USACE CWMS - Mississippi River Watershed MVS

The Corps Water Management System (CWMS) includes four interrelated models to assist with water management for the basin:

- GeoHMS (Geospatial Hydrologic Modeling Extension)
- ResSIM (Reservoir System Simulation)
- RAS (River Analysis System)
- FIA (Flood Impact Analysis)

The Mississippi River Basin is the largest river system in the United States, covering approximately 1.15 million square miles, or over 40% of the area of the Continental U.S. Several large tributary rivers flow into the Mississippi, including the Missouri, Ohio, and Arkansas Rivers. Maximum topographic relief varies from approximately 1,475 feet near the headwaters at Lake Itaska to 0 feet at the Gulf of Mexico. The portion of the Mississippi River Basin that is covered in this CWMS project drains approximately 15,475 square miles.

The Mississippi River in the St. Louis District covers a centerline distance of about 300 miles, flowing generally from the northwest to southeast, from Lock and Dam #22 in Saverton, MO to the mouth of the Ohio River near Cairo, IL. The topography of the basin is characterized by hilly upland terrain and broad, flat floodplain area near the main stem of the river, although there are some areas with steep bluffs above the channel banks. The Mississippi River channel invert ranges in elevation (within the St. Louis District) from about 430 feet at Lock and Dam 22 to about 250 feet at the confluence with the Ohio River. The typical estimated Mississippi River channel invert slope in the District is 0.5 feet per mile. Within the St. Louis District, the main tributaries are the Salt, Cuivre, Illinois, Missouri, Meramec, Kaskaskia, Big Muddy, Castor, and Cache Rivers.

Soils in the basin were predominantly deposited by the succession of continental glaciers that advanced and retreated across the area during the Great Ice Age. These sediments fall into three major categories: till, lacustrine deposits, and outwash sediments. Loess soils can also be found within the basin. In general, the soils in the basin are rich in organic matter and help explain the major land use categories: agriculture and forested areas. The climate for the basin is considered moderate and is characterized by hot summers and cool winters. The basin lies within the humid continental climate, and the area experiences four distinct seasons. Average annual rainfall is approximately 45 inches across the basin, and typically the maximum precipitation occurs in the spring (April, May, and June) and again in late November.

美国陆军工程兵团水管理系统（Corps Water Management System, CWMS）包含四个相互关联的模型，用于辅助流域水管理工作：
- GeoHMS（地理空间水文模拟扩展工具，Geospatial Hydrologic Modeling Extension）
- ResSIM（水库系统模拟工具，Reservoir System Simulation）
- RAS（河道分析系统，River Analysis System）
- FIA（洪水影响分析工具，Flood Impact Analysis）

密西西比河流域（Mississippi River Basin）是美国规模最大的河流水系，流域总面积约115万平方英里，占美国本土面积的40%以上。多条大型支流汇入密西西比河，包括密苏里河、俄亥俄河与阿肯色河。流域最大地形起伏差异约1475英尺，源头位于伊塔斯卡湖，至墨西哥湾处高程降至0英尺。本次CWMS项目覆盖的密西西比河流域子区域汇水面积约15475平方英里。

圣路易斯辖区内的密西西比河段中心线长度约300英里，流向大致自西北向东南，起点为密苏里州萨弗顿的22号船闸大坝，终点为伊利诺伊州开罗附近的俄亥俄河河口。该流域地形以丘陵高地为主，干流沿岸分布着宽阔平坦的洪泛平原，部分区域河道岸坡上方存在陡峭崖壁。圣路易斯辖区内的密西西比河河道河底高程范围约为430英尺（22号船闸大坝处）至250英尺（与俄亥俄河汇流处）。该辖区内密西西比河河道河底平均坡度约为0.5英尺每英里。圣路易斯辖区内的主要支流包括索尔特河、库伊弗河、伊利诺伊河、密苏里河、梅拉梅克河、卡斯卡斯基亚河、大穆迪河、卡斯特河与卡什河。

流域内的土壤主要由大冰期期间多次进退的大陆冰川沉积形成，可分为三大类：冰碛物、湖相沉积物与冰水沉积。流域内还分布有黄土。总体而言，该流域土壤有机质含量丰富，这与区域两大主要土地利用类型——农业用地与林区——形成了良好契合。流域气候温和，夏季炎热、冬季凉爽，属于湿润大陆性气候，四季分明。流域年均降水量约为45英寸，降水峰值通常出现在春季（4月、5月、6月）及11月下旬。