FOREST COYER IX PROTECTING RESERVOIRS 17 
REGIMEN AND TURBIDITY OF THE MAIN STREAM SYSTEMS IN 
THE UNITED STATES 
The important factors which determine (1) the volume and (2) 
the character of the flow of streams of the United States are : 
Source of water supply ; amount, character, and distribution of precipitation. 
Lake storage. 
Underground storage. 
Character of surface of the basin. 
Character of soil and subsoil and especially its susceptibility to erosion. 
The streams of the United States may be separated into eight 
groups, on the basis of regimen, turbidity, and the influence of 
forest protection on their watersheds: 
Rivers of the Northeastern States and the Great Lakes region. 
Rivers of the Middle Atlantic coast region. 
Rivers of the southern Appalachians. 
Rivers of the eastern slope of the Rocky Mountains. 
Streams rising in the plateau region of central Texas. 
Colorado River and interior basin. 
Sacramento and San Joaquin Rivers. 
Columbia River. 
RIVER SYSTEM OF THE NORTHEASTERN STATES AND THE GREAT LAKES REGION 
The northeastern and Great Lakes regions embrace the rivers in 
the Xew England States, the Hudson River, the rivers in the region 
of the Great Lakes, and the headwaters of the Mississippi. The 
basins of the streams of the northeastern region are well forested as 
a rule or their surfaces are well covered. The natural permeability 
of the soil depends largely upon texture and structure, and the ab- 
sorptive and water-holding capacities are increased by a good humus 
content. Many of the soils of this general region are of such char- 
acter as to accumulate and maintain a liberal quantity of organic 
matter. The freezing of the soil during a considerable period of 
the year not only protects it from erosion but also retards the 
oxidation of its humus. The humidity is relatively high and the 
evaporation low. An extensive system of lakes acting as natural 
reservoirs, at the heads of many of the large rivers, is instrumental 
in furnishing an equable stream flow from a moderate but evenly 
distributed precipitation of 30 to 40 inches, which in winter occurs 
largely as snowfall, and which passes off as spring freshets after 
warm rains. Dams at lake outlets increase storage. Xatural storage 
is also favored by the deep glacial drift and the spongy moss and 
deep humus. Except on very sandy soils, sod naturally sets in 
ditches, on stream banks, and in waste places, and forms nearly as 
perfect a protection against erosion as the forest cover. Erosion is 
slight and the silt burden of the streams is insignificant. 
The Kennebec River may be taken as a type of the streams of 
the northeastern group. The tidal estuary which forms its mouth 
is free from silt bars, and this indicates the small quantity of solid 
material which it bears. In the discussion of Portland Harbor by 
the Chief of Engineers, 16 the statement is made that "There are 
16 Mackenzie, A. improvement of rivers and harbors in maixe and new Hampshire. 
[IT. S.] War Dept. Ann. Rpt. 5 : 33. 1906. (Rpt. Chief Engin., U. S. Army.) 
