Hydraulic studies of bottom regulatory devices

Introduction. Accidents at underwater pipeline crossings lead to serious environmental consequences. The choice of the location of the pipeline junction made without accounting the general dynamics of the channel process, use of improper construction technology of underwater trenches and pipeline laying often result in their destruction, which are caused by erosion and pipe sagging. Existing methods for protecting the pipeline by soil or crushed stone filling, exposure embedding with sandbags, strengthening with flexible concrete mats and other materials are not always effective and, as a rule, are expensive. Materials and methods. The article considers a method of protection of the main pipeline against erosion by means of through bottom devices of various types to determine their efficiency. Velocities of the flow are measured behind the bottom obstacles at the flow axis at several points in depth using the microcomputer flowmeter/velocimeter. The measuring sections are located at distances of 1 to 10 of flow depths from the bottom obstacles. The near-bottom velocities at the height of the roughness protrusions are calculated according to the dependences suggested by V.N. Goncharov. Results. The article shows results of laboratory hydraulic investigations of a tray flow around four types of bottom obstacle models: solid flat wall, slotted flat wall, volumetric round-section obstacle of fixed synthetic strings and volumetric soft structure. All the studied design models cause a rearrangement of the velocity diagrams and a decrease of near-bottom velocities. However, only through-passing structures are suitable for sediment deposition behind the barriers. If the bottom velocities are reduced to values less than sediment-washing ones, sediments will be deposited behind the barriers at a certain relative distance determined in the work. Conclusions. The investigated models of through bottom structures showed themselves to be quite effective in reducing the near-bottom speed and depositing sediments at a certain distance behind them. The most effective is the “volumetric” construction, since it gives the greatest reduction in relative velocities at a certain relative distance.

Overflow Waters at the Iceland–Faroe Ridge Observed in Multiyear Seaglider Surveys

This paper presents new observations of the overflow waters downstream of the Faroe Bank Channel (FBC) and the Iceland–Faroe Ridge (IFR). Between 2006 and 2009, over 17 400 hydrographic profiles were collected during quarterly deployments in the region by autonomous gliders, providing previously unrealized spatial resolution to observations downstream of the FBC. Observations show that the second sill of the FBC coincides with the largest changes in the overflow plume, including significant thinning, widening, and entrainment. Between the second sill and a topographic feature 75 km downstream, the plume bifurcates with the densest portion (65% of the transport), descending below 1000 m. On the IFR, near-bottom velocities are directed alongslope with speeds averaging 21.5 cm s−1. Observations indicate that 80% of baroclinic velocities associated with mesoscale variability of the overflow plume are smaller than the alongslope topographically induced circulation. Evidence of overflow is found at all locations on the Atlantic flank of the IFR. However, the meridionally oriented portion at 13°W has anomalously warm bottom water and divides FBC and eastern IFR overflow from overflow found in the Western Valley. Individual Seaglider sections identify IFR overflow in a narrow current (8–14 km wide) along the Iceland shelf with a mean transport of 0.43 Sv (1 Sv ≡ 106 m3 s−1) with significant variability from days to weeks. A lower-bound estimate of 0.8 Sv of total IFR overflow is presented. These results provide constraints on regional models that inform the representation of this crucial, yet underresolved, region in large-scale ocean and climate models.

The Interaction of Tsunamis With Ocean Swell: An Experimental Study

Our objective is to investigate the effect of combined swell–tsunami interaction on the nature of the tsunami — in particular the surface elevation, the runup speed and the near-bottom velocities. Laboratory testing in the Tsunami Wave Basin at Oregon State University has been performed to simulate this interaction, with free surface elevations and near-bottom velocities measured at various locations over a plane sloping beach. Random wavetrains with varying initial mean steepness were generated in concert with the tsunami. Preliminary analysis of the data reveals that high steepness ocean swell changes the spectral signature of the tsunami, particularly at high frequencies. There is also a significant difference in location of the breakpoint of the tsunami with overriding swell.

Winter operation of an on-stream stormwater management pond

The winter operation of an on-stream stormwater management pond in Kingston, Canada is characterised. The pond froze over in late November. Ice thickness varied from 0.2 to 0.5 m, and initially, was well described by Stefan's formula. The measured and modelled velocity field indicated a fast flow region, a small dead zone and a large recirculating zone. During a snowmelt event, near-bottom velocities reached 0.05 m·s-1, but were not sufficient to scour the bottom sediment. Pond water temperature increased with depth, from 0.5°C to 3.5°C. The dissolved oxygen (DO) levels observed in the pond (6-13 mg·L-1) indicated stable aerobic conditions at the sediment-water interface. In one brief episode, DO fell to zero after a long cold spell. Reduction in DO readings from inlet to outlet indicated an oxygen consumption of about 1.7 kg·day-1. pH ranged from 7.1 to 8.9. Conductivity readings indicated large quantities of total dissolved solids, representing mostly chloride from de-icing agents. During baseflow, conductivity increased with depth (total dissolved solids concentrations up to 1,200 mg·L-1 near the bottom), indicating density stratification. Average trace metal concentrations were mostly below detection limits.