Pulaski and Saline Counties constitute an area of 1,506 square miles in the geographic center of Arkansas. The area is divided into a hilly western part, known as the Interior Highlands, and a relatively flat eastern part, known as the Coastal Plain. In the Interior Highlands, surface water offers greater possibilities than ground water for water supplies. Alum Fork, Middle Fork, and North Fork of the Saline River offer excellent impoundment possibilities and will yield water of good quality. In addition, with storage, many of the smaller streams are suitable for development of small supplies. In contrast, in the Coastal Plain it is easier to develop ground water than surface water in relatively large quantities. Two aquifers, units 3 and 9, yield as much as 350 and 2,000 gallons per minute of water, respectively. A third acquifer, unit 7, is as yet relatively undeveloped in the project area, but yields 860 gallons per minute to a well south of the project area. These aquifers yield water that, with treatment, is suitable for most uses.

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Clark, Cleveland, and Dallas counties constitute an area of 2,151 square miles in south-central Arkansas. The area is in two physiographic provinces the Ouachita Mountains of the Ouachita province of the Interior Highlands, and the West Gulf Coastal Plain of the Coastal Plain province. The area is drained by the Ouachita, Saline, and Little Missouri Rivers and their tributaries.Although some of the streams in the project area can furnish dependable water supplies without storage, the amount of water available for use can be increased by the construction of reservoirs. The average surface-waiter yield in the area is about 1.4 cubic feet per second per square mile, or a total of about 3,000 cubic feet per second. Generally, the water quality is good; but water from some of the streams, particularly from the smaller tributaries, may require treatment for excessive iron content and high color.Ground-water yields in the project area vary considerably. The consolidated rocks in the Interior Highlands generally yield less than 10 gallons per minute to wells, precluding the development of large municipal or industrial groundwater supplies in that area.Of the 17 geologic units present in the Coastal Plain part of the project area, 12 yield water but in varying amounts. Among the formations of Cretaceous age, the Tokio yields good-quality water in the outcrop, but the quality deteriorates downdip; the Brownstown Marl yields small amounts of water for domestic purposes, mainly in the outcrop area; the Ozan Formation yields a highly mineralized water that is generally unsuitable for most purposes; the Nacatoch Sand yields as much as 100 gallons per minute of good-quality water in and near the outcrop, but the water becomes very salty and corrosive at distances ranging from 2 miles downdip from the outcrop in northern Clark County to 17 miles downdip in the southern part of the county.The formations of Tertiary age offer the best possibilities for ground water, particularly in Dallas and Cleveland Counties. The Wilcox Group contains no thick widespread sands but contains thin sands locally. The quality of the water tends to deteriorate downdip, as the water becomes more mineralized and changes from a bicarbonate to a chloride type. The Carrizo Sand is undeveloped but may yield several gallons of water per minute per foot of drawdown in a large part Al A2CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES of these two counties. High iron content may be a problem in water from the Canrizo. The Cane River Formation yields 50 gallons per minute of good-quality water to each of two wells at Sparkman. Elsewhere, high iron content of the water may be a problem. The Sparta Sand is the best aquifier in the project area, particularly east of central Dallas County. Well yields of 700 gallons per minute or more are possible. With minor treatment, the water is suitable for most purposes. The Oockfield Formation is utilized mainly for domestic supplies, but where the sands are thick, yields of as much as 300 gallons per minute are possible...

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Bacterial quality._____________________________________ Use of water._____________________________________________________ Conclusions-______________________________________________________ 43 Selected references.________________________________________________ Page FIGURES 4-6. Graphs Continued 6. Eleven Point River near Raven den Springs and Strawberry River near Poughkeeps^'e (Sharp County)-______.___.___-.________ B8 7. Flow-duration curves for continuous-record gaging stations.________________________________________ 8. Map showing dissolved-solids content and hardness as CaCO3 at sampling stations during periods of low flow. _ 23 9. Dissolved-solids and temperature-duration curves for Spring River at Imboden and Black River ner.r Corning (Clay County)-_-___-__._-_____________ 10. Diagram showing well-numbering system._____________ 26 11-14. Maps showing: 11. Thickness of deposits of Quaternary age ________ 27 12. Configuration of the water table in deposits of Quaternary age, spring 1966____-_-___-_-_-__ 13. Configuration of the water table in deposits of Quaternary age, fall 1966_-__-___-14. Water-level declines in deposits of Quaternary age, spring to fall 1966_________-_._____._-31 15. Hydrographs of wells 19N-2E-9dbd, 18N-lE-34abd, and 15N-lW-llddd-__-__-______________-_-______-_ 16. Map showing areas of potential development of ground water from the Wilcox Group and the Nacato?.h Sand. _ 33 17. Map showing dissolved-solids and combined iron and manganese content of water from selected wells in the Coastal Plain__-___-_____________________ 18. Map showing dissolved-solids content and hardness as CaCOa of water from selected wells in th^ Interior Highlands. __________________________ 40 TABLES Page TABLE 1. Low-flow characteristics of streams___-_-___-______-_ B9 2. Magnitude and frequency of floods at continuous-record gaging stations.___-____-____-___-_-__-_____-__ 3. Selected chemical analyses of water from streams.______ 16 4. Inventory of information on the quality of surface water in the vicinity of Randolph and Lawrence Counties, Ark__-___________________________-___-________-5. Specific capacity of selected wells in deposits of CJ uaternary age___________________________________________ 6. Chemical analyses of water from wells in Quaternary and Tertiary deposits of the Coastal Plain.._________ 7. Chemical analyses of water from wells in Paleozoic rocks of the Interior Highlands.