Best Methods of Obtaining a Good Water Supply

JAMES P. WELLS
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Best Methods of Obtaining a Good Water Supply

Filtration System and Pumping Station—Uses of Auxiliary Reservoir—Causes of Insufficient Pressure—Preparations for Bond Issue—Surveys, Plans and Specifications—Personnel of Engineers

(Continued from page 1301, Vol. LXVlll)

Construction of Filter Plant

If it is necessary to filter the water coining from the reservoir, then it probably will be best to build a filtration plant directly in front of the dam, though, under some conditions, the filtration plant may be located on high ground near the city. In two instances where the writer has designed and supervised the construction of filter plants in connection with gravity systems, the filter plant in each case has been located at the dam. From the dam or from the filtration plant, if such is necessary, one or more conduits will lead to the city. The conduit must be large enough so that when the water flows through it the amount of head or fall lost in friction will not he so great but that there will be sufficient pressure remaining for the needs of the city. There are several types of conduits in use, pressure pipes, tunnels and open channels. All three types of construction, the pressure pipe, the tunnel or the open channel, might have to be used in different sections of the conduit. In the majority of cases a pressure pipe alone will be used.

Newark, N. Y., Gravity Water Supply Coffer dam construction for pipe line across Canandaigua Lake outlet. Pipe was imbedded in concrete

Pipe lines are built of four different materials, cast iron, steel, wood or reinforced concrete. It is not possible to say which of these materials is the most suitable. It depends entirely upon the conditions which exist in each particular problem.

Uses of Auxiliary Reservoir

If there is a convenient hill located in the city or on its outskirts, an auxiliary reservoir should be constructed to hold enough water so that if the pipe line leading from the storage reservoir to the city should break there would be an adequate supply of water in the city while the break was being repaired. Such a reservoir would serve not only the above purpose, but it would act as an equalizer upon the flow of water through the conduit from the storage reservoir to the city. If there were no reservoir at the city, there would be a great variation in the amount of water flowing through the conduit, for the amount of water that is used during the twenty-four hours in any city varies greatly from hour to hour. During the day when the factories are operating and when everybody is using water there is about four of five times as much water used as during the earlier morning hours when most people are asleep. This being the case, if there were no reservoir in the city there might at certain times during the day be twice as much water flowing through the pipe as the average rate of flow for the entire day. If such were the case there would be approximately four times as much friction in the pipe, and in order to have sufficient pressure in the city at all times it would be necessary to have a pipe much larger than would be the case with the equalizing reservoir located in or near the city. For in the latter case the flows through the conduit would be uniform. During the night the water would flow into the equalizing reservoir and during the day it would flow out again to supply the excess required. If there is no high ground in or adjacent to the city, then it is essential that an elevated steel tank or standpipe be constructed. This will permit of a limited amount of water being stored in the city. However, the cost of such a structure in proportion to the amount of water stored is considerable as compared with a reservoir located on high ground.

Diagram Showing the Actual Comparative Cost of Operation of a $45,000 Pumped Supply and a $300,000 Gravity Supply

Location of Pumping Station

In case there is no chance of getting water by gravity and it is necessary to pump the water, then the essential points to be sure of are, first that the pumping station be so located on the stream from which the water is to be pumped that it will be above any points where the stream is contaminated or may be contaminated in the future. This, of course, is not always possible, but an effort should be made to accomplish it. The writer has recently been studying a water supply situated in a large city where the present pumping station is located a short distance down the river from the most logical outlet of the city sewer system. Had the pumping station been located a short distance farther up the stream this could have been avoided. In pumping water from a stream one of the most essential considerations is the selection of the kind of power to be used in driving the pumps. Ordinarily, with any large installation, there are two methods of doing this: either by steam or electric power. In the first case it is necessary for the city to build its own power house, have its own boilers, and furnish the necessary steam to the pumps. In the second case the electricity may be purchased and the first cost of installation will be much less than in the case of the steam-driven pumps. One of the most important questions to be considered in making a choice of supply is the question of the reliability of service. If the plant is to be operated by electricity, is it certain that the electricity can be furnished at all times; or, if not, will the interruptions in the service be such as to cause an interruption in the supply of water?

As in the case of the gravity system, the construction of a reservoir in or near the city at an elevation high enough to insure sufficient pressure from the water in the reservoir will materially benefit pumping conditions. If such a reservoir has been constructed, then there is a reserve supply and if the pumps fail for any reason the reservoir can furnish what water is needed during the time the pumps are being repaired. Further than that, in the case of electrically driven pumps, it will probably be possible to buy electric power very cheaply for use during certain times of the day, when very little power is being used by other customers of the electric company.

LeRoy, N. Y., Gravity Water Supply Excavating trench for LeRoy pipe line. Twenty-two thousand feet of 14-inch cast iron pipe for this supply were laid in twenty-five days

Filtration Plant Near Pumping Station

If the water from the pumping station is to be filtered, the filtration plant should ordinarily be located adjacent to the pumping station. In fact, in many cases the pumping station and the filtration plant are in one building. The water is first pumped to the sedimentation basin passing from there on to the filters, then into the clear water basin, and from there is pumped directly into the city mains. This arrangement requires two sets of pumps and this is in most cases necessary wherever a pumping station and filtration plant are installed. The first set of pumps are usually known as low-lift pumps as they only have to raise the water to the level of the sedimentation basin. The other pumps are spoken of as high-lift pumps as they pump the water under high pressure directly into the city mains. In some cases the reverse is true; that is, the filtration plant is located at an elevation high enough so that the water after it is pumped to the filtration plant need only to be pumped under low pressure into the city system. From the writer’s observations, however, the filtration plant located at the pumping station is a more economical arrangement than to have the two widely separated, though this depends upon the local conditions.

Newark, N. Y., Gravity Water Supply Spillway showing first overflow of lake after completion of project

In studying the water supply situation of a city it often develops that water can be obtained in more than one way and it is a question which way is the best. It may be possible to pump and filter water from some nearby river or lake, or it may be possible to get water by gravity by building a storage reservoir on a stream distant from the city. In the latter case the water may or may not have to be filtered. In the case of the pumping proposition the first cost is low and depreciation and operating cost is high. The more water that is pumped the greater is the annual cost, so that the cost increases each year. In the latter case the first cost is ordinarily much higher, but the annual cost decreases as the bonds are paid off, and eventually there will be a very small annual expense. One advantage of the gravity plan over that of pumping, which must not be overlooked, is that there is no danger of the water supply being cut off by inability to operate the pumps, as might be the case with a prolonged coal strike. The subject of getting water by gravity from storage reservoirs is one that has not been given sufficient attention by a great many city officials. It is almost always true that a city located in a hilly or mountainous country can get a much more satisfactory water supply by gravity from a storage reservoir than by pumping. The writer knows this to be a fact by actual experience in designing and building such gravity supplies to replace pumping plants.

Causes of Insufficient Pressure

Even though the supply of water is pure and there is an adequate supply of water, it is not always the case that there is sufficient pressure for ordinary usage, so that in the case of a large fire the pressure may be inadequate. Insufficient pressure results from two causes. The first is that the pressure of the water as it comes from the source of supply, whether it be from pumping or from gravity, is not high enough; and the second is that even though the initial pressure is high enough, the mains through the city are not large enough to carry the water where it is needed without excessive loss in friction. The first condition can be remedied by the installation of what is known as the Booster Pump, which takes the water at a certain pressure and repumps it, adding pressure to the water. If this is not possible for fire protection, the pressure will have to be increased to the required amount by the use of portable pumping engines. In the case where the mains are not large enough the best remedy is to put in larger mains where they are necessary. Until this is done portable pumping engines will have to be used, but if the mains are very small even these may not furnish the required pressure. As soon as it is certain that the funds will be available for the proposed undertaking, surveys, plans and specifications should be made under the direct charge of a competent hydraulic engineer for the carrying out of the proposed work. When this work has been completed contracts should be let and the work carried out to completion. In the letting of contracts for public works there are four principal methods of proceeding with the work: 1st, by day labor, in which case the city pays directly for all labor and materials; 2nd, by the cost-plus percentage contract, in which a certain contractor is engaged to do the work, he buying the materials and paying the labor and receiving a certain percentage of the cost as his compensation for doing the work; 3rd, the costplus fee basis, where the contractor carries on the work, buying the materials and paying the labor himself, and is paid a fixed amount for his services instead of a percentage; 4th, where the contract is advertised and the bids are competitive, the contract being awarded to a contractor who agrees to do the work for a lump sum or at certain unit prices. The unit price is in most cases more satisfactory than the lump sum. It is fairer toboth parties and fewer disputes arise. With the unit price contract the total amount paid the contractor varies in proportion to the amount of work done. That is, he may agree to put in 10,000 cu. yds. of concrete at $15.00 a yard, or a total of $150,000, and if there are 11,000 cu. yds. he would be paid $15,000 additional to the amount bid; or if there were 9,000 cu. yds. he would be paid $15,000 less than the amount bid. If the bid were a lump sum the price would be the same whether there was more or less work done than was originally expected.

145,000,000 Gallon Reservoir and Filtration Plant When under construction at LeRoy, N. Y. Has been in successful operation four years

Enough has been said about the actual construction work that needs to be done, in improving a city’s water supply system. Once the city official is satisfied that the water supply system needs improvement, the first step to take is to have a competent hydraulic engineer make a thorough investigation of the needs of the city. After such an investigation is made the engineer should make a report to the city officials. This report should in a general way cover the following subjects: A brief description of the existing water supply system, with a study of the conditions of operation, an estimate of the future needs of the city in regard to its water supply, as based upon population statistics, and the general industrial future of the city; a study of the available sources by which the water supply of the city may be increased, estimates of cost of different possible improvements and also estimates of annual cost. These estimates of cost should be on the safe side; that is, if an engineer is satisfied that an improvement will cost a certain sum of money, he should make his estimates large enough so that there will be no possible chance of the work finally costing more than his estimates. Several other important points should be touched upon in the report, depending upon the particular conditions. The entire report should be so worded and arranged and sufficiently free from technical phrases so that the entire water situation as stated by the engineer with his recommendations can be clearly understood by the average citizen. After such a report has been made, there should be no question as to what are the proper steps for the city to take in the improvement of its water supply.

Once a definite improvement has been decided upon by the city officials, the next step is to raise the money to carry out the undertakings. The manner of doing this will depend on the city’s charter and the legal power of the city officials. In some cases money can be appropriated by the city officials without a vote of the taxpayers, and in others a bond issue has to be voted upon by the taxpayers.

Preparation for Bond Issue Election

The greatest care should be exercised by the municipal officials in drawing up resolutions and in proceeding correctly in the preparations for an election where a bond issue is to be voted upon. A great many times a technical error has made the election illegal, and as a result a new election has had to be held before the bonds could be issued and sold. There are attorneys who make a special business of such work, and it oftentimes will result in a considerable saving of time and money if they are consulted. It has been the writer’s own experience that it is much more satisfactory in the successful carrying out of any large improvement that the public be fully informed through the city newspapers as to just what it is proposed to do and the reasons for doing it.

Surveys, Plans and Specifications

(Continued on page 72)

Obtaining a Good Water Supply

(Continued from page 60)

Methods of Carrying Out Work

Of the four methods mentioned above the first method of doing the work—by day labor—especially where any large quantity of work is involved, is rarely satisfactory, and can only be so where one man is put in absolute charge of the work who is a competent executive and who is not hampered in any wav by requests to buy his materials of certain favored people, or to place certain men on the work, regardless of their ability. The second method—that of letting a contract on the cost-plus percentage basis, is also ordinarily unsatisfactory. However honest the contractor might be in his desire to keep the cost of the work down, it will be known throughout the entire job that the work is on a cost-plus percentage basis and that the greater the cost of the work the more will be the contractor’s profit. This being the case, the foremen and men on the work who are working for the contractor are inclined to take their time about doing work, and often deliberately increase the cost, thinking that by so doing they are benefiting their employer. The third method, that of doing work on a cost-plus fixed fee basis, gives no incentive to increase the cost either on the part of the contractor or on the part of the men working for him. If the cost is increased his fee remains the same, and his natural impulse will be to get the work done as soon as possible, so that his plant and his organization may be busy on some other work. The fourth and most common method of letting contracts is to advertise for bids and then award the contract to the lowest bidder or to one of the low bidders. There are some features of doing the work in this way which are not satisfactory. When the bids are received they may vary greatly in their magnitude. One contractor may be willing to do a certain piece of work for $300,000 and there may be several others willing to do it from prices varying from this amount up to $500,000. Even though the contract is let to the lowest bidder whose bid we will say is $300,000, this does not signify that the work can be done for this amount of money. After the contractor has started the work and partially completed it, labor conditions and the prices of material may increase to such an extent or other conditions may arise such that he will be unable to complete the work and he may have to abandon the contract or the city officials may decide to take the contract away from him. Ordinarily in the case of such contracts it has been necessary for the contractor to furnish a bond with the contract. To those unfamiliar with the carrying out of public works this bond may appear to be the greatest safeguard; however, in many cases bonds have been of no value. In case the contractor falls down on his contract the bonding company may immediately begin to look for places whereby it can be released from its responsibility. Almost all public work is carried through with some changes in the original plans. The bonding company may contend that these changes have released them from their responsibility, or there may be several other reasons why they should not fulfill the requirements of the bond and in very many cases it means a long drawn out legal battle which in the end is more costly than if there had been no bonding company whatever. As a safeguard against this last trouble it is essential that the city officials let their contracts to responsible contractors, even though they are not the lowest bidders, but whom they know, even though the work may cost them more than they anticipate, will be able and willing to carry through the work to completion. Of the four methods of letting contracts, the third method is probably the fairest to all concerned and the most satisfactory if the city officials have the authority to let contracts in such a manner. The essential precaution is that a contractor be selected who is absolutely certain to do the work efficiently and economically. If authority is lacking to let a contract on a cost plus fixed fee basis, then the best method is to advertise for bids and award the contract to a contractor who has done work of a similar nature and who without question is financially able to carry out the work.

Personnel of Engineers.

A word as to the personnel of the engineer in charge of making the plans, specifications and carrying out the work. It is necessary first of all that he be a practical man of some business knowledge and not a theorist. It is necessary that he should have had special training in the work which he has to do. It is also essential that he should have had some practical experience in dealing with men. Many contractors have been forced into bankruptcy because the engineers on the work loved to split hairs and insisted on refinements in construction absolutely beyond all reason. Too often the attitude toward contractors is that they are dishonest and will attempt to beat the city whenever they have a chance. The writer’s own experiences with contractors have been that they are just as honest as men in any other business and if treated fairly will do their utmost to give the best kind of work for the money which they receive.

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Best Methods of Obtaining a Good Water Supply

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Best Methods of Obtaining a Good Water Supply

Practical Suggestions by Hydraulic Engineer as to How to Accomplish This Object — Necessity of Careful Planning by Competent Engineers—Various Problems to Be Met

Hydraulic Engineer, Rochester, N. Y.

HAVING had considerable experience in the carrying out of municipal water supply improvements, and knowing some of the pitfalls that municipal officials are apt to get into in connection with such undertakings, I have thought that some suggestions based on the writer’s own experiences might save the readers of FIRE AND WATER ENGINEERING considerable time and money. Any city official, whether it be the mayor, water commissioner, commissioner of public works, city manager, or water works superintendent, is vitally interested in his city’s water supply. A good water supply is one of a city’s greatest assets. If the water is impure, the general health of the residents will be low. There may be typhoid epidemics. If the water is discolored, it may do no actual harm, yet people will not like to use it. The fact that the water is bad will become a matter of common knowledge in other parts of the country, and prospective residents will hesitate to bring their families to the city. If there is an inadequate supply of water, many new industries considering locating in the city may decide not to come because they are not sure that they will have sufficient water for their needs, and there are many industries which require great quantities of water. If the water is hard, not only will this condition have an ill effect on the health of the people, but wherever boilers are used there will be considerable scale formed on their interior which will mean a constant expense to the owners of boilers. As a further inconvenience from this condition, much more soap will have to be used for washing purposes, the total extra cost of which represents a considerable sum of money. If the pressure on the water system is bad, the losses from fire will be excessive. If the water for the city is obtained at an excessive annual expense as compared with other cities, then the city is at a disadvantage in that the expense to its citizens is much greater than in other cities having a more economical water supply.

James P. Wells

Perfect Water Supplies Are Rare

If the water supply is perfect in every respect, then the municipal officials need have no cause for worry. They are extremely fortunate. However, such is rarely the case and improvements of some nature are invariably needed.

If the water is discolored and impure, the safest way to take care of the situation is to install a filter plant with sterilizing devices. There are two types of filters which are most common at the present day, slow sand filters and the rapid sand or mechanical filters. The first mentioned, the slow sand filter, is the older type, which mainly consists of a settling basin, large beds of sand with under-drains and a basin to collect the filtered water. The first step in the process is either to pump the water or allow it to flow by gravity into a settling basin. The water passes from the settling basin to the top of the filters, passes slowly through the sand to the drain beneath and from these drains to the clear water reservoir or basin. The slow sand filters cover a considerable area and periodically the sand has to be removed from the surface and washed. In some cases it has been necessary to use chemicals at the settling basin to assist in settling out the suspended matter in the water. In cold climates the filters should be covered, otherwise they will freeze and their effectiveness will be greatly reduced and the cost of operation will be excessive.

The Mechanical or Rapid Sand Filter

The rapid sand or mechanical filter is similar in its construction and operation to the slow sand filter, but there are some points in which they differ widely. With the rapid sand or mechanical filter a much smaller space is required for the construction of the filter plant. Like the slow sand filter, it consists essentially of three parts, the sedimentation basin, the filters and the clear water well. The water first comes to the sedimentation or settling basin. As the water enters the sedimentation basin a chemical is introduced. This is ordinarily alum or sulphate of aluminum, though sulphate of iron is used for the same purpose. The sulphate of aluminum when it is added to the water produces a slight flakey precipitate. This precipitate as it settles in the water takes with it a large part of the suspended matter. The effect of the sulphate of aluminum is to greatly hasten the settling action, from the sedimentation basin the water, still containing some of the precipitate, passes on to the filters. As the water passes through the filters quite rapidly, they do not need to take up much space. The filters are ordinarily arranged in units, each having the capacity to filter a certain amount of water during the day, say 500,000 or a 1,000,000 gallons. A plant built to filter 20,000,000 gallons per day might have twenty filter units. The filter bed itself is made up of approximately 2 1/2 to 3 feet of sand underlaid by from 9 to 12 inches of gravel. Below the gravel are the strainers and underdrains and also the air system which will be mentioned later. After the water filters through the sand and gravel it passes through the strainers located in the bottom of the filter bed into a system of drains and from these into the clear water basin. After the water reaches the clear water basin it is fit to drink. Because of its small area the rapid sand filter gets dirty much quicker than the slow sand filter. The method of cleaning the filler differs radically. With the rapid sand filter the sand is washed without removing it from the bed. This is done by simply reversing the flow and forcing filtered water through the filter in the opposite direction and agitating the entire filter by compressed air blown through it. Any filth or dirt in the filters comes to the surface and passes from the filter into gutters above the level of the sand and from these into a sewer. Ordinarily each filter unit has to be washed every day. However, there is no fixed rule as to this, in some cases they have to be washed two or three times a day. It depends upon the condition of the water when it enters the filter plant. After a storm when the water entering the filter plant may be muddy or turbid, larger quantities of chemical have to be used, and the filters have to be washed more frequently.

Typical Earth and Concrete Section of Several Dams

In recent years there has been a tendency to construct rapid sand or mechanical filters in preference to slow sand filters. The principal reasons for this are that the rapid sand filter is ordinarily much lower in its cost of installation. It takes up less space and it is much easier to handle satisfactorily the different conditions of water which exist from day to day. Generally speaking, the total annual charges, consisting of interest, depreciation, sinking fund deposits and cost of operation are less with the mechanical filters than with the slow sand filters.

Use of Liquid Chlorine in Sterilization

The effect of the chemical, sulphate of aluminum and the filtration process toward bettering the quality of the water is mainly to remove the suspended matter and as this process takes place the bacteria are also removed. However, filtration is not always absolutely effective, and in the water after it is filtered there will often be found harmful bacteria. This being the case, it is necessary to use some other means of securing complete sterilization. The most common methods of obtaining satisfactory sterilization are by the use of chloride of lime and liquid chlorine. Of the two, liquid chlorine is generally the more satisfactory. This material comes in small cylinders and is introduced into the water in minute quantities by a small compact apparatus. Liquid chlorine is often used with very satisfactory results where no filtration plant is needed. Great care must be taken in the use of chlorine to be sure that it is put in the water in proper proportions. Where the quantity of water used by the city varies greatly during the day, an apparatus should be installed so that the supply of chlorine is automatically regulated in proportion to the amount of water used. Otherwise there will be a very unpleasant taste and odor to the water.

Typical Section Through Spiliway Dam on Cork Creek No Sheet Piling was Necessary at LeRoy and Newark, as Foundation was Impervious MaterialFront View, Earth and Concrete Storage Dam Recently Constructed in Eastern New York on Cork Creek 50,000 Yards of Earthen Embankment. 6,000 Yards of Concrete. Height, 50 Feet. Bottom Thickness, 260 Feet.

A very effective agent in improving the quality of water from the standpoint of odor is by aeration. Aeration may be obtained by allowing the water to come through a fountain or by allowing it to run over a series of artificial waterfalls. The essential purpose is to permit the air to mix with the water so that any offensive odors may pass off in the atmosphere. Not all water needs to be filtered and in fact some waters are of a sufficient degree of purity that no sterilizing agents are needed to purify them, yet aeration is almost always desirable, especially at certain seasons of the year when algae are prevalent.

Problem of Hard Water

A very serious trouble in water and one that is very difficult to remedy is hardness. While there are several ways of softening water, they are in general expensive. The first cost of installation is high and the cost of operation is excessive. In general, where a city has a supply of hard water, the city officials should do their utmost to see that a new supply of pure, soft water can be obtained. This is not always as difficult as it first seems. While the underlying rock formation in the vicinity of the city and the region in which the city is located may be limestone or other rock tending to produce hardness in water, yet at some point some distance from the city it may be possible to find soft water which can be piped economically to the city by gravity.

In many cities the water is both pure and soft and yet there is not enough of it. Though the water system was entirely satisfactory when the city was small, as the years have gone by steps have not been taken to insure a sufficient supply for the future. This being the case, the present supply is entirely inadequate. There may be a pressing need for an additional supply. The question immediately arises where to go to get an additional supply of water.

Three Principal Sources of Supply

There are three principal sources of supply, springs, wells and surface water from streams or lakes. The first source of supply, that from springs, is only in a few isolated instances adequate to supply a large population. Springs are ordinarily small and often the water is hard and only a very limited number of people can be supplied from them. The writer has just prepared some plans for a small city that gets its supply from a large spring right in the center of the city and the additional supply will be from another spring only a mile distant. However, the water is hard and it is eventually planned to obtain a supply of soft water from the mountains about ten miles distant. Water supplies from wells are more common and there are several instances where large cities have an adequate supply of pure water from wells. Yet as is the case with springs, wells are not ordinarily large enough in their capacity to furnish large cities with an adequate supply of water and it is also the case that such water is often hard. Then, too, wells may furnish an adequate supply for the first few years of their operation, and as the years go on the quantity of water that may be obtained from them may diminish to such an extent that they will prove to be entirely inadequate for their purpose.

The principal source of supply which communities of any size must depend on is surface water. This may be from streams and lakes near the city from which the water must be pumped, or streams at some distance from the city from which the water will flow by gravity. If estimates are made, based on low water conditions, streams or lakes will generally prove more reliable as a means of furnishing an adequate quantity of water than springs or wells. The streams can be measured and the amount of water flowing into a lake can be measured. From these measurements, or, in fact, from measurements on adjacent streams, it is possible to estimate how much water can be obtained from a certain definite source. Such estimates must of course be conservative and there must be a with! margin of safety in estimating low water conditions. Water supplies obtained in this manner may be properly divided into two divisions, those in which the water has to be pumped and those in which it flows to the city by gravity. Ordinarily where a city obtains its water supply by pumping from a stream or lake, this stream or lake is located relatively near to the city. Probably the first cost of installation was low. Later the safety of the public health of the community may have required the installation of a filtration plant. In other cities, especially those located in hilly country, it has been possible to build a storage reservoir and bring the water to the city by gravity without filtration. Perhaps the most essential point in selecting such a source of supply as the above, whether the water is to be pumped or whether it will flow by gravity, is to be sure that there will be a sufficient supply of water at all times of the year. Also that the supply will be sufficient not only for the present needs of the city, but for many years to come. If the proposed source of supply is a large river or lake, then it is probable that no reservoir to increase the supply of water during the dry season will be necessary. However, if the stream is a small stream which has a very low flow during the dry season, then it will be necessary to build a storage reservoir large enough so that the flood waters of the stream may be stored in order that they may be used during the dry season. Such a storage reservoir not only increases the supply of water during a dry season, but it has a very beneficial effect upon the quality of water, for if the stream carries any sediment when it enters the reservoir, the sediment will settle and the water leaving the reservoir will be in a much better condition than the water entering it. While storage reservoirs have in some cases been built where it has been necessary to pump the water to the city, yet as a general rule storage reservoirs are built where it is possible to get water by gravity.

Strainers in Bottom of Filter Bed, Newark, N. Y., Water Supply Lateial Drains Are Benrath, Imbedded in Conc______te

(Continued on page 1312)

End View, Earth and Concrete Storage Dam on Cork Creek

Obtaining a Good Water Supply

(Continued from page 1301)

Storage Reservoir and Pipe Line

To obtain water by gravity by the construction of a storage reservoir and a pipe line to the city, there are certain things that must be done. First, a dam must be constructed on the stream. Ordinarily the type of dam will depend upon the local conditions. If there is abundant quantity of earth near the site that can be easily moved to the dam, it may prove most economical and desirable to build a dam out of earth and concrete. That is, there would be a concrete core in the center and earth on each side of this core. If there is no earth near the dam perhaps the most economical construction would be a concrete dam built heavy enough that the pressure of the water cannot tip it over. If the site of the dam is in a narrow gorge, perhaps an arch dam will prove most economical. There are two points which are of greatest importance in the construction of a dam. The first is to be sure that the dam goes down deep enough to prevent the water from going under it. The second is that the dam be so constructed that the water that will pass down the stream in a maximum flood will go by the structure without damaging it. More dams have failed from neglect to look after these two conditions than for any other reason.

(To be continued)

For the first time in a number of years the Willimansett, Mass., water department’s receipts have considerably run over its expenditures. Under the guidance of Superintendent Dillon, who took office last February, the department has been conducted on business-like lines and the foregoing has been the result. Superintendent Dillon has devoted all of his energies to bring the department’s administration to a condition of efficiency and results show that he has succeeded. Superintendent Dillon’s department received this year $124,855.63 and expended $121,402.67, leaving a balance of $3,452.96. In the fiscal year of 1919 appropriations to the amount of $219,171.95 were made to the department. In that year expenditures were $183,305.25, and receipts were $95,988.97.

It is expected that the selection of a site for the new dam that will house the surplus water supply of Columbus, Ohio, in connection with the proposed $3,500,000 extensions to the water works, will be made within the next month or six weeks, according to Clarence Hoover, chief of the extension bureau. All contour surveys have been completed and very little now remains to be done before selecting the site for the dam.

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