Hydraulic and earth engineering – Fluid control – treatment – or containment – Flow control
Patent
1997-10-17
1999-03-16
Graysay, Tamara L.
Hydraulic and earth engineering
Fluid control, treatment, or containment
Flow control
405 90, 405 94, 405102, 405108, E02B 300, E02B 806
Patent
active
058821449
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a device for triggering the destruction of a selected portion of a hydraulic structure, and to a hydraulic structure including such a devices
The invention applies in particular to an earthfill or rockfill embankment dam, dike, or levee, or to a composite dam or dike built in part as an embankment and in part out of concrete or masonry. The dike may be a front dike (across a water course) or a side dike (along a water course, to protect surrounding land from flooding). If the structure is a dam, it may be any kind of embankment or composite dam that creates a reservoir of water, or a saddle dam associated with the above-specified dam.
In numerous hydraulic structures of the above-indicated kind, it is known to provide privileged break points which, under exceptional flooding that is in danger of destroying the structure, give way at predetermined locations of the structure which are selected so as to minimize damage caused to the structure itself and/or to people or property flooded by the structure breaking. One of the major problems associated with such a system is that of satisfying the following criteria:
it must be very stable and reliable during normal operation of the hydraulic structure; and
it must be very unstable when exceptional events occur that threaten the survival of the hydraulic structure.
The system that is presently in most widespread use for this function is known as a "fuseplug dike". It comprises either a portion of the hydraulic structure itself or else a dike built at a distance from the hydraulic structure at some other point on the periphery of the reservoir, e.g. in a saddle. The top of the fuse-plug dike is positioned or levelled at a level such that water spills over it only during exceptional flooding. This level is higher than the normal operating level (RN) of the hydraulic structure in which the fuseplug dike is integrated or with which it is associated, but it is lower than the maximum water level (RM) that the structure is designed to withstand. The fuseplug dike is built of materials suitable for ensuring that it is destroyed by hydraulic erosion in the event of water spilling over its top. The principle on which such a fuseplug dike operates is simple, but it suffers from uncertainty concerning the water level at which the erosion phenomenon will begin and as to the speed with which said fuseplug will be destroyed.
The resistance to erosion of an embankment dam or dike depends on numerous parameters, and in particular: density thereof (and thus in particular the extent to which the embankment is compacted in an earthfill dam); the nappe, determines the speed water flows over the downstream slope; and the presence of grass or other vegetation on the downstream slope increases the resistance of the dike to erosion.
Since fuseplug dikes must destruct only for flooding of very low probability, in particular exceptional floods of the kind that occur once in 100 years or in 1,000 or more years, there is uncertainty concerning how some of the above-mentioned parameters will vary over time (e.g. the plant cover on the downstream slope).
Tests on scale models and real-life experience on embankment dams or dikes that have suffered spillage over their tops have shown that they are sometimes capable of withstanding nappes that are several tens of centimeters thick (i.e. the height of the nappe is several tens of centimeters) for several hours (see the report of the 16th International Congress on Large Dams, Q.63-R.35, 13-17 Jun. 1988, pages 560 to 569, and in particular Table 1 on page 563). As a result, in the event of an exceptional flood, if the fuseplug dike is not destroyed rapidly, water can continue to accumulate upstream of the dike and can rise to a level that presents a danger for the remainder of the hydraulic structure before the fuse-plug dike has been destroyed.
In an attempt to remedy this drawback, proposals have been made to create at least one pilot channel or breach in the top of the fuseplug dike wit
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Graysay Tamara L.
Hydroplus
Lee Jong-Suk
LandOfFree
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