In order to obtain the volumes of water discharged at the different machines, flumes were established in the out‑fall canals of the present drainage stations, for the purpose of obtaining uniform sections through which all the water lifted by each machine would pass. The dimensions of these flumes were such as to suit the existing conditions at the different stations:
|At the Melpomene machine, the flumes had a width of||16 feet.|
|At the Bienville||23 feet.|
|At the Dublin||24 feet.|
|At the London||24 feet.|
Across the top of each flume a suitable wharf was placed for the operator, provided with a strong substantial rail, which rail was graduated to facilitate the use of the meter. The gauging was performed with a "Price" current meter, and the operation was as follows:
The elevation of the water in the drainage and out‑fall canals was observed and noted every 30 minutes, the difference in elevation being the height to which the water was lifted. Each time the gauging was made, a cross-section of the bottom of the channel was carefully taken and plotted. The meter was then placed in position six inches below the surface of the water and moved across the canal at a uniform rate. After which, the meter was lowered six inches more or one foot below the surface and moved in the same manner, and so on, the number of times necessary for the meter to be moved across the channel every 6 inches of its depths, and the calculation of velocity and discharge made in the usual manner, from the number of revolutions recorded by the register.
There was, also, located on each shaft, at each of the draining machines, a counter, which was constantly observed and recorded. The coal consumed was carefully weighed and a daily report made. The gauging of the discharge from the machines has been carried on very carefully from April 1st to , 1894, and all the varying conditions carefully noted, recorded and tabulated; and from the information thus obtained, a curve has been plotted from which can be obtained the discharge of the wheels, knowing the number of revolutions of the wheel and the elevation of the water in the inside and outside canals. These gaugings of the discharge of the machines were extremely arduous, as it was necessary for the work to be carried on continuously during and after rains, in order to obtain positive information of the amount of rainwater discharged, thus rendering it necessary for the men to remain at work day and night, oftentimes incessantly for periods of 36 hours.
The records of the gaugings of precipitation and discharge have been accurately compiled and tabulated, and graphical charts showing the amount of precipitation, in millions of cubic feet, falling on the area drained by each of the machines, have been prepared. These charts also show graphically the amount of water, in millions of cubic feet, discharged by each machine, the lift in feet and the coal consumed in tons.
p64 Plate V is a chart showing graphically, from April 1st to December 31st, 1894, the volume of precipitation falling on the entire area of the city now subject to drainage, the volume discharged by all the draining machines, the duration of storms in hours, the lift in feet, the coal consumed in tons, and the total rainfalls in inches, as registered at the City Hall Station.
Table VI is a record of the gaugings from April 1st, to December 31st, 1894, of the total volume of precipitation and the total volume of discharge by the different draining machines for the entire area of the city now subject to drainage.
Table VII is a record of the gaugings from April 1st to December 31st, 1894, of the total volume of precipitation and discharge from the area now drained by the Bienville Draining machine, which area is designated as the "First Drainage District" on Plate III.
It will be observed from this table that the proportion of storm water pumped in the aggregate after deducting the daily or normal flow varies greatly with the character of soil, as to its degree of saturation and imperviousness, and with the intensity of rainfall, as shown by the following table:
The largest proportion of the precipitation ultimately discharged by the draining machines was during the months of July and August, when heavy rainfalls occurred nearly every day.
During the month of October, after deducting the normal flow, the zzz djh exceeded the total volume of precipitation due to the fact that this month was very dry and a famine of cistern water prevailed. To alleviate the situation in the district drained by the Bienville Machine an extensive use was made of the water from the water works to supply, through gutters, the sections not having mains and a most liberal use of hydrants where mains existed, so that the normal flow was very largely increased. For the months of November and December it was from similar causes, also increased, so that the results for October, November and December cannot be considered as furnishing proper proportions as only comparatively light rains occurred during these months, a consideration of the results can be properly omitted.
The results from the other six months can be assumed as giving a reasonable proportion, under varying conditions, of the precipitation ultimately discharged by the present system. It will be noted that
p65 The soil during these four months was moderately saturated.
The soil during these two months was excessively saturated. During the two months of July and August it rained almost daily, but in July the daily rate of precipitation was more uniform than in August.
Table VIII is a record of the gaugings of the volume discharged by the several draining machines from the entire area of the city now subject to drainage, during a period of forty consecutive days, when no precipitation occurred. This Table also gives the volume of the average present normal discharge.
The area drained by the Dublin and Melpomene Stations (which stations act in conjunction in draining the area) has an aggregate of 7,709 acres. The present daily flow from this area, as determined by the foregoing table, equals 3.56 cubic feet per acre per hour.
The area drained by the Bienville draining machine (which is independent) has an aggregate of 2,170 acres. The daily flow, as ascertained from Table VIII would therefore amount to 20.8 cubic feet per acre per hour.
The area drained by the London Avenue Station has an aggregate of 3,478 acres. The daily flow from this area, as determined from Table VIII equals 5.8 cubic feet per acre per hour.
The ultimate daily flow to be discharged by the proposed system, will not be at a rate per acre, in excess of the daily flow now reaching the drainage stations. The sewerage system will be completed at an early date, and will receive a considerable portion of the water which now constitutes the daily flow, and an efficient system of drainage will deliver the run‑off into the outfall canals quickly, not allowing the water to remain on the soil, as it now does. This will very materially reduce the amount of percolation and the seepage forming a large part of the present normal or dry-weather flow.
The conclusion reached concerning the volume of daily flow to be handled is, that from the commercial part of the city, it will not exceed twenty (20) cubic feet per acre per hour, and, from the suburban and vacant portions of the city, five (5) cubic feet per acre per hour. On this basis, the system is arranged for the removal of the daily flow, which aggregates, at the different Pumping Stations, the following quantities:
Pumping No. 1 receives the drainage from 8,887 acres, aggregating 44,435 cubic feet to be delivered per hour.
Pumping Station No. 2 drains 5,384 acres (of which 1200 acres are allowed for at the rate of 20 cubic feet per acre per hour, aggregating 24,000 cubic feet, and 4184 acres at 5 cubic feet per acre per hour, aggregating 20,920 cubic feet per hour), making the total flow which will be required to be delivered from the section 44,920 cubic feet per hour.
The area drained at Pumping Station No. 3 contains 4,682 acres, and will furnish a normal flow of 23,410 cubic feet per hour.
Pumping Station No. 4 drains 2,153 acres, which will produce a normal flow of 10,765 cubic feet per hour.
Pumping Station No. 5 drains 2,878 acres, which will produce 14,390 cubic feet of normal flow per hour.
Algiers Station drains 948 acres, which will produce a normal flow of 4,740 cubic feet per hour.
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Sewerage & Water Board
of New Orleans
U.S. Corps of Engineers
New Orleans District
1895 Advisory Board Report
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