Suspended-sediment characteristics of Indiana streams, 1952-84

Suspended-sediment concentration and discharge data were collected at 7 daily record stations and 70 partial-record stations during 1952- 84. Median suspended-sediment concentrations ranged from 24 to 61 milligrams per liter at daily record stations; concentrations ranged from 6 to 539 milligrams per liter at partial-record stations. Most suspended sediment transported in Indiana streams is silt and clay size (particles between 0.062 and 0.004 millimeter in diameter and particles less than 0.004 millimeter in diameter).

Large suspended-sediment concentrations were associated with storm runoff but not always with peak streamflow. Some peak concentrations of suspended sediment preceded peak streamflow by as much as 18 to 30 hours during storms. Suspended-sediment concentrations frequently were largest during a storm that occurred after a period of low streamflow, when large amounts of sediment were eroded and transported into the stream and little base flow was available for dilution. For most of the streams studied, reliable predictive equations could not be developed to quantify the relation between suspended-sediment concentration and streamflow because of the extreme variability in the data. Annual suspended-sediment yields at four daily record stations ranged from 186 to 1,914 tons per square mile.

Annual suspended-sediment yields for 70 partial-record stations, estimated by use of the suspended-sediment transport, flowduration-curve method, ranged from 11 to 2,310 tons per square mile. However, because of the poor correlation between suspended-sediment discharge and streamflow, these estimates are imprecise.

Periods of record at 4 daily record and 32 partial-record stations were sufficient to test for trends. The trend in suspended-sediment concentration, adjusted for streamflow, was significant for only 9 of the 36 stations. At six of the nine stations, flow-adjusted suspended-sediment concentrations decreased with time.