Physical modeling of air injection as a scour remediation technique near gated weir stilling basins

The South Florida Water Management District (SFWMD) manages and operates numerous water control structures that are subject to scour. In an effort to reduce scour downstream of these gated structures, laboratory experiments were performed to investigate the effect of active air-injection downstream of the terminal structure of a gated spillway on the depth of the scour hole. A literature review involving similar research revealed significant variables such as the ratio of headwater-to-tailwater depths, the diffuser angle, sediment uniformity, and the ratio of air-to-water volumetric discharge values. The experimental design was based on the analysis of several of these non-dimensional parameters. Bed scouring at stilling basins downstream of gated spillways has been identified as posing a serious risk to the spillway’s structural stability. Although this type of scour has been studied in the past, it continues to represent a real threat to water control structures and requires additional attention. A hydraulic scour channel comprised of a head tank, flow straightening section, gated spillway, stilling basin, scour section, sediment trap, and tail-tank was used to further this analysis. Experiments were performed in a laboratory channel consisting of a 1:30 scale model of the SFWMD S65E spillway structure. To ascertain the feasibility of air injection for scour reduction a proof-of-concept study was performed. Experiments were conducted without air entrainment and with high, medium, and low air entrainment rates for high and low headwater conditions. For the cases with no air entrainment it was found that there was excessive scour downstream of the structure due to a downward roller formed upon exiting the downstream sill of the stilling basin. When air was introduced vertically just downstream of, and at the same level as, the stilling basin sill, it was found that air entrainment does reduce scour depth by up to 58% depending on the air flow rate, but shifts the deepest scour location to the sides of the channel bed instead of the center. Various hydraulic flow conditions were tested without air injection to verify which scenario caused more scour. That scenario, uncontrolled free, in which water does not contact the gate and the water elevation in the stilling basin is lower than the spillway crest, would be used for the remainder of experiments testing air injection. Various air flow rates, diffuser elevations, air hole diameters, air hole spacings, diffuser angles and widths were tested in over 120 experiments. Optimal parameters include air injection at a rate that results in a water-to-air ratio of 0.28, air holes 1.016mm in diameter the entire width of the stilling basin, and a vertically orientated injection pattern. Detailed flow measurements were collected for one case using air injection and one without. An identical flow scenario was used for each experiment, namely that of a high flow rate and upstream headwater depth and a low tailwater depth. Equilibrium bed scour and velocity measurements were taken using an Acoustic Doppler Velocimeter at nearly 3000 points. Velocity data was used to construct a vector plot in order to identify which flow components contribute to the scour hole. Additionally, turbulence parameters were calculated in an effort to help understand why air-injection reduced bed scour. Turbulence intensities, normalized mean flow, normalized kinetic energy, and anisotropy of turbulence plots were constructed. A clear trend emerged that showed air-injection reduces turbulence near the bed and therefore reduces scour potential.

A Bentonite Deposit near Warm Springs, Montana

This report deals with a bentonite deposit recently developed, approximately seven miles northeast of Warm Springs, Montana. A group of claims have been staked on the deposit and are owned by the Lincoln Mining Company of Anaconda, Montana. The company also has several claims prospected for silver one mile from its present site of operations, but the silver prospects have failed to produce. The bentonite deposit was discovered incidentally during the course of other development work, and at present two adits have been driven into the side of a mountain, each crosscutting a vein-like mass of bentonite varying from two to three feet in width.

Investigations Concerning Bentonite Deposits Near Ramsay, Montana

The purpose of Part I of this report is to determine the origin of the bentonite deposits, also to locate them with reference to section corners in the vicinity and to determine their extent. The field work for this report was done in the fall of 1933 and during the spring of 1934. The roads, geologic contacts, and culture in general were mapped with the use of an open sight alidade and plane table. Distances were determined on the roads by the speedometer on the automo­bile; the detailed survey in the immediate vicinity of the deposits was done with use of the Brunton compass and pac­ing. The purpose of Part II in this report is to determine if the bentonite deposits immediately west of Butte, Montana are of com­mercial importance and also to determine the use to which they are best suited.

Auriferous Tertiary Gravels Near Rocker, in Silver Bow County, Montana

Between the villages of Rocker and Silver Bow, in south­western Montana, are found an interesting group of placers. Gold occurs in Tertiary gravel beds that are interstratified with beds of rhyolitic volcanic ash. With the aid of a plane table and open-sight alidade, a small portion of the lake-bed area near Rocker was mapped; all distances were paced, but numerous checks assure a fairly accurate map.

Study and Correlation of Belt and Cambrian Arkoses near Limespur, Montana

In the vicinity of Limespur, Montana, a siding along the Northern Pacific Railroad near Whitehall, Montana, occurs a characteristic type of arkose where­ in many small red mineral grains are distributed throughout the rock mass. It is in this respect that this arkose differs from other arkoses in the surrounding region.

Chromite Deposits Near Red Lodge and Silver Star, Montana

The Red Lodge and Silver Star chromite deposits of Montana have stimulated much interest during periods of war. The Red Lodge deposit is 25 miles southwest of Red Lodge which is also the nearest railroad point. Several workings are scattered throughout the area, exposing lense-like ore bodies averaging 33% chrome oxide. Silver Star is a much smaller deposit 5 miles west of Silver Star, Montana, which is its nearest rail­road point. Lenses of chromite are exposed by pits and trench­es, which average approximately 36% chromic oxide.

Concentration by Flotation of a Complex Galena - Sphalerite - Chalcopyrite Ore from the Nine Mile District Near Missoula, Montana

At the present time ore bodies being mined are becoming more and more complex in mineral association, thus presenting a more difficult problem in their concentration. Lead-zinc sulphide ores are among the more common ores which present such difficulties.

Fluorite Near Silver Bow, Montana

The wartime demand for fluorspar has caused renewed interest in fluorite deposits. Near Silver Bow, Montana, a deposit of massive, coarsely crystalline fluorspar, which has not been described in the literature, has attracted the atten­tion of the United States Geological Survey.

Occurrence of Native Copper Near Jefferson City, Montana

Sometime prior to 1870, a group of prospectors made what was believed to be a "rich strike' on one of the tributaries of Prickly Pear Creek in Jefferson County, Montana. Instead of striking it rich, they had uncovered a native copper deposit, worthless to them because of its limited extent and remote location, but now of much interest to the geologist, and to the mining engineer because of its possible commercial value.

Geology of a Kyanite Deposit Near Ennis, Montana

A deposit of kyanite, an aluminum silicate mineral used in the ceramic industry, occurs in the low foothills of the Gravelly range about 10 miles south of Ennis, Montana. This study deals primarily with the character and origin of the deposit, and its relationship to the surrounding rocks.

Foraminifera from Pleistocene beds near San Pedro, California

The age of rocks found in drill cores, and consequently the depths to possible oil-bearing formations has in many localities been determined by micro-paleontologic studies during the past three decades. Of the different micro-fossils used in this work, foraminifera have been studied most, are the best described, and hence, by far the most helpful.

An Evaluation of Potential Occupational Exposure to Asbestiform Amphiboles near a Former Vermiculite Mine

Amphibole asbestos (AA) has been detected on the surface of tree bark in forests neighboring an abandoned vermiculite mine near Libby, Montana. In the present study, simulations were performed to assess potential AA exposure associated with United States Department of Agriculture Forest Service (FS) occupational activities. Bark samples were collected prior, and personal breathing zone (PBZ) and Tyvek clothing wipe samples were collected during and immediately after trials that simulated FS activities. Transmission electron microscopy (TEM) analyses revealed AA bark concentrations up to 15 million structures per square centimeter (s/cm2). AA was detected in 25% of the PBZ TEM samples. AA was detected on wipe samples collected from all activities evaluated. This research demonstrates the potential for airborne exposure and transport of AA in the Kootenai National Forest. These findings are especially relevant to those that work in the area and to the general public who may conduct recreational activities.

Manganese Oxide Deposits Near Butte and Development Since 1942

The manganese minerals occur in the peripheral zone of the Butte district with quartz in veins, which at depth contain galena and sphalerite closely associated with silver-bearing minerals. The manganese oxides are all oxidation products formed by weathering of primary rhodochrosite or rhodonite.