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Drop Inlet Spillways in Lithuania

Author(s): V. Damulevicius; B. Ruplys

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Keywords: Drop inlet; Spillway; Characteristics

Abstract: Drop inlet spillway, DIS, (usually called, , shaft’’in Lithuania) is the most popular spillway type in our country. They are built at 274 (77, 6% ) hydroschemes of 353registered (which create a reservoir area≥5 hectares). The design discharge of 1. .. 3% probability of our DISs varies from several up to 300 m3/s, the overflow head is in limits of 0, 5. .. 2 m, and the height of dams concerned reaches 21 m. Prevailing drop inlet shape in plan is quadrangular and hexagonal, in profile-straight vertical. Several special types of drop inlets are proposed to receive more compact and economic structure. Geometric proportions and hydraulic parameters of those types were optimized by hydraulic simulations in our laboratory. On the drop inlet crest small piers and bar screens, in the front wall-bottom outlets are provided. The conduit is made of precast reinforced concrete pipes of 1. .. 4 parallel lines. The stilling basin width is constant or increasing downstream, the side walls are vertical. Various energy dissipators are used in stilling basins, including the, , comb’’-type dissipator. Transition to the downstream apron usually is of straight wall type; then the trapezoidal channel follows. Construction of small DISs was carried out by local teams of land reclamation building organizations; bigger DISs were build by specialized hydrotechnical units. Nowadays, after 20-25 years from the start of extensive DIS commissioning, one can say that, in general, our DISs are good and reliable spillways. Of course, sometimes unexpected hydraulic phenomena take place; several DISs (usually built by local teams) should be repaired; several DOSs, alas, are out of service, together with dams and reservoirs. More and more attention to ageing DISs is to be paid.


Year: 1999

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