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stadia rod which gives the present H. I. He also reads the upper cross hair, and then the entire stadia interval (telescope remaining level). (In this way he had a check not only on the distances, but also on the level reading, because if either were in error, the half interval consisting of the level reading and the upper cross hair reading would not be consistent with the entire stadia interval. In that case the observation was repeated until there was agreement.) This check was of especial importance because, owing to the fact that only every alternate station was occupied by the instrument, there was only one stadia determination of the distance between stations. On the later surveys the following check for azimuth was used: The compass box was set for the magnetic deflection and the bearings of the rear and forward stations read.

Then the compass box was set for zero deflection and the bearings again read. If the readings were all correct the latter set differed from the former by the amount of the deflection. Section lines and corners were also tied in wherever possible, giving an additional rough check.

The rear rodman, having given the above described rear shot, moves forward, giving such side shots as are necessary to give the topography adjacent to the river banks and as far back as the bluff line where this is within a few hundred feet of the river. (It must be borne in mind that it is not the function of these surveys to show the topographic features in elaborate detail, but only to show them in a general way and thus indicate the most feasible reservoir and dam sites, which it is expected will be surveyed in detail by those interested. In general, sufficient side shots are taken to sketch in the 5-foot contours.) The rear rodman having given the necessary side shots-which are augmented by hand level and pacing by the topographer in the vicinity of the station occupied-proceeds to a point on the river bank from 1,500 feet to 2,000 feet beyond the front rodman, so that when the transitman mives up he will occupy a position midway between the two, thus giving a back shot and front shot of from 750 feet to 1,000 feet each. Of course if the river was very winding it was not possible to take shots as long as this, as the rodman was not visible.

During the open season the traverse points were chosen on the banks of the stream, the two rodmen keping on one side and the topographer and transitman on the other. In this way every odd numbered station (transit station) was on one side of the river and every even numbered station (not occupied by transit) on the other side. Canoes were used getting across the river whenever necessary.

During the winter season, however, the party walked along the channel of the river, and as the ice was usually from 1 to 2 feet thick, the stations were taken directly on it. In both seasons the elevation of the water surface was taken at the head and foot of all rapids, falls or dams, and at least every half mile in smooth stretches. These water surface elevations were the most important part of the survey, as from them the profile was made.

In order to determine the magnetic variation, observations on Polaris or solar observations were made every few miles, and whenever local attraction was suspected the station was occupied by the transit and azimuth carried in the regular way, but very little evidence of local magnetic attraction was found.

To show the true conditions the river profile must be referred to a stage that is constant throughout the length of the stream. Gages were accordingly set at different points and read daily during the survey. As river surveys could be made only during the summer, fall, and winter, when flow is fairly steady, it was possible to determine a low-water stage at one gage where the gage reading was practically constant long enough for water to traverse the entire length of the river, and during this time readings were also made on all the other gages. These simultaneous readings determined for each gage the low-water stage, which was taken as the reference plane. Whenever the gages indicated a stage differing from the determined standard, the water elevations for those days were properly corrected by the amount indicated by the nearest gage. As there was no great variation in condition of flow of the rivers surveyed, the relation of discharge to gage height was fairly constant between two adjacent gages and little appreciable error was caused by correcting water elevations according to the nearest gage.

The initial elevations for each river survey were taken from a bench mark of the Mississippi River Commission, United States Geological Survey, or from a railroad bench mark, and thus all elevations were referred to mean sea level. By utilizing the surveys of various Federal and State organizations it was possible to get occasional independent cheeks in the level line. The results. of these checks showed that though the accuracy was not equal to that of good wye-level work, it was well within the limits required for a preliminary survey of this type.

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RESERVOIR SURVEYS

The lakes were surveyed to ascertain their availability for use as reservoirs. As the storage of the entire runoff for a year at any of the lakes would require only a few feet additional feet capacity, data were needed to determine whether it would be more feasible to create the necessary storage by raising the water surface, or by lowering the surface by dredging the outlet and allowing the difference between the lower surface and the natural surface to represent the storage. For this purpose it was only necessary to locate the 5-foot contour above the water surface and the contour of 5-foot depth.

A closed main traverse was run around each lake and to this traverse were tied the necessary side shots or side traverses to locate the 5-foot above-surface contour and the necessary soundings to locate the contour of 5-foot depth. These soundings were usually made by means of a stadia board held at the proper place by a rodman in a canoe or boat.

As no greater storage was needed than would be given by lowering the lake surface to a maximum of 5 feet, soundings at greater depths were not taken except in the Mille Lacs survey, where soundings across the lake were made from a steamer running at uniform speed on a definite course, from a station on the main traverse, to the opposite shore. The soundings were taken at regular intervals, and plotted at equal intervals along the projected

course.

The principal shots were plotted as in the river surveys and the 5-foot contour was sketched in the field.

Ottertail Lake was surveyed by the topographic branch of the United States Geological Survey in connection with work in that section of the State. The standard methods of that branch were used except that the scale was somewhat larger, and at the request of the water resources branch special soundings were made for the contour of 5-foot depth, in order that the results of the survey · might be used to determine the reservoir capacity.

DEVELOPED WATER POWER.

The work of compiling data relative to the developed water power in Minnesota was carried on in 1909 and 1910, altho where necessary the data were revised to show the situation existing in 1912. Most of the plants (including all of the larger ones) were visited by one of the engineers connected with this office. When all the plants on the main rivers and their chief tributaries had been visited, a letter was sent each County Auditor asking at which points

in the county water power was being developed. In this way information was obtained concerning a number of additional plants (most of them developing less than 100 horsepower) and data for most of these were procured by mail. As a result of this work it is believed that from the completed list very few plants were omitted, and those of very small size.

For each plant, answers to the following questions were obtained so far as possible from the owner or operator:

1. Name of stream on which power is located.

2. To what large river is the stream tributary?

3. Location of power in township, county; above or below what tributaries?

4. Name of mill or power station.

5. Name and address of owner, or operator.

6. Have any records of height of water been kept?

7. What discharge measurements have been made in this locality? By whom?

8. Installed horsepower; average horsepower actually devel

oped.

9. Use to which power is applied.

10. Market price of power in this locality.

11. Method of supplying water to wheels (canal or flume, pipe

line, etc.).

12. Operating capacity of canal or pipe line.

13. Pondage (approximate area, range of head, capacity, flash

boards).

14. Total operating head forebay to tail race.

15. Water wheels (kind, make, age, size, usual gate opening, rated power at usual gate and head).

16. Water wheel governors (automatic or otherwise, make). 17. Generators (make, kilowatts, voltage, phase, current, connec

tion, remarks).

18. Transmission lines (location, length, voltage, size of wire, kind of poles, etc.).

19. Hours per day plant runs.

20. Auxiliary steam horsepower.

21. Portion of stream flow plant is entitled to.

22. What part of year is water supply sufficient?

23. Additional remarks.

No tests were actually made, altho the installed rating of the wheels was checked by the manufacturers' tables, using the average head available. The installed horsepower in hydro-electric plants was taken as the rating of the water wheels and not from the electrical generators attached. Exciter wheels were omitted.

UNDEVELOPED WATER POWER.

The estimates of undeveloped water power are based on the special surveys showing fall and contour (latter for possible dam sites) and on stream-flow records. As the minimum flow of the streams almost without exception occurs during the winter months, and as from the character of the records only monthly estimates. of flow are made, the unit of flow is the monthly mean.

The flow for some days may fall somewhat below the mean for the month, but this shortage is partly or wholly offset by the fact that the horsepower is estimated for continuous flow although in practice the demand for power may not be continuous. It there is sufficient pondage at the power site the water supply during the hours of minimum demand can be stored for release during the hours of the peak load..

In estimating the water power available for commercial uses it is necessary to consider the amount that can always be developed, except at manufacturing plants (such as pulp mills) where the output can be increased and decreased with the water supply.

From the profile of the river and the sketch of the topography adjacent to the shore line possible dam sites have been selected. In general no head of less than 15 feet has been considered, as the low-water flow of the streams is so small that developments at lower head would hardly prove commercially feasible.

Although the records for most of the stations cover only the last three or four years, two distinct periods of extreme low flow occurred during that time. In most parts of Minnesota the rainfall for 1910 was lower than for many years. Plate I. shows the rainfall at three stations in different parts of the State. The great deficiency in precipitation caused the lakes and the ground water to fall so low that during the following January and February, when the flow was dependent on those two sources of supply, it reached the lowest stage in many years, as is shown by certain . long-time records. This statement applies to Rainy, Red, St. Louis, Snake, Kettle, lower Minnesota, lower Rum, Sauk, and Root rivers. On the Crow Wing the lowest flow occurred in the summer of 1910. On the Red Lake and upper Rum rivers the drought of 1910 so dried out the swamps surrounding Mille Lacs and Red Lake that the lakes were probably at minimum level in the latter part of 1911, for the rain that fall at that time was absorbed by the ground and did not reach the lakes. Thus, the extreme cold weather in the first part of 1912, taken with the extreme low lake levels, caused the flow of the Red Lake and upper Rum rivers during that period to be less than during January and February, 1911. The long-time records on the Mississippi show that the flow

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