FORESTATION.

The headwaters of the main stream and its tributaries which lie in Wisconsin and in Minnesota, north of the line drawn diagonally through Douglas, Stevens, Meeker, McLeod, Sibley, Le Sueur, Rice and Dakota counties, are in a region that was originally forested. Most of this area has been cut over extensively, although a comparatively little land has been cleared, except in the southern part of the area where agriculture is making rapid strides. The remainder of the drainage area is prairie land. The upper stretch of the basin is in the jack-pine region, the middle part is in the region of hardwood timber. Although the timbered areas have been cut over extensively, conditions are favorable for forest reproduction and in many places are growths of young conifers which are just beginning to have a commercial value.

RAINFALL AND RUNOFF.

Rainfall records have been kept for many years in various parts of the basin, and from them it is seen that the mean annual rainfall decreases from 33 inches in the extreme southeastern part of the State to 24 inches in the western part. The mean annual rainfall for the entire basin is about 27 inches and from 3 to 4 inches occurs as snow which remains during the winter months.

A number of records in the upper part of the basin show that since 1888 the wettest year was 1905 when the rainfall was about 37 inches. In the driest year, 1910, the precipitation was 17.5 inches. In the southern part of the area the longest records are those at St. Paul which are continuous since 1837. The wettest year was 1849 when the rainfall was 49.7 inches and the driest 1910 with a precipitation of 10.2 inches.

Owing to the regulation of the upper river by the reservoirs, comparisons of annual rainfall and runoff at points on the upper river do not show the natural conditions. Since 1898, however, the mean runoff for the upper 4,500 square miles of drainage area has been 7.55 inches, or 27.5 per cent of the rainfall. At St. Paul complete runoff records are available since 1900, and as the runoff from only 15 per cent of the drainage area at that point is controlled, the comparison between rainfall and runoff will be more nearly natural. The runoff has varied from 1.62 to 7.26 inches or from 5.1 to 23.9 per cent of the mean rainfall over the basin.

The following table shows the annual variation in rainfall and runoff at St. Paul:

Relation between rainfall and runoff of Mississippi River at St. Paul.

According to some authorities, the basin of the upper Mississippi contains from 5,000 to 6,000 lakes, nearly all of which are near the sources of the main river and its northern tributaries. In addition there are vast swamp areas in this region, so that there is a great natural reservoir for steadying the flow of the river. Very little of this swamp land has been drained at the present time.

Far overshadowing the natural effect of the lakes and swamps on the flow of the Mississippi is the reservoir system operated by the United States Engineer Corps, chiefly in the interest of navigation below St. Paul. There are six reservoirs in the system described as follows:

Lake Winnibigoshish reservoir, which includes Cass Lake, is the unit nearest the source of the river. It is situated within the main channel of the river in Itasca, Beltrami and Cass counties, and is formed by a dam at the outlet of Lake Winnibigoshish which also controls the water of Cass Lake, further upstream. The first dam was a timber structure built in 1883-4 while the present dam is of the steel concrete type and was built in 1899-1900. The area of water surface at low water is 117 square miles and at highwater, 161 square miles. These areas with a range of 14 feet give a capacity of about 43,992,000,000 cubic feet. Cass Lake which forms a part of the Winnibigoshish reservoir has a range of about 4.75 feet between high and low water, representing a storage of some 7,500,000,000 cubic feet or 16 per cent of the total reservoir capacity. When the reservoir is full and there is a strong runoff from the drainage basin, the water elevation of Cass Lake is about one foot higher than that of Lake Winnibigoshish.

It is

Leech Lake reservoir is the next lower unit to Winnibigoshish. not located on the main river but 27 miles distant, being connected by Leech Lake River which enters Mississippi River in the northeastern corner of Cass County. It is formed by a dam at the outlet of the lake, which was originally a timber structure, built in 1883-4, but rebuilt of reinforced concrete in 1900-2. The area of water surface at low water is 173 square miles, and at high water, 234 square miles. These areas with

a range of head of 5.74 feet give a capacity of 33,094,300,000 cubic feet. The area of the water shed including lake area is 1,163 square miles.

Pokegama Falls reservoir which is the third unit, is formed by a dam located above Pokegama Rapids near the town of Grand Rapids. This dam which was originally a timber structure built in 1883-4 was rebuilt as a reinforced concrete dam in 1902-4, and holds the water on Pokegama Lake which is not in the main river channel but situated a short distance from it. The area of the water surface in the reservoir varies from 24 to 25 square miles, which with a range of 7.5 feet gives a capacity of 5,260,000,000 cubic feet. This reservoir is considered to be the distributor for the three upper reservoirs, the water from all of which pass Pokegama dam.

Sandy Lake reservoir is located on Sandy River which flows into Mississippi River near Libby P. O. in Aitkin County, and is formed by a dam 1 mile above the mouth of Sandy River. The dam is a timber structure built in 1895. The area of water surface at low water is 8 square miles and at high water is 16.5 square miles. These areas with a range of 9.4 feet give a capacity of about 3,157,900,000 cubic feet. In times of extreme flood stage, Mississippi River drowns out the main dam and fills Sandy Lake Reservoir as much as three feet higher than is intended for reservoir purposes.

Pine River reservoir, the next lower unit in the system, is formed by a dam across Pine River, 15 miles above its junction with Mississippi River, in the central part of Crow Wing County. The dam which was originally built in 1886, and afterwards rebuilt, is located at the outlet of Cross Lake, and raises the water level in Cross, Pine, Daggett, Rush, Whitefish, Trout, and Hay lakes by varying amounts. The area of water surface at low water is 18 square miles, and at high water, 24 square miles. areas with a range of 16.15 feet, give a capacity of 7,732,900,000 cubic feet.

These

Gull Lake reservoir, the lowest unit in the system, is located in the southern part of Cass and Crow Wing counties, and comprises Gull, Round, and Long lakes which are to be connected by ditches not yet constructed. The dam which was completed in 1912 is located on Gull River a half mile below the outlet of Gull Lake, and provides for a range of stage of 6 feet in the reservoir. The area at low water is 28.2 square miles and at high stage 30.2 square miles. The reservoir capacity is 4,910,100,000 cubic feet.

Although the reservoirs are operated primarily in the interest of navigation, they also have a beneficial effect on water power and flood control. The operation during the winter, or non-navigation season, is based on the necessity for having 39,000,000,000 cubic feet empty storage capacity on April 1 to take care of the spring high water. Thus if the preceding year has been very dry and the storage has been nearly exhausted, the reservoirs allow only the normal minimum winter flow (as determined previous to building the reservoirs) to pass down the river. If the preceding navigation season has not drawn heavily on the reservoirs the winter flow is increased by a sufficient amount to make possible the required. empty storage capacity April 1. During the navigation season the

stored water is held until the Weather Bureau gage at St. Paul registers a stage lower than 3 feet. Then the reservoirs are opened in an attempt to hold the river at the 3-foot stage which will insure sufficient water for navigation as far down stream as Lake Pepin, below which point the effect of the stored water is largely lost.

NAVIGATION.

At the present time the head of navigation for the lower river is St. Paul, although the Federal government is building a high dam just above the mouth of the Minnesota, which will make possible slack water navigation nearly to St. Anthony Falls in Minneapolis. On the upper river there are navigable stretches from a point 10 miles below Brainerd to Grand Rapids; from Cohasset to Pokegama Lake and Ball Club; on Winnibigoshish and Cass lakes; Lake Bemidji; Lake Irving and Lake Plantagenet. The Mississippi River is used extensively for log driving as far down as Minneapolis and St. Paul.

DRAINAGE.

The upper part of the Mississippi basin is flat and contains a large amount of swamp land. The following table, compiled from the report of the State Drainage Commission, shows the present status of drainage in this section:

Itasca
Hubbard

Artificial drainage in the Mississippi River basin in Minnesota.

County

Original Area of Swamp Land (Acres)

Area Benefited
by Drainage
(Acres)

23,500

Cass.

Wadena.

Aitkin

Crow Wing.

Total.

590,600

77,000

5,900

This table shows that less than 20 per cent of the swamp land

has been either wholly or partly drained.

DRAINAGE AREAS.

The following drainage areas have been measured in the Mississippi basin":

Drainage areas in Mississippi River basin.

For areas in the basins of Crow Wing, Sauk, Elk, Crow, Rum, St. Croix, Minnesota, Cannon, Zumbro, Root, Cedar, and Des Moines rivers, see descriptions of those rivers.