70. Read the texts again and get ready to speak about the process of construction and main features of one type of dams. Use the information from the previous task.

UNIT V SPILLWAYS, GATES AND OUTLET WORKS

1. Study the following picture. Translate the terms into Russian.

a) spillway - ________	f) spillway crest - ________
b) cross section - ________	g) tainter gates - ________
c) forebay - ________	h) hydraulic jump - _______
d) tailwater - ________	i) bedrock - ________
e) flip lip - ________	j) stilling basin - ________

2. Find the translation of the following terms and memorize their meaning.

to narrow	elevation	overflow spillways
to widen	sufficient	chute spillways
the discharge of water	velocity	shaft spillway
the release of water	expansion	siphon spillway
gate	joint	side-channel spillway
safety valve	trench	past(prep.)
appurtenant	clay tile	a trough
flood	a conduit	perforated steel pipe
close limits	steep-slope	a sluiceway
to prefer	to maintain

3. Read the text to get the gist of it. Answer the following questions.

a) What is a spillway?

b) What are the spillways used for?

Text A Spillways

In the design of almost every dam there must be a spillway to permit the discharge of water. A spillway is necessary to discharge floods and prevent the dam from being damaged. Gates on the spillway crest, together with sluiceways, permit one to control the release of water downstream for various purposes.

A spillway is the safety valve for a dam. It must have the capacity to discharge major floods without damage to the dam or any appurtenant structures at the same time keeping the water level in the reservoir below some predetermined maximum level.

An overflow spillway is a section of dam designed to permit water to pass over its crest. Overflow spillways are widely used on gravity, arch and buttress dams.

Water flows over the crest of a chute spillway into a steep-sloped open channel which is called a chute, or trough. The channel is usually constructed of reinforced- concrete slabs 10 - 20 in thick. Such a structure is relatively light and is well adapted to earth or rock-fill dams when topographic conditions make it necessary to place the spillway on the dam. A chute spillway may be constructed around the end of any type of dam when topographic conditions permit. Such a location is preferred for earth dams to prevent possible damage to the embankment. The chute is sometimes of constant width. But it is usually narrowed for economy and then widened near the end to reduce discharge velocity. Expansion joints are usually required in chute spillways at intervals of about 30 ft. They should be as watertight as possible. Drains under the spillway are highly desirable. The drains may be rock-filled trenches, clay tile or perforated steel pipes.

A side-channel spillway is one in which the flow after passing over the crest is carried away in a channel running parallel to the crest. This type of spillway is used in narrow canyons where sufficient crest length is not available for construction of overflow or chute spillways.

In a shaft spillway the water drops through a vertical shaft to a horizontal conduit which conveys the water past the dam. A shaft spillway can often be used where there is no adequate space for other types of spillways. Small shaft spillways may be constructed entirely of metal or concrete pipe or clay tile. The large vertical shaft is usually of reinforced concrete.

If space is limited, the siphon spillway may be used. Siphon spillways have the advantage that they can automatically maintain water-surface elevation within very close limits.