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DEPARTMENT OF THE INTERIOR Prepared in cooperation with the GEOLOGICAL SURVEY, WRD UNITED STATES GEOLOGICAL SURVEY : : VIRGIN ISLANDS PUBLIC WORKS DEPARTMENT WATER RESOURCES INVESTIGATIONS REPORT 84-4184 LOCATION THE STORM THE FLOOD FLOOD OF APRIL 18 1983 On ST THOMAS AND Between midnight and 2 a.m., on the 18th of The unusually intense rainfall produced THe tee : 5 a The Virgin Islands, forming part of the April about 3.5 in. of rainfall were recorded. almost instantaneous runoff on St. Thomas and St. 10,000 -~— SESH REGESRREREGESE AE CGR ERES ER ST JOHN UJ S VIRGIN ISLANDS Lesser Antilles separating the Caribbean Sea from Relatively light rain continued during the re- John because the drainage basins are very steep. ee a The flood heights were measured at the two The effects of sediment and debris on the ‘ 8 p Van sid RREARR Oeeaa. gs abent 1.400 mi aouthease mainder of the night as the cell of heavy rain Normally-dry creeks or "guts" overflowed as the ia = stream-gaging stations on St. Thomas and the one flood peaks cannot be fully evaluated because of at Haw Yare aud a 1.000 mi ee sash ee wit moved eastward into the Leeward Islands. Around tremendous quantity of floodwater and accompanying ie 4 on St. John (fig. 4). Indirect measurements of lack of data. However, it is likely that runoff Mi. eee te” " Weegin Sas ee sunrise an east-west line of heavy showers devel- mud, rocks and debris discharged toward the sea. | BONNE RESOLUTION GUT AT BONNE RESOLUTION, | the rates of flow at these sites during the flood rates and volumes are subject to more error than Thomas, §t. John, bed Se. Geet, St. Uhonad ie oped over St. Thomas and St. John. By 6 a.m. The areas of most widespread flooding were those ST. THOMAS, V.I. peak are shown in Table 1. Note the, large unit normal because of the unknown effects of these ; F ee about 5.3 in. of rain had accumulated at Dorothea. near the coastline as the floodwaters could not ti a discharges, all exceeding 2,500 cfs/mi’. Based located about 50 mi east of Puerto Rico; St. John, : : : ages eas on factors. another 5 mi to the east, and St. Croix is about Intense rain contributed about 4 in. during the discharge to the sea fast enough. data for similar streams in Puerto Rico (Lépez, WATER RESOURCES DIVISION 40 mi due south of St. John (fig. 1).- 3-hour period from 6 to 9 a.m. Moderate steady 1000 wa] 1979, p. 26), flooding of this magnitude can be Federal Emergency Management Administration rain continued until about 11 a.m. when the final _The flood consisted of three distinct periods S E > expected to occur on the average less than once officers estimated the damages on St. Thomas and RESOURCES INVESTIGATIONS REPORT 84-4184 ae Pan: en ee and most intense downpour began. By oo) pail. of intensive runoff, each more severe than the 9 = 4 Suet omer bnndced years. Figure 7 is a reprint of St. John were 3.5 million dollars to structures WATER cams — oO - oO 30 S500 pone - another 6.0 in. had accumulated as the storm previous one. The flow pattern for Bonne Resolu- ws a a Lopez's figure 13 with the 1983 peak flow rates and contents, 5 million dollars to public works aupetaed., tion Gut, St. Thomas (fig. 5), exemplifies the : E - for the three gaging stations plotted for compari- and “schools, and 4 million dollars’ to. roads, progression of the flood as well as the intensity. wi son to other outstanding floods. Although these bridges and culverts (San Juan Star, April, 1983). A total of 16.5 in. of rainfall were recorded Runoff was equal to 12.9 in. of rainfall. By ie ~ ea do not exceed the upper peaks, they are in the 18° : 3 in the 19-hour period from 7 p.m. on April 17 to 2 midday a major emergency had developed along the a same range as other maximum known floods. Accord- 30 BRA : . p.m. on April 18. During that period, there were heavily-populated south coast. Most businesses Sent. a ing to local residents, this was the worst flood- : Ty amounts of 2.5 in. in 1 hour (twice), 6.0 in. in 3 along the main street of Charlotte Amalie in St. o i = ing ever experienced in these islands. 15 PUERTO RICO _ST. THOMAS | | | hours, 8.0 in. in 6 hours, 12.3 in. in 12 hours, Thomas were flooded with up to 4.7 ft of water and s a = 18° : . §T. JOHN and 16.0 in. in 18 hours. mud (fig. 6). A resident drowned when he slipped ea = “a 00) WS ~nf je a into a drainage gutter and was swept away by the = eS =] Table 1. Peak discharges at gaging stations in St. Thomas and St. John, U.S. Virgin islands. os The recorded rainfall-data for the station at current. At Harry S. Truman Airport, the runway a a es 5 10 Caneel Bay, St. John show an almost identical and the terminal building were under 2-3 ft of mud c & al Maximum previously Maximum discharge for 4 15 3T. CROIX pattern of timing and intensity. and water. The airport remained closed several x Drain- : known discharge April 18, 198 z 179 — _ = days for cleanup operations. On St. John, the 4 Station age Period i Unit _ 30 _ 40 MILES — The storm totals on St. Thomas ranged from rural areas near Guinea Gut, Fish Bay and Coral Q is = number Station name area of Dis- Unit Dis- dis- rror 35 ‘ 14.5 in. in the extreme east to 18.7 in. in the Bay were flooded. Numerous landslides blocked re = (mi?) record oa oS? aie. | TAee | ene ge | ee | quency 2 102 west. On St. John, totals ranged from 12 in. in roads and brought down utility poles; the islands ES a (ft"/s) | charge (ft'7s) (ft/sec/ (years) z 2 Figure 1. Geographic setting of U.S. Virgin Islands. the exthese Geer Ged Werk Coes Ue te.16 in. dh WEE welieur electric ‘power or telephone sevice o a mo « = the higher elevations of the interior (fig. 4). for several days. The National Guard was called — = St. Thomas 0 = CLIMATE to assist the clearing of roads and to prevent | }+ [| 50252000| B eae jueae 5 i In contrast, the storm affected St. Croix looting. Flood-related damages in the two islands oe oe. soe ees ay Si ae fay = ; = l feel 4 h er about a day later and totals were relatively small were estimated at 12-13 million dollars. St. meee Tia : oe i kaa 2 ae era es a = oo U.S. i‘ yeh (4.0 to 6.7 in.). Thomas and St. John were declared disaster areas 1 vi a 2 oF: : APRIL 17 < mini asinis haan eaeaiolas $oes Teeee Ee. by Federal Officials (San Juan Star, April 1983). 5 . = about 30 in. in the flat lowlands to a high of = ( “oe ) TIME, IN HOURS 50276000 | Turpentine Run : 1963-69 : 0 about 60 in. at the mountain peaks (fig. 2). The 18° Socee 65°00’ 55' 64°50’ Figure 5. Flow pattern for Bonne Resolution Gut at Mariendal 2.97 1979-83 9-4-79 | 2,500 840 = 9,710 3,270 | 100+ , weather is dominated by the almost constant 24 : = ad ; at Bonne Resolution, St. Thomas. a : easterly trade winds. Most rainfall is caused by St. John APRIL 17 APRIL 18, 1983 APRIL 19 the lifting and cooling of the humid air as it 64°50' 45’ 40' 64°35' 50295000 | Guinea Gut at 1963-66, oe tie passes the islands. February and March are T ST T T Bethany 0.37 1982-83 | L1-4-65 i 300 = 946 2,560 | 100+ ; usually the dryest months and September and 4.98 f siticicn a bah October the rainiest. Most rainfall occurs during 18° 17° 4.09 1.000.000 brief showers. Heavy intense rains result from 20 45). cs] SELECTED REFERENCES Gaede - a BBS [ Pa PL - N A 7 I py N Py eee TS ARAN ee gee eee eee Pepe ee 0 1 2 3 4MILES or Curtis, Russell E., and Others, 1984, Wat i N ! “ H H H ‘ a Se ae da 14. > “s rs, » Water eae MAXIMUM KNOWN FLOODS | ITED STATES - pl Prepared in cooperation with the sions, tropical etorms, and hurricanes. _—<—= : Amalie , (2760) nae? 8 rien nie ot ey Rico and the U.S. 2 ~ pine from nee eon eo cctepmeent a ’ ST. CROIX F rgin Islands, 3: U.S. Geological Survey : : ; VIRGIN ISLANDS PUBLIC WORKS DEPARTMENT e450 ‘he folowing tactofemmatonal System ot Unite (80. Water-Data Report. 8 ee nerenon 271 “NEBRASKA ~ fo] —_ 560 MAXIMUM KNOWN FLOODS IN PUERTO RICO - pe 1g ae 5 18.772 sal +7 012 3 4 MILES a Multiply inch-pound units By To optain Si units Lapse Mane abe Gebel. STU, <Ctecia dia Raerbo : ° ee is dhe eRusENCGCe aidting namber. 9900610 = 1984 ST. JOHN | >. - i aaa oe ee 2760 FLOOD OF APRIL 18, 1983 U.S. VIRGIN a “440 BS = : (Data from NOAA NWS ca urvey water-Resources nvest gations Py oWDe . . ‘ ss foot (it) S.oasni” ae ; cata 100.0007 7 ISLANDS - Number is the abbreviated . ie 0550 ou = : acai 5 5 LINE OF EQUAL RAINFALL ~ Contour interval 1 inch. aac eels beaten. Haire, W.J., and Johnson, K.G., 1977, Floods of ra a = — &~480 = @4-67 NOAA WEATHER S = b Aree : november 12, 1974 in the Charlotte Amalie Oo Epes APPROXIMATE UPPER LIMIT 1478 4 mate Seacigin inches square miles (mi?) 2.590x 10° square kilometers (km) Area, St. Thomas, U.S. Virgin Islands: U.S. oa = CURVE FOR PUERTO RICO Pitas i les280 | 18° Je - _ Geological Survey Water-Resources Investiga- 2 560 410 aI | ete EAS — cubic feet per second (ft/s) 2.832x1072 cubic meters per second (m/s) Zz iz Aso? 818 1360 pel ne ™ oe silat a ” snail 2 3MiILES ¢ win : : . aay see and Others, 1972, Water records eS a 810 390 - "| Biliary deauiiiad Figure 4. Precipitation patterns for April 18, 1983 in the U.S. Virgin Islands, sesloeiea Simeey Oper hile ee eas S NORTH CAROLINA g- HiG.ec . f.. (Prepared by R.J. Calvesbert, NOAA, NWS). (unnumbered publication). 2 2760 = 64°50’ | 64°40’ wana 3 = oe 70 °540 = ! 45. I = 2 = = a FLOODS OF APRIL 18, 1983 ON ST. THOMAS 18°22! er . So, 2520 WY S - ie el : Si : Wipe \ ; FLOOD PEAKS SHOWN ARE a AND ST. JOHN, U.S. VIRGIN ISLANDS 4 = & 20 ui 647 PRIOR TO JANUARY 1, 1976. i 60! 3 ‘ 4 , ° Q is 2) B : LDS SC BM ; 2520 ' Russell ane Jr 18°20’ : <2 = R n pee a ae Se | ee ey ‘ie fee eS . , . .) lL 17°42" 9 1 2 3 MLIES : 2 ‘ beads 2950" 1 10 100 1000 a 5 DRAINAGE AREA, IN SQUARE MILES ABSTRACT | x q on \s ; SES Figure 7. Comparison of maximum known floods in Puerto Rico, The U.S. Virgin Islands of St. Thomas and St. 18°18’ ae 3 MILES « EXPLANATION ez Peer 07 ( = S\N (Cab A < United States and U.S. Virgin Islands to Myers rating. John experienced the most intense rainfall event S as A Gan SS) SS8 64°52’ in recorded history on April 18, 1983. Rainfall j a LINE OF EQUAL RAINFALL IN INCHES i Ss hes IGE IAN intensities of 2.5 inches per hour, and more than = 10 at = <> a 4 (act 16 inches in 18 hours were recorded. Almost ’ Figure 2. Average-annual rainfall in the U.S. Virgin Islands (Prepared by R.J. Calvesbert, NOAA, NWS). ae SS ei 00 ‘ instantaneous runoff caused widespread flooding : Ds SSS iN . near the coastlines of both islands. Parts of Wi7YS Py eee ae =RE* | Charlotte Amalie in St. Thomas were inundated with DATE TIME ZS —=— <° Flood boundaries not delineated beyond this line.! Ny, z se SS ; ms four feet or more of mud and flood water. Harry aoe THE STORM f _ Sy Se ee ~ S wy : Fe SS es za Same S. Truman Airport was flooded for two days with 12 “— sad 24 ie a 24 ig ee she ; : : i Aes : tes : two to three feet of ponded water. On St. John, | ; | T 1 ea tee pear wae aiena ae S © rural areas near Guinea Gut, Fish Bay, and Coral i i : . ee ee = oe > “> : SS tere ~ : Bay were flooded. 1s | | | caused by an upper-level trough located west of re, ? a Nips 2° | Puerto Rico. After 3 months of unusually dry “es 6 - a SRO aR Se conditions affecting Puerto Rico and the Virgin i \ : hy WW OG eal a Q | Islands, a low-pressure weather system moved into 36 5 @,| } Tes SP INTRODUCTION = DOROTHEA BAY | the area late on April 17 and remained stagnant 4 ts A} -aNe . 10;— ST. THOMAS * 18°] s\ oB SV: 2.0- . : : z ‘ | for most of April 18. \ = Severe flooding as a result of intense a | | 20° awe ‘li = : + i i ‘ “os = ) 30"’ S ki BEX {<< eiatatt oh poem: a ees para psa le sia Se 3 ! | a A cell of heavy showers developed over water = 2.2 47 What “| 4.6 : y VZYARER OH) OSS). Te ap a 2 (|| |, Sco EZR RR SSAC (CE Virgin Islands during April 18, 1983. Rainfall ~ i | = cai: Wk Hale mina wk aha Soe ee ee . . b ‘eo __ 10) WT REL O_o ENS LE NSENEWY S| 1 ee EN SS ORR intensities of 2.5 in./hr, and more than 16 in. in < 2 : Sess P ibe tee i ce om ericksber Zs u 5 It moved northeastward into southern Puerto Rico ee Ae f 18 hrs were recorded at St. Thomas and St. John. z z uk Genta dake SAK cea See ieee \ D> — ee 12 j The almost instantaneous runoff turned the usually < ° - 8 pen \' ae 25 \ Long Ba ; ; ; : 3 ar Amounts of 2 to 3 in. were recorded during the s 8 BS A dry streams on both islands into raging rivers of = night if sobthorn sad eacecen Meette Rico. bi bie 2 ~ ae e jin a S\N ° bs b e : ra : : e i Se a ee 3 = a . Ff / fs sediment-laden water and debris (0) s U.S. Virgin Islands, the trough produced one of + i ‘ —— ey mae : = ES of Vf) The U.S. Geological Survey, Caribbean Dis- « Bie iar 4 fai ok > coke events ee record (R.J. e rats &, ne Y, ar : Flood boundaries not = “({q_ ///)> ) ) YSL/ Hofman FAAS SORE ROIS trict initiated a project to document the extent alvesbert, ES » oral commun., 1983). tk oo = $9 FES of the flooding and the magnitude of the dis- ; EXPLANATION 7x i ee charges at the most important streams and guts in oe ee ee ee 0 Bo) % HavensightWQS Wx. C224 6 both islands. A team of 10 hydrologists and : ries ee Se ae as Oe ( @ i ee gh technicians was detailed to survey flood- marks Recording rain gages maintained by NOAA-National AREA FLOODED IN APRIL 1 . Ww iN Rupert ; : flood Pek wien. 12 18 24 12 18 24 6 Weather Service at Dorothea Agricultural Station 5 cai \ a Y \ “Rock edind: ) She immediately after the ee Me . APRIL 17 APRIL 18, 1983 APRIL 10 in St. Thomas and at Caneel Bay in St. John = 7 ji “ = tions were measured and marked, for later surveys DATE. TIME s ; y ee FLOOD BOUNDARY é x S : iy r lie a? h t from Lon : provided data on the intensity of the rainfall Se ees aN G ; : ; ; on St. Thomas along the south coast area g : © : (£4 3) is wie ae. dials need 7 —S ee ee 3Squito & ., Te iS | / Ni SW < 5= Flood boundaries not \4 Byy to Harry S. Inman Aixport. The gaticey =: Figs 2. ee ee eee —— a the 17th and about 0.6 fn had accumulated ihc ‘J S \ A i y = fA KE? Ee Q pea antes Beyond olecidladoced and computed records will be essential for future St. Thomas and St. John, U.S. Virgin Islands a “piduaee ee a period ae hese petal A 252. USGS GAGING STATION a - Lad q Shock Se) WG C y = ZFS = basin planning, emergency management activities (NOAA, National Weather Service) = i aaa : ees Weg ZF yh 6 & , SS Ses mney ; i . ’ . started. Pt } io S \ mi fa and to help define actual flood frequencies. 5 Muhlenfels : 2g: a ; eae 4 2 : 1 48 Pt] WE<visnth otis2* 5 a ne Se : é oS ; = CA \ j ar ma oo heu oS ie 'e 2 to Lf T T T iat “ se eS NY ~ : 3 = er 3); Se ae . aN A o Pr Q 6 1 2 KILOMETERS we e | Bay La = A eS p Ss er = / \ SY 7 og. We \: ? ole 2 1 sack a iE a if < ee oY nl rare AAA L i et . 4 C ne ; y= Base from U.S. Geological Survey topo maps, Central and Eastern St. Thoana, 1982. a — : S Aw ata Figure 6. Areas inundated April 18, 1983 in vicinity of Charlotte Amalie, St. Thomas. SE ES Sana me U.S. GEOLOGICAL SURVEY WATER RESOURCES DIVISION CARIBBEAN DISTRICT SAN JUAN, PUERTO RICO