Flood of August 1950 in the Waimea Area ,

> 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 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 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 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 , caused by a storm associated with the only 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 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. --Gage heights to tenths for periods of surging in well. 332 FLOOD OF AUGUST 1950 IN KAUAI

Kawaikoi Stream near Waimea, Kauai Location. --Lat 22°08'00", long. 159°37'15", at old trail crossing, 12| miles northeast of Waimea. Altitude of gage, 3, 420 ft (by barometer).

Drainage area. --4. 1 sq mi. Gage-height record. --Water-stage recorder graph except for period 6 a.m. Aug. 17 to 12 p. m. Aug. 18; graph for this period drawn on basis of record­ er graph for Mohihi Stream near Waimea. Discharge record. --Stage-discharge relation defined by current-meter meas- urement below 279 cfs (180 mgd) and extended by logarithmic plotting on baris of slope-area determination at peak stage. Gage heights used to tenths be­ tween 3. 4 and 5.0 ft, hundredths below and tenths above those limits.

Maxima. --August 1950: Discharge, 7> 980 cfs (5, 160 mgd) 12 p. m. Aug. 15 (gage height, 13. 43 ft). 1909-17, 1919 to July 1950: Gage height, 15. 2 ft Dec. 18, 1916 (dis­ charge not determined). Mean discharge and runoff, August 15-18, 1950 Day Cfs Day Cfs August 15 2,040 August 17 1, 360 16 1,930 18 128 Mean discharge, in cfs, for period .. 1, 360 Runoff, in inches ...... 49. 3 Gage height and discharge at indicated time, 1950 August 15 August 16 August 17 August 18 Hour Gage Dis­ Gage Dis­ Gage Dis­ Gage Dis­ height charge height charge leight charge height charge (ft) (cfs) (ft) (cfs) (ft) (cfs) (ft) (cfs) 12:30 - - - - 6.58 1, 380 - - 1 3.25 71.2 11.44 5,540 7.40 1,870 4.25 296 1:30 . _ _ _ 9.02 3, 170 - - 2 3.15 60.3 10.57 4,670 7.95 2,320 4.12 249 2:30 _ _ _ _ 7.44 1,870 - - 3 3.09 54.9 10.08 4, 190 7.85 2, 170 4.00 218 4 3.06 52.6 9.55 3,730 8.85 2,990 3.90 190 5 3.06 52.6 8.50 2,710 10.82 4,890 3.81 166 6 3.11 56.5 7.37 1,870 8.65 2,800 3.74 155 7 3.23 68.1 7. 13 1,690 7.78 2, 170 3.68 144 8 3.43 95.9 7.75 2, 170 7.05 1, 620 3.63 135 9 3.88 190 6.75 1,500 6.60 1,380 3.57 118 10 3.92 190 6. 32 1, 200 6.20 1, 140 3.52 108 11 6.31 1,200 5.90 982 5. 90 982 3.47 104 N 5.91 982 5.45 727 5.60 820 3.43 95.9 12:30 6.32 1, 200 ______1 6.12 1,090 5.13 588 5.35 727 3.40 91.3 2 5.16 634 4.90 511 5. 15 634 3.39 89.7 3 6.45 1,250 4.80 472 5.00 549 3.37 86.6 4 8.20 2,480 5.59 820 4.85 492 3.35 83.6 5 11.94 6,080 5.43 727 4.75 455 3.33 82.0 6 10.82 4,890 5. 30 681 4.65 421 3.32 80.5 7 11. 11 5, 210 5.07 588 4.75 455 3.31 78.9 8 9.86 4, 010 5.18 634 5. 10 588 3.29 75.8 9 10.96 5, 110 5.61 820 5.80 928 3. 27 74.3 10 11.12 5, 210 7.90 2,240 5.05 549 3.26 72.7 10:30 - _ 8. 92 3,080 _ _ - - 11 11.74 5,860 7.55 2,010 4.65 421 3.25 71.2 12 13.43 7, 980 6.95 1,620 4.40 342 3.24 69. 6 STAGES AND DISCHARGES AT STREAM-GAGING STATIONS 333

Mohihi Stream near Waimea, Kauai

Location. --Lat 22°07'05", long. 159C36'15", at upper trail crossing, 3. 8 miles northeast of confluence of Waiahulu and Poomao Streams, and 12 miles north­ east of Waimea. Altitude of gage, 3, 350 ft (from topographic map).

Drainage area. --1. 6 sq mi.

Gage-height record. --Water-stage recorder graph. Discharge record. --Stage-discharge relation defined by current-meter meas- urements below 32 cfs (21mgd) and extended to peak stage by logarithmic plotting. Gage heights used to half-tenths between 2. 3 and 5. 0 ft, hun- dredths below and tenths above those limits. Maxima. --August 1950: Discharge, 1, 930 cfs (1, 250 mgd) 11:30 p. m. Aug. 15, 1950 (gage height, 7. 23 ft). 1920-26, 1936 to July 1950: Discharge, 1, 420 cfs (915 mgd) Oct. 2,1940 (gage height, 6. 40 ft, from floodmarks), from rating curve extended above 32 cfs by logarithmic plotting. Mean discharge and runoff, August 15-18, 1950 Day Cfs Day Cfs August 15 463 August 17 435 16 457 18 48.6 Mean discharge, in cfs, for period . . 351 Runoff, in inches ...... 32. 6 Gage height and discharge at indicated time, 1950 August 15 August 16 1 August 17 August 18 Hour Gage Dis­ Gage Dis­ Gage Dis­ Gage Dis­ height charge . height charge height charge height charge (ft) (cfs) (ft) (cfs) (ft) (cfs) (ft) (cfs) 1 2. 20 26.3 5.90 1,110 5.20 735 3. 13 99.0 2 2.12 22.4 5.62 952 5.10 681 3.02 82.0 3 2.08 20.7 5.89 1,110 5.25 735 2.94 77.4 4 2.06 20.0 5.60 952 6.32 1,350 2.85 68.1 5 2.05 19.5 5.00 631 &12 1,230 2.79 63.4 5:30 - - - _ 6.54 1,480 _ _ 6 2.25 28.6 4.50 415 5.80 1,060 2.73 59.6 7 2.49 41.8 4.28 347 5.20 735 2.68 55.7 8 2.45 38.7 4.20 316 4.85 559 2.63 51.8 9 2.49 41.8 3.98 257 4.52 415 2.58 48.0 10 2.70 55.7 3.92 232 4.25 331 2.55 44. 9 11 3. 10 92.6 4.15 300 4.05 271 2.51 41.8 N 3.72 187 3.84 220 3.90 232 2.48 41.8 1 3.89 232 3.64 176 3.75 198 2.45 38.7 2 3.62 167 3.55 158 3.61 167 2.43 38.7 3 4.35 364 3.55 158 3.49 149 2.40 36.4 4 5.70 1,010 3.62 167 3. 38 133 2.38 36.4 5 6.00 1, 170 3.60 167 3.29 119 2.35 34.0 6 5.60 952. 3.51 149 3.25 111 2.33 34.0 7 5.40 843 3.53 158 3.32 119 2.31 30.9 8 5.42 843 3.73 198 3.43 141 2.28 30.9 9 5.52 897 3.86 220 3.59 167 2.26 29.1 10 6. 30 1,350 5.00 631 3.48 149 2.24 28.2 11 6.80 1,670 5.20 735 3.37 127 2.22 . 27. 2 11:30 7.23 1,930 ______12 7.01 1,790 4.95 607 3. 25 111 2. 20 26.3 334 FLOOD OF AUGUST 1950 IN I^AUAI

Makaweli River near Waimea, Kauai Location. --Lat 21°58'15.", long. 159°38'55",0.7 miles upstream from confluence with Waimea River, 1.9 miles northwest of Waimea, and 3.8 miles northwest of Makaweli. Altitude of gage, 30 ft (hand levels from estuary at confluence with Waimea River). Drainage area. --25. 0 sq mi. Gage-height record. --Water-stage recorder graph. Discharge record. --Stage-discharge relation defined by current-meter meas- urements below 260 cfs (168 mgd) and extended to peak stage by logarithmic plotting on basis of slope-area determination at gage height 9. 46 ft. Gage heights used to half-tenths between 2. 1 and 4. 0 ft, hundredths below and tenths above those limits. Maxima. --August 1950: Discharge, 9, 220 cfs (5, 960 mgd) 12:30 a. m. Aug. 17 (gage height, 9. 82 ft). 1943 to July 1950: Discharge, 11, 900 cfs (7, 700 mgd) Feb. 7, 1949 (gage height, 10. 66 ft), from rating curve extended above 260 cfs (168 mgd) by logarithmic plotting on basis of slope-area determination at gage height 9. 46 ft. Mean discharge and runoff, August 15-18, 1950 Day cfs Day cfs August 15 729 August 17 4, 310 16 3,070 18 564

Mean discharge, in cfs, for period . . 2, 170 Runoff, in inches ...... 12. 9 Gage height and discharge at indicated time, 1950 August 15 August 16 August 17 August 18 Hour Gage Dis­ Gage Dis­ Gage Dis­ Gage Dis­ height charge height charge height charge height charge (ft) (cfs) (ft) (cfs) (ft) (cfs) (ft) (cfs)

12:30 _ _ _ _ 9.82 9, 220 _ _ 1 1.31 11. 3 7.25 3,640 9.70 8,960 5.34 1,390 1:30 - - - _ 9.44 8, 170 - . 2 1.32 11.8 6. 15 2, 290 9.64 8,700 4.83 1,050 3 1.47 20.0 6.85 3,060 9. 17 7,640 4.60 928 4 1. 85 53.4 8.60 5, 150 8.90 6, 890 4.40 805 5 1.78 45.6 8.97 7rf 120 9.50 8, 430 4.24 696 5:30 - - 8.65 6, 200 9.75 9, 220 . . 6 1. 69 37. 1 9.05 7,120 9.55 8,700 4. 10 650 7 1.64 32.5 8.66 6,420 9. 25 7,640 3.97 580 8 1.59 28.6 7.40 3,950 8.48. 5,990 3. 87 538 9 2.50 149 6.60 2,790 7.94 4,780 3.77 498 10 3. 74 498 6.45 2,540 7.80 4,600 3.67 461 11 3. 68 480 6.35 2,540 7.34 3,790 3. 60 441 N 3.55 424 7.00 3, 340 7.04 3,340 3.54 424

12:30 _ _ 7.95 4,970 _ _ _ _ 1 4.43 805 7.15 3,640 6.66 2, 920 3.48 405 2 4.65 928 6.00 2,070 6.32 2, 410 3.44 388 3 4. 28 743 5.50 1,550 5.82 1,860 3.41 371 4 3.85 538 5.20 1,320 5.42 1, 470 3.40 371 5 3.70 480 5.17 1,320 5. 19 1,320 3.53 424 6 5. 11 1,240 5.00 1, 180 4. 95 1, 180 3.46 388 6:30 - - - _ 4.70 990 _ - 7 5.96 2,070 4.75 1,050 5.04 1, 180 3.35 356 8 5. 20 1, 320 4.65 928 5. 30 1, 390 3.27 326 9 5.40 1,470 4.50 866 5.85 1,860 3.20 313 10 5.63 1,640 4.54 866 5.60 1,640 3. 17 300 11 6.05 2, 070 6.80 3,060 5.85 ' 1,860 3. 13 300 11:30 - - _ _ 6.14 2, 180 _ _ 12 7.87 4,780 8.70 6,420 5.93 1,960 3.08 286 STAGES AND DISCHARGES AT STREAM-GAGING STATIONS 335

Combined flow of Waimea and Makaweli Rivers near Wainrtea, Kauai

Discharge at indicated time, 1950

August 15 August 16 August 17 August 18 Hour Discharge Discharge Discharge Discharge (cfs) (cfs) (cfs) (cfs) 12:30 _ _ 32, 700 _ 1 13.5 33,800 31,600 7, 200 1:30 - _ 29, 600 - 2 14.2 29,700 29, 300 6, 330 3 22.4 27, 400 29, 400 5,820 4 55.8 33,000 32,400 5,200 5 48. 1 39, 100 38, 600 4,600 5:30 - 38, 300 42, 000 - 6 39.6 39,000 42, 700 4, 190 7 35. 0 34, 300 36, 800 3,800 8 31.3 25, 400 29,500 3,540 9 233 .18,900 24, 300 3, 190 10 684 15,700 20, 700 2, 970 11 978 14, 900 17,700 2,760 N 1, 100 16,500 16, 200 2,560 12:30 _ 18,900 _ _ 1 l,58t) 18, 000 * 14, 400 2, 440 2 3, 160 15,500 12,800 2, 350 , 3 3,740 12,600 11, 100 2,260 4 2,950 10,500 9, 830 2, 260 5 2,710 9,680 8,440 2, 310 6 7,630 9,070 8,610 2,200 6:30 . _ 8, 110 - 7 18,200 8,630 7,990 2, 170 8 15,700 8,510 7, 500 2,060 9 15,400 8,760 7,410 1,970 10 17,700 9,230 8, 170 1,960 11 23,500 20,700 8, 670 1, 880 11:30 - - 8,710 - 12 32,700 30,700 8, 350 1, 790

Mean 5,500 20,500 19, 800 3, 380 336 FLOOD OF AUGUST 1950 IN KAUAI

DISCHARGE. IN SECOND-FEET PER SQUARE MILE

X _^ XI XI 00 > X 9 O1 Ol

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X *! U w t->-8 *.' ,s x*

*5 -»< 5I - «x

o o x z o m 00 00 0 0* Ok J 3D 9 m X XI O o

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rn H^ Ifl O c -n "** 3 ~ - sf i a 2 *S f r 2 o 3. 3 x e 8- g a| 8 f 5 «5^ ! - cog U) § If S § . §

o FLOOD OF AUGUST 1950 IN KAUAI 337

SUMMARY OF FLOOD DATA

Flood stages and discharges

Table 1 summarizes the maximum flood stages and discharges given in the preceding section of this report. It gives also the maxi­ mum stages and discharges for the gaging stations on the island of Kauai outside the Waimea River basin, thereby providing a summary for all currently operated gaging stations on the principal rivers and streams on Kauai. The map reference numbers on this table are applicable to figure 46.

Figure 48 shows the flood discharges, in second-feet per square mile, which are listed in table 1, plotted against the corresponding drainage areas.

Annual floods in Waimea River

In addition to detailed information on a specific flood, the engineer is interested in the relative magnitude of the flood with respect to other floods that are known to have occurred at the same point. Table 2 lists the annual floods in Waimea River. Records prior to the fiscal year 1940-41 have been revised on the basis of tests of a model of the station site. Table 1. --Summary of flood stages and discharges in Kauai, T. H., in August 1950 [Maximum discharges for flood of August 1950 were obtained from gaging-station records except as otherwise indicated by the following symbols: M, model study; S, slope-area determination]

Maximum previously known ' Maximum during present flood No. Stream and place Drainage Period Gage Cfs Date Gage Cfs on of determination fig. 46 area of Date height Discharge per and height Discharge per (sq mi) record (ft) (cfs) . sq mi hour (ft) (cfs) sq mi 1 Wdimea River be­ low Kekaha ditch Feb. 7, intake, nearWaimea 45.0 1921-50 1949 24. 2 27, 900 620 Aug. 17 a 25 30, 900M 687 2 Waimea River 1910-19 Feb. 7, Aug. 17 near Waimea 57.8 1943-50 1949 19.3 37, 100 642 6 a.m. al8.7 34, OOOS 588 3 Waimea River Feb. 7, Aug. 17, makai at Waimea 88.0 1943-50 1949 11.40 (b) - 6 a.m. 7.50 (b) - 4 Kawaikoi Stream 1909-17 Dec. 18, Aug. 15, near Waimea 4.1 1919-50 1916 15.2 (c) - 12 m. 13.43 7, 980S 1,950 5 dMohihi Stream e!909-12 Oct. 2, near Waimea 1.6 1920-26 1940 6.40 1,420 888 Aug. 15, 1936-50 11:30 p. m. 7.23 1,930 1,210 6 Waiahulu Stream 1916 Feb. 7, near Waimea* 20.0 1917-18 1949 17.0 24, 800 1,240 Aug. 17 a!8.3 28, 000 1,400 1925-50

7 Makaweli River Feb. 7, Aug. 17, near Waimea 25.0 1943-50 1949 10.66 11,900 476 12:30 a. m. a9. 82 9, 220S 369 Hanapepe River at 1917-21 Dec. 17, Aug. 16, Koula, near Eleele 18.8 1926-50 1949 11.73 16, 100 856 5 a. m. 8.90 9. 110M 485

Hanapepe River Dec. 17, Au3. 16. at Hanapepe 26.9 1949-50 1949 6.58 (b) - 6 a. m. 4.55 (b) -

10 South Fork Wailua Jan. 16, River near Lihue 22.4 f!911-50 1920 11.25 44, 900 2,000 Aug. 16 alO. 6 15, 900M 710 % 11 North Fork Wailua I River at altitude June 2, > 650 ft, near Lihue 6.6 g!910-50 1943 h9.96 6,220 942 Aug. 16 all. 85 6, 030M 914 3 O 12 East Branch of North Fork Wailua Dec. 24, Aug. 16, River near Lihue 6.2 1912-50 1927 10.57 5,170 834 6 a. m. 5.79 1, 020M 164 r

13 Kapaa River at U910-15 8O Kapahi ditch intake, J1913-20 Feb. 7, Aug. 15, near Kapaa 3.3 1936-50 1949 4.65 5,520 1,670 4:30 p. m. 2.72 1,520 461 g

14 Anahola River near Apr. 1, Aug. 15, Kealia 5.5 1912-50 1948 11.06 12, 300 2,240 4:30 p. m. 4.83 1,350 245 a Faulty or no gage-height record; maximum stage from floodmarks. b This station is for collection of gage-height record only. c Discharge not determined. d Formerly published as Mohihi Stream at altitude 3, 500 ft, near Waimea. e Fragmentary record at site 2 mi downstream. f December 1911 to November 1918 at site and third of a mi upstream. g December 1910 to September 1914 at site 300 ft downstream from confluence of main and east branches; records not equivalent. h Datum then in use. i At site half a mile upstream, published as Kapaa River at Kapaa. j At site three-quarters of a mile upstream, published as Kapaa River near Kealia. * This gaging station, although published as on Waiahulu Stream, is on Waimea River, formed by the confluence of Waiahulu and Poomao Streams. Table 1. --Summary of flood stages and discharges in Kauai, T. H., in August 1950--Continued

Maximum previously known Maximum during present flood No. Stream and place Drainage Period Gage Cfs Date Gage Cfs on of determination area of Date height Discharge per and height Discharge per fig,46 (sq mi) record (ft) (cfs) sq mi hour (ft) (cfs) sq mi

15 Hanalei River at altitude 625 ft, Apr. 1, Aug. 17, near Hanalei 7.4 1914-50 1948 11.20 21, 400 2,890 1 a. m. 6.82 4,800 649 16 Hanakapiai Stream Dec. 23, Aug. 17, near Hanalei 2.6 1931-50 1937 8.41 4, 150 1,600 1:30 a. m. 6.93 2,520 968 17 Hanakoa Stream Dec. 21, Aug. 16, near Hanalei 1. 1 1931-50 1946 5.98 1,060 964 10 p. m. 7.29 1,730 1,570 18 Kalalau Stream Feb. 7. near Hanalei 1.6 1931-50 1949 4. 46 959 599 SUMMARY OF FLOOD DATA 341

Table 2. --Annual floods in Waimea River, for years ending June 30, 1922-51

Waimea River below Waimea River near Kekaha ditch intake, Waimea (drainage near Waimea (drain­ Calendar area, 57. 8 sq mi) Month Day age area, 45.0 sq mi) year Gage Gage height Discharge height Discharge (ft) (cfs) (ft) (cfs)

1922 Jan. 31 ab!5.£5 ell, 000 1923 .Jan. 10 or 12 abl8.47 c!5, 800 1923 Dec. 23 ab!8. 01 c!4, 900 1925 Mar. 23 abll.76 c4, 330 1925 Dec. 30 ablO. 12 c2, 180

1927 Feb. 15 16.20 ell, 600 1927 Dec. 24 20.40 c!9, 300 1928 Nov. 4 16.20 ell, 600 1930 Feb. 27 17. 92 c!4, 700 1930 Nov. 18 14.0 c7, 890

1931 Aug. 4 14.90 c9, 420 1932 Nov. 18 16.40 c!2, 000 1933 Dec. 21 15.04 c9, 660 1935 Feb. 26 16.64 c!2, 400 1935 Dec. 9 13.80 c7, 550

1937 Mar. 19 15.0 c9, 590 1938 Mar. 26 16.95 c!2, 900 1939 May 11 15.20 c9, 930 1940 Jan. 7 15. 12 c9, 790 1940 Oct. 2 17.60 14, 100

1942 Feb. 19 13. 22 6,560 1942 Dec. 6 15.65 10,700 1943 Aug. 11 15.40 10, 300 1945 Apr. 6 11.45 10,300 14.80 9,250 1945 Dec. 6 12.80 13, 600 13.90 7,720

1946 Dec. 22 13.10 14, 400 16.90 12,800 1947 Dec. 17 10.79 8,850 - - 1949 Feb. 7 19. 3 37, 100 24. 2 27, 900 1950 Jan. 6 9. 1 5,550 13.78 7,550 1950 Aug. 17 18.7 34, 000 25 30,900 a Converted to present datum. b Maximum stage recorded; may be too low owing to faulty intake action. c Revised. 342 FLOOD OF AUGUST 1950 IN KAUAI

PHYSICAL FEATURES OF KAUAI

Kauai is the fourth in size of the eight main islands in the Hawaiian Archipelego, and lies at the northwest end of the group. The island is 555 square miles in area," and is approximately circular in outline. The central mountain mass gives the island an approximate cone shape. The apex of the cone is formed by the two peaks Waialeale and Kawaikini, altitudes 5, 080 and 5, 17U feet respectively. Kawaikini, the higher, but less well known of the two peaks, is about a mile due south of Waialeale, and the connecting ridge is nowhere less than 5, 000 feet in altitude. From this central mountain mass, streams radiate in all directions.

Kauai is the oldest of the eight principal islands, and because it is more maturely dissected than others, its various natural features are better differentiated. The valleys are longer, deeper, and broader than those of the other Hawaiian islands. The island has luxuriant veg­ etation owing to abundant rainfall, and it has been properly termed the Garden Island.

According to the territorial health department, the population of Kauai as of January 1951 was 30,374. The people live in small towns and villages, the largest of which are Waimea, Lihue, and Kapaa. The island has excellent roads around the perimeter except for a section along the northwestern coast where precipitous cliffs drop almost verti­ cally into the Pacific Ocean. That section is known as Na Pali coast (in English, The Cliff coast ).

Rainfall varies greatly in different parts of the islands according to exposure to trade winds and to elevation above the sea. The average annual rainfall along the coast line ranges from 15 inches at Mana, which is at the leeward, or western, side of the island, to 45 inches at Lihue at the east end, and to 100 inches at Hanalei, which is on the windward, or northern, side of the island where the moisture-laden trade winds strike first. The increase in rainfall is rapid with in­ crease in elevation. At the summit of Waialeale the maximum annual rainfall recorded by the U. S. Geological Survey was 624 inches in 1948.

The Waimea River basin lies on the leeward side of the island and comprises an area of about 58 square miles exclusive of the Makaweli River basin. It is the largest river basin on the island. It is shaped like a square in its upper part, 7 miles on a side. Almost all the tri­ butary streams rise on the northeastern side at an elevation of 4, 000 to 5, 000 feet and flow southwestward to the main stream, which flows southward in a spectacular canyon 2, 000 to 3, 000 feet deep. This Waimea Canyon is especially noteworthy. It is about 10 miles long and about a mile wide and in coloring and sculpture it may be compared with the Grand Canyon of the Colorado.

The main Waimea is called Poomao River in the upper part of the canyon. The chief tributaries from north to south are Kawaikoi, METEOROLOGICAL FEATURES OP THE FLOOD 343

Waiakoali, Mohihi, Waiahulu, Koaie, Waialae, and Mokihana Streams. The northern part of the Waimea basin consists of an open rolling but swampy country called the Alakai swamp, which serves to some ex­ tent as a natural reservoir, regulating the flow of the streams.

At present gaging stations are operated on Waiahulu, Kawaikoi, Mohihi, and Waimea streams in the northern part of the basin, and on Waimea River and Makaweli River, which joins the Waimea River lj miles above the outlet into the ocean, at the lower portion of the basin.

METEOROLOGICAL FEATURES OF THE FLOOD

Precipitation

The storms that occur in the Hawaiian Islands are generally of two types, referred to as trade wind storms and kona storms. The source of the trade wind storms is in the North Pacific subtropical . A characteristic of a trade wind storm is that the total rainfall increases with altitude. The projection of the mountains far up into the prevailing trade winds is a dominant factor in the produc­ tion of precipitation over the windward slopes of the islands. Records of past storms indicate that the trade wind type does not produce floods of such magnitude as the kona type.

The kona storms generally occur during the cooler months of the year. They are preceded by strong and persistent southerly winds, and are generally produced by frontal advance associated with the extratropical over the North Pacific. The direction of the kona storm is generally from southwest, with highest precipitation being recorded on the lee side of the mountain ranges. * In August 1950 the Hawaiian Islands came under the influence of a tropical of full hurricane force. According to the U. S. Weather Bureau this was the first instance in 45 years of meteoro­ logical records in this area that a storm of such intensity had ap­ proached so close to the islands. Inasmuch as this was the first Hawaiian hurricane, it was designated as Able , or, in the Hawaiian language, Hiki

Isohyetal lines shown on the map (fig.46) were based on all avail­ able rainfall records. Most of the gages were located in relatively low-lying areas and permitted the plotting of ishoyetal lines with a satisfactory degree of accuracy in these districts. The rain gages located in the area of greatest rainfall are read at bi-monthly in­ tervals, however, but fortunately were read a short time before the storm. Thus the amount read after the hurricane could all be attributed to the precipitation due to the storm.

Rainfall records collected froA the rain gages in the Waimea basin are presented in table 3. The gage at the ranger station at 344 FLOOD OF AUGUST 1950 IN KAUAI

Kokee is read daily, and the installation at Waialeale is a continuous recorder. Their records afford some hint as to the daily precipitation at the other gages, which give only the total rainfall for the storm.

Table 3. -- Daily precipitation, in inches, August 14-19, 1950 f Data published by the U. S. Weather Bureau]

No. Altlr A UG U S T on Rain gage tude fig. 46 (ft) 14 15 16 17 18 19 Total

1 Kanalo Huluhuhu Ranger Station, Kokee 3, 600 9.13 28.62 12.23 2.36 52.34 2 Kilohana 4, 023 a60 3 Mohihi Crossing 3, 500 41.4 4 Mohihi Divide 3, 920 32. 4 5 Paukahana 3, 723 38.5 6 Waiakoali 3, 450 43. 9 7 Waialeale 5, 080 1.80 7.65 8.45 13.05 0.90 0.10 31. 95

a Estimated

Meteorology

By R. H. Simpson, United States Weather Bureau

The Hawaiian hurricane Hiki was first detected on the charts at the Honolulu Airpost during the night of August 13. It moved into the Hawaiian area from the vast expanse of ocean southeast of the islands, from which reports are rarely available and about the meteorology of which little is known. Such data as have been available in previous years indicate that the intertropical convergence zone between 120° and 168° west longitude normally does not advance far poleward into the summer hemisphere. Hence, the trade winds of the northern and southern hemispheres rarely converge at large angles, the shift fre­ quently being only from east-northeast to east-southeast.

Scattered reports from ships in the area during the summer of 1950 had on several occasions shown the intertropical convergence zone to be farther north than usual with a westerly flow as far north as the 10th parallel--conditions favorable for the development of trop­ ical cyclones. The research ship-*Horizon"encountered these wester­ lies near the 145th meridian, south of the region where Hiki probably formed, at approximately the time of the storm's inception. Figure 49shows the progress of the storm from -a point southeast of the Hawaiian Islands to a point in the eastern hemisphere where the storm had largely spent its force. Figure 49. --United States Weather Bureau map showing path of hurricane "Hiki, " August 1950. 346 FLOOD OF AUGUST 1950 IN KAUAI

Hiki arrived east of Hilo an immature storm of very small diam­ eter. Airplane reconnaissance on August 14 estimated the velocity of surface winds to be 45 to 50 knots (52 to 58 miles per hour) near the center. During the next 24 hours the storm intensified, reaching full hurricane force; however, it remained of small diameter, and winds of gale force extended outward less than 150 miles. The northwest movement of the hurricane became blocked temporarily on August 17 as a high pressure ridge west of the Hawaiian Islands intensified. During the next 24 hours the hurricane was forced slowly southward, seemingly poised between lower troposphere currents, which would have carried it farther westward, and higher-level westerlies, which tended to carry it northeastward. At this stage an airplane recon­ naissance reported winds up to 90 miles per hour just south of the storm center, and it became necessary to alert the populations of Kauai and Oahu against possible loop movement of the hurricane, which would have carried it east and northeastward through the Kauai channel.

Fortunately the blocking action to the west eased and Hiki resumed its westward movement, passing south of French Frigate Shoal and Midway Island before it began its curvature near 170° in the eastern hemisphere.

Distinguishing features of Hiki's curvature were that the movement of the hurricane was not accelerated and that, as colder air circulated into its lower vortex from the north on August 29 and 30, it came virtually to a standstill and filled rapidly. Ships reporting near the storm center at that time indicated that the maximum winds diminished there from more than 85 miles per hour to less than gale force.

The eye of the storm was entered by two reconnaissance planes and several ships. It was described as being 20 to 25 miles in diameter, overcast, with lowest pressure 29. 00 inches.

As all of Hawaii remained in the southern or less dangerous semi­ circle of the hurricane, Hiki caused little wind damage. The highest sustained winds reported were 68 miles per hour at Kilauea, Kauai; 50 miles per hour on the island of ; and 48 miles per hour at Lanai airport on the island of Lanai. The roofs of several houses were blown off, and unbraced masonry walls of one house under con­ struction were blown over. One life was lost at Kohala, Hawaii, by electrocution through contact with a live wire blown down by strong winds. The greatest damage resulted from flooding of the Waimea River on Kauai, where more than 200 residents had to be evacuated.

Hurricane Hiki differs from kona storms in that Hiki had most of its energy concentrated around a small center, whereas kona storms generally have their energy spread over much larger areas. Me­ chanically the two storms are quite different. The kona storms de­ pend upon cool air for sustenance whereas tropical cyclones such as Hiki depend upon uniformly warm moist air. Upper air currents of the average kona storms are nestled.in p.ools of cold air, whereas tropical cyclones like hurricane Hiki may be described as pools of METEOROLOGICAL FEATURES OF THE FLOOD 347 warm air. Both types of storm, however, produce cloudy and very rainy weather and also humid and depressive conditions near the sur­ face.

Tropical cyclones of the eastern Pacific are called hurricanes, while in the western Pacific they are known as . In the south Pacific tropical cyclones are generally called hurricanes; near Australia they are sometimes called willy-willys ; in the Phillipines they are called baguios ; and in the Indian Ocean near India they are sometimes called Bay of Bengal cyclones. In the Atlantic they are known as hurricanes. Actually they are the same phenomenon and the difference in nomenclature is only a geographical one.

INDEX

Page Combined flow of Waimea and Makaweli Rivers near Waimea, Kauai ...... 335 Floods, annual, in Waimea River ...... 337,- 341 Flood data, summary of...... 337 Flood stages and discharges ...... 337 Flood stages and discharges, summary of ...... 338 - 340 Introduction...... 327 Kawaikoi Stream near Waimea, Kauai ..... 332 Makaweli River near Waimea, Kauai ...... 334 Meteorology ...... 344 - 347 Meteorological features of the flood ... .343 - 347 Mohihi Stream near Waimea, Kauai ...... 333 Physical features of Kauai ...... 342 - 343 Precipitation ...... 343 - 344 Stages and discharges at stream gaging stations ...... 327 Waimea River near Waimea ...... 331

349

U. S. GOVERNMENT PRINTING OFFICE : O 1952