Flood of August 1950 in the Waimea Area Kauai, Hawaii
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Flood of August 1950 in the Waimea Area Kauai, Hawaii > R. K. CHUN :^LOODS OF 1950 GEOLOGICAL SURVEY WATER-SUPPLY PAPER 1137-C ^repared in cooperation with the Territory of Hawaii UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1952 UNITED STATES DEPARTMENT OF THE INTERIOR Oscar L. Chapman, Secretary GEOLOGICAL SURVEY W. E. Wrather, Director For sale by the Superintendent of Documents, U. S. Government Printing Office Washington 25, D. C. - Price 15 cents (paper cover) PREFACE This report on the flood of August 1950 in Kauai, T. H., was prepared in the Surface Water Branch, J. V. B. Wells, Chief. The material was assem bled and the text was written by R. K. Chun, hydraulic engineer, under the immediate super vision of M. H. Carson, District Engineer. Base data used in this report were collected in cooperation with the Territory of Hawaii. The Weather Bureau furnished a discussion on the meteorology of the storm and a map showing the path of the hurricane. The collection of data for indirect determination of peak discharges was supervised, and the computations made, by Hollister Johnson, hydraulic engineer. Ill CONTENTS Page Introduction ..................................................... 327 Stages and discharges at stream-gaging stations ..................... 327 Waimea River near Waimea, Kauai .............................. 331 Kawaikoi Stream near Waimea, Kauai ............................ 332 Mohihi Stream near Waimea/ Kauai .............................. 333 Makaweli River near Waimea, Kauai ............................. 334 Combined discharge of Waimea and Makaweli Rivers ............... 335 Summary of flood data ............................................ 337 Flood stages and discharges ..................................... 337 Annual floods in Waimea River ................................... 337 Physical features of Kauai'........................................ 342 Meteorological features of the flood ................................ 343 Precipitation................................................... 343 Meteorology, by R. H. Simpson, United States Weather Bureau ..... 344 ILLUSTRATIONS Page Figure 46. Map showing location of flood determinations and rain gages, and isohyetal lines for the period August 14-19, 1950 .............................................. 328 47. Graphs of hourly discharge, 1950 ....................... 330 48. Relation of unit discharge to size of drainage area ........ 336 49. United States Weather Bureau map showing path of hurricane "Hiki, " August 1950. ........................ 345 TABLES Page Table 1. Summary of flood stages and discharges in Kauai, T. H., in August 1950 ....................................... 338 2. Annual floods in Waimea River, for years ending June 30 . 341 3. Daily precipitation, in inches, August 14-19, 1950 ........ 344 FLOODS OF 1950 FLOOD OF AUGUST 1950 IN THE WAIMEA AREA KAUAI, HAWAII By R. K. CHUN INTRODUCTION On August 15-18,' 1950, Waimea River on the island of Kauai, T. H., had one of the severest floods in its history as a result of tor rential rains, caused by a storm associated with the only typhoon ever recorded in the proximity of the Hawaiian Archipelego.- At one rain fall station in the basin, 50 inches of rain was recorded during a 72- hour period. Kawaikoi Stream, in the headwaters of Waimea River basin, reached a maximum discharge of 7, 980 second-feet, or 1,950 second-feet per square mile. A rubble wall along the right bank of Waimea River just below the mouth of Makaweli River, constructed to contain the flow, was over topped and the entire town of Waimea was flooded. The. water was about a foot over the top of the wall at most places. No lives were lost, but damage to property was about $200, 000. This report presents detailed records of stages and discharges at four gaging stations in the basin during the flood period August 15-18 in the Waimea River basin, a summary of flood discharges at gaging stations on the principal streams on the island of Kauai, a description of the physical features of the drainage basin, a description of the two types of storms that prevail on the Hawaiian Islands, and a section on the meteorology of the storm of August 15-18. Figure 46 is a map of the island of Kauai, which shows the location of the gaging stations re ferred to in this report, the location of .rain gages in the area where rainfall was the greatest, and lines of equal rainfall for the period August 14-19, 1950. STAGES AND DISCHARGES AT STREAM-GAGING STATIONS Records of daily mean discharge for the year July 1950 to June 1951 at gaging stations covered by this report will be found in a forth- 327 Figure 46. --Map showing location of flood determinations and rain gages, and isohvetal lines for the oeriod August 14-19, 1950. STAGES AND DISCHARGES AT STREAM -GAGING STATIONS 329 coming Geological Survey water-supply paper, Surface Water Supply of Hawaii, 1950-51. Daily mean discharge, however, is generally insufficient for the detailed analysis involved in flood studies, which require knowledge of the rate of discharge and corresponding stages at more frequent intervals. The main purpose of this report is to provide such detailed information. Detailed records of discharge for the gaging stations in Waimea River basin appear on the following pages. For each station, the records include a description of the gaging station, daily mean dis charge, and total runoff for the"4-day period August 15-18, and hour ly gage height and discharge for the 4-day period. Hydrographs for Waimea River near Waimea and Makaweli River near Waimea for the 4-day period are plotted in figure 47. As peak discharges were much greater than the range covered by the stage-discharge relation as defined by current-meter measure ments, it was necessary to determine the peak discharge by some in direct method--in this case, by the slope-area method. A fuller des cription of the slope-area method is presented in Water-Supply Papers 773-E, 796-G, 798, 799, 800, 816, 843, and 888. 206719 O- 52 - 2 DISCHARGE, IN THOUSANDS OF SECOND-FEET STAGES AND DISCHARGES AT STREAM-GAGING STATIONS 331 Waimea River near Waimea, Kauai Location. --Lat 21°58'55", long. 15Q°39'5Q n ,13 miles upstream from confluence with Makaweli River and 1.8 miles north of Waimea. Altitude of gage, 25 ft (hand levels from estuary at confluence with Makaweli River). Drainage area. --57. 8 sq mi. Gage-height record. --Water-stage recorder graph except for periods 3 a.m. to 5 p. m" Aug. 16, 5 a. m. to 1 p. m. Aug. 17, and 7 a. m. to 12 p. m. Aug. 18, record for which was based on readings on Aug. 16 and 17, current-meter measurement on the 18th, and shape of stage graphs at nearby streams. Discharge record. --Stage-discharge relation defined by current-meter meas- urements below 5, 100 cfs (3, 300 mgd) and extended by logarithmic plotting on basis of slope-area determinations at gage heights 10. 28 ft, 13. 6 ft, and 19. 0 ft. Gage heights used to half-tenths between 3. 0 and 4. 2 ft, hundredths below and tenths above those limits. Maxima. --August 1950: Discharge, 34, 000 cfs (22, 000 mgd) 6 a. m. Aug. 17, r9~5TT(gage height, 18. 7 ft). 1943 to July 1950: Discharge, 37, 100 cfs (24, 000 mgd) 2:30 p. m. Feb. 7, 1949 (gage height, 19. 3 ft), from rating curve extended above 5, 100 cfs by logarithmic plotting on basis of slope-area determinations at gage heights 10. 28 ft, 13. 6 ft, and 19. 0 ft. Mean discharge and runoff. August 15-18, 1950 Day Cfs Day Cfs August 15 4,760 August 17 15,500 13 17,400 18 2,820 Mean discharge, in cfs, for period ... 10, 100 Runoff, in inches ................... 26. 0 Gage height and discharge at indicated time, 1950 August 15 August 16 August 17 August 18 Hour Gage k, Dis Gage Dis Gage Dis Gage Dis height charge height charge height charge height charge (ft) (cfs) (ft) (cfs) (ft) (cfs) (ft) (cfs) 1 1.45 2.24 18.0 30, 200 16. 31 22, 600 9.3 5; 830 2 1.46 2. 38 17.4 27, 400 15.8 20, 600 8.9 5, 280 3 1.46 2.38 16.7 24, 300 16.1 21,800 8.6 4,890 4 1.46 2.38 17.5 27, 900 17.0 25,500 8.2 4,390 5 1.47 2.54 18.4 32, 300 18.0 30, 200 7.8 3,900 6 1.47 2.54 18.3 31,900 18. 7 34, 000 7.5 3,540 7 1,47 2.54 17.5 27, 900 17.8 29, 200 7.2 3, 220 8 1.48 2.71 16.0 21,400 16.5 23, 500 7.0 3,000 9 2.55 84.3 14.5 16, 100 15.5 19,500 6.7 2,690 10 3.00 186 13.5 13,200 14.5 16, 100 6.5 2,510 11 3.74 498 13.2 12, 400 13.8 13, 900 6.3 2, 320 N 4.03 681 13.5 13, 200 13.4 12, 900 6.1 2, 140 1 4.20 774 14.0 14,400 12.8 11,500 6.0 2,040 2 6.20 2,230 13.6 13,400 12.2 10, 400 5.9 1,960 3 7.00 5,000 12.5 11,000 11.5 9, 210 5.8 1,890 4 6.36 2,410 11.5 9,210 11.0 8, 360 5.8 1,890 5 6. 15 2,230 11.0 8, 360 10.2 7, 120 5.8 1,890 6 9.70 6,390 10.7 7,890 10.4 7,430 5.7 1,810 7 14.48 16,100 10.5 7,580 10.0 6,810 5.7 1,810 8 14.00 14,400 10.5 7, 580 9.5 6, 110 5.6 1, 730 9 13.80 13,900 10.7 7,890 3.1 5, 550 5.5 1, 660 10 14.50 16,100 11.0 8,360 9.8 6,530 5.5 1, 660 11 16.00 21,400 15.0 17,600 10.0 6,810 5.4 1,580 12 17.50 27,900 16.7 24, 300 9.7 6, 390 5.3 1,500 Note.