1. The Mississippi River basin covers a vast area with diverse climatic conditions, leading to variations in hydrological characteristics along different stretches of the river.
2. In its upper reaches, where latitudes are higher, spring snowmelt and rainfall contribute to the river's flow. The highest water levels are typically recorded in April and June, with the flooding season lasting from March to July, and the lowest levels occur in December. The annual average flow is 2900 cubic meters per second, and the river occasionally freezes during winter, with low sand content.
3. In the middle reaches, the annual average flow increases to 5800 cubic meters per second. The flooding season spans from March to August, with June witnessing the second-highest water levels, and December experiences the lowest levels. The inclusion of tributaries from the semi-arid areas on the river's west bank leads to an increase in sand content.
4. The lower reaches experience a significant surge in water volume after the confluence with the Ohio River at Wabash. The average annual discharge reaches 13,400 cubic meters per second. The flooding season extends from January to June, with the highest water levels in April and the lowest in October. The river has a high sand content, with the Missouri River on the right bank being longer but with less water and more pronounced seasonal variations, while the shorter Ohio River on the left bank has higher water volume and milder seasonal changes.
5. Most of the basin is characterized by plains, which provide abundant irrigation, industrial, and domestic water sources for the American South and Midwest. However, the gentle gradient and extensive floodplains in the middle and lower reaches can lead to severe flooding during the spring and summer, causing damage to adjacent low-lying areas.
6. The Mississippi River experienced a severe flood in 1927, resulting in substantial property loss and casualties. This event prompted engineers to reassess hydrological issues related to the river.
7. Since 1927, the average flows of the river's main tributaries have been monitored. The average flow at Vicksburg is recorded at 16,131 cubic meters per second. The spring and early summer witness the highest flows in the western tributaries, while winter flows are also considerable.
8. The Ohio River is a major factor contributing to the downstream floods of the Mississippi. Its peak flows usually occur in March and can account for more than 3/5 of the flow recorded at Vicksburg.
9. The intensification of floods is attributed to factors such as early spring rainfall in the Great Plains, melting snow in the north, and heavy storms downstream. These events can cause the river to overflow its banks, threatening levees.
10. Pollutants in the Mississippi River water and sediments stem from urban, industrial, and agricultural sources. Concentrations of organic compounds and trace metals are generally low, but high levels of microorganisms have been found in certain areas downstream of cities, which are related to improper waste disposal. Despite this, the overall level of pollution in the Mississippi River is not severe.
