Non-point
Source Pollution (continued)
By calculating the sediment yield for a river basin, it is possible to develop a sediment budget. Calculating the difference between the amount of sediment entering and leaving a river basin, leads to the amount of sediment deposited. The ISWS evaluates the sediment data for the period of 1981 and 1990. Table 34 shows the results of this analysis. At Valley City, the Illinois River discharges 5.6 million tons of sediment every year, leaving 8.2 million tons of sediment from tributary streams deposited each year. Additional sediment is delivered from bank and bluff erosion, although it is not possible to estimate these values.
Table 34: Sediment Budget of the Illinois River (Demissie 2003)
| Water Year | Total inflow from tributary streams (tons x 1000) |
Outflow from Illinois River at Valley City (tons x 1000) |
Deposition (tons x 1000) |
Percent Deposited |
| WY81 | 18579.1 | 7350.5 | 11228.6 | 60 |
| WY82 | 15245.9 | 9018.6 | 6227.3 | 41 |
| WY83 | 17275.0 | 5885.9 | 11289.1 | 65 |
| WY84 | 12211.5 | 5217.3 | 6994.2 | 57 |
| WY85 | 10068.0 | 5438.3 | 4629.7 | 46 |
| WY86 | 12753.6 | 7881.9 | 4871.7 | 38 |
| WY87 | 6933.0 | 4629.2 | 2303.8 | 33 |
| WY88 | 3388.0 | 2059.6 | 1328.4 | 39 |
| WY89 | 2124.8 | 1805.4 | 319.4 | 15 |
| WY90 | 11605.5 | 7051.8 | 4553.7 | 39 |
| WY91 | 14985.5 | 10050.9 | 4934.6 | 33 |
| WY92 | 5194.6 | 3716.2 | 1478.4 | 28 |
| WY93 | 41945.7 | 5462.6 | 36483.1 | 87 |
| WY94 | 11086.4 | 5482.1 | 5604.3 | 51 |
| WY95 | 13166.9 | 5559.9 | 7607.0 | 58 |
| WY96 | 8699.1 | 5385.8 | 3313.3 | 38 |
| WY97 | 6704.9 | 4096.6 | 2608.3 | 39 |
| WY98 | 17412.8 | 4629.2 | 12783.6 | 73 |
| WY99 | 10085.9 | 4415.2 | 5670.7 | 56 |
| WY2000 | 2272.3 | 2911.4 | -638.1 | -28 |
| Average | 12087.0 | 5407.4 | 6679.5 | 55 |
The sediment budget can also be portrayed pictorially (Figure 48). The band shown for different tributaries and the main channel are proportional to the average annual sediment in tons per year (Bhowmik 1999).
Figure 48: Sediment contributions by tributaries to the Illinois River sediment budget (ISGS)
