Rivers (Case Study)

River Mississippi

• The Mississippi river is the largest and longest river in North. America. The river (and its tributaries) gather water from 31 US states & flows 3734km.

• Steamboats have been used on the river since the 1830s, transporting goods (food, coal, gas, timber, etc.) to and from New Orleans.

• This led to the growth of many US cities such as St Louis and Memphis.

Human interaction with upper course

• 29 locks & dams been developed to support river on the Upper Mississippi where the slope's steepest and water level's lowest.

• This has made lakes that allow small vessels to pass through.

• The process of erosion was interrupted due to these dams & material was being deposited rather than transported. This deprived agricultural land in floodplains downstream.

Human interaction with middle course

• In the middle course, lateral erosion caused the river to move hundreds of feet.

• This made many towns out of range for the banks, meaning no more boats passed, causing businesses to close.

• Over 230km of wing dykes were constructed over the last century.

• Boulders were placed perpendicular to river to slow the flow of weter near riverbank & force wate centrally.

Human interaction with lower course

• The lower course is 15m deep which allows large cargo ships to travel inland (Baton Rouge, Louisiana).

• However, the river loves energy & sandbars are made which can damage bulls & propelles of large ships.

Engineering on Mississippi River

• Engineers dredge the riverbed to make it deeper and navigable. It's expensive but done annually.

• Around 2,500km of artifical levees made of impermeable concrete have been built to counter flooding.

• Diversion channels were developed to divert huge levels of water around major cities like New Orleans. This doubled the carry point of the river during critical periods.

• Flood walls were made in cities since they were strong and took up less space. They open for traffic but during storms they close.

Impact on river processes

• The flow of water along the Mississippi's more controlled now. Flooding only affects 10% of the land.

• Revetment works reduced the amount of lateral erosion in the mature stage.

• Disasters can be detrimental when walls break, from flooding from 1993, which caused $15B in damages.