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FLOOD OF OCTOBER 8, 1977 IN ST. CROIX, U.S. VIRGIN ISLANDS CARIBBEAN SEA MON BIJOU CHRISTIANSTED [EDERIKSTED AIRPORT, CA RIBB E A N SEA UNITED STATES GEOLOGICAL SURVEY WATER - RESOURCES INVESTIGATIONS 82-262 OPEN-FILE REPORT PREPARED IN COOPERA WITH THE GOVERNMENT OF THE U.S. VIRGIN ISLANDS DEPARTMENT OF PUBUC WORKS- FLOOD OF OCTOBER 8, 1977 IN ST. CROIX, U.S. VIRGIN ISLANDS BY KARL G. JOHNSON, RAMON A. CARRASQUILLO, AND RALPH GONZALEZ U.S. GEOLOGICAL SURVEY WATER-RESOURCES INVESTIGATIONS 82-262 OPEN-FILE REPORT PREPARED IN COOPERATION WITH THE GOVERNMENT OF THE U.S. VIRGIN ISLANDS DEPARTMENT OF PUBLIC WORKS SAN JUAN, PUERTO RICO DECEMBER 1982 UNITED STATES DEPARTMENT OF THE INTERIOR JAMES Q. WATT, Secretary GEOLOGICAL SURVEY DALLAS L. PECK, Director For additional information write to: District Chief U.S. Geological Survey GPO Box 4424 San Juan, PR 00936 Copies of this report can be purchased from: Open-file Services Section U.S. Geological Survey Box 25425, Federal Center Lakewood, Colorado 80225 CONTENTS Page Abstract....................................................... 1 1.0 Introduction.............................................. 2 1.1 Objective............................................ 2 1.2 Study area........................................... 4 2.0 Historical floods......................................... 6 3.0 The flood of October 8, 1977.............................. 8 3.1 Precipitation........................................ 8 3.2 Flooded areas........................................ 10 3.3 Flood profiles (Plates 1,2, and 3 in Pocket)......... 12 3.4 Depth of flooding.................................... 14 3.5 Areas inundated...................................... 16 4.0 Elevation of bridges and culverts and reference marks..... 18 5.0 List of references........................................ 20 APPENDIX....................................................... 21 PLATE 1 Flood map of Frederiksted area...............(In Pocket) PLATE 2 " " " Mon Bijou area..................(In Pocket) PLATE 3 " " " airport area .......*...........(In Pocket) ill FACTORS FOR CONVERTING INCH-POUND UNITS TO INTERNATIONAL SYSTEM OF METRIC UNITS (SI) For the convenience of readers who may want to use International System of Unit (SI), the inch-pound units may be converted by using the following factors: Multiply the. inch-pound units inches (in) feet (ft) feet per mile (ft/mi) miles (mi) square miles (mi ) 3 cubic feet per second (ft /s) By To obtain the SI units 25.4 millimeters (mm) 0.3048 meters (m) 0.1894 meters per kilometers (m/km) 1.609 kilometers (km) 2 2.590 square kilometers (km ) 0.02832 cubic meters per second (m3 /s) ACKNOWLEDGMENTS Manuscript Typing............Carmen A. Garcia Drafting and Art.......................-Jose' Alicea Report Review.................Donald G. Jordan IV FLOOD OF OCTOBER 8, 1977 IN ST. CROIX, U.S. VIRGIN ISLANDS BY KARL G. JOHNSON RAMON A. CARRASQUILLO, AND RALPH GONZALEZ ABSTRACT Severe flooding throughout St. Croix, United States Virgin Islands occurred on October 8, 1977. A tropical storm moving across the island produced as much as 16 inches of precipitation. The most affected areas were near Frederiksted, Mon Bijou, and the Airport. The peak discharge of River Gut near the Airport was about 11,400 cubic feet per second. The water depth in some urban areas exceeded 4.0 feet. Flood maps and flood profiles show the inundated areas near Frederiksted, Mon Bijou and the Airport. 1.0 INTRODUCTION 1.1 OBJECTIVE FLOOD OF OCTOBER 8, 1977 IN ST. CROIX DELINEATED This report presents maps of three areas in St. Croix, U.S. Virgin Islands, inundated during the October 8, 1977 flood. St. Croix, in the U.S. Virgin Islands, is located in the pathway of tropical storms and hurricanes, in the western edge of the Lesser Antilles (fig. 1.1-1). Tropical disturbances also occur frequently, creating intense precipitation which occasionally may exceed 18 inches in a 48-hour period (Jordan, 1975) . A tropical storm moved across St. Croix during October 7-8, 1977. Severe flooding at several places in the Island occurred on October 8, from the intense precipitation generated by the disturbance. This report documents the magnitude of the floods and defines the inundated areas. The information in the report will be useful to planners and managers involved in flood-plain development. It will also provide a record for future studies seeking to define the frequency of these and other floods. The report was prepared in cooperation with the Government of the U.S. Virgin Islands, Department of Public Works. COo O £2 i= I < S z > < CO a. x LU CC O LU CO LU QQ QQ QC ^ O CO Ul O- 0} "O c5 w c '5) CO D 0) +* *-o c CO O O CD h. 3 O) CO I 1.0 INTRODUCTION 1.1 OBJECTIVE 1.0 INTRODUCTION (Continued) 1.2 STUDY AREA FLOODING DEFINED IN THREE AREAS IN ST. CROIX The most severe flooding occurred in the Frederiksted, Mon Bijou, and Airport areas. St. Croix is the largest of the U.S. Virgin Islands, with an area 2 of about 84 mi . It lies about 50 mi east of Puerto Rico, and about 40 mi south of St. Thomas and St. John. The northwestern part of St. Croix is a rugged area of mountains of volcanic origin (fig. 1.2-1). The crest of the mountains ranges from 600 to 1,100 feet above mean sea level. The south and southwest parts of the Island form a gently rolling alluvial plain underlain by limestone and marl. The eastern part of St. Croix is a penninsula of mountain and shallow valleys, with some peaks reaching 800 ft above mean sea level. Four major streams flow intermittently in St. Croix, all in the western half of the Island. River Gut, the largest, has a drainage area 2 of about 11 mi . The principal areas affected by the flood of October 8, 1977 were near the Frederiksted, (Jolly Hill Gut); and Mon Bijou, (Salt River); Airport (River Gut). 1C CO CD IO t o 10 <D CO MJ tO H u m = 5 2 O _ lft - t CO h-evi evi- o-"-o 10 t o O * o CO ca cd o CD o O O ok.o *- CO CO CD cd k. CD C CD O I CM CD U) il 1.0 INTRODUCTION (Continued) 1.2 STUDY AREA 2.0 HISTORICAL FLOODS FREQUENT FLOODS HAVE OCCURRED DURING THIS DECADE Severe flooding occurred in 1974 and 1977. The island of St. Croix has been affected by severe floods twice during the last ten years. The storm of November 11-13, 1974 inundated large areas at Campo Rico, Whim, Carlton, Plessen, Christiansted, and Tide Village (fig. 2.0-1). In 1977, these areas as well as areas near Frederiksted, Mon Bijou, and the Airport were flooded. The storms of 1974 and 1977 were of similar magnitude. The recurrence interval of the 1974 floods ranges from 3 to 25 years (Haire and Johnson, 1978). Sufficient information to estimate the recurrence interval of the 1977 floods is not available. in CO CO IO CO CCtu U4 CO UJ =f 2 5 - Uj QQ 10- CMH CO hCM o» T- _c o o> o o o (0 (0 0> q cJ IO o r*. o ^t o 2.0 HISTORICAL FLOODS 3.0 THE FLOOD OF OCTOBER 8, 1977 3.1 PRECIPITATION PRECIPITATION DURING THE OCTOBER 7-8 STORM RANGED FROM 8 TO 16 INCHES In the area northeast of Frederiksted , cumulative precipitation averaged 16 inches. Annual precipitation on St. Croix averages about 40 inches, ranging from 30 inches in the east to 50 inches in the mountains of the north- west. Temperature averages about 79°F, with prevailing winds from the east or northeast. The tropical disturbance that produced the floods of October 8, 1977, moved over St. Croix on October 7. Precipitation was intense and cumulative totals over the Island ranged from 8 to 16 inches (fig. 3.1-1 and table 3.1-1). The largest amounts of rainfall during the storm (about 16 inches) were recorded in the headwater of Jolly Hill Gut, northeast of Frederiksted. From 12 to 14 inches were recorded at sites in the basins of River Gut and the Salt River. The drainage basins in St. Croix are generally steep, and river stages peak within a short time after precipitation. Although a signi- ficant amount of precipitation may be required before runoff exceeds 20 percent of precipitation (Jordan, 1975), antecedent wet-soil condi- tions can contribute to sizable runoff and flooding. 8 64°50' 45' 40 64°35' CO O « H L Im TJaj -n 2 r 2 O 2 O O O H O DOm 33 CO (0 17045' 17040' CARIBBEAN SEA BUCK ISLAND CARIBBEAN SEA eo- 01 234567 KILOMETERS i i i i i i i i___ EXPLANATION DAILY PRECIPITATION STATION RECORDING PRECIPITATION STATION STATION NUMBER (TABLE 3.1-1) PRECIPITATION TOTAL, IN INCHES 5 MILES Figure 3.1-1. Rainfall distribution during October 7-8, 1977 storm in St. Croix. (See Appendix) Table 3.1-1 Precipitation stations, and cumulative rainfall. STATION 1 NUMBER 1 2 3 4 5 6 7 LOCATION ALEXANDER HAMILTON AIRPORT ANNALY ANNAS HOPE BETH UPPER NEW WORKS CASTLE NUGENT CHRISTIANSTED FORT EAST HILL CUMULATIVE PRECIPITATION, IN INCHES 10.04 16.00 14.25 13.20 12.60 14.09 10.94 STATION 1 NUMBER 8 9 10 11 12 13 14 LOCATION ESTATE RUST-UP TWIST FOUNTAIN FREDERIKSTED GIANARD HAM BLUFF LH STATION KINGS HILLS TAGUE BAY CUMULATIVE PRECIPITATION, IN INCHES 14.75 13.00 - 12.04 12.38 8.00 II. 20 Figure 3.1-1 (Data from National Weather Service) 3.0 THE FLOOD OF OCTOBER 8, 1977 (Continued) 3.2 PEAK DISCHARGE FLOODING WAS MOST SEVERE IN THE FREDERIKSTED, MON BIJOU, AND AIRPORT AREAS Peak discharge at River Gut near the airport was about 11,400 ft3/s, while at Mon Bijou it was about 6,200 ft3/s. The flooded areas described in this report include Frederiksted, Mon Bijou, and the vicinity of the Airport (fig. 3.2-1 and plates 1, 2, and 3). The magnitude of the flooding in the other affected areas was similar to or less than that of the floods of November 11-13, 1974, as reported by Haire and Johnson (1974). Therefore, flooded areas defined by Haire and Johnson are not delineated in this report. Peak discharges at two of the flooded sites were estimated using indirect-measurement techniques. At River Gut near the Airport, the 3 estimated peak discharge was about 11,400 ft /s. At Mon Bijou, the 3 estimated peak discharge was about 6,200 ft /s. Peak discharges can be compared on the basis of drainage area to maximum discharges at other basins throughout the world (Lindsey and others, 1949). The discharge data for Mon Bijou and River Gut, as well as Myers comparison curves, are plotted in figure 3.2-2. The comparison shows that the Airport flood was less than 50-percent Myers rating. The Mon Bijou flood on the other hand, was greater than the 50-percent Myers rating and approaches the 80-percent yield curve, indicating a flood of greater relative magnitude. As a comparison, 9 sites of 24 affected by the floods of 1960 in eastern Puerto Rico exceeded the 80-percent Myers rating (Barnes and Bogart, 1961). These floods were the greatest known in Puerto Rico. 10 (Q C "i CD CO fo oo Q. CD Q. 0>-i CD Q) CO Q. C "i5' (Q CD O o r* Ocr CD"i CO CD >l >l CO »* O "1 3 CO o I m o u 52-5 s o CO O o o o m O H O CDm DO CO CD oo <Q C -i CD CO roiro o -o o CD 5 S: a n a o - « o » DISCHARGE, IN CUBIC FEET PER SECOND PER SQUARE MILE -* 10 co * en o> CD ro co * en o> CD o o ooooo o o o o o o o o ooooo oo o ooo o o_____o o o o o o ik a. If D) "1 » !" o o o CD O -L 30 O o m > to m CD co C m o> 2 r CD m co -*o I I I I I > o Om COo C _ m o a» - m z ? o _ C z co o m m H D m m co co mo Oz o JJ 3 O O "0 5 co m 2 o Z I coco mo 331 o oo i i 3.0 FLOOD OF OCTOBER 8, 1977 (Continued) _. 3.3 FLOOD PROFILES FLOOD PROFILES DEFINED AT THREE SITES Flood profiles were defined at Jolly Hill Gut near Frederiksted, Salt River at Mon Bijou, and River Gut near the airport. A flood profile is a schematic drawing of a floodwave. The profile shows the water-surface elevation referenced to a datum (pormal.ly mean sea level) and distances along a base line following the general flow direction. The profiles can be defined from actual floodmark elevations or analyses, using computer techniques (Chow, 1959). Normally the profiles include the elevation of bridges, culverts, and other constraining structures along the channel. Flood profiles were determined near Frederiksted (Jolly Hill Gut), Mon Bijou (Salt River), and near the Airport (River Gut). (Figure 3.3-1, and plates 1, 2, and 3 in pocket). The profiles are referenced to an arbitrary base line shown on plates 1-3. The base line and the profiles are not confined to the channel configuration, but follow a smoother path along the flood plain in the general direction of the floodflow. The profiles are based on actual floodmarks surveyed by personnel of the U.S. Geological Survey, Water Resources Division, shortly after the flood. 12 3.0 THE FLOOD OF OCTOBER 8, 1977 (Continued) 3.4 DEPTH OF FLOODING IN URBAN AREAS DEPTH OF WATER EXCEEDED 4 FEET The Mon Bijou housing area was the most seriously affected, with water depths of as much as 4.5 feet. The depth of the the water in some of the flooded urban areas ex- ceeded four feet. The housing project in Mon Bijou (plate 2), was the most affected area. The water depth in some of the houses was about 4.5 feet (fig. 3.4-1 and 3.4-2). Water depths of about 4 feet were also recorded in some areas near the Airport (fig. 3.4-3 and 3.4-4). In Frederiksted (plate 1), water depths did not exceed 2.5 feet (fig. 3.4-5 and 3.4-6). Most of the flooding occurred west and north of town. Flooding as a result of the October 7-8, 1977 tropical disturbance was widespread throughout St. Croix. Although estimates of damages to public and private properties are not available, severe losses were reported by citizens and government officials. Flooding and damages were more intense in the populated areas near Mon Bijou and Frederiksted. 14 Figure 3.4-1. Depth of water at abandoned house at entrance to Mon Bijou housing area,lot 471. (photo A) Figure 3.4-4. Depth to water in the vicinity of service station, about 200 feet north of fourth bridge on airport road, (photo D) Figure 3.4-2. Depth of water in front of house at lot 465, at Mon Bijou housing project. (photo B) Figure 3.4-5. Depth of water in front of ballpark about 200 feet south of most downstream culvert at Frederiksted.(photo E) Figure 3.4-3. Depth of water at farthermost downstream bridge over River Gut on airport road, (photo C) Figure 3.4-6. Depth of water on fence at east side of ballpark at Frederiksted. (photo F) +~ 3.0 THE FLOOD OF OCTOBER 8, 1977 (Continued) 3.4 DEPTH OF FLOODING IN URBAN AREAS 3.0 THE FLOOD OF OCTOBER 8, 1977 (Continued) 3.5 AREAS INUNDATED THREE FLOOD MAPS DELINEATED Maps delineate the inundated areas and show water surface contours at Federiksted, Mon Bijou , and the airport. The areas inundated by the October 8, 1977 flood are delineated on variable contour-interval topographic maps (fig. 3.5-1 and plates 1-3). The base maps for the Frederiksted and Airport areas (plates 1 and 3), were provided by the U.S. Virgin Islands Department of Public Works. The Mon Bijou area Map was delineated from a field survey by U.S. Geological Survey employees. Flood boundaries were delineated from high-water marks and field inspections of the affected areas shortly after the flood. The limits of the flood boundaries are approximate and may not reflect areas where shallow flooding occurred. Water-surface contours on the flood maps (plates 1-3) are based on the elevations of the floodmarks and the flood profiles. The contours represent lines of equal elevation of the water surface at about a normal angle to the direction of flow. Obstructions to the flow, such as man-made structure and vegetation, can cause irregularities in the contours. In the Mon Bijou area, the flow of the floodwaters was ob- structed by the buildings in a housing project. A similar condition was observed in the Frederiksted area, where fences and buildings also obstructed some of the flow. The approximate depth of flooding at any point in the inundated areas can be estimated by substracting the ground elevation from the water-surface contour. Interpolation can be used to estimate points between contours. 16 w 'ifc. O if m J.-t'. I pjg*£8 ! <D^ O O Q. O Q. Q) i_ CO T3 Q) *- C <D CO Q) CO Q. CO E o Oo U) CO <Di- 0> il 3.0 THE FLOOD OF OCTOBER 8, 1977 (Continued) 3.5 AREAS INUNDATED 4.0 ELEVATION OF BRIDGES AND CULVERTS AND REFERENCE MARKS ELEVATION OF 14 BRIDGES OR CULVERTS AND FOUR REFERENCE MARKS ESTABLISHED Elevations of 3 structures in the Frederiksted area. 6 in the Mon Bijou area, and 5 in the airport area were established. The elevations of bridges and culverts in the flooded area are im- portant hydrologic data. The depth of the floodwaters relative to bridge structures can be obtained from flood profiles (see section 3.3). These elevations can be used for future flood studies, design and alteration of structures. Flood stages and back-water conditions may be affected by such structures. Elevations of bridges in the Frederiksted, Mon Bijou, and the Air- port areas are shown in tables 4.0-1 to 4.0-3. The locations of the bridges are referenced to the base line on plates 1-3 and shown by means of a map symbol. Reference marks are usually established to define the depth of water along a flooded area. The marks can also be utilized for future studies and comparisons between different floods. The elevation of the marks is referenced to a mean sea-level datum (MSI,). The permanent marks established during this study are listed in table 4.0-4. 18 Table 4.0-1 Elevation of bridges in the Frederiksted area, (plate 1) Map Symbol A B C Stationing along base line, in feet 350 910 3060 Bridge elevation in feet (mean sea level datum) Top of Low Deck Beam 5.5 3.0 5.4 4.3 14.2 12.7 Table 4.0-2 Elevation of bridges in the Mon Bijou area, (plate 2) Map Symbol A B C D E F Stationing along base line, in feet 260 1580 3350 .3530 4035 4240 Bridge elevation in feet (mean sea level datum) Top of Low Deck Beam 86.1 83.4 114.7 110.5 150.1 149.5 152.1 151.5 Underground channel outlet 163.7 162.9 Underground channel inlet 171.0 170.2 Table 4.0-3 Elevation of bridges in the airport area, (plate 3) Map Symbol A B C C 1 D Stationing along base line, in feet 2970 4230 5180 5180 5400 Bridge elevation in feet (mean sea level datum) Top of Low Deck Beam 16.7 12.1 8.0 7.0 21.7 18.5 Left opening 20.3 17.1 Right opening 26.0 23.9 Table 4.0-4 Reference marks established by the U.S. Geological Survey Water Resources Division in St. Croix, U.S. Virgin Islands after the October 8, 1977 flood, (plates 1-3) Map Symbol Description FJevation in feet above mean sea level PM 1 Chiselled square, painted red, on downstream side of culvert 172.23 headwall at entrance road to Mon Bijou; the most upstream culvert. RM 2 Chiselled square, painted red, on left upstream side of bridge 17.81 at handrail foundation, over River Gut at the most downstream bridge of the Airport road. RM 3 Chiselled square, painted red, on upstream side of bridge 18.46 abutment of left bridge, over River Gut at New Center Line highway . RM 4 Chiselled square, painted red, on right upstream side of 6.45 culvert headwall on second culvert in upstream order, over Jolly Hill Gut on north side of Frederikstfitf. 4.0 ELEVATION OF BRIDGES AND CULVERTS AND REFERENCE MARKS 5.0 LIST OF REFERENCES Barnes, H.H., Jr., and Bogart, D.B., 1961, Floods of September 6, 1960 in eastern Puerto Rico: U.S. Geological Survey Circular, 451, 13 p. Haire, W.J., and Johnson, K.G., 1978, Floods of November 11-13, 1974 in St. Croix, U.S. Virgin Islands: U.S. Geological Survey Water- Resources Investigations 77-136, 7 plates. Lindsey, R.K., Kohler, M.A., and Daulhus, J., 1949, Applied Hydrology: New York, McGraw Hill Inc., 689 p. Jordan, D.G., 1975, A survey of the water resources of St. Croix, U.S. Virgin Islands: U.S. Geological Survey Open-File Report, 51 p. Robison, T.M., 1975, Ground water in central St. Croix, U.S. Virgin Islands: U.S. Geological Survey Open-File Report, 18 p. U.S. Geological Survey, 1976, Flood-prone area maps of St. Croix, U.S. Virgin Islands: unpublished maps (3) available for inspection at the U.S. Geological Survey Office, WRD, Ft. Buchanan, Puerto Rico. 20 APPENDIX PRECIPITATION STATIONS AND CUMULATIVE PRECIPITATION DURING THE OCTOBER 7-8, 1977 AND SEPTEMBER 4, 1979 STORMS MAP NUMBER 1 2 3 4 5 6 7 8 9 10 11 12 13 14 STATION LOCATION Alexander Hamilton Airport Annaly Annas Hope Beth Upper New Works Castle Nugent Christiansted Fort East Hill Estate Rust-Up Twist Fountain Frederiksted Gianard Ham Bluff LH Station Kings Hill Tague Bay CUMULATIVE PRECIPITATION OCTOBER 7-8, 1977 10.04 16.00 14.25 13.20 12.60 14.09 10.94 14.75 13.00 - 12.04 12.38 8.00 11.20 SEPTEMBER 4.1979 17.15 16.00 20.00 15.50 - 16.36 15.32 17.97 12.00 11.40 15.56 - - IB. CO Figure 3.1-1 (Data from the National Weather Service) ADMINISTRACION DE SERVICIOS GENERALES Area de Compra, Servicios y Sumlnistros Negociado de Imprenta San Juan, P. R.