Modern Methods of Constructing Reservoirs
Some Suggestions as to Best Types—Proper Size of Reserve Reservoir—Advantages of the Covered Style—Making Them Watertight
THE general subject of reservoir construction is one that is of vital importance to the water works superintendent, as errors along these lines are expensive and hard to rectify. The following hints from one who is an expert on this subject will therefore be found of considerable value:
The general term of reservoir refers to the storage of a reserve supply. A reserve supply of water is essential whether the water comes from wells, springs, rivers, impounding lakes, or any other source. It is the safety valve of the entire water system. A prudent business man will safeguard his family by insurance or safe investments. A far-seeing water works official will likewise protect the community by adequate storage reservoirs. It is an insurance policy that protects both lives and property. Its size or capacity is often inadequate, for in providing water improvements, if funds are short, the common practice is to cut down the size of the reservoir. Many small plants are operating with scarcely any* reserve supply, but why should a water works official shoulder the risk and responsibility of trying to “get by” and flirt with danger?
Breakdowns in Pumps, Pipe Lines and Equipment
The superintendent is treading on thin ice by putting all his dependence in the safety of pumps, pipe lines and equipment. They are always subjected to breakdowns, floods and unusual accidents. One superintendent’s excuse for not attending a water works convention was that he was afraid to leave home for fear of a breakdown. I’m wondering if that community would sleep peacefully at night if they knew the small margin of safety with which their lives and property were protected. The right kind of a water works official is fully justified in making known the needs of the water department and taking into his confidence the public not by written reports, for they are seldom read, but by warnings before civic organizations and the public press regarding the needs of his water department.
Lessons of the Berkeley Disaster
I recall clearly the disaster that happened at Berkeley, Cal., just a year ago. There, a city of about the size of Topeka suffered a loss of twelve million dollars, and in three hours, 1,200 of the finest homes in the city were totally destroyed. The circumstances surrounding that loss were unusual. The city had employed a city manager, who had previously had some water works experience in another state. He had been on the job less than one month and soon saw the need of larger reservoir capacity and larger feeder mains, and reported his recommendations toward a survey of the water needs. The city council replied that his advice was not new and such matters had been discussed for years. However, the manager insisted upon a report being made, but unfortunately their disastrous fire occurred upon the very day our engineers arrived to begin the surveys. Within an hour after the fire started, using twenty-five fire streams, the reserve reservoir was exhausted. Direct pressure through small diameter mains with their high friction loss produced ineffectual streams.
Proper Size of Reserve Reservoir
The size of a reserve reservoir supply as recommended by most Boards of Underwriters is three and one half times the maximum daily consumption. Some cities have far greater volume than this, one Western town, Flagstaff, Arizona, having fifty times its daily consumption, and will soon add another 50 million gallon reserve reservoir, their need of such a large reserve being due to the cold weather freezing through a porous volcanic ash ten to twelve feet deep, stopping the spring flow when a temperature of 20 to 25 degrees below zero is reached, and to tide over these extremely cold periods, a large reservoir is needed. The springs are at an elevation of over ten thousand feet, where low temperatures prevail. Reservoirs being such an important and also such an expensive feature of the plant, much time and thought has been given in recent years to the adoption of more modern methods of construction.
We can all recall the old, slow, tedious and expensive methods of slip and wheel scrapers and hand shoveling for earth removal and how it has given way to steam shovels, excavating machines, tractors, etc.; also the changes in mixing, handling and pouring of concrete regardless of weather conditions. With the advent of modern methods, the saving in time is a big item, one ten-million-gallon reservoir having been constructed in ninety-six days, the concrete walls and bottom being poured in one continuous pouring with three eight-hour shifts. The roof slab, 318 feet in diameter and nine inches thick being poured in sixty hours. With modern methods of construction, concrete covered reservoirs are displacing the open reservoirs with their algae and filth accumulating features. It has not been unusual to fish drowned cats. dogs, cows and even babies out of these uncovered reservoirs.
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Methods of Constructing Reservoirs
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Reservoirs Made Water Tight
In many of the earlier constructed reservoirs, there was too little attention paid to making them water tight, but now. by double floors, water-proofed concrete and various kinds of water-proofing membranes, these reservoirs are made absolutely water tight. By modern methods of construction, it is not uncommon now to have swimming pools of a million gallons or more capacity occupying and built on upper floors of fifteen or twenty story buildings.
Accomplishments of Good Sized Reservoir Supply
The value of a good sized reservoir supply can hardly be measured in dollars and cents, for in many instances, they have saved more than their entire cost by accomplishing:
First—Supplying the entire city when a break occurs in the main feeder of a gravity supply or pumping plant.
Second—Supplying a portion of the water at peakhours of consumption, thus avoiding the necessity of larger pumps and pipe lines.
Third—Enables pumping equipment to operate at uniform load, thereby securing higher efficiency in operation.
Fourth—Avoids drawing too heavily on wells, ruining their yield, through pulling sand against well strainers.
Fifth—Permits the smaller plants to shut down at night and the larger plants to have time for pump repairs.
Sixth—Enables the electrically operated plants to fill reservoirs at off peak loads at lower rates.
Seventh—Secures for cities lower insurance rates.
Eighth—Frequently gives fire protection when a breakdown in mains or equipment occurs.
Ninth—Often prevents an entire water famine for long periods of repair in floods or other disasters.
Tenth—Gives to the superintendent and community a feeling of greater security and peace of mind in knowing their lives and property are well protected.
(Excerpts from paper read before the Southwest Water Works Association’s Annual Convention.)