Non-point
Source Pollution (continued)
Table 35 indicates the sediment input by tributary. The Spoon River delivers about 1.6 million tons of sediment per year followed by the Sangamon River with a sediment delivery of 1.7 million tons per year. The annual sediment budget shows that on average 12.1 million tons of sediments per year are delivered to the Illinois River, out of which 6.7 million tons are being deposited within the Illinois River valley, and 5.4 million tons annually are being discharged at the Valley City station and then to the Mississippi River (Bhowmik 1999).
Table 35: Illinois River tributary sediment inputs per year (Bhowmik 1999)
| Name of Tributary | Sediment Input (tons x 1000) |
| Des Plaines River | 179 |
| Kankakee River | 847 |
| Mazon River | 206 |
| Fox River | 443 |
| Vermilion River | 805 |
| Big Bureau Creek | 252 |
| Mackinaw River | 648 |
| Spoon River | 1,552 |
| Sangamon River | 1,738 |
| La Moine River | 874 |
Backwater lakes are the major areas impacted by the sediment deposition. Studies show that lakes could lose 20-100% of their capacities by the year 1990. The average capacity loss for the lakes is 72% (Demisse 1992).
As discussed earlier, soil erosion and sediment yield are directly related to land use practices. Eighty percent of the Illinois River basin is in agricultural land use (Figure 49). Agricultural acreage increases slightly from 1925 to 1981 and then declines. The major crops grown are corn, soybeans, wheat, oats, and hay. Acreage devoted to corn remains steady for 62 years, from 1925-1987, with over 6 million acres harvested. Soybeans are very different. Acreage devoted to soybeans increases dramatically from virtually none in 1925 to almost 6 million acres in 1987. Production of wheat, oats, and hay declines in proportion to the increase in soybean production.
Figure 49: Land Use in the Illinois Watershed (ISGS)
