SUSPENDED SEDIMENT BUDGETS FOR POOL 13 AND LA GRANGE POOL OF THE UPPER MISSISSIPPI RIVER SYSTEM: RESULTS FOR THE 1995 WATER YEAR. Robert F. Gaugush, U.S. Geological Survey, Biological Resources Division, Environmental Management Technical Center, Onalaska, WI 54650. The transport of sediment into and out of the navigation pools of the UMRS must be quantified as a first step in predicting the long-term configuration of the system. To address this issue, a cooperative effort by the Environmental Management Technical Center, the United States Geological Survey/Water Resources Division, and the States of Illinois and Iowa was initiated in 1994 to develop pool-scale budgets for Pool 13 on the Mississippi River and the La Grange Pool on the Illinois River. Work conducted in 1994 primarily consisted of site reconnaissance and upgrading gaging stations from discharge only to discharge and suspended sediment stations. Work was also conducted to place additional gaging stations on the Mississippi River. Actual sampling (suspended sediment) and recording gage measurements began in October 1994 (the beginning of the 1995 water year). This sampling effort will continue through the end of water year 1997. Pool 13 stretches from river mile 522.5 at L/D 13 to river mile 556.7 at L/D 12. Drainage area for Pool 13 at L/D 13 is 221,400 km2, of which 96 percent (213,400 km2) is contributed by the Mississippi River at L/D 12. The remaining 4 percent, approximately 8,000 km2, is contributed by smaller tributaries feeding directly into Pool 13. The largest of these are the Maquoketa and the Elks Rivers entering from the Iowa side and the Apple and Plum Rivers entering from the Illinois side. The work associated with Pool 13 involves monitoring two sites on the Mississippi River (at Lock and Dam 12 (above Pool 13) and at Clinton, Iowa (below Pool 13)) and the above four tributaries to Pool 13 for discharge and suspended sediment concentrations. The LaGrange Pool extends from river mile 80.2 at the LaGrange L/D to river mile 157.7 at the Peoria L/D with a total length of 48.2 km (77.5 mi). Drainage area for the LaGrange Pool at the LaGrange L/D is 66,400 km2, of which 57 percent (37,700 km2) is contributed by the Illinois River at the Peoria L/D. The remaining 46 percent, approximately 28,700 km2, is contributed by a number of smaller tributaries feeding directly into the LaGrange Pool. Four major tributaries, the Sangamon, Mackinaw, Spoon, and La Moine Rivers, account for 88 percent of the 28,700 km2 that drain directly into the LaGrange Pool. In La Grange Pool, monitoring involves two sites on the Illinois River (at Pekin, Illinois (above the La Grange Pool) and at Valley City, Illinois (below the La Grange Pool)) and the above four tributaries to the pool. The Mississippi River at Lock and Dam 12 accounts for 97 % and 83 % of the annual water and sediment load, respectively, to Pool 13. The four tributaries provide the remaining 3 % of the water inflow and 17 % of the sediment load. It is quite evident that the water and sediment mass balance for Pool 13 is dominated by the Mississippi River. This is not unexpected when the Mississippi River accounts for 96 % of the pool's drainage area. The situation is quite different for the LaGrange Pool where the drainage area represented by the Illinois River is almost equal to that of the tributaries. The Illinois River above the pool accounts for 65 % of the water inflow and only 23 % of the sediment load to the pool. The four tributaries provide 35 % of the water inflow and 77 % of the sediment load. The average sediment export rate to Pool 13 is 13,000 kg/km2 whereas the rate per unit area to the LaGrange Pool is over 5 times greater at 67,500 kg/km2. Keywords: sediment, Mississippi River, Illinois River, Pool 13, LaGrange Pool Robert F. Gaugush Environmental Management Technical Center 575 Lester Avenue Onalaska, WI 54650 Phone: 608-783-7550 ext. 59 Fax: 608-783-8058 e-mail: robert_gaugush@nbs.gov Platform presentation Willingness to convert format: No