WHY PICK THIS LOCATION?
The formula for a successful irrigation project is a combination of many variables. The general layout of the land must lend itself to irrigation, and the soils and underlying rock must provide fertility and the drainage necessary for farming. The length of the growing season of an area is a primary determiner of what crops can be raised in the area. Also, an irrigation project should be located on transportation routes so that products of the land can easily reach processing and marketing centers.
In the Columbia Basin, all of these factors have combined to make the area highly suitable for irrigation. The geology of the Columbia Basin Project makes a particularly interesting story.
The oldest rock on the project is the granitic rock which forms the hills to the north and east of Grand Coulee Dam and is the base on which the dam rests. This rock was formed deep within the earth's crust about 60 million years ago. Millions of years later, adjustments in the earth's crust and erosion by wind and water gradually exposed this granitic rock and established a river drainage system which flowed south out of Canada and across the eastern half of Washington before turning west to the Pacific Ocean.
The next significant geologic event in the region was the extrusion of vast quantities of basalt lava through cracks in the earth's surface from depths of 30 to 50 miles. These outpourings of lava through numerous widespread fissures occurred time and again. Eventually a vast plain was formed on top of hundreds of horizontal layers of basalt, which today extend over the eastern part of Washington and into Idaho and Oregon. These basalt flows completely disrupted this area's southward-flowing streams and forced them westward into the present Columbia River system which skirts the northern and western margins of the basalt plateau that form what is locally called the "Big Bend."
The Ice Age brought great geologic changes to the area about a million years ago. A huge ice sheet which originated in Canada and the Canadian Arctic moved south, and the entire northern end of North America took on the appearance of present-day Antarctica, completely covered by ice except for the emergence of the highest mountain peaks.
In the Columbia Basin Project area the fringe of this ice front extended from Dry Falls, west of Coulee City, to Grand Coulee. Eastward from Grand Coulee the ice extended to Cheney, and westward from Coulee City it reached a point between Waterville and Mansfield.
For a while the large volumes of water that resulted from the melting of the edge of the ice flow in the summer coursed down the established valley of the Columbia River. However, as the ice continued to move southward it blocked the Columbia River between Grand Coulee and Chelan, diverting the river and the meltwater into new watercourses southward along the Grand Coulee.
These new streams and rivers, occupying courses which had never before been subjected to their powerful forces, settled downward in their new environments dramatically. Roaring waterfalls plunged over cliffs, formerly dry divides were crossed and incised, and the low-lying areas were covered with a coarse mixture of basalt debris and material carried into the region by glacial meltwater and icebergs.
The volume of water discharged across the eastern part of Washington varied widely from a winter trickle to huge floods which covered the land when large lakes of meltwater broke through temporary ice dams which blocked the Cabinet Gorge of the Clark Fork River. Under these conditions, the glacial streams never achieved a normal water flow and the result within the project area is a physiography that is unique, complex, awe-inspiring, and of great geologic interest.
As successive annual and sporadic floods poured across the land, a huge waterfall which first plunged over the hill north of Coulee City eroded a waterway from the high Big Bend back into the Columbia River Valley to form the Upper Grand Coulee. The plunge at what is now Dry Falls took the river into the Lower Grand Coulee and thence meandering back to the present river channel.
As a result of the violent erosive forces and the massive grinding glaciers that shaped this area, today's soil composition in the basin varies widely from deep, fine, windblown materials with moderately low clay content to shallow sandy wind-deposited soils. Long periods of semiaridity during the project's formation resulted in the formation of a very hard calcium carbonate-sulfate caliche deposit in most subsoils usually covered by 18 inches to 15 feet of fertile soil. The soils of the project area are generally easily worked and low in alkali and other injurious chemicals. Given water, they make an excellent grass-roots host.
Without irrigation water the project area would certainly be hostile to crops, for the climate is dry with much of the 6- to 10-inch rainfall that the area receives annually falling in the winter and early spring. Most of the moisture in the area is dropped on the Cascade Mountains before it reaches the basin.
The growing season, or frost-free period, in the project averages about 165 days and there are many areas in the project where the long frost-free period proves ideal for orchard and other crops that demand a long growing season. Winds over the project are strong, and contribute to the long crop-growing period by preventing the formation of frost pockets.
These strong winds caused some trouble in the early days of the project by blowing away the topsoil of the newly cleared lands. However, the cropping of the land and the planting of permanent pasture and heavy cover crops have tied down the fine soil of the project and minimized dust-storms. For an irrigation project then, the climate of the basin area is very good.
Finally, as previously mentioned, an irrigation project must be located so that its produce can be easily exported to processing plants and markets. The approximate center of the irrigated lands of the Columbia Basin is 135 air-miles from Seattle, 105 miles from Spokane, and 150 miles from Portland. The area is served by seven major trucklines, four major rail lines, four branch rail lines, two buslines, and one airline. It is also crossed by three State highways, three Federal highways, and a network of county roads.
Markets of the world can be reached through the ports of Vancouver, Portland, and Seattle. Barges range upriver as far as Pasco at the south end of the project, where there are water terminal facilities.
In summary, the Columbia Basin Project was a "natural" for a successful irrigation development. Favorable geological conditions have made it a place of good land, abundant water, and a topography which lends itself well to transporting water to the land. A long, frost-free growing season allows the farmer to raise a large variety of crops, and a favorable location places him within easy reach of many of the major markets. These factors have helped to make the Columbia Basin Project a success and consequently a vital part of the Nation's economy.
Last Updated: 01-Feb-2008