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.

水系管理部队（Corps Water Management System，简称 CWMS）集成了四个相互关联的模型，旨在协助该流域的水资源管理：

- 地理水文模型扩展（GeoHMS，Geospatial Hydrologic Modeling Extension）
- 水库系统模拟（ResSIM，Reservoir System Simulation）
- 河流分析系统（RAS，River Analysis System）
- 洪水影响分析（FIA，Flood Impact Analysis）

密西西比河流域是美国最大的河流系统，覆盖约115万平方英里，约占美国大陆面积的40%以上。密西西比河接纳了包括密苏里河、俄亥俄河和阿肯色河在内的多条大型支流。该流域的地形起伏最大值从伊塔斯卡湖源头附近的约1475英尺变化至墨西哥湾的0英尺。在本 CWMS 项目中涉及的密西西比河流域部分，排水面积约为15475平方英里。

在圣路易斯区，密西西比河的河中心线长度约为300英里，大致从西北流向东南，从密苏里州萨弗顿的22号船闸和坝到伊利诺伊州卡霍加附近俄亥俄河的河口。该流域的地形特征为丘陵高原和宽阔平坦的河漫滩区域，尽管河岸附近也有一些陡峭的峭壁。在圣路易斯区，密西西比河的河槽底部高程从22号船闸和坝的约430英尺变化至与俄亥俄河交汇处的约250英尺。该区密西西比河河槽底部高程的平均估计坡度为每英里0.5英尺。在圣路易斯区，主要支流包括盐河、库伊尔河、伊利河、密苏里河、默雷克河、卡萨斯基亚河、大泥河、卡斯托河和卡奇河。

该流域的土壤主要由大冰期期间在该地区进退的陆地冰川的沉积物形成。这些沉积物可分为三大类：冰碛、湖相沉积和冲积沉积。在流域内也可以找到黄土。总体而言，该流域的土壤富含有机物质，有助于解释主要土地利用类型：农业和林地。该流域的气候被认为是温和的，夏季炎热，冬季凉爽。该流域位于湿润大陆性气候区，并经历四季分明。该流域年平均降雨量约为45英寸，通常在春季（四月、五月和六月）和晚秋（十一月下旬）达到最大降雨量。