ALLUVIAL AQUIFERS ALONG MAJOR STREAMS
INTRODUCTION
Alluvial aquifers of major importance are along many of the larger streams in the two-State area (fig. 11). These streams are the Salt Fork Arkansas and the Arkansas, the Cimarron, the North Canadian, the Canadian, the Washita, the North Fork Red and the Red, the Brazos and the Neosho Rivers. The alluvial deposits, with the exception of those along the Brazos and the lower Arkansas Rivers, are limited to the Central Lowland Physiographic Province. The Brazos River deposits are in the Great Plains and the Coastal Plain Provinces, and the lower Arkansas River deposits are in the Ouachita Province.
The aquifers are generally in deposits of Quaternary age, are unconfined, and consist of sand and gravel with some clay and silt. Locally, they include deposits of Tertiary age. The aquifer materials are commonly segregated by size into lenses and beds, which can affect the movement and availability of water. Beds and lenses of sand, gravel, or mixtures of the two yield most of the water. The deposits may be more than 100 feet thick and several miles wide, much of their total thickness is saturated throughout the year, and, in many places, they yield large amounts of water.
Collectively, withdrawals from the alluvial aquifers in Oklahoma and Texas were 71 million gallons per day during 1985. The aquifers are especially important in Oklahoma, where yields of wells completed in them are generally larger than yields of wells finished in adjacent or underlying bedrock. The water in the alluvial aquifers in many places is less mineralized than water in the adjacent streams.
Deposition and downcutting by the major streams were extensive at the end of the Tertiary Period and during the Quaternary Period. Repeated deposition and erosion left remnants of alluvial deposits at higher elevations as the streams progressively lowered their beds. A series of alluvial terraces was often the result, the youngest of which might be only a few feet higher than the present-day flood plain. Alluvium, as distinguished from alluvial terraces, is the most recent material deposited within the confines of the present flood plain. The alluvial terraces and alluvium usually form a single aquifer, although some outlying alluvial terraces are hydraulically independent. Highly permeable windblown sand derived from the alluvium and alluvial terraces overlies the alluvial deposits in many places and readily stores recharge from precipitation and conducts the recharge downward.
Average annual precipitation in the areas of the alluvial deposits varies from about 22 inches in western Oklahoma to about 44 inches in eastern Oklahoma. Precipitation varies from about 32 to 46 inches in the area of the Brazos River alluvial aquifer in southeastern Texas.
Most natural recharge to the aquifers occurs as precipitation that falls directly on the alluvial deposits, infiltration of runoff from adjacent slopes, and infiltration from the streams that cross the deposits, especially during higher flows. Large, additional recharge may occur from induced stream infiltration when ground-water pumpage lowers the water table below the stream levels (fig. 12). During dry periods, water may discharge from the alluvium into the streams, thus contributing to base flow. Discharge also takes place as transpiration from phreatophytes.
The chemical quality of water in the alluvial deposits may vary between the alluvium and alluvial terraces, thus reflecting the quality of the major source of recharge. The source of recharge for the alluvium may be the river and that for the alluvial terraces may be precipitation and leakage from underlying or adjacent aquifers.
SALT FORK ARKANSAS RIVER AND ARKANSAS RIVER
The Salt Fork Arkansas River originates in the so-called gypsum hills of southern Kansas and contains water with large concentrations of calcium sulfate as it enters Woods County, Okla. The river then receives large amounts of sodium chloride downstream from natural brine springs and salt plains in Alfalfa County, Okla. The river contains saline water, which is unsuitable for most uses, downstream to its junction with the Arkansas River.
Alluvium and alluvial terrace deposits as much as 10 miles wide and 150 feet thick are located along the entire length of the Salt Fork Arkansas River. Water in alluvium close to the river can reflect the chemical quality of the river water. For example, the water in the alluvium that formerly supplied a small city in Woods County, Okla., is a hard, calcium sulfate type. Downstream from the salt plain in Alfalfa County, water from the alluvium that supplies a small city in Grant County, Okla., had a reported chloride concentration of about 370 milligrams per liter.
The main stem of the Arkansas River also enters Oklahoma from Kansas (fig. 11). The alluvium and alluvial terraces along the Arkansas River between its confluence with the Cimarron River and Tulsa average more than 5 miles in width and 45 feet in thickness. The deposits consist mostly of sand and gravel, and the water table is generally less than 20 feet below land surface. Wells constructed mostly for irrigation use yield as much as 600 gallons per minute and average 350 gallons per minute.
Between about the mouth of the Cimarron River and the mouth of the Canadian River, the alluvial aquifer consists mostly of sand and gravel about 40 feet thick. The water table is generally from 10 to 20 feet below land surface. Direct recharge from precipitation results in ground water with smaller concentrations of dissolved solids than the river water. Yields of wells constructed mostly for irrigation purposes commonly are 300 to 500 gallons per minute.
Between the Canadian River junction and the Arkansas State line, the alluvium and alluvial terraces along the Arkansas River are about 40 feet thick and consist mostly of sand and gravel. The diagrammatic section shown in figure 13 represents conditions about 5 miles upstream from the Arkansas border. The alluvial deposits are about 5.5 miles wide at this location and average about 50 feet thick. The saturated thickness averages about 35 feet. Finer grained material, as shown in the figure, typically overlies medium to very coarse sand and gravel, and the water table slopes toward the Arkansas River from either side.
CIMARRON RIVER
The Cimarron River enters Oklahoma from Kansas (fig. 11) and flows across Permian red beds in Harper, Major, and Woodward Counties. The red beds contain thick layers of salt and gypsum that are easily dissolved and are responsible for highly mineralized surface waters and ground water in the alluvium. The alluvium on the southwestern side of the Cimarron River in these counties is a poor source of ground water. The limited supplies taht can be pumped are highly mineralized (calcium sulfate and sodium chloride); some of the water is suitable for livestock, but not for human consumption. However, the alluvial terraces on the northeastern side of the river compose one of the best aquifers in Oklahoma. The alluvial terraces extend for 110 miles from southern Woods County to western Logan County and range from 3 to 15 miles in width; average width is about 10 miles. The terraces consist of sand and gravel with some clay and sandy clay and have an average thickness of about 60 feet and an average saturated thickness of about 40 feet. The alluvial terraces are overlain by windblown sands that readily transmit recharge from local precipitation downward into the alluvial aquifer.
Water in the Cimarron River alluvial terraces is a calcium-magnesium bicarbonate type with dissolved-solids concentrations of about 400 milligrams per liter or less. Hardness is generally less than 200 milligrams per liter. The water is suitable for municipal purposes as well as for domestic and irrigation supplies. Wells completed in the terrace deposits yield as much as 600 gallons per minute, and 100 gallons per minute usually can be obtained.
Water in the alluvial terraces generally moves toward the alluvium adjacent to the Cimarron River. Where the alluvium is recharged from the alluvial terraces with water that has low dissolved-solids concentrations, it becomes a source for municipal supplies. Wells in the alluvium that are intensively pumped or are too near the river are subject to infiltration of highly mineralized river water.
NORTH CANADIAN RIVER
The North Canadian River originates in New Mexico and flows eastward across Oklahoma. Alluvial deposits border the river from western Texas County to eastern Beaver County in the Oklahoma Panhandle but supply little water. Between the western edge of Harper County and the northwestern corner of Blaine County, alluvial deposits are mainly on the north side of the river and consist of sand and basal gravel with some clay and silt. High alluvial terraces of Pleistocene age on the north side of the river are 1.5 to 11 miles wide and average about 70 feet thick. Low alluvial terraces of late Pleistocene age are along both sides of the river and average about 50 feet thick; the thickness of the Holocene alluvium in the flood plain adjacent to the river averages about 30 feet. The combined width of the low alluvial terraces and the alluvium ranges from 0.5 to 2 miles. Dune sands that overlie the alluvium and alluvial terraces in much of the area temporarily store recharge from local precipitation and subsequently release the recharge to the underlying deposits.
The water table in the alluvial deposits between western Harper County and northwestern Blaine County ranges from about 20 to 80 feet below land surface. The general direction of ground-water flow is toward the North Canadian River. Specific yield of the deposits is estimated to average 0.29. Specific yield is the volume of water that will drain by gravity from a given volume of soil or rock. It can be expressed as a percentage; in this example, 29 percent of the water in each volume of saturated alluvial material will drain under the influence of gravity alone. Hydraulic conductivity is a measure of the rate at which water will pass through an aquifer-the higher the hydraulic conductivity, the more permeable the aquifer. Hydraulic conductivity of the aquifer is as much as 160 feet per day and averages 59 feet per day. Recharge by infiltration from precipitation is on the order of 1 inch per year. Wells completed in the deposits yield as much as 1,000 gallons per minute. The water is a calcium-magnesium bicarbonate type, has small concentrations of dissolved solids, and is suitable for municipal and irrigation uses. The aquifer supplies water for several small towns in the area. An estimated 18 million gallons per day was withdrawn from this segment of the alluvial aquifer during 1977.
The lithologic, hydrologic, and water-quality characteristics of the alluvial aquifer along the North Canadian River between northwestern Blaine County and Oklahoma City are similar to those described, above, but the areal extent and thickness of the aquifer are somewhat less in this reach of the river. Pumpage during 1977 was estimated to be 12 million gallons per day, or about two-thirds of the rate for the upstream segment.
Alluvium along the North Canadian River from Oklahoma City to its confluence with the Canadian River in McIntosh County is about 2 to 3 miles wide and about 30 to 40 feet thick. Scattered alluvial terraces on either side of the alluvium reach a maximum width of 8 miles but usually have a width of from 2 to 3 miles. The alluvial terraces have a reported maximum thickness of about 80 feet. The alluvium and alluvial terraces consist of sand and gravel with some clay and silt. Locally, windblown sand covers the alluvium and terraces and acts to promote rapid infiltration from local precipitation. In places, the alluvium and alluvial terraces overlie aquifers in Permian and Pennsylvanian bedrock. In such places, the alluvial deposits and the upper part of the bedrock aquifers are hydraulically continuous, and the water levels are the same in the bedrock and alluvial aquifers. Water in this stretch of the North Canadian River is generally more mineralized than water in the alluvial aquifer. At times, the river level is higher than the water level in the alluvial aquifer, and river water could enter the aquifer and degrade the quality of the ground water.
Annual estimates of recharge from precipitation range from about 1 inch at Oklahoma City to about 4 inches downstream at Eufaula Lake. The water table slopes toward the river, and the aquifer contributes to stream base flow. The withdrawal rate from this segment of the alluvial aquifer was reported to be about 19 million gallons per day during 1982. This rate represents the maximum permitted withdrawal rate and is probably larger than the actual rate.
CANADIAN RIVER
The Canadian River enters Texas from New Mexico and flows eastward across the Texas Panhandle. Alluvium and alluvial terraces are located along the river from Dewey County, Okla., southeastward and eastward to the western part of McIntosh County, Okla.
Wells completed in the alluvium and alluvial terraces yield as much as 500 gallons per minute. Where the ground water is not highly mineralized, the aquifer is a source of supply for various uses. However, the chemical quality of the water is variable, and, although the aquifer can be used locally, it has little potential for wide-scale development.
Results of a study of the potential of the alluvial aquifer along the Canadian River near Norman, Okla. (fig. 14), indicate that the alluvial terraces contain a large amount of potable water. The alluvial terraces are about 50 feet above the flood plain. The alluvium and alluvial terraces consist of clay, silt, sand, and basal gravel and are as much as 80 feet thick. Dune sands that cover the alluvial terraces and alluvium in many places allow the ready infiltration of precipitation. Under natural conditions, movement of water in the aquifer is from recharge areas where precipitation infiltrates the alluvial terraces downgradient to discharge into the river as base flow.
Ground-water recharge in the Norman area is about 8 inches per year, or about one-fourth of normal annual precipitation. The specific yield of the saturated deposits is estimated to be 15 percent, and the average hydraulic conductivity of the aquifer is 134 feet per day.
Water in the terrace deposits is less mineralized than that in the alluvium. In places, more mineralized river water can infiltrate the alluvium, which causes sulfate, chloride, and dissolved-solids concentrations in the ground water to exceed the limits recommended for drinking water by the U.S. Environmental Protection Agency.
WASHITA RIVER
The Washita River originates in the Texas Panhandle and flows eastward into Oklahoma and then southeastward to discharge into the Red River. Alluvium and alluvial terraces are along the Washita River mainly in Grady and Garvin Counties, Okla.
Between the Caddo-Grady County line and southeastern Garvin County, the alluvial valley averages about 2 miles in width and has a maximum width of 3 miles. The alluvium has an average thickness of about 64 feet and a maximum thickness of 120 feet. Depth to water in the alluvium is generally less than 20 feet. Maximum thickness of the alluvial terraces is 50 feet. Wells are commonly between 50 and 100 feet in depth. Yields are about 100 to 300 gallons per minute from wells completed in the alluvium and 20 to 100 gallons per minute from wells completed in the alluvial terraces.
Recharge to the older alluvial terraces is mainly from local precipitation and runoff from adjacent uplands; generally, the older terraces are not hydraulically continuous with the younger terraces and alluvium. Discharge from the alluvium contributes to the base flow of the Washita River. During high river stages, the normal hydraulic gradient can be reversed, and river water can enter the alluvium.
Water from the alluvium and alluvial terraces is used for municipal, industrial, and irrigation supplies. The water is generally a calcium-magnesium bicarbonate type with dissolved-solids concentrations usually less than 1,000 milligrams per liter.
NORTH FORK RED RIVER AND RED RIVER
The North Fork Red River heads just east of Amarillo in the Texas Panhandle and flows eastward into Oklahoma. Quaternary alluvium and alluvial terraces compose an aquifer of major importance along the North Fork Red River from Beckham County, Okla. at the border of the Texas Panhandle to its junction with the Red River and along the Red River eastward to Jefferson County, Okla. Alluvium and alluvial terraces are covered by dune sands in most of the area. The Quaternary deposits are underlain by poorly permeable Permian bedrock.
In central Beckham County, the extensive alluvial terraces, which consist of varying proportions of clay, silt, sand, and gravel, are mainly south of the river's flood plain. The maximum width of the saturated part of the deposits is about 7 miles. The terraces range from 18 to 195 feet in thickness, and average about 70 feet; the saturated part averages about 33 feet in thickness. The water table in the alluvial terraces of central Beckham County slopes toward the North Fork Red River, and water discharges from the aquifer to the river.
Wells completed in the moderately to highly permeable terrace deposits supply water for municipal, industrial, rural domestic, and agricultural uses. The common range of well yields is from 200 to 500 gallons per minute. The water is slightly saline, and concentrations of dissolved solids range from 1,000 to 2,000 milligrams per liter.
Another area of alluvium and extensive terraces is at the junction of the North Fork Red River and the Red River in western Tillman County. Alluvium and alluvial terraces in this area consist of sand and gravel with some clay and sandy clay. The alluvium has an average thickness of about 34 feet, and the alluvial terraces average about 42 feet in thickness. The alluvium along the east side of the North Fork Red River and on the north side of the Red River is generally less than 2 miles wide; the adjoining alluvial terraces are 8 to 10 miles wide. Permian red beds that have low permeability underlie and adjoin the unconsolidated deposits. The alluvial aquifers in Cotton County, Okla., and in Wilbarger, Wichita, and Clay Counties, Tex., apparently supply only small quantities of water.
The water table in the alluvial deposits in western Tillman County, Okla., and northern Wilbarger County, Tex., generally slopes toward the North Fork Red and Red Rivers. Recharge to the terrace deposits from local precipitation is estimated to be about 3 inches per year. Well yields, water quality, and water use are similar to those discussed for the aquifer in Beckham County.
BRAZOS RIVER
The Brazos River heads in New Mexico and flows southeastward across Texas to discharge into the Gulf of Mexico. Large quantities of water are available in the alluvial aquifer along the river between northern McLennan and central Fort Bend Counties, Tex. In this reach, the alluvium and alluvial terraces are as much as 8 miles wide. The alluvial terraces, which are of much less significance as a source of water than the flood-plain alluvium, are as much as 75 feet thick and consist of clay, silt, sand, and gravel. The flood-plain alluvium consists predominantly of gravel and fine to coarse sand, with lesser amounts of clay and silt. Generally, coarser-grained material is present in the lower part of the alluvium. Maximum thickness of the alluvium is about 100 feet, and average thickness is about 45 feet.
The deposits that compose the alluvial aquifer are of Quaternary age and are underlain by rocks that range in age from Late Cretaceous to Quaternary. The underlying rocks dip toward the Gulf of Mexico and contain several major aquifers that crop out in bands parallel to the coast. Where the Brazos River crosses these aquifers, the alluvial aquifer is hydraulically connected to them.
Hydraulic conductivity values determined by laboratory tests on samples of the alluvium are as great as 2,400 feet per day for gravel. Estimated transmissivity values average about 5,600 feet squared per day, and the average specific yield is estimated to be about 15 percent. Transmissivity is a measure of the ease with which water will pass through an aquifer; transmissivity is hydraulic conductivity multiplied by aquifer thickness. The higher the transmissivity, the more productive the aquifer.
The water table in the alluvium ranges from less than 10 to nearly 50 feet below land surface. The water table slopes toward the river, and seepage from the alluvium contributes to stream base flow. Recharge to the alluvial aquifer is mainly from precipitation that falls directly on the flood plain and alluvial terraces; estimates of recharge range from 2 to 5 inches per year.
Diagrammatic sections for the area where the Brazos River is the boundary between Burleson and Brazos Counties, Tex. are shown in figure 15. In west-central Brazos County and east-central Burleson County, the saturated part of the alluvial aquifer is about 8 miles wide, and the saturated thickness of the basal sand and gravel is as much as 50 feet (fig. 15A).
Water from most wells completed in the alluvial aquifer is used for irrigation. In addition to irrigation, the chemical quality of the water is generally suitable for domestic and livestock watering purposes, although concentrations of dissolved solids in the water commonly exceed 1,000 milligrams per liter and the water is classified as hard. An estimated 1,000 irrigation wells pump water from the alluvial aquifer; yields of most of the wells range from 250 to 500 gallons per minute. An estimated 30 million gallons per day was pumped from the Brazos River alluvial aquifer during 1985.
FRESH GROUND-WATER WITHDRAWALS
Withdrawals of fresh and slightly saline water from the collective alluvial aquifers in Oklahoma and Texas totaled about 71 million gallons per day during 1985 (fig. 16). About 53 million gallons per day was withdrawn for agricultural purposes, the principal water use. Withdrawals for public supply were about 12 million gallons per day. About 3 million gallons per day was withdrawn for domestic and commercial uses; withdrawals for industrial, mining, and thermoelectric-power uses were also about 3 million gallons per day.
