Velocity and water-layer thickness of overtopping flows on sea dikes: Report of measurements and formulas development
The study aims to establish a set of formulas estimating velocity and depth of overtopping flows at sea dikes including seaward-side slope, crest and landward-side slope. These formulas are applicable to flows which are generated by natural waves and the simulator giving associated characteristics of any arbitrary value of exceedance probability. Note that the probability is based on the total number of incident waves and not to be confused with the total number of overtopping events. The difference between the fictitious wave run-up level and the crest level (Ru2% - Rc) is widely considered as a measure of the (potential) energy of wave overtopping. This term is therefore used to estimate values of the mean overtopping discharges, ow velocities, water-layer thickness and overtopping volumes. In line with many existing research works and guidelines, the potential term is crucial to derive other parameters. Experimental data of Van Gent [2002] is reanalyzed with a slightly different perspective to achieve the study objective. The analysis procedure basically consists of three main steps:  from wave conditions and dike cross-section to calculate wave run-up levels;  from wave run-up levels to estimate flow parameters on the dike crest;  from flow parameters on the dike crest to further compute the corresponding parameters on the landward slope. The obtained equations are verified with flow measurements of the simulator on real dike slopes. Consequently, feasible values representing the roughness of different grass coverings are determined.
Wave overtopping simulator on a 1/15 slope protected by two local grass species
The phenomenon of wave overtopping during storms was simulated by the Wave Overtopping Simulator on a 1/15 grass covered slope. The four 'Wave Overtopping Simulator' tests were done within the framework of the Research project 'Super sea dike with high safety level and environmental friendly' funded by Viet Nam government. The main objective of these tests was to test the resistance of the gentle slope (steepness of 1/15) protected with local grass against wave overtopping with the Wave Overtopping Simulator. The super dike model was built up at the outdoor laboratory of the Viet Nam academy for water resources, in Yen Binh ward, Thach That district, Ha Noi. In June 2012, the super dike slope covered with one year grass mat was tested with the simulator. The front velocity of overtopping flows were estimated at three positions along the slope using digital camcorders. In general, increasing volume generates higher front velocity and it is likely to become larger downward the slope. Under attack of overtopping flows generated by the simulator, the super dike slope covered with Bermuda and Carpet grass was damaged moderately. Damage was in the form of a shallow erosion which took place around the dike crest and toe (geometric transitions). The mechanism is defined as 'roll up' or 'turf set-off', the grass mat of about 5 to 7 cm thick is lifted and rolled up gradually to expose the underneath soil body. Small damaged spots were observed around two obstacles of YB1 and YB4 sections therefore, influence of these objects on slope performance was unclear. Man-made eroded spots were introduced at two positions on YB3 slope by removing the grass turf which was about 10 cm thick of the top layer including most of roots. Applying discharges of 40, 60, 80 and 100 l/s per m with a wave height of 2.0 m caused a gradual extension of the artificial damage downward while depths and widths remained the same. Apparently, the destructive impact of overtopping flow is most effective in its direction, from crest to toe. The super dike slope was 1/15 of inclination and protected by two local grass species, Bermuda and Carpet. When being tested, the grass mats were about one year old. The maximum discharge of the simulator 100 l/s per m was applied for 6 to 10 hours, thus resulting in moderate damage to the grass cover. These damaged spots were limited within 7 to 10 cm under the slope surface and insufficiently significant that might threaten the function of the super dike. The simulator was designed to test the normal sea (river) dike slopes with a steepness of 1/3 to 1/6 under a mild wave condition, significant wave heights not above 2.0 m. Therefore, to assess the super dike slope which is unbreachable even in extreme condition, a device with much higher capacity is clearly required.
Immunization with Brucella melitensis Rev 1 against Brucella ovis infection of rams.
The efficacy of Brucella Melitensis Rev 1 vaccine (Rev 1) for the prophylaxis of Brucella ovis ram epididymitis was evaluated. Twenty-nine 3-month-old rams were vaccinated with 2 X 10(9) Rev 1 and 14 were revaccinated with 5 X 10(8) at 14 months of age. Six rams remained unvaccinated as a control group. All rams were challenged with 5 X 10(8) B. ovis at 21 months of age. Before being slaughtered 8 weeks later, only one vaccinated ram developed epididymitis while four of the six control rams developed testicular alterations. Genital and selected extragenital organs and lymph nodes were removed at slaughter and inoculated on selective media. B. ovis was isolated from 26.6% of the vaccinated rams, 21.4% of the revaccinated rams and 100% of control rams. Portions of epididymis, testes and vesicular glands were also used for pathological studies. More severe lesions were observed in control rams than in vaccinated ones. In conclusion, these results show that vaccination of young lambs, followed or not by revaccination, is a suitable method for the prophylaxis of B. ovis infection of rams.