Gavin's Point Dam EarthCache
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In order to count this Earthcache as a find, you must complete the following tasks and email the answers to me.
1. Estimate the width of the river at ground zero. How do you think the width changed with the implementation of the dam?
2. Describe the appearance of the river and the land around it.
3. What evidence do you see of past glaciation periods?
4. Estimate the height of the dam.
5. Estimate the amount and the rate per minute at which water flows at the dam.
This Earthcache is located along the Missouri River at the Lewis and Clark Recreation Area. Very close to ground zero towers Gavin’s Point Dam, which creates the man-made Lewis and Clark Lake to the west and allows the Missouri River to continue its course to the east. The Lewis and Clark Recreation Area offers camping, boat access points, and tons of fishing. Enjoy!
The basin of the Missouri River was initially formed two billion years ago after a period of major volcanic activity and geologic stresses that created the mountains that cover North America. Following significant erosion, several depressions in the ground were carved, including the valley in which the Missouri River now flows. Much later, the area was flooded by the seas that covered central North America. This flooding further eroded the landscape and left a lot of water behind--one example being the Missouri River.
The drainage system of North America and the current course of the Missouri River as we know it today is drastically different from how it first began. During the Oligocene Epoch (34-23 million years ago), the Rio Grande was the continent’s major drainage system. During this time, the Missouri River and the majority of North America’s other rivers drained to the Hudson Bay. A shift in the Miocene Epoch (23-5 million years ago) caused all of this to change. This shift, which was a result of continental tectonism (plates converging or diverging), reorganized the continent’s drainage systems and established the Mississippi as the dominate drainage system, which the Missouri River now drains into. Instead of draining north to the Hudson Bay, this shift caused most of the rivers, the Missouri included, to now drain south to the Gulf of Mexico.
Continental glaciations of the Pleistocene Epoch (2.5 million - 12,000 years ago) have further rearranged the course of the Missouri River. With each glaciation period, glaciers up to 6500 feet thick repeatedly advanced and retreated upon the land, leaving scars and depressions. These glaciers constantly forced the Missouri River to redirect its channel due to blockage from the glaciers or new depressions cut by the glaciers.
The Meandering Missouri River roughly follows the edge of the glaciation during the last Ice Age winding from bluff to bluff in the flat midwestern states, such as South Dakota. Prior to its modification by man, the Missouri River was known for its shifting channels, high turbidity (murkiness), and periodic floods. This river was commonly referred to as the “Big Muddy” because of its high silt content.
The Missouri River is the longest river in the United States (2.5 miles longer than the Mississippi). Before interference of mankind, the Missouri River was the longest river in North America. Now, nearly seventy-two miles of the river have been cut off in channeling, making it comparable in length to the Mississippi River.
The headwaters of the Missouri River are in the Rocky Mountains in southwestern Montana, near the town of Three Forks. From there, the Missouri flows east through Montana and into North Dakota before turning southeast and making its way through South Dakota. On the southern end of the state, the Missouri River forms a partial boarder between Nebraska and South Dakota and acts as the border between Nebraska and Iowa. From there, the Missouri continues south forming the border between Missouri and Kansas. At Kansas City, the Missouri River turns sharply east where it flows for a bit before joining the Mississippi River just north of St. Louis.
The Missouri River serves as a tributary of the Mississippi River. At 2341 miles long, the Missouri River drains about one-sixth of the continental United States. The extensive system of tributaries of the Missouri River drain nearly all of the Great Plains and small portions of southern Alberta and southwestern Saskatchewan. Some of the Missouri’s longer tributaries drain portions of the eastern Rocky Mountains.
Humans have lived along or near the Missouri for a long time--evidence suggests the first settlers along the Missouri lived some 10,000 years ago. Archaeological remains of their tools and weapons, campsites and homes, foods, and religious and ceremonial objects provide clues to their lifestyles. Most of the sites have been defined by the presence of surface materials, and only limited excavations have been conducted in the area.
The Missouri River, like the Oregon and Santa Fe trails, is known for being one of the three main thoroughfares to the Far West. It was the great waterway of Native Americans, Lewis and Clark, trappers and traders, steamboat captains, and settlers. Interaction between traders and Omaha, Ponca, and other tribes took place as these groups traveled up and down the river. As the federal government moved tribes to reservations, land in the region became available for settlement. The 1858 Treaty between the Yankton Sioux and the federal government opened up Dakota Territory, while the Homestead Act of 1862 encouraged further immigration to the region. These settlers built a number of communities along the river corridor.
Steamboats regularly traveled the river until the late 1800s. During this time, the Missouri River was characterized by a constantly shifting channel, numerous smaller braided channels, chutes, sloughs, islands, sandbars, and backwater areas. The river was infamous for its sudden and dramatic shifts in course. Well over 200 steamboats are known to have sunk in the river from 1819 to 1897. These wrecks now lie beneath the river’s silt and sandbars.
Flooding has also been a huge issue with the Missouri River. In his article “Mighty Mite,” Roger Holtzmann describes the character of the Missouri River: “Once the great continental glaciers of the Pleistocene Epoch had receded … the stream was left to do just as it pleased. And no willful child ever exercised its freedom more erratically, creating and destroying islands here, doubling back almost upon itself there, never choosing the shortest path between two points. Even when it stayed put, the river couldn’t settle upon an identity. In the spring, the Missouri was a bully, rushing water downstream in a torrent, devouring everything in its path. During high summer and fall, it seemed a lethargic old man, hardly capable of managing its long journey to the sea.”
Near Yankton, Native Americans of long ago, with their portable homes and villages, were content to deal with the river on its terms. They moved as the Missouri’s whims dictated. Then the white settlers moved in. They were far from being content with moving at whim. They wanted to build homes, lay out streets, and grow cities.
The Missouri River of today has now been “tamed” and divided into approximately three equal parts. The lower one-third, below Sioux City, Iowa, is channelized; one-third is impounded by six large dams (Gavin’s Point being one of those dams); the final one-third consists of “free flowing” stretches of water. Today, only one percent of the river’s entire length remains truly uncontrolled by humans.
In South Dakota, four large dams impound the Missouri River. Oahe Dam, forming Lake Oahe near Pierre, is one of the largest rolled earthen dams in the world and was completed in 1958. Big Bend Dam, creating Lake Sharpe near Ft. Thompson, was finished in 1963 and was the last of the Missouri River impoundments to be finished. Ft. Randall Dam, impounding Lake Francis Case near Pickstown, was the first dam to be completed (1952) on the Missouri River in South Dakota. Gavin’s Point Dam, where you currently are, was finished in 1955 and forms the Lewis and Clark Lake. This is the smallest impoundment on the main stem of the River. There are also two-semi-natural segments of regulated free-flowing Missouri River in South Dakota. A forty-five mile stretch below Ft. Randall Dam flows into Lewis and Clark Lake. The second section is a fifty-eight mile stretch below Gavin’s Point Dam that flows into the channelized portion of the Missouri River near Sioux City, Iowa.
Prior to the construction of these dams in South Dakota, every town along the river had similar tales of flooding woe in their histories. For the people in these towns, floods were a certainty of life--swallowing whole farms and towns. The flood of 1943 was particularly vengeful. More than fifty people lost their lives and more than $100 million dollars in property damage occurred from North Dakota to Missouri. Because of this flood, Congress took time out from pressing World War II business to pass the Flood Control Act of 1944. One of the projects authorized by this act was the Pick-Sloan Plan--a merger of two Missouri River proposals. The Pick-Sloan Plan promised to protect towns along the Missouri from flooding, provide water for irrigation and hydroelectric power, and create stable river levels for navigation. The Plan also called for five major dams to be built on the Missouri--four in South Dakota.
Construction on the dam began in 1952. More than seven million cubic yards of fill went into Gavin’s Point Dam. This is enough to fill a string of dump trucks from Yankton to New York City. This number only reflects a portion of what was moved at Gavin’s Point. More fill went into temporary structures like the diversion dam and roads around the site. Thirty-eight months and forty-nine million dollars later, the mile-and-a-half long dike was finally complete. On July 30, 1955, closure of the dam began. Closure is the moment when a dam becomes a dam--when the water begins to flow only when and where man decides. Throughout this day, two large draglines began dumping load after load of fill into the water. Crews worked through the night by floodlight until closure was complete. At 4:05am on July 31, closure was complete and Lewis and Clark Lake was born. From that moment on, the Missouri River would flow only through the spillway or power plant of Gavin’s Point Dam.
Even though Gavin’s Point is the smallest of the five main stem dams, it serves a vital purpose in the system by smoothing out surges in flow from the dam at Pickstown and keeping downstream water levels at a constant, predictable depth for navigation. The reservoir system on the Missouri River--Lewis and Clark Lake being an example of one--was designed for multipurpose use. Hydroelectric power, flood control, navigation, municipal water, irrigation, fish and wildlife habitat, and recreation are all authorized uses of the system.
Resources:
Holtzmann, Roger. "Mighty Mite." South Dakota Magazine, July/August 2007: 26-33. Print.
"Missouri River." Northern State University. Web. 12 Feb. 2010. (visit link)
NOT A LOGGING REQUIREMENT: Feel free to post pictures of your group at the area or the area itself - I love looking at the pictures.
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