lii FISHES OF ILLINOIS 



SANGAMON RIVER 



The Sangamon River has the largest watershed of any of the 

 tributaries of the lUinois. Its drainage basin, covering an area 

 of 5,390 square miles (Leverett), includes extensive plains 

 which are now inadequately drained, but which may by extensive 

 tiling be drained into the river. 



The Sangamon rises in eastern McLean county, flowing 

 southeast for about 10 miles into Champaign county, and thence 

 south and west until, in Sangamon county, it takes a northwest- 

 ward course. In northern Menard county it unites with Salt 

 creek and, flowing westward, soon empties into the Illinois. 

 The length of the river is about 200 miles. Its source is in the 

 Bloomington morainic system at an altitude of about 850 feet. 

 The mouth has an altitude of 429 feet, making a total descent 

 of about 420 feet. In the first 10 miles it makes a descent of 

 120 feet, thus leaving about 300 feet of fall for the remaining 

 170 miles of its course. The fall is far from regular, there being 

 sections, often several miles in length, in which it is slight, 

 between which are sections with more rapid fall. 



The river flows for its first 90 miles within the limits of the 

 Wisconsin drift, but leaves this a few miles west of Decatur. 

 In these 90 miles it receives no tributaries of importance, its 

 immediate watershed being only 15 to 20 miles wide. 



That part of the river valley lying outside of the Wisconsin 

 drift, although generall}^ shallow, is much wider than the portion 

 within the limits of that drift sheet, and bears evidence of having 

 been opened prior to the Wisconsin stage of glaciation. The 

 river and its branches are bordered throughout most of their 

 length by strips of timber about half a mile wide on either side. 



The river is subject to great variations in volume, there 

 being in the annual flood-stages a rise sufficient to overflow 

 banks 8 to 12 feet in height. At such times, being a swift 

 stream, it probably discharges not less than 15,000 cubic feet 

 per second, and in extreme floods the discharge probably exceeds 

 20,000 cubic feet per second. Formerly the flow of the river 

 was more or less regular. This was due to the fact that the 

 portion of the basin lying within the v^helbyville moraine was 

 filled with swamps which absorbed the water as it fell and then 

 gave it forth very gradually. Now, however, a very complete 

 system of tile drainage carries off this water very quickly, and so 

 leaves the river subject to low stages for a large part of the year. 



The principal branch of the Sangamon is Salt creek. 



