Summaries C jmpletion of the storm surge barrier behind c Dsed gates Ir order to facilitate the final execution of the si arm surge barrier the three sluice gaps will b temporarily wholly or partially closed. There h s been extensive research beforehand as to hi w this should be tackled. For example the e: tuary bed protection will under certain ci cumstances have to bear a heavy load with si ch a manoeuvre, and undesirable erosion or si ting of the flats can occur. Tl e consequences for the workability of the et uipment and for the estuary bed protection w re investigated in the physical model 1 80 of the mouth of the Oosterschelde. The most fa ourable closure designs were selected and a pi n was set up for the reinforcement of the es uary bed defence. By way of mathematical m dels it was calculated what consequences th se measures would have for the environment an J fishery. No irreparable damage will be ca ised. The only problem remaining is the clr sure of the whole barrier which will be ne :essary in order to install the upper beams in he middle of the Roompot. A ^recasting system for current speeds su rounding the axis of the storm surge barrier Th s article deals with the middle and long ter m forecasts in the Oosterschelde mouth. W h long term forecasts - three months and loi ger - the statistical data on the tides must be taken into account, and for middle long tei n forecasting - between one week and thi =e months - there are astronomical ca ;ulations available. Current speeds are de luced form these basic data using different m< thods. Most important is the use of m; thematical models. But hydraulic models an I nature measurings are used for supervision an I for reconnoitring of details. Finally this master system enables forecasting per separate location. Under water inspection Divers have been inspecting executed works in the Delta area since 1959. A diving fleet consisting of three ships and three observer divers in regular service had already been formed in 1972 when preparation for the Oosterschelde works had begun. As work on the Oosterschelde barrier progressed more diving work became necessary, so that during the peak time in 1983 and 1984 it was not unusual for sixty divers to be working at the same time. This was not only for inspection but also for all kinds of repair work carried out under water. For position-finding under water, use was made of a transponder, whose co-ordinates were made visible on board the help-ship. The repair works consisted of repairs carried out on the concrete piers. Further the too high-lying positioned stones in the sill were marked and provided with chemical anchors, and silting and mussel seed were removed. The biggest job arose as a result of the technical set-back with the piers: the tin sheeting underneath became unstuck and it proved necessary to strip the piers completely. This meant half a year's work for thirty divers. For certain activities a diver's clock and an underwater chamber with a surface of 3 by 6 metres were available. Shift changing could be considerable speeded up when a decompression tank with a triple-lock room was brought into use. During the above mentioned diving activities improvements were made in the diving equipment as well as in the medical supervision and instruction. Diving work for the Oosterschelde barrier is not yet finished. Preparatory work will have to be carried out by divers before the sill-beams can be placed and a constant supervision will have to be maintained on the estuary bed protection. The article also describes two mechanical inspection methods. The 'Trigla' is a free swimming inspection vessel not more than one metre long and with a thickness of two inches. With the assistance of a photo-sensitive chip and a sand-density sensor this instrument can locate pollution under the pier foot. This space of 35 cm height should be free of sand and overgrowth before under-grouting can proceed. The other underwater vessel is the 'Portunus' which has carried out successful inspection on the position and condition of the foundation mattresses. 103

Tijdschriftenbank Zeeland

Driemaandelijks bericht Deltawerken | 1985 | | pagina 57