Don't Always Put Dam in Narrowest Part of Valley

by Fernando Abecasis, Head; Hydraulics Dept., National Civ. Engrg. Lab., Lisbon, Portugal,

Serial Information: Civil Engineering—ASCE, 1980, Vol. 50, Issue 6, Pg. 93-94

Document Type: Feature article


Hydraulic factors must be taken into account in dam planning and design, because the best structural design is not always the most economical. When the potential for downstream flood damage is high, the spillway assumes particular importance. Valleys may be too narrow to construct a spillway wide enough to ensure flow is not deep enough to cause problems. The energy in a deep flow is more difficult to dissipate than is the same amount of energy in a more shallow flow. Picote dam on the Duoro River between Spain and Portugal is an example. A 1962 flood discharge from the dam's bucket-type spillway formed a 65-ft-deep pit in the granite river bed beginning about 130-ft downstream from the dam. Further downstream, a 50-ft-high rubble bar formed. This happened even though the water was 100 ft deep. The rubble bar reduced the head at the dam, reducing its electric power generation capacity until repairs could be made.

Subject Headings: Spillways | Hydraulic design | Dams | Economic factors | Structural design | Floods | Energy dissipation | River and stream beds | Europe | Spain | Portugal

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