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.

Corps 水资源管理系统（简称 CWMS）包含四个相互关联的模型，旨在协助流域水资源管理：

- 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）

地理位置：罗阿诺克河流域位于弗吉尼亚州南部和北卡罗来纳州北部。该河流起源于阿巴拉契亚山脉的东部斜坡，从史密斯山坝向南东方向流去，全长300英里，最终注入位于北卡罗来纳州普利茅斯下方约7英里的阿尔伯马尔湾。该流域长约220英里，宽度在10至100英里之间。弗吉尼亚州15个县和北卡罗来纳州17个县的部分地区属于该流域。

排水情况：罗阿诺克河流经9,580平方英里的土地，其中7,800平方英里位于约翰·H·克尔大坝以上，212平方英里位于菲尔波特大坝以上。最大的支流丹河在弗吉尼亚州克拉克维尔注入罗阿诺克河。在这一点，丹河和上游罗阿诺克河的排水面积分别为3,855平方英里和3,465平方英里。在威廉斯顿，距离河口38英里处，水流受到阿尔伯马尔湾水位的影响，该湾无月潮，但其表面受风力影响。

降水量：整个流域的平均年降水量约为43英寸，年极端降水量为27至56英寸。降水量全年分布均匀。平均年降雪量约为13英寸，不足以对洪水流量产生显著影响。

风暴降水量特征：罗阿诺克河流域的洪水产生风暴发生在全年任何季节。通常，洪水是由流域主要部分短暂而强烈的降雨引起的。在夏末和秋季，强烈的降雨往往与热带飓风有关。

径流：罗阿诺克河流域的年径流平均为14英寸，占年降水量的32%。在北卡罗来纳州罗阿诺克瀑布附近测量的罗阿诺克河流域的径流，平均每平方英里流域面积每秒1.0立方英尺。

洪水损失：罗阿诺克河流域的洪水对农业利益、城市地区以及交通和通信设施造成了相当大的损失。尽管损失发生在整个流域，但主要洪水损失主要限于罗阿诺克河、丹河和史密斯河。上游罗阿诺克河谷、丹河和史密斯河谷的洪水平原通常较窄，两侧为峭壁，在源头地区变得陡峭。这些地区的重大洪水损失对农业区域影响不大，因为农场企业主要位于洪水平原以上，不依赖于底部土地上的作物以维持其连续性。在韦尔登以下，洪水平原宽度在1至6英里之间，占总面积的约78%，占主要易受洪水淹没的河流洪水平原上的农业面积的61%。这个山谷中的几乎所有农场都位于宽阔的洪水平原上，并完全被重大洪水淹没。流域内的绝大多数城市和城镇都位于高地。

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

目的：调节约翰·H·克尔大坝出水口的目标将涉及以下特征的考虑：防洪、水力发电、蚊子控制、污染控制、鱼类和野生动物保护、航运和娱乐。该项目的首要目标是防洪，并在海拔300英尺NGVD至320英尺NGVD之间预留了1,278,000英亩英尺的蓄水量，专门用于洪水蓄水。该大坝还将作为调峰电站运行。大部分产生的能源将在客户指定的峰时期间以不同速度产生。其余产生的能源将伴随水库调节洪水流量而产生。

流量预测：预测水库入流流量的主要目标是（a）在洪水上涨初期确定径流，以便根据水库调节的批准方法确定水库的排放，以及（b）确定正常流量中保证的径流量，以便预测可用于发电的水量。