5.2 ARKANSAS RIVER BASIN - Amazon S3s3.amazonaws.com/loa.data/inv/275620/Aquifer Map.pdf · 5.2...

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5.2 ARKANSAS RIVER BASIN The Arkansas River basin drains a 28,273 square mile area in the southeastern quarter of Colorado ( Figure 5.2-1 ). The basin defines Water Division 2 with the divisional office in Pueblo. As of early 2001, there were over 5,450 alluvial wells of record in the Arkansas River basin. Figure 5.2-1 Location of the Arkansas River basin showing extent of mapped alluvium and distribution of alluvial wells. The Arkansas River has its origin high in the Rocky Mountains near Leadville, Colorado, flowing south-southeast through the mountains before it turns east and enters the plains near Pueblo. Well known tributaries include the Purgatoire, Huerfano, Cucharas, and Apishapa Rivers, and Fountain and Big Sandy Creeks. The total annual flow in the Arkansas River within Colorado is approximately one million acre-feet. There are 10 major trans-basin diversions of surface water into the upper Arkansas River that provide an additional source of recharge to the underlying alluvial aquifer. The diversions consist of tunnels and ditches that routed 144,288 acre-feet of water into the basin in 1998. Over 1.8 million acre-feet of water are stored in 19 reservoirs within the basin.

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Page 1: 5.2 ARKANSAS RIVER BASIN - Amazon S3s3.amazonaws.com/loa.data/inv/275620/Aquifer Map.pdf · 5.2 ARKANSAS RIVER BASIN The Arkansas River basin drains a 28,273 square mile area in the

5.2 ARKANSAS RIVER BASIN

The Arkansas River basin drains a 28,273 square mile area in the southeastern quarter ofColorado ( Figure 5.2-1 ). The basin defines Water Division 2 with the divisional office inPueblo. As of early 2001, there were over 5,450 alluvial wells of record in the ArkansasRiver basin.

Figure 5.2-1 Location of the Arkansas River basin showing extent of mapped alluvium and distribution of alluvial wells.

The Arkansas River has its origin high in the Rocky Mountains near Leadville, Colorado,flowing south-southeast through the mountains before it turns east and enters the plainsnear Pueblo. Well known tributaries include the Purgatoire, Huerfano, Cucharas, andApishapa Rivers, and Fountain and Big Sandy Creeks. The total annual flow in the ArkansasRiver within Colorado is approximately one million acre-feet. There are 10 major trans-basindiversions of surface water into the upper Arkansas River that provide an additional sourceof recharge to the underlying alluvial aquifer. The diversions consist of tunnels and ditchesthat routed 144,288 acre-feet of water into the basin in 1998. Over 1.8 million acre-feet ofwater are stored in 19 reservoirs within the basin.

Page 2: 5.2 ARKANSAS RIVER BASIN - Amazon S3s3.amazonaws.com/loa.data/inv/275620/Aquifer Map.pdf · 5.2 ARKANSAS RIVER BASIN The Arkansas River basin drains a 28,273 square mile area in the

John Martin Reservoir is the largest water storage facility on the Arkansas River. Photo by U.S. Army Corps of Engineers.

Current land use in the upper Arkansas River valley is primarily recreation and tourism withlimited agriculture and industry. Land use in the lower Arkansas River valley is heavilyagricultural, with both surface and ground water being utilized to grow a significant amountof farm crops, including the famous Rocky Ford cantaloupes. The alluvial aquifer is animportant source of ground water in the plains.

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5.2 ARKANSAS RIVER BASIN

Alluvial Aquifer

The primary alluvial aquifer along the Arkansas River consists of unconsolidated river-deposited sediments. The sediments are more varied in size in the upper basin, upstream ofPueblo, ranging from glacial silts to large boulders. In many areas along the upper Arkansasthe alluvium is missing where the river is actively eroding in deep bedrock canyons. Alluviumin the lower Arkansas valley is composed of a heterogeneous mix of interbedded sands,gravels, silts, and clays. Alluvium is not a significant aquifer along many of the Arkansastributaries.

Well depths along the upper Arkansas River range from less than 10 feet to greater than100 feet below ground surface, with a mean depth of 53 feet. The Division of WaterResources well permit database contains over 3,400 wells that have been completed in thelower Arkansas River valley alluvium. Over 90 percent of these wells are completed atdepths less than 120 feet below ground surface with a mean depth of only 58 feet.

Recharge to the Arkansas River alluvium is primarily through infiltration of surface waterthrough the streambed of the river. Infiltration from irrigation canals and surfaceapplication of irrigation water also provides a significant amount of recharge to the alluviumdownstream from the Pueblo/Crowley County line.

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5.2 ARKANSAS RIVER BASIN

Water Levels/Aquifer Characteristics

Arkansas River alluvium is an unconfined, water-table aquifer in direct hydraulic connectionwith the Arkansas River surface water system. The water table typically slopes toward thevalley center and downstream along the river, except where localized pumping causes agradient reversal.

Depth to water ranges from about 5 to 30 feet below ground surface along much of thelower Arkansas River and its tributaries. In the upper Arkansas River Basin, depths to waterranged from 5 to 58 feet below ground surface during the 1990s (Fig. 5.2-2). Many of theupper basin wells record strong seasonal fluctuations with the highest water levelscorresponding to snowmelt and spring runoff in the mountains.

Figure 5.2-2 Ground-water hydrographs from wells in the upper Arkansas River alluvium from 1992 to 1996. Modified from USGS, 1997.

Basin-wide hydraulic characteristics for the Arkansas River basin alluvium are presented inTable 5.2-1.

Table 5.2-1 – Basin-wide hydraulic characteristicsArkansas River basin alluvium.

Stream ReachTransmissivity

(ft 2 /day)

HydraulicConductivity

(ft/day)

Discharge(gpm)

SpecificCapacity(gpm/ft

drawdown)

SpecificYield

Upper ArkansasRiver nd nd Up to 500 nd ndLower ArkansasRiver 2,000-60,000

70-1,200*530 10-4,000 7-54 0.13-0.20

Fountain Creek nd 400-1,600 100-3,000 nd 0.2-0.3

nd = no data, * upper value represents the range, lower value is the average.

Water Use/Withdrawals

Current land use in the upper Arkansas River valley is primarily recreation and tourism withlimited agriculture and industry. Public supply is the primary use of ground water in ChaffeeCounty and probably in Lake County, with just over 5,000 acre-feet of fresh ground waterwithdrawn from the two counties in 1995. Mining was historically the major industry in thevalley, with silver and gold mines dominating the area in the late 1800s into the 1900s.

Land use in the lower Arkansas River valley is heavily agricultural, with both surface andground water being utilized to grow a significant amount of farm crops. About 2.0 millionacre-feet of river water were diverted for irrigation in 1998 (Colorado Water ConservationBoard, 2002) and 174,383 acre-feet of ground water were withdrawn in 1995 in ProwersCounty along the lower Arkansas at the Colorado-Kansas state line.

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5.2 ARKANSAS RIVER BASIN

Water Quality

Ground water in the lower Arkansas River basin alluvial aquifer is classified as sodium-calcium, sulfate-bicarbonate in character and is typically of fair to good quality, although itbecomes increasingly saline and marginally unusable downstream due to heavy irrigationuse. Water quality within the upper Arkansas River basin alluvium is generally potable witha few exceptions of elevated metals produced by natural acid rock drainage andanthropogenic septic effluent contamination.

Summary

A summary of the hydraulic characteristics and water quality for the Arkansas River alluvialaquifers follows:

Upper Arkansas River Basin Lower Arkansas River BasinAquifercharacteristics

Unconsolidated river-depositedsediments. The sediments rangein size from glacial silts to largeboulders

A heterogeneous mix ofinterbedded sands, gravels, silts,and clays. Width varies from 1 to10 miles; 30 to 200 ft thick.Designated ground water basinsinclude the Upper Black Squirreland Big Sandy.

Primary uses Domestic AgricultureWater levels 5-58 feet 5-30 feetWell data 1,600 completed wells

90% <85 feet deepmean depth = 53 feet

3,400 completed wells90% <120 feet deepmean depth = 58 feet

Yield Variable: up to 500 gpmmean = 25 gpm

Variable: 10-4,000 gpmmean = 360 gpm

Water quality Generally potable with a fewexceptions of elevated metalsproduced by natural acid rockdrainage and anthropogenicseptic effluent contamination.

Degrades downstream from goodin the upper reaches to salinenear the Kansas state line.Nitrates and herbicides areperiodically detected in shallowalluvial wells in the areas ofintense agricultural use.