From the history of dam construction

Less than thirty miles from Cairo, in the Wadi-el-Garrawi one can still see the abutments of a huge dam. Its failure was so catastrophic that nothing of the sort was attempted again till over 3,000 years passed. It is supposed to have been built from 2,950 to 2,750 B.C. by some unknown Pharaoh with an architect far ahead of his time.

For an initial experiment in dam construction the size of the structure is surprising. It is 348 feet long at the top and about 265 feet at the base. It originally had a height of 40 feet. The construction of so huge a dam must have occupied the energies of many hundreds of men and animals for a whole season in this desert place. Quite possible the construction took place in summer to avoid interruption by floods. The dam was faced on the upstream side with a carefully laid covering of limestone blocks of about 50 lb. weight.

Except for the carefully laid upstream face, the dam appears to have been built in haste, particularly the downstream portion or, rather, what remains of it. One obtains the impression that the architect was pressed for time. He didn't think that the water might one day overflow the dam and ruin the structure.

One observes, too, that no spillways were provided to carry off surplus water. This absence of spillways leads us to the conclusion it was never intended to fill the reservoir completely. The problem before the ancient engineer was to build a dam large enough to withstand any flood that was likely to come down the Wadi-el-Garrawi. The ancient Egyptians had a formula for computing the volume of a cylinder and may have had some rough idea of how much water their reservoir would hold if filled.

Evidently the dam had been erected to provide drinking water for the workers and beasts at alabaster quarries.

How much rain was it reasonable to expect? We, moderns, have an advantage over the designer of the Wadi-el-Garrawi dam. We know the area of the catchment's upstream the dam and we have rainfall records for over forty years. To estimate the proportion of runoff to rainfall is always difficult since it depends on the intensity as well as the actual amount of the fall. The slope of the catchments is very important, as well as absorption on a parched desert surface, the latter being a diminishing factor..

A rainfall of 10 millimeters or over in a single day occurs on the average in three years out of four in that place. During forty years there were 20 such falls, 10 of which exceeded 20 millimeters.

The ancients were obviously ignorant of the fact that a single millimeter of runoff from the catchments area of the Wadi-el-Garrawi is represented by a volume of water of 185,000 tons.

And so we came to the catastrophe. Not long after the dam was finished, perhaps with the very first flood to come down the Wadi — there is no silting upstream the dam — a breach took place. A fall of 20 millimeters, of which there have been ten in forty years, would be quite sufficient. Of those 20 millimeters, 8 would be immediately absorbed and a quarter of the remainder, between 500,000 and 600,000 tons would rush down the Wadi, fill the reservoir and overflow the dam. In a thundering cataract it was pouring down the downstream face and in a few hours the dam was destroyed. The contents of the dam would then rush down the Wadi to the cultivated lands and the Nile. So, in a few hours and probably at night were destroyed all the results of the labor of many hundreds of men and animals and the reputation of the engineer.

For us, situated at the distance of 5,000 years, it is hard not to feel sympathy with the unknown engineer who so boldly attempted the impossible — for that age. Had he made use of mortar, had he provided a spillway, had he chosen a gentler slope, how different might have been the history of Egyptian irrigation?

Word List

abutment - Опора	to withstand - витримувати
huge - великий	volume - об’єм
failure - провал	ancient - стародавній
to attempt - спроба	rough idea - мати деяку уяву
to be supposed - здається	to hold - утримувати
far ahead - далеко вперед	evidently - очевидно
initial - початковий	beasts - тварини
size - розмір	alabaster quarries - алебастрові кар'єри
feet - фут (1 фут=30см)	to expect - очікувати
top - верхівка	catchment - водозбірна площа
base - основа,	rainfall records - статистика опадів
to occupy - займати	to estimate - оцінювати
desert - пустинний	proportion - частка
to avoid - уникнути	actual amount - дійсна кількість
interruption - порушення	slope - нахил
upstream - проти течії	absorption - поглинання
carefully - ретельно	parched desert - випалена пустеля
limestone - вапняк	surface - поверхня
lb. - фунт (450 гр.)	to occur - траплятися
weight - вага	to exceed - перевищувати
to except - за винятком	ignorant - неосвічений
to appear - з’явитися	silting - замулювання
in haste - поспіхом	breach - розрив
particularly - особливо	sufficient - достатній
downstream - за течією	to rush - стрімко рухатися
to remain - залишатися	cataract - сильна злива
to obtain - отримувати	to pour - переливати
impression - враження	a few - декілька
to carry off - зливати	labor - праця
surplus - надлишок	sympathy - співчуття
absence - відсутність	boldly - сміливо
conclusion - висновок	mortar - скріпляти вапняним розчином
to intend - мати намір	completely - повністю
to fill - заповнити

Вправа 1

Визначте значення слів за подібністю з українською мовою і за словоутворюючими суфіксами:

cylinder, empirical, formula, intensity, absorption, portion, reputation, factor, fact, catastrophe, sympathy, architect, energy, problem, idea, Egyptian

Вправа 2

Знайдіть у тексті антоніми до наступних слів:

to increase, to construct, to begin, the former, upstream, presence, ancient

Вправа 3

Знайдіть у тексті синоніми до наступних слів:

to destroy, to reduce, to get, to try, to finish, to calculate, evident, the rest, excess, initial

Вправа 4

Доберіть правильні словникові визначення до слів: flood; rainfall; dam; catchments; runoff

Ø The amount of rain, usually expressed in millimeters or inches; depth of water on an area that reaches the surface of the earth.

Ø A barrier across a water course for the purpose of impounding water barriers built to raise water-level, to divert water, to create a hydraulic head which can be used to generate power.

Ø A relatively high flow in a river, markedly higher than usual; a body of water, rising and overflowing land.

Ø The area from which a lake stream or reservoir receives surface flow which originates as precipitation.

Ø Portion of total precipitation from a given area that appears in natural or artificial streams.

Вправа 5