns, and magnitude of the vibrations on these gates were determined and related to the gate openings, tailwater levels, lip designs, seal designs, structural rigidity, and several other factors. Lip design, rubber seal design, and structural flexibility were concluded to be the major causes of gate vibrations. Factors which should be considered in future tainter gate designs to provide vibration-free operation include: (1) lip designs with a clean, sharp flow breakoff point; (2) elimination of rubber gate bottom seals wherever possible; (3) structurally rigid gate lip designs; and (4) testing of unusual gate designs to check for vibration tendencies.

Experiences with Flow-Induced VibrationS

Difficulties encountered in U. S. Bureau of Reclamation structures because of flow-induced vibrations show that similar problems can occur elsewhere and that measures can be taken to avoid or control them. Vibrations interfered with operation and caused structural damage in several radial gates in canals because of control shifting front the flexible bottom seals to the backing plates and back again. It was eliminated by redesigning the seals to produce a positive spring point. In Parker Dam Powerplant, turbine runner blade vibration was induced by vortex trails in the flow behind the blades. Tapering the trailing edge of the blades changed the frequency of vortex shedding and eliminated resonance. At Grand Coulee Pumping Plant vibration in steel discharge lines was reduced by modifying the pumps to lower the magnitude of periodic impulses, and by stiffening the pipeline to avoid resonance. Low frequency vibration or surging in the Coachella Pipeline Distribution System was reduced by changing the natural periods of sections to avoid resonance, reducing the number of sections, and providing a snubbing action. Fluttering in overfalling nappes was eliminated by splitting the jets so full aeration occurred under the nappes.

Problems Concerning Use of Low Head Radial Gates

Three principal hydraulic features of low head radial gates are discussed; general discharge equation, effect of gate seat location on discharge capacity and pressure distribution along spillway surface, and side and bottom seals.