All values for turbidity are in NTU.
During dredging, there are two buoys and a water current detector positioned around the dredging area (dredge). One buoy is positioned upstream of the dredge and the other downstream of it. The water current detector identifies which direction the water is flowing past the dredging area so that “upstream” or “downstream” can be assigned to each buoy.
Each buoy has two turbidity sensors, one near the surface of the water (high) and another lower down (low). Turbidity readings are reported every fifteen minutes for each of the four sensors (DownstreamHigh, DownstreamLow, UpstreamHigh, UpstreamLow).
The dredge contribution is the amount of turbidity that is caused by dredging activities. The dredge contribution is calculated as the largest value of the downstream sensor minus the smallest value of the upstream sensor. The issues in the table will alter the turbidity value as noted.
|Negative dredge contribution||0|
|Water current detector indicates no water flow||0|
|Upstream sensor is offline||Largest value of the downstream sensor is used|
|Downstream sensor is offline (no data collected, dredging should be stopped)||Offline|
The "Flags" column indicates the status of the sensors at the time of the reading:
|S||At least one of the sensors was offline|
|C||Current detector indicated no water flow|
|M||Current detector is offline (upstream/downstream is not applicable, dredge contribution is largest of all sensors)|
Turbidity data is available for daily maximum, daily minimum, and daily mean FNU statistics from March 2011 to the present. Recent USGS monitoring data is considered provisional until the data quality can be verified.
In addition to turbidity data, USGS monitors other water quality parameters at the Indiana Harbor Canal gauge, including chemical parameters and streamflow statistics. These archived data and annual reports are available on the USGS web site.
While USACE is working with USGS to correlate the dredging turbidity data with the USGS gauge to monitor dredging operations, several factors may affect the two turbidity monitors differently, including but not limited to: