As explained by the signage at the Melvin Price Locks and Dam and the National Great Rivers Museum, when European/Anglo settlement increased in the area of the Upper Mississippi Valley, the booming nineteenth-century river towns were reliant on steam-powered paddle-wheelers to move goods and people. 

But the Mississippi was a wild and unpredictable river, with a meandering channel, rapids, sand bars and times of low and high water. These conditions were not ideal for transportation and communication along the great river. In response, Congress appointed the U.S. Army Corps of Engineers to control the river. The USACE actions began with the dredging of the river bottom and removal of old tree roots (called snags). 

The U.S. Army Corps of Engineers began to create the lacks-and-dams system on the upper Mississippi River in the 1930s. 

Melvin Price Locks and Dam is one of 29 lock and dam structures on the Upper Mississippi River. Melvin Price Locks and Dam began to be built as No. 26 at Alton in 1936. 

The structure we see today, and that is named Melvin Price Locks and Dam, replaced the original No. 26 in 1994.  The amount of cargo that passes through the MPLD is extraordinary as we see in the graphic below. 

The locks function like stairs to climb and descend the river. The water level in a lock is raised and lowered by gravity to life the boats up, or to lower them down. This “stairway of water” runs from Minneapolis to Alton as seen in the illustration below. 

MPLD has two locks. Recreational boats and towboats with few barges can use the 600-foot auxiliary lock. The long wall in the water that is closest to the shore helps guide the smaller water vehicles (noted above) into the smaller lock.

The 1,200-foot main lock is used by tows with up to 15 barges. See our wonderful illustrated interview with Captain Luke Moore to understand the movement of large barges on the river.

Here we are looking down at the locks in the MPLD complex. 

MPLD was constructed with nine tainter gates, each 110 feet wide and 42 feet high. The gates control the flow of the Mississippi River through the dam. The USACE can adjust the position of the tainter gates to increase or decrease the flow of water. By carefully adjusting the gates, the USACE maintains a pool behind the dam with a channel that is at least nine feet deep so that commercial tows can safely navigate the river. 

The dams do not control flooding (something we have witnessed quite dramatically around Alton in recent years). Rather, their purpose is to divide the river into 29 pools. Each pool holds enough water to maintain a river channel that is at least 9-feet deep, even when river levels are low. The goal is to ensure safe conditions for commercial river traffic.

As can be imagined, the powerful Mississippi River exerts tremendous pressure on Melvin Price Locks and Dam. To ensure that the dame is not being moved by the force of the river, the USACE performs a detailed yearly movement survey of the dam. Surveyors use special instruments to measure the precise distance from towers (such as the one at MPLD) to more than one hundred fixed points on the locks and dam structure. 

Parenthetically, Melvin Price was a U.S. Congressman from East St. Louis, Illinois, who lobbied tirelessly to get the old No. 26 replaced. He was successful but did not live to see his project realized. He died in 1988.