Les grands principes de coupure des écoulements fluviaux et maritimes

Abstract

There are many different ways of cutting off a river, which largely depend on hydraulic and site conditions. A distinction can be made between a number of main classes of cutoff methods. I. - The main factors among the hydraulic conditions are discharge, water level difference, and the product of both. The following distinction can be made in this respect: (i) Fluvial or river flow cutoffs, where the natural factor to be considered is a flow to be diverted or stored. The water level difference will depend on the discharge capacity and length of the diversion, storage volume, and the rate at which the work progresses. (ii) Tidal or water leuel difference cutoffs, where the natural factor to be considered is a difference in water levels (generally tidal). Here, the discharge will depend on this water level difference and the discharge capacity of the cross-section remaining to be closed off. Typical water level variations during the closure are shown in Figure 1. II. - Cutof procedures fall within the following categories ; - 1. "plugging" procedures, with the "plug" a bridge (see Figure 2) an "obelisk" (Figure 3), or a floating caisson. (Figure 4). 2. Dyking or piled-structure procedures, using rock fill, concrete blocks, earth, fascines, etc. In making this type of closure, work can proceed : - either (i) from the banks out into the river (Figure 5), in which case considerable difficulties arise at water level differences approaching or exceeding 3 m and with highflows; or (ii) in horizontal layers (Fig. 6 to 9). which is a suitable method for large differences in water level, and for rivers with loose bed materials as there is no scour. 3. Permeable framework cutton's. The rock fill or blocks are given a firmer hold by a permeable framework in the form of a net, piled "hedgehogs", or cribs placed on the river bed. 4. Sheet piling cutoffs. These are generally only practicable for small water level differences. 5. cutoffs by blasting. 6. Composite cutoffs, nearly always a combination of several of the above procedures. An example of this type is the Rance project. The article gives a typical example of each case.