USACE CWMS - Willamette Watershed

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 Willamette River, a major tributary of the Columbia River, is 187 miles long. Flowing northward between the Oregon Coast Range and Cascade Range, the river and its tributaries form a basin called the Willamette Valley. The valley, fed by rainfall on the western side of the Cascades, is one of the most fertile agriculture regions of the United States.
The main stem of the Willamette River is formed by the confluence of the Middle and Coast Forks of the Willamette River near Springfield, Oregon. The main stem flows north for 187 miles to the Columbia River. Significant tributaries of the Willamette River, from source to mouth, include the Middle and Coast Fork Willamette, the McKenzie, Long Tom, Marys, Calapooia, Santiam, Luckiamute, Yamhill, Molalla, Tualatin, and Clackamas rivers. The main stem of the Willamette River has an elevation of 438 feet at its headwaters and loses 428 feet in elevation between source and mouth or about 2.3 feet per mile. The gradient is slightly steeper from the source to Albany than from Albany to Oregon City. The main stem of the Willamette varies in width from about 330 to 660 feet. The average flow at the mouth is approximately 32,400 cubic feet per second and contributes 12 to 15 percent of the total flow of the Columbia River. The Willamette’s flow varies seasonally, averaging about 8,200 cfs in August to more than 79,000 cfs in December.
The Willamette River basin contains thirteen USACE dams. The primary purpose of these projects is to prevent flood damages to the downstream metropolitan areas of the Willamette Valley but other purposes include hydropower generation, fish and wildlife, water quality, recreational use and water supply. The regulation of flood and conservation storage in each reservoir is coordinated with the regulation of storage in all of the other reservoirs in the basin.
Communities along the main stem at risk of flooding include Springfield and Eugene in Lane County; Harrisburg in Linn County; Corvallis in Benton County; Albany in Linn and Benton Counties; Salem in Marion County; Newberg in Yamhill County; Oregon City, West Linn, Milwaukie, and Lake Oswego in Clackamas County, and Portland in Multnomah and Washington counties. The Willamette River is known for flooding because of the high amounts and variations of precipitation in the valley. The largest flood on the Willamette River, in recorded history, occurred in 1861 when rainstorms and warm temperatures combined with a well-above-average snowpack in the Cascades. From Eugene to Portland, thousands of acres of riverside farmland were washed away and many towns in the valley were damaged or destroyed. Peaking at 635,000 cubic feet per second, the 1861 flood inundated approximately 353,000 acres of land. Although the Willamette River is regulated and controlled by a complex system of dams, severe flooding is still a concern. In 1996, a low elevation snowpack combined with massive rainfall and warm temperatures, caused some of the costliest floods to ever affect the Willamette Valley.

军团水资源管理系统（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）
- 水库系统模拟（ResSIM）
- 河流分析系统（RAS）
- 洪水影响分析（FIA）

威廉姆特河，作为哥伦比亚河的主要支流，全长187英里。该河流自俄勒冈州海岸山脉与喀斯喀山脉之间向北流淌，与其支流共同构成了被称为威廉姆特谷的流域。该谷地得益于喀斯喀山脉西侧的降雨，是美国最肥沃的农业区域之一。

威廉姆特河的主干流由位于俄勒冈州斯普林菲尔德附近的威廉姆特河中游和海岸支流汇合而成。主干流向北流淌187英里，汇入哥伦比亚河。从源头到河口，威廉姆特河的重要支流包括中游威廉姆特河、海岸支流威廉姆特河、麦肯齐河、朗汤姆河、玛丽河、卡拉波亚河、桑蒂亚姆河、卢克亚穆特河、亚姆希尔河、莫拉拉河、图阿拉廷河和克拉卡马斯河。威廉姆特河的主干流源头海拔438英尺，在源头与河口之间海拔降低428英尺，或每英里约降低2.3英尺。从源头到阿尔巴尼的海拔梯度略大于从阿尔巴尼到俄勒冈城的梯度。威廉姆特河主干流的宽度从约330英尺到660英尺不等。河口平均流量约为每秒32,400立方英尺，占哥伦比亚河总流量的12%至15%。威廉姆特河的流量季节性变化显著，8月份的平均流量约为每秒8,200立方英尺，而在12月份则超过每秒79,000立方英尺。

威廉姆特河流域内共有十三座美国陆军工程兵部队（USACE）大坝。这些工程项目的首要目的是防止威廉姆特谷下游的都市地区遭受洪水损害，但其他目的还包括水力发电、鱼类和野生动物保护、水质管理、休闲利用和供水。每个水库的洪水调节和蓄水管理均与流域内所有其他水库的蓄水管理相协调。

位于主干流沿线且面临洪水风险的社区包括莱恩县的斯普林菲尔德和尤金、林恩县的哈里斯堡、本顿县的科瓦利斯、林恩县和本顿县的阿尔巴尼、马里县的塞勒姆、亚姆希尔县的纽伯格、克拉卡马斯县的俄勒冈城、韦斯特林恩、米尔沃基和奥斯维戈湖、以及在马多姆县和华盛顿县的波特兰。威廉姆特河因其流域内降水量高且变化大而闻名。在记录的历史中，1861年发生的大洪水，是由于暴雨和温暖气温与卡斯喀山脉上高于平均水平的积雪相结合所致。从尤金到波特兰，数千英亩的河岸农田被冲走，山谷中的许多城镇遭到破坏或毁灭。1861年的洪水峰值达到每秒635,000立方英尺，淹没约353,000英亩的土地。尽管威廉姆特河通过一个复杂的坝系进行调节和控制，但严重洪水仍然是关注的问题。1996年，低海拔的积雪量与大量降雨和温暖气温相结合，引发了有史以来影响威廉姆特谷最昂贵的洪水之一。