GLACIER RUNOFF AND SEDIMENT TRANSPORT AND DEPOSITION EKLUTNA LAKE BASIN, ALASKA by Timothy P. Brabets U.S. GEOLOGICAL SURVEY Water-Resources Investigations Report 92-4132 Prepared in cooperation with the MUNICIPALITY OF ANCHORAGE Anchorage, Alaska 1993 U.S. DEPARTMENT OF THE INTERIOR MANUEL LUJAN, JR., Secretary U.S. GEOLOGICAL SURVEY Dallas L. Peck, Director For additional information write to: Copies of this report can be purchased from: District Chief U.S. Geological Survey U.S. Geological Survey Books cind Open-File Reports Section 4230 University Drive, Suite 201 Federal Center, Box 25425 Anchorage, Alaska 99508-4664 Denver, Colorado 80225 11 CONTENTS Page Abstract ...................................................................... 1 Introduction................................................................... 2 Purpose and scope ......................................................... 2 Methods of study........................................................... 2 Description of study area........................................................ 4 Watersheds................................................................ 4 Surficial geology........................................................... 4 Glaciers. .................................................................. 5 Eklutna Lake............................................................... 5 Glacier mass balance ........................................................... 6 Glacier runoff ................................................................. 12 Streamflow characteristics. .................................................. 12 Runoff components......................................................... 13 Runoff prediction .......................................................... 19 Statistical relations ..................................................... 21 Precipitation-Runoff Modeling System.................................... 22 Sediment transport and deposition ............................................... 26 Streams................................................................... 28 Suspended-sediment discharge .......................................... 28 Bedload discharge. ..................................................... 32 Eklutna Lake .............................................................. 37 Delta progradation ..................................................... 37 River plume dispersion ................................................. 38 Rate of sediment accumulation........................................... 38 Water storage in Eklutna Lake ................................................... 39 Summary and conclusions ...................................................... 43 References cited................................................................ 45 Glossary...................................................................... 47 ILLUSTRATIONS Plate 1. Map showing geology and location of hydrologic data sites in the In Pocket Eklutna Lake drainage basin, southcentral Alaska Figure 1. Map showing Eklutna Lake and vicinity............................... 3 2. Photograph of Eklutna Lake, 1987 .................................... 4 3. Graphs of area-altitude distribution of the East Fork and West Fork Eklutna Creeks basins............................................... 5 4. Photograph of headwaters of East Fork Eklutna Creek, 1987 ............. 6 5. Photograph of Eklutna Glacier, 1965 .................................. 7 6. Graph of water temperature profiles of Eklutna Lake showing: A, summer stratification and B, winter inverse stratification ....................... 8 7. Map showing bathymetry of Eklutna Lake and locations of core samples..... ...................................................... 9 iii ILLUSTRATIONS-Cohtinued Page Figure 8. Graphs of characteristics of Eklutra Lake, 1986 water year, showing: A, monthly inflow; and B, monthly lake level.......................... 10 9. Graph of ablation of snow and ice on Eklutna Glacier, 1985 water year............................................................... 12 10. Hydrograph showing streamflow of East Fork and West Fork Eklutna Creeks, July 28-30,1985...................................... 13 11-12. Hydrographs showing daily streamflow and air temperature for East Fork and West Fork Eklutna Creeks: 11. 1985 and 1986 water years ....................................... 14 12. 1987 and 1988 water years ....................................... 15 13-14. Graphs showing monthly runoff for East Fqrk and West Fork Eklutna Creeks: 13. 1985 and 1986 water years ....................................... 16 14. 1987 and 1988 water years ....................................... 17 15. Graph showing altitude distribution of prec ipitation as rain and snow, accumulation, icemelt, snowmelt, and runo ff for a glacier in southcentral Alaska............................................................ 19 16-17. Graphs showing observed daily mean streafnflow and daily mean streamflow predicted from statistical equations, June to September 1985-88: 16. East Fork Eklutna Creek......................................... 21 17. West Fork Eklutna Creek........................................ 21 18. Diagrams showing West Fork and East Fork Eklutna Creek basins partitioned into hydrologic response units.!............................ 23 19-20. Hydrographs showing observed daily mean streamflow and daily mean streamflow simulated from the PRMS, June? to September 1986-88: 19. East Fork Eklutna Creek.......................................... 25 20. West Fork Eklutna Creek. ........................................ 26 21-22. Graphs showing daily mean streamflow and suspended-sediment concentration, June to September 1985,1986, and 1987: 21. East Fork Eklutna Creek.......................................... 29 22. West Fork Eklutna Creek. ........................................ 30 23. Graphs showing suspended-sediment discharge and water discharge for East Fork and West Fork Eklutna Creeks ........................... 31 24. Graphs showing suspended-sediment loads for East Fork and West Fork Eklutna Creeks, June to September 1985,1986, and 1987....... 33 25. Graphs showing particle-size distribution and median diameter of bedload for East Fork and West Fork Eklutia Creeks................... 34 26. Graphs showing bedload discharge and water discharge for East Fork and West Fork Eklutna Creeks....................................... 35 27. Graphs showing bedload for East Fork and West Fork Eklutna Creeks, June to September 1985,1986, and 1987.... L ........................... 36 28. Diagram showing types of sediment layers formed by inflow to Eklutna Lake .......................... [ ........................... 37 29. Graphs of profiles of density current in Eklutna Lake at various times showing: A, underflow; B, no density current; C, overflow; and D, interflow ....................................................... 39 IV TABLES Page Table 1. Morphometry of Eklutna Lake at 860.00 feet water-surface altitude ......... 8 2. Snow density at various altitudes on Eklutna Glacier..................... 10 3. Mass balance measurements on Eklutna Glacier, 1985-88 .................. 11 4. Precipitation measured in the Eklutna Lake basin, 1985-88................. 18 5. Estimated distribution of unit runoff of the West Fork and East Fork Eklutna Creeks, June to September, 1985-88 ............................. 20 6. Calculated and simulated icemelt for East Fork and West Fork Eklutna Creeks, June to September, 1986-88 ..................................... 27 7. Observed and simulated average monthly discharges for East Fork and West Fork Eklutna Creeks, June to September, 1986-88 .................... 27 8. Active storage of Eklutna Lake......................................... 40 9. Changes in storage, outflow, and inflow for Eklutna Lake, 1985-88.......... 42 10. Risks of failure to supply withdrawal rates during the year at Eklutna Lake................................................................ 44 CONVERSION FACTORS, VERTICAL DATUM, AND ABBREVIATED WATER-QUALITY UNITS Multiply By. To obtain inch (in.) 25.4 millimeter foot (ft) 0.3048 meter mile (mi) 1.609 kilometer square mile (mi2) 2.590 square kilometer acre-foot (acre-ft) 1,233 cubic meter cubic foot per second (ft3/s) 0.02832 cubic meter per second cubic foot per second per day [(ft3/s)/d] 0.02832 cubic meter per second per day ton, short 0.9072 megagram ton per square mile (ton/mi2) 0.3503 megagram per square kilometer pound per cubic foot (lb/ft3) 16.02 kilogram per cubic meter million gallons per day (Mgal/d) 0.04381 cubic meter per second degree Fahrenheit (°F) }C = 5/9 x (°F-32) degree Celsius (°C) Other abbreviations in this report are: g/cm3, gram per cubic centimeter mg/L, milligram per liter Sea level: In this report "sea level" refers to the National Geodetic Vertical Datum of 1929 (NGVD of 1929), a geodetic datum derived from a general adjustment of the first-order level nets of both the United States and Canada, formerly called Sea Level Datum of 1929. GLACIER RUNOFF AND SEDIMENT TRANSPORT AND DEPOSITION EKLUTNA LAKE BASIN, ALASKA by Timothy P. Brabets ABSTRACT Two streams in the Eklutna Lake basin, sediment transported past the West Fork sta­ the East Fork Eklutna Creek and the West tion. Most of the suspended sediment was Fork Eklutna Creek, provided more than 80 composed of silt and clay; most of the bedload percent of the water to Eklutna Lake during consisted of coarse sand and fine gravel. the period of study, 1985-88. The