Measuring River Discharge – The Great Mississippi River Flood of 2011
Measuring River Discharge is a common project as the Gulf South representative of Teledyne RD Instruments. We are often called in to support important measurements. During the record flood event in spring 2011, we demonstrated the capability of the RDI RiverRay ADCP for the USACE ERDC. Their local support consultant Dimco, needed a capable Acoustic Doppler Current Profiler (ADCP) to get critical measurement while the Mississippi River at Vicksburg, Mississippi crested.
With an RDI RiverRay ADCP, we were able to demonstrate this new technology working in some very challenging conditions.
The following pictures were taken just downstream of the I-20 Bridge in Vicksburg, MS.
The discharge measured during the flood was in excess of 2 Million cubic feet/second and the average velocity was 10.06 ft/s.
RDI Software easily presents bathymetry and velocity data using a contour graph. In this graph, each area of color represents the speed of the water in that area. While the average velocity of the river is around 10 ft/second, it indicates the velocity in some parts of the river is in excess of 14 ft/sec. At this speed, you could travel the entire distance of the River from the headwaters at the Minnesota Itasca State Park to the mouth at Louisiana’s Southwest Pass in under 9 Days.
This system not only measures the depth and speed of the water it also measures the direction of the water. The following cross section shows data collected with the USGS on a synoptic survey at the Mouth of the Mississippi River at Southwest Pass in September of 2003. In this color contour graph each block of color represents the compass heading of the water. In the bottom of the graph from a depth below 14.50 feet we can see the direction of the flow is around 30 degrees heading North while above 14.50 feet the flow is on a heading around 180 Degrees to the South indicating a saltwater wedge moving upstream underneath the fresh water moving downstream.
As this technology allows for a short measurement period, multiple measurements can be made in a short time span to ensure data quality. In this report of data collected on May 17th 2011 we can see the river is rising to its peak discharge of 2,196,378 cubic feet/second.
You don’t need to measure the Mississippi River at peak flood state to need an RDI ADCP. This same technology is available for smaller waterways and streams.
Flow measurement is a critical step in calculating the load of a river, stream or any outfall. Having the right tool for the job is critical. Throughout the watershed, and across the Gulf South States, C.C. Lynch & Associates provides state of the art technology for measuring the quality and quantity of water; with a strong emphasis on field service and support. Our staff is factory trained and we have a large inventory of instrumentation that we can apply to support your projects.