USACE CWMS - Roanoke River 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)

Geography: The Roanoke River Basin is located in the southern part of Virginia and northern part of North Carolina. The river rises on the eastern slope of the Appalachian Mountains, flows 300 miles from Smith Mountain Dam in a southeasterly direction toward the Atlantic Coast, and empties into the Albemarle Sound, approximately 7 miles below Plymouth, NC. The basin is about 220 miles long and from 10 to 100 miles wide. Parts of 15 counties in Virginia and 17 counties in North Carolina are included in the watershed.

Drainage: The Roanoke River drains 9,580 square miles, of which 7,800 square miles is above John H Kerr Dam and 212 square miles is above Philpott Dam. The Dan River, the largest tributary, empties into the Roanoke at Clarksville, VA. Areas drained by the Dan and Upper Roanoke at this point are 3,855 and 3,465 square miles, respectively. As Williamston, NC, 38 miles above the mouth, the stream is affected by the elevation of the water in Albemarle Sound, which has no lunar tides, but whose surface is affected by wind.

Rainfall: The average annual precipitation over the entire basin is about 43 inches with annual extremes of 27 and 56 inches. Precipitation is well distributed throughout the year. The average annual snowfall is about 13 inches and does not accumulate sufficiently to have a noticeable effect on flood flows.

Storm rainfall characteristics: Flood producing storms in the Roanoke River Basin occur in all seasons of the year. Generally floods are caused by brief periods of intense rainfall on a major portion of the watershed. In the late summer and fall, intense rainfall is often associated with tropical hurricanes.

Runoff: The annual runoff from the Roanoke River Basin averages 14 inches or 32 percent of the annual precipitation. The runoff of the Roanoke River Basin, measured near Roanoke Rapids, NC, averages 1.0 cubic feet per second per square mile of watershed area.

Flood Damages: Floods in the Roanoke River Basin cause considerable loss to agricultural interests, urban areas, and to transportation and communication facilities. Although the damages occur throughout the watershed, the major flood losses are confined mainly to the Roanoke, Dan, and Smith Rivers. The flood plains in the Upper Roanoke River Valley and in the Dan and Smith River Valleys are usually narrow and flanked by bluffs which become precipitous in the headwater reaches. Damages from a major flood in these areas are not of major consequence to the agricultural areas are the farm enterprise is mainly situated above the flood plain and is not dependent for its continuity on the crops raised on the bottomlands. Below Weldon the floodplain is from 1 to 6 miles wide and contains about 78 percent of the total area and 61 percent of the agricultural area on the floodplains of the tree main rivers subject to inundation from floods. Practically all the farms in this valley are located on the wide flood plains and are completely inundated by a major flood. The majority of the cities and towns in the watershed are located on high ground.\

Location: John H Kerr Dam is located on the Roanoke River about 180 miles above the mouth, 20 miles downstream of Clarksville, VA, 18 miles upstream from the Virginia-North Carolina State line, and 80 miles southwest of Richmond, the capitol of Virginia.

Purpose: The objectives of regulating the outflow from John H Kerr dam will involve consideration of the following features: flood control, hydroelectric power, mosquito control, pollution abatement and fish and wildlife, navigation, and recreation. The primary objective of the project is flood control and a storage of 1,278,000 acre-feet between elevations 300 ft NGVD and 320 ft NGVD has been reserved exclusively for the detention storage of flood waters. The dam will also operate as a peaking plant. Most of the energy produced will be generated at varying rates during some portion of those hours designated as on-peak by the customers. The remainder of the energy produced will be generated incidental to reservoir regulation of flood flows.

Flow Forecasting: The main objective of forecasting stream flows into the reservoir is (a) to make an early determination of runoff in a flood rise so that releases from the reservoir can be established in accordance with the approval method of reservoir regulation and (b) to determine the amount of runoff assured in normal flows so that a forecast can be made of the water available for power generation.

兵团水管理系统（Corps Water Management System, CWMS）包含四个相互关联的模型，用于辅助该流域的水管理工作：
- 地理空间水文建模扩展工具（Geospatial Hydrologic Modeling Extension，简称GeoHMS）
- 水库系统模拟工具（Reservoir System Simulation，简称ResSIM）
- 河道分析系统（River Analysis System，简称RAS）
- 洪水影响分析工具（Flood Impact Analysis，简称FIA）

地理范围：罗阿诺克河流域位于弗吉尼亚州南部与北卡罗来纳州北部。该河发源于阿巴拉契亚山脉东坡，从史密斯山水坝向东南方向流淌300英里，最终注入阿尔伯马尔湾，入海口位于北卡罗来纳州普利茅斯下游约7英里处。流域全长约220英里，宽度介于10至100英里之间，涵盖弗吉尼亚州15个县以及北卡罗来纳州17个县的部分区域。

流域水文特征：罗阿诺克河流域的汇水面积为9580平方英里，其中约翰·H·克尔水坝以上流域面积7800平方英里，菲尔普特水坝以上流域面积212平方英里。最大支流丹河在弗吉尼亚州克拉克维尔处注入罗阿诺克河，该点以上丹河与罗阿诺克河上游的汇水面积分别为3855平方英里与3465平方英里。在距离河口38英里的北卡罗来纳州威廉斯顿处，河道水位受阿尔伯马尔湾水面高程影响——该海域无月球潮汐，但水面会受风力作用发生变化。

降水特征：全流域年平均降水量约为43英寸，年降水极值介于27至56英寸之间，降水在全年分布较为均匀。流域年平均降雪量约为13英寸，积雪量不足以对洪水流量产生显著影响。

致洪风暴特征：罗阿诺克河流域的致洪风暴全年均可发生，洪水通常由流域大部分区域出现的短历时强降雨引发。夏末与秋季的强降雨往往与热带飓风相关。

径流特征：罗阿诺克河流域年平均径流量为14英寸，约占年降水量的32%。在北卡罗来纳州罗阿诺克拉皮兹附近测得的流域径流量平均为1.0立方英尺每秒每平方英里流域面积。

洪水损失：罗阿诺克河流域的洪水会对农业产业、城区以及交通通信设施造成严重损失。尽管流域全域均可能发生洪水，但主要洪灾损失主要集中在罗阿诺克河、丹河与史密斯河流域。罗阿诺克河上游河谷以及丹河、史密斯河河谷的洪泛平原通常较为狭窄，两侧为陡崖，上游河段的陡崖尤为险峻。该区域的农业生产多布局于洪泛平原上方，且农业生产的持续性并不依赖河漫滩种植的作物，因此重大洪水在此区域造成的农业损失相对有限。在韦尔登下游区域，洪泛平原宽度介于1至6英里之间，该区域涵盖了三条主要河流洪泛平原总面积的约78%，以及农业用地总面积的61%。该河谷内几乎所有农场均位于宽阔的洪泛平原上，遭遇重大洪水时会被完全淹没。流域内绝大多数城镇均选址于高地之上。

约翰·H·克尔水坝位置：约翰·H·克尔水坝位于罗阿诺克河上，距离河口约180英里，弗吉尼亚州克拉克维尔下游20英里处，弗吉尼亚-北卡罗来纳州界上游18英里，弗吉尼亚州首府里士满西南80英里处。

工程目标：调节约翰·H·克尔水坝出库流量的目标需综合考虑以下要素：防洪、水力发电、蚊虫防控、污染治理、鱼类与野生生物保护、航运以及休闲娱乐。本工程的核心目标为防洪，已在300英尺至320英尺（NGVD，美国国家大地垂直基准面）高程区间内预留了127.8万英亩-英尺的库容，专门用于洪水滞蓄。该水坝同时可作为调峰电厂运行，大部分发电量将在用户划定的高峰时段内以变动速率产出，剩余发电量则伴随洪水调度过程同步产生。

流量预报：水库入库流量预报的主要目标包括：(a) 提前判断洪水涨水过程中的径流量，以便按照获批的水库调度方法确定水库出库流量；(b) 确定常态流量下的径流量，从而预测可用于发电的水量。