RAINFALL FREQUENCY ANALYSIS FOR NEW BRAUNFELS, TX
Transcription
RAINFALL FREQUENCY ANALYSIS FOR NEW BRAUNFELS, TX
RAINFALL FREQUENCY ANALYSIS FOR NEW BRAUNFELS, TX (or Seems like we’ve been having lots of 100-yr storms) Presented By: SAUL NUCCITELLI, PE, CFM (LAN) BLAKE KRONKOSKY, EIT (LAN) JIM KLEIN, PE (CITY OF NEW BRAUNFELS) PLANNING | ENGINEERING | PROGRAM MANAGEMENT 1. 2. 3. 4. 5. AGENDA RECENT STORM REVIEW HISTORY OF RAINFALL ANALYSIS UPDATED ANALYSIS 1950 FLOOD IN NEW BRAUNFELS CONCLUSIONS Q&A PLANNING | ENGINEERING | PROGRAM MANAGEMENT 1998 FLOOD NWS APPROXIMATED RAINFALL DEPTHS • PRODUCED >20” RAINFALL IN 24-HRS • APPROACHING 500-YR FREQUENCY • ~$750M DAMAGES, 31 DEATHS ACROSS TEXAS DECEMBER 1998 NRCS STUDY PLANNING | ENGINEERING | PROGRAM MANAGEMENT 1998 FLOOD GUADALUPE RIVER AT IH-35 PLANNING | ENGINEERING | PROGRAM MANAGEMENT 2002 FLOOD NWS APPROXIMATED RAINFALL DEPTHS • PRODUCED EXCESS OF 30” RAINFALL IN 5 DAYS • 30” IS SIMILAR TO YEARLY AVERAGE RAINFALL DEPTH FOR COMAL COUNTY PLANNING | ENGINEERING | PROGRAM MANAGEMENT 2002 FLOOD • VOLUME ≈ 3 TIMES CANYON DAM’S CAPACITY OVERTOPPING THE EMERGENCY SPILLWAY CANYON DAM EMERGENCY SPILLWAY • CANYON DAM SPILLWAY FLOWS > 70,000 CFS CANYON DAM GORGE FROM SPILLWAY EROSION • CANYON DAM GORGE CREATED • EXPOSED MILLIONS OF YEARS OF GEOLOGIC TIME PLANNING | ENGINEERING | PROGRAM MANAGEMENT 2002 FLOOD SOUTH ACCESS ROAD AFTER FLOOD WATERS RECEEDED PLANNING | ENGINEERING | PROGRAM MANAGEMENT 2004 FLOOD • AROUND 6” RAIN IN 6 HOURS NRCS DAM #3 AT BLIEDER’S CREEK AT FULL CAPACITY • HEAVY RAINFALL DOWNSTREAM OF CANYON DAM, BLIEDER’S CREEK, AND DRY COMAL WATERSHEDS NRCS DAM #3 AT BLIEDER’S CREEK AT FULL CAPACITY PLANNING | ENGINEERING | PROGRAM MANAGEMENT 2004 FLOOD DRY COMAL AT LOOP 337 PLANNING | ENGINEERING | PROGRAM MANAGEMENT 2010 FLOOD GUADALUPE RIVER AT COMMON ST. • EXCESS OF 8” RAIN IN 3 HRS • FLOODING ALONG GUADALUPE AND COMAL RIVERS NWS NEXRAD IMAGERY PLANNING | ENGINEERING | PROGRAM MANAGEMENT 2010 FLOOD GUADALUPE RIVER AT IH-35 PLANNING | ENGINEERING | PROGRAM MANAGEMENT 2010 FLOOD COMAL RIVER AT SCHLITTERBAHN PLANNING | ENGINEERING | PROGRAM MANAGEMENT QUESTIONS AND APPROACH • WHY SO MANY BIG RAINS/FLOODS? • ARE ALL THESE BIG STORMS ENOUGH TO CHANGE DEFINITION OF A 100-YR RAIN? – 1998 TO 2010 HAD AT LEAST 4 LARGE EVENTS • LAN’S ANALYSIS APPROACH – REVIEW RAINFALL DATA – FILTER DATA – PERFORM STATISTICAL ANALYSIS – COMPARE TO PREVIOUS VALUES – RECOMMEND CHANGES, IF APPROPRIATE PLANNING | ENGINEERING | PROGRAM MANAGEMENT RAINFALL FREQUENCY TERMINOLOGY • P = 1/T • P = % ANNUAL CHANCE • F = FREQUENCY (YEARS) • P = 1-(1-F)N • P = % PROBABILITY OF AT LEAST ONE EVENT IN N # YEARS COMMON MISCONCEPTIONS • 100-YR EVENT ONLY HAPPENS EVERY 100 YEARS • 100-YR RAINFALL IS SAME AS 100-YR FLOOD PLANNING | ENGINEERING | PROGRAM MANAGEMENT TP-40 NATIONAL RAINFALL ATLAS TP-40 100-YR 24-HR RAINFALL • FIRST NATIONAL STUDY (1962) BY NOAA • FAIRLY SHORT RECORD OF GAGE DATA • GUMBEL DISTRIBUTION PLANNING | ENGINEERING | PROGRAM MANAGEMENT 1998 USGS TEXAS RAINFALL STUDY NWS RAINFALL STATIONS • USGS WRIR 1998-4044 (STUDY) • USGS SIR 2004-5041 (ATLAS) • REVIEWED NWS STATIONS • 174 15-MIN • 274 HOURLY • 865 DAILY • DATA THROUGH 1994 • UPDATED STATISTICAL METHODS PLANNING | ENGINEERING | PROGRAM MANAGEMENT 1998 USGS VS. 1962 TP-40 RAINFALL CONTOURS PLANNING | ENGINEERING | PROGRAM MANAGEMENT USGS 100-YR, 24HR DEPTH COMAL COUNTY 24-HR 100-YR DEPTH PLANNING | ENGINEERING | PROGRAM MANAGEMENT NEW BRAUNFELS DEPTH-DURATION-FREQUENCY TABLE PLANNING | ENGINEERING | PROGRAM MANAGEMENT RAINFALL STATION MAP PLANNING | ENGINEERING | PROGRAM MANAGEMENT RAIN STATION FILTER • FILTER 1 = NATIONAL WEATHER SERVICE STATIONS – CONSISTENT WITH USGS METHOD • FILTER 2 = ACTIVE STATIONS – CAPTURE RECENT STORMS • FILTER 3 = RECORD LENGTH ≥ 20 YEARS – LONG ENOUGH TO MINMIZE DATA SKEW • FILTER 4 = WITHIN 30 MILES OF NEW BRAUNFELS – RELEVANCE TO CITY PLANNING | ENGINEERING | PROGRAM MANAGEMENT FILTER 1 – NWS STATIONS PLANNING | ENGINEERING | PROGRAM MANAGEMENT FILTER 2 – ACTIVE STATIONS PLANNING | ENGINEERING | PROGRAM MANAGEMENT FILTER 3 – RECORD LENGTH ≥ 20 YEARS PLANNING | ENGINEERING | PROGRAM MANAGEMENT FILTER 4 – WITHIN 30 MILES OF NEW BRAUNFELS PLANNING | ENGINEERING | PROGRAM MANAGEMENT STATIONS USED IN ANALYSIS PLANNING | ENGINEERING | PROGRAM MANAGEMENT NWS STATIONS USED PLANNING | ENGINEERING | PROGRAM MANAGEMENT DATA PROCESSING •SEPARATED THE YEARS •DEVELOPED ANNUAL MAXIMA •HOURLY DATA USED TO GENERATE THE 1,2, 3, 6, 12, & 24-HR DEPTHS 1 HR = 1 HOURLY DATA POINT 2 HR= Σ ( 2 CONSECUTIVE DATA POINTS) 3 HR= Σ ( 3 CONSECUTIVE DATA POINTS) 6 HR= Σ ( 6 CONSECUTIVE DATA POINTS) 12 HR= Σ ( 12 CONSECUTIVE DATA POINTS) 24 HR= Σ ( 24 CONSECUTIVE DATA POINTS) 48 HR= Σ ( 48 CONSECUTIVE DATA POINTS) 72 HR= Σ ( 72 CONSECUTIVE DATA POINTS) •DAILY DATA CALCULATED SIMILAR TO HOURLY 1 DAY = 1 DAILY DATA POINT 2 DAY= Σ ( 2 CONSECUTIVE DATA POINTS) 3 DAY= Σ ( 3 CONSECUTIVE DATA POINTS) PLANNING | ENGINEERING | PROGRAM MANAGEMENT CANYON DAM - ANNUAL MAXIMA 1 HR TO 6 HR PLANNING | ENGINEERING | PROGRAM MANAGEMENT NEW BRAUNFELS - ANNUAL MAXIMA 1 DAY TO 3 DAY PLANNING | ENGINEERING | PROGRAM MANAGEMENT EXTREME VALUE STATISTICS • REVIEW OF (HIGHEST OR LOWEST VALUE) FROM A REOCCURING SAMPLE • INTERVAL DATA -HOURLY ANNUAL MAXIMA (8,760 hr / YR) -DAILY ANNUAL MAXIMA (365 DAY / YR) • INDEPENDENT RANDOM VARIABLES • CLIMATE PHENOMENA SUCH AS : -RAINFALL/FLOODING -EARTHQUAKES -TEMPERATURE -DROUGHT CONGRESS BRIDGE AT COLORADO RIVER AUSTIN, TX PLANNING | ENGINEERING | PROGRAM MANAGEMENT EXTREME VALUE STATISTICS PLANNING | ENGINEERING | PROGRAM MANAGEMENT EV- DISTRIBUTIONS • LOG PEARSON TYP III STREAM FLOW • GUMBEL TP-40 • GENERALIZED LOGISTICS (GLO) 1998 USGS 1-24 HR • GENERALIZED EXTREME VALUE (GEV) 1998 USGS 1-3 DAY PLANNING | ENGINEERING | PROGRAM MANAGEMENT STATISTICAL MOMENT STANDARD MOMENTS • Mr = E( ( X-M )r) r = MOMENT ORDER (0, 1, 2, 3, 4…∞) • CALCULATIONS REPRESENTING THE SHAPE OF DATA – PROVIDE SUMMARY – COEFFICIENTS TO STATISTICAL • DERIVED WITH RESPECT TO “MEAN”: M ( 0 ) = MEAN M ( 1 ) = VARIANCE M ( 2 ) = SKEW M ( 3 ) = KURTOSIS “AVERAGE” “WIDTH” “LOPSIDEDNESS” (+) = LEFT (-) = RIGHT “SQUATTINESS ” • SIMILAR TO PHYSICS: X = F(t) V = dX/dt A = dV/dt J = dA/dt DISTANCE VELOCITY ACCELERATION JERK OR JOLT r (0) INTIAL EQUATION r (1) 1ST ORDER r (2) 2ND ORDER r (3) 3RD ORDER PLANNING | ENGINEERING | PROGRAM MANAGEMENT L-MOMENT STATISTICS • SIMILAR TO STANDARD MOMENTS – SUMMARY TO DATA – COEFFICIENTS TO STATISTICAL DISTRIBUTIONS – CALCULATED FROM FINITE SAMPLES • DIFFERENT FROM STANDARD MOMENTS – TAKE IN ACCOUNT DATA RANKING IN ASCENDING ORDER – DERIVED WITH RESPECT TO MOMENT ORDER (NOT THE MEAN) – CALCULATION INTENSIVE “ REQUIRING AID OF COMPUTER” PLANNING | ENGINEERING | PROGRAM MANAGEMENT NEW BRAUNFELS STATION ANNUAL MAXIMA 1 DAY PLANNING | ENGINEERING | PROGRAM MANAGEMENT NEW BRAUNFELS STATION ANNUAL MAXIMA 2 DAY PLANNING | ENGINEERING | PROGRAM MANAGEMENT NEW BRAUNFELS STATION ANNUAL MAXIMA 3 DAY PLANNING | ENGINEERING | PROGRAM MANAGEMENT PULLING THE STATIONS TOGETHER 1998 USGS STUDY FOR TEXAS ≈ 270,000 MILES2 • 1998 USGS USED KRIGING TO PRODUCE CONTOURS • USED ~850 STATIONS, GROUPED 5 AT A TIME 2011 LAN STUDY FOR NEW BRAUNFELS ≈ 30 MILES2 • • • • RAINFALL CONTOURS NOT NEEDED SMALLER STUDY AREA THAN 1998 USGS STUDY 1, 2 , 3, 6, 12-HR DURATIONS USED 7 HOURLY STATIONS 24-HR ; 2 , 3-DAY DURATIONS USED 7 HOURLY & 2 DAILY STATIONS PLANNING | ENGINEERING | PROGRAM MANAGEMENT DDF RESULTS 1-HR PLANNING | ENGINEERING | PROGRAM MANAGEMENT DDF RESULTS 6-HR PLANNING | ENGINEERING | PROGRAM MANAGEMENT DDF RESULTS 24-HR PLANNING | ENGINEERING | PROGRAM MANAGEMENT DDF RESULTS (PRELIMINARY) PLANNING | ENGINEERING | PROGRAM MANAGEMENT DDF RESULTS (PRELIMINARY) PLANNING | ENGINEERING | PROGRAM MANAGEMENT CONCLUSIONS • ANALYSIS CURRENTLY UNDERGOING PEER AND CITY REVIEW • DIFFERENT STATISTICAL METHODS FOR RAINFALL ESTIMATION CAN SHOW VARIED RESULTS • RAINFALL VALUES FROM THE 1998 USGS STUDY COULD BE UPDATED IN AREAS WHERE EXTREME EVENTS HAVE BEEN OBSERVED PLANNING | ENGINEERING | PROGRAM MANAGEMENT Q&A • Definition of Statistics: The science of producing unreliable facts from reliable figures. Evan Esar • Facts are stubborn, but statistics are more pliable. Mark Twain • Odds of this week’s satellite re-entry hurting someone in the world is estimated 1 in 3,200. Odds of any one person being struck is 1 in 21 Trillion. NASA, 9/21/11 Saul Nuccitelli, LAN, [email protected] PLANNING | ENGINEERING | PROGRAM MANAGEMENT