As part of my research assistantship with Dr. Robert Brooks during spring 2016, I compiled and processed USGS river discharge data to map the 30-year average discharge of tributaries of the Mississippi River. The intent of the project was to examine and compare the flow input of each of the Mississippi’s tributaries over the past 30-years.

The map shows the proportional representation of the discharge rate in cubic feet per second at gage stations along the Mississippi River and its tributaries focusing on comparing the flow contribution of each of the Mississippi’s tributary – the Ohio and Missouri Rivers. Additionally, the stations for the Allegany and Monongahela Rivers – two tributaries of the Ohio River – are included.

To construct the map, we conducted a general survey of available hydrographic discharge and gaging data for the interested hydrographic features. We solely relied on data from the USGS Water Data service, which provides a centralized source for US hydrographic data. The project required us to extract the discharge and water flow data from gaging stations along the interested rivers. The data was then processed, scrubbed and compiled for mapping. Annual discharge rates were averaged over a 30-year period to calculate the desired rates. Gage stations were chosen based on its proximity to the confluence and in addition to the requirement for constant annual discharge recording.  Thus, chosen stations had to be constructed before 1985. Annual discharge rates were averaged for the period between 1985-2015. Approximate station locations were subsequently mapped using ArcMap 10.4. Corresponding 30-year averages were mapped as proportional symbols. River lines width were mapped based on its hydrographic classification. Basemap data were obtained from Natural Earth Data. Cartographic design for the project prioritized the discharge averages and the corresponding river.

The resulting map shows that the 30-years average discharge from the Ohio River before the confluence with the Mississippi River at Smithland is greater than the discharge from the Missouri River at the Hermann at 132261 cubic feet per second (cfs) versus 92693 cfs, respectively. Conversely, the discharge from the Ohio River before the confluence with the Mississippi River at Smithland is less than the discharge of the Mississippi at Thebes, at 132261 cfs versus 239819 cfs, respectively. However, if we exclude the discharge stemming from the Missouri River and compare the discharge at Smithland (Ohio River) with the discharge at Grafton (Mississippi River), the 30-year average discharge from the Ohio River is marginally greater than the discharge of the Mississippi on its own, at 132261 cfs versus 119354 cfs, respectively. Therefore, the 30-year average discharge stemming from the Ohio River is 12907 cfs greater than from the Mississippi River before the confluence with the Missouri River. Additionally, the discharge from the Missouri at Hermann is less than the discharge of the Mississippi at Grafton, at 92693 cfs versus 119354 cfs, respectively.

Click on the image to see the full-resolution version of the map.