River Colorado
This extraordinary river has many unique features and runs through 7 American states including Colorado, Utah, Arizona, Nevada, California, Baja, California, and Sonora. Humans have benefitted from the river for the last 2000 years due to its huge potential. More water is exported from the colorado basin than from any other river basin in the US. However these human uses have caused various effects on the river discharge.

Key Features:
Big Thompson Trans-Basin Diversion
Reservoirs including Mead, Powell, Flaming, Gorge and Fontenelle
Dams such as Hoover, Davis and Parker
Glen Canyon
Grand Canyon
The Colorado River Delta

Figure 1 - shows the course of the river.

The Upper Colorado starts at the source at La Poudre Pass Lake in the Rocky Mountain national Park in Colorado. Here the annual precipitation is very high in the park with as much as 2540mm of snow during the winter. Under the Rocky Mountains there is the Big Thompson Trans-Basin Diversion, which diverts water to 2 million people living in Colorado. The Colorado River begins to flow to the west into Grand Lake in Colorado. Once the Colorado River meets the U.S. southwest, it begins to meet several more dams and reservoirs including the Fontenelle (the first of 11 dams) and receives its principle tributary, the Green River before it reaches the Glen Canyon Dam which forms the reservoir Lake Powell in Southern Utah. Here the Colorado also joins with San Juan River.

From here, the Colorado River begins its decent through its lower course, initially through a series of massive canyons, which it created millions of years ago, including the 217 mile long Grand Canyon which is a narrow winding deep gorge created in sedimentary rock. Beyond the Grand canyon the river meets the virgin River, a tributary, in Nevada and flows into lake Mead, which is the largest man-made lake in the U.S. after being blocked by the Hoover Dam (the largest producer of hydroelectric power) at the Nevada/Arizona border.

Figure 2 - The Grand Canyon

During the water’s journey through the southwest of America it experiences around 90 different rapids some of which are considered to be very dangerous. After flowing through the Hoover Dam, the river continues towards the Pacific Ocean through several more dams, including the Davis, parker and palo Verde Dams, and finally into its delta, in Mexico, after flowing southwest for 2,304km with an average discharge of 503m3 /sec. Although this delta was once a rich marshland, toady it is dry due to the human use of most of the rivers water. Over the whole of the river, the drainage basin covers 244,000 square miles, which is a significant 7% of the United States.

How humans use the river to their own benefit
The main use of the Colorado River is that it has been a source of water for 2000 years and it supply’s the demands of 24 million people. In the past 50 years there has been an increased demand for water as the west and southwest of America have significantly increased demand for water as the west and southwest of America have significantly increasing populations, for example Nevada’s population increased by 58.2% from 1881 to 1991. Factories near the river also use the water to make their products but this may lead to the leaching of chemicals into the river. Moreover, water is a essential part of American life in urban areas and is used for irrigation, swimming pools, and air conditioning as well as domestic use.

The rivers are used for irrigation and cattle farming as 810,000 hectares of farmland across the southwest use water from the Colorado. Some of the places where water is used in this way include irrigated land in the Imperial valley and also east of the Great divide where 283000 ha of farmland is supplied with water via the Big Thompson and other diversion projects. Water for irrigation benefits humans as it provides water to grow crops and feed animals, which are then used to feed the growing populations in Nevada and California. The river has always been a source of water for farming and irrigation even back in the 19th century, when Mormon settlers used the river for subsistence farming.

Additionally there are recreation uses, such as boating, white water rafting and other water sports on Lakes including the Mead, Havasu, and Powell, which attract over 1.5 million tourists each year, by road and air. This is favourable because with tourists comes income, which can be used to preserve the river and help maintain dams. Eleven U.S. national parks are in the river’s watershed, which offer activities like hiking, camping, skiing and fishing.

Furthermore, the Colorado has 11 dams in 7 major states. Which together hold 74 billion cubic meters of stored water and produce 4000 megawatts of hydroelectric power. this benefits humans, as it is a key source of renewable energy. Dams along the river course that provide hydroelectric power include Fontanelle, Flaming Gorge, Glen Canyon, Hoover Dam and Davis Imperial. These Dams also help to prevent floods.

Figure 3 - The Hoover Dam and Lake Mead

Effects on River Discharge
As population increases, the demand for water increases as well as the demand for food thus having an effect on river discharge. As a consequence the river discharge has decreased, as more water is needed for irrigation and cattle farming to supply food for the growing populations. Evidence of this decrease is in Mexico’s Baja California. A total of 1848 million cum a year should be supplied to the Yum and Morelos Dams. However due to California’s plan to line the All-American Canal carrying water to the Imperial Valley means a loss of 130.5 million cum a year.

Also water evaporates from the reservoirs as temperatures along the Colorado can reach 40 degrees and this has had an effect on the river discharge, as evaporation can be as high as 18830mm/ annum, thus meaning less water travelling along the rivers course. The high rate of evaporation in this hot, dry climate leads to a problem with salinisation which puts the farmers in the lower course at a disadvantage as their crops are not getting good quality water. farming and factories along the course can also lead to wasted chemicals being put into the river.

The hot climate may also lead to droughts causing the amount of water in a reservoir to decrease. one drought in the summer of 2004 meant that water levels in Lake Mead were at 347m, which is the lowest levels since 1955. Due to the decrease in the amount of water stored in reservoirs, restrictions had to be put on cities in 2005, such as Las Vegas, on the use of irrigation water for the next agricultural season.

Dams have had an impact as discharge below the Hoover Dam site has changed massively after the storage began in lake Mead in february 1935. it decreased from about 100 thousands of cubic feet per second to around 20 thousands of cubic feet per second and later to 15 thousands of cubic feet per second later storage began in Lake Powell in march 1963. dams can also control the amount of water they let through thus changing the river discharge

Figure 4 - Glen Canyon Dam and Lake Powell

Today less than 1% of the natural river reaches the Gulf of California die to the distribution of water along the rivers course whereas before the construction of the Hoover and Glen Canyon Dam, 24669 million cum reached the delta. The delta is a now a waste land that used to be home to birds, wild cats, marine species and marine grasses.

To conclude, the Colorado is a key river in the 21st century for the southwest of the USA as its uses are essential for everyday life. However there is a clear need for management to help preserve its amazing features along its river course.