WATER RESOURCES OF THE UPPER HENRYS FORK BASIN IN EASTERN IDAHO Idaho Department of Water Resources Water Information Bulletin No. 46 May 1978 Henrys Fork of the Snake River drops 65 feet over Lower Mesa Falls near Ashton, Idaho (Division of Tourism and Industrial Development Photo) WATER INFORMATION BULLETIN NO. 46 WATER RESOURCES OF THE UPPER HENRYS FORK BASIN IN EASTERN IDAHO By R .. L. Whitehead Prepared by the U.. S .. Geological Survey in cooperation with the Idaho Department of Water Resources May 1978 CONVERSION FACTORS For the convenience of those who prefer to use International System (SI) units rather than English units, the conversion factors for terms used in this report are listed below,, Chemical data for concentrations are given only in milligrams per liter (mg/L) or micrograms per liter (µg/L), These values are (within the range of values presented) numerically equal to values expressed in parts per million, or parts per billion, respectively, Specific conductance is expressed as micromhos per centimeter at 25 degrees Celsius (µmhos),, Multiply English units By To obtain SI units Length inches (in) 25.40 millimeters (mm) feet (ft) 0,3048 meters (m) miles (mi) 1609 kilometers (km) 2 acres 4047 square meters (m ) 2 2 square miles (mi ) 2,590 square kilometers (km ) cubic feet per second (ft3 is) 0,,02832 cubic meters per second (m 3 /s) gallons per minute (gal/min) ,06309 liters per second ( Lis) Transmissivity feet squared per day (ft2 /d) 0,0929 meters squared per day (m 2 /d) Volume 3 acre"feet (acre"ft) 1233 cubic meters (m ) Temperature-Conversion Table Conversion of degrees Celsius (° C) to degrees Fahrenheit (° F) is based on the equation, ° F =(LB)(° C) + 32,, Temperatures in ° F are rounded to the nearest degree., Underscored equivalent temperatures are exact equivalents, oc OF oc OF oc OF _Q_ 32 10 50 20 68 +1 34 11 52 21 70 2 36 12 54 22 72 3 37 13 55 23 73 4 39 14 57 24 75 _Q_ 11 15 59 25 77 6 43 16 61 41 106 7 45 17 63 8 46 18 64 9 48 19 66 ii TABLE OF CONTENTS Page Conversion factors ii Abstract 1 Introduction 3 Purpose and scope 3 The study area 4 Previous studies 4 Acknowledgments 6 Gaging-station-numbering system 6 Well- and spring-numbering system 6 Geology 9 Geologic history 9 Surficial distribution of geologic units 9 Subsurface distribution of geologic units 10 Ground water 11 Occurrence 11 Aquifer transmissivities 11 M6vement of ground water 13 Water-level fluctuation 13 Springs 15 Thermal water 15 Surface water 17 Variability of annual discharge 17 Monthly discharge 18 Low-flow discharge 22 Peak flows of record 22 Gains and losses 25 Precipitation 27 Relation between streamflow and precipitation 27 Water quality 31 Major ions 31 Specific conductance 34 Nutrients 34 Pesticides 35 Turbidity and suspended solids 35 Microbiological analyses ,. .., ... ,, .... , 36 Water-quality conditions in lakes and reservoirs 36 Suggested monitoring networks 43 Ground-water levels 43 Ground-water quality 43 Streamflow 44 Surface-water quality 44 Summary ... , .. ,, .. 45 Selected references 47 Basic-data tables 49 iii ILLUSTRATIONS Figure Page L Maps of Idaho and the upper Henrys Fork basin 2 2. Graph showing mean monthly temperature and precipitation at Ashton and Island Park Dam 5 3. Diagram showing well- and spring--numbering system 7 4, Map showing generalized geology in pocket 5. Map showing location of data sites and selected hydrologic information ....... in pocket 6, Hydrographs for selected observation wells 14 7. Map showing location of stream-measuring sites and subbasin boundaries .. , in pocket 8. Hydrographs of mean annual and annual mean discharge for period of record at correlative stations and annual mean participation at Ashton 19 9. Frequency curves of annual means for selected sites . ,. .. 20 10.. Map showing mean annual streamflow characteristics and mean annual precipitation in pocket 11 Low-flow frequency curves for selected streams 24 12 Relation of altitude to average April water content of snow at selected snow courses 28 13. Altitude-precipitation relations 29 14. Map showing ground-water quality at selected sites in pocket 15. Map showing surface-water quality at selected sites , ... in pocket 16.. Dissolved··oxygen and temperature profiles for Henrys Lake ...... 37 17.. Dissolved-oxygen and temperature profiles for Island Park Reservoir 38 TABLES Table Page 1. Description and water-bearing characteristics of geologic units 8 2. Specific capacities of wells and estimated transmissivities 12 3. Springs in the upper Henrys Fork basin 16 4. Mean discharges for selected streams 21 5. Low-flow characteristics of selected streams 23 6.. Gains and losses in Henrys Fork, fall 1975 25 7. Gains and losses in Warm River, fall 1975 26 8 Significance of selected chemical and biological properties ... 32-33 9, Specific conductance, pH, and microbiological analyses of ground water 39 10.. Phytoplankton analyses of water samples from Henrys Lake and Island Park Reservoir 40 11 Nutrient concentrations in water from Henrys Lake and Island Park Reservoir, May 1974 to September 1975 41 BASIC-DATA TABLES Table Page A.. Selected wells and their geohydrologi'c characteristics in and adjacent to the upper Henrys Fork basin ........ 50-55 B .. Selected stream- and spring-measuring sites, selected characteristics, and period of record , .........., . 56-58 C.. Discharge measurements, pH, specific conductance, and temperature, 1974-·75 ...... 59-81 D .. Chemical analyses of water from selected sites . 83-91 iv ABSTRACT Upper Henrys Fork basin, comprising 1,070 square miles in eastern Idaho and a small area in western Wyoming, has a permanent population of about 1,500, Ashton is the major population center,, Because the area attracts thousands of summer vacationers and winter sports enthusiasts, related land- and water-,use pressures are increasing,, Surface water is stored in Henrys Lake and Island Park Reservoir for irrigation outside the basin, Ground water is used chiefly for municipal, domestic, and stock supplies,, Volcanic rocks and alluvium compose most of the aquifer materials. Permeable vol­ canic rocks in the eastern part of the basin greatly influence water yields and ground-water movement between subbasins, Data suggest that movement across the basin boundary is minimal,, Mean annual precipitation on the basin is estimated to be about 35 inches, of which about 50 percent contributes to the mean annual discharge in Henrys Fork near Ashton, which is 1,441 cubic feet per second, or about 18 inches,, This represents the discharge from the basin, except for that lost to evapotranspiration. Annual mean discharge of streams generally varies directly with the annual mean precipitation,, Water quality in the basin is generally excellent, Although, in the Ashton area and in areas of intermittent high usage by man, some deterioration of the quality is evident, Values for specific conductance range from less than 100 to about 300 micromhos per centimeter at 25° C, except in the Ashton area, where as much as 800 micromhos was measured in the ground water,, 1 • 111°05' 111°20' ? I I :_Drainage basin .. \ boundary Continental Divide 2 :~ .. ~··-........ ·· 3 .. ..• "'. .·- '\,·· '\ .. ~_:; Sheridon'·~=-""".. Res\ . .. > 0 ( Boundary of lowland .>within caldera,--: iapproximot:l; !!c.a!ed .,,··' ....... / /·.. .....L. : • <"-,, '··, ·.. Ashton R• t : .. / I/·;_ Ashton - •• Boundary of Snake River.- \ / "" Plain, approximately/' ... -'o IOMILES located. ' .________ ....., - Upper Henrys Fork basin Location map FIGURE 1. Maps of Idaho and the upper Henrys Fork basin .. 2 INTRODUCTION The upper Henrys Fork basin is sparsely populated; thus, related land- and water-use pressures are generally minimal,. However, because of its recreational opportunities, scenic vistas, and proximity to Yellowstone National Park (fig., 1), the area attracts thousands of vacationers during the summer and sports enthusiasts (including snowmobilers) during the winter. Thus, the related pressures are increasing., Present high-use areas include summer-home developments along selected reaches of Henrys Fork and a few of its main tributaries and the farming community near Ashton (population about 1,200), the major population center In 1970, the total permanent population of the basin was estimated to be about 1,500 (Forsgren, Perkins and Associates, 1971) .. The annual transient population has not been estimated, but it is substantial.. Purpose and Scope The purpose of this report is to provide managers, planners, developers, and water users with hydrologic information needed to assist in planning the development and management of land and water resources in the basin., To fulfill this need, the U.,S., Geological Survey, in cooperation with the Idaho Department of Water Resources, began a 2-year hydrologic study of the basin early in 1974., Prior to this, a comprehensive study of the water resources had not been made Three main objectives of the study were: (1) To describe on a reconnaissance level the general availability, distribution, quality, and uses of the water resources of the basin; (2) to compile a data base from which effects of future development can be gaged; and (3) to make suggestions for establishing networks to monitor surface-water flows, water-level fluctuations, and water-quality changes., To fulfill these objectives, a network of collection sites was established to collect data on ground water, surface water, and quality of water., Data were collected from 88 sites on 47 streams, 15 sites on 5 lakes or reservoirs,