5.3 COLORADO RIVER BASIN
Chapter 5.3, Page 2 of 4

Alluvial Aquifer

The valley fill deposits or alluvium in the Colorado River basin consist generally of unconsolidated boulders, cobbles, gravel, sand, silt, and clay. The thickness of the alluvium can be extremely variable depending on location. Alluvium in the upper reaches of the basin tends to be thin due to increased slopes and higher flow velocities. Thicker deposits tend to accumulate in the lower reaches. Alluvium is very limited or nonexistent in the canyon sections of the Colorado River, such as the Gore, Glenwood, DeBeque, Ruby, and Horsethief Canyons where bedrock is exposed. Table 5.3-1 summarizes reported alluvial saturated thickness for some tributaries of the Colorado River.

Table 5.3-1 Reported saturated thickness of alluvium.

River or Creek Drainage

Saturated Thickness Range (in feet)

Average Saturated Thickness (in feet)

North Fork Colorado River

24 to 46

35

Blue River

25 to 56

41

Eagle River

17 to 75

47

Gore Creek

91

--

Roaring Fork River

19 to 62

41

From Apodaca and Bails, 2000

Well depths along the Colorado River range from less than 10 feet to greater than 175 feet below ground surface. The Division of Water Resources well permit database contains records of approximately 1,370 wells that have been completed in the Colorado River alluvium. Over 90 percent of these wells are completed at depths less than 120 feet below ground surface with a mean depth of 72 feet. A listing of reported alluvial well depths for a number of locations along the Colorado River is presented in Table 5.3-2.

Table 5.3-2. Reported alluvial well depths along the Colorado River.

Location

Alluvial Well Depth (feet)

Granby area

25 to 85

Hot Sulphur Springs area

50 to 70

Silt area

Less than 140

Rifle area

10 to 115

DeBeque area

35 to 148

Grand Valley area (Palisade to Fruita)

15 to 80


From Apodaca and Bails, 2000

Chapter 5.3, Page 2 of 4