Flood Mitigation and Prevention

Transcription

1 PROPERTY OF THE UNITED STATES GOVERNMENT COPYING, DISSEMINATION, OR DISTRIBUTION OF THIS REPORT TO UNAUTHORIZED PERSONS IS PROHIBITED Do not remove this notice Properly destroy documents when no longer needed Flood Mitigation and Prevention Draft Study GSA INTERNAL REVENUE SERVICE DEPARTMENT OF JUSTICE DEPARTMENT OF COMMERCE OLD POST OFFICE ANNEX January 23, 2007 General Services Administration National Capital Region Washington, D.C. Setty & Associates, Ltd. S&A No PROPERTY OF THE UNITED STATES GOVERNMENT FOR OFFICIAL USE ONLY Do not remove this notice Properly destroy documents when no longer needed

2 SECURITY NOTICE PROPERTY OF THE UNITED STATES GOVERNMENT COPYING, DISSEMINATION, OR DISTRIBUTION OF THIS REPORT TO UNAUTHORIZED USERS IS PROHIBITED DO NOT REMOVE THIS NOTICE PROPERLY DESTROY DOCUMENTS WHEN NO LONGER NEED

3 Draft Study January 23, 2007 INTERNAL REVENUE SERVICE DEPARTMENT OF JUSTICE DEPARTMENT OF COMMERCE OLD POST OFFICE ANNEX GSA PROPERTY OF THE UNITED STATES GOVERNMENT FOR OFFICIAL USE ONLY Do not remove this notice Properly destroy documents when no longer needed

4 TABLE OF CONTENTS Page 1. Executive Summary Overview 1.2 Results and Findings 1.3 Recommendations 2. Introduction June 2006 The Flood Event Peak Rainfall 3.2 Peak Stage / High Water Marks 3.3 Historical Flooding Events 4. Causes and Extent of Flooding Constitution Avenue: Street Flooding Evaluation 4.2 Street Level 4.3 Internal Revenue Service Building 4.4 Department of Justice Building 4.5 Department of Commerce Building 4.6 Old Post Office Annex 5. D.C. Water and Sewer Authority WASA Organizational Structure 5.2 WASA System Overview 5.3 Combined Sewer Overflows (CSO) 5.4 June 2006 Event 5.5 Possible Scenarios to Rapid Rise and Fall of Flooding on Constitution Avenue 5.6 WASA Related Questions and Answers SETTY & ASSOCIATES, LTD. TOC-i

5 6. Government Communications Protocols Department of Homeland Security 6.2 Internal Revenue Service Building 6.3 Department of Justice Building 6.4 Department of Commerce Building 6.5 Old Post Office Annex 6.6 D.C. Water and Sewer Authority Communications 6.7 D.C. Emergency Management Agency 6.8 Protocol Recommendations 7. Flood Mitigation Alternatives Introduction 7.2 Site and Exterior Modifications 7.3 Internal Revenue Service Building 7.4 Department of Justice Building 7.5 Department of Commerce Building 7.6 Old Post Office Annex Appendices: (Separate report) Appendix A: WASA System, Existing Conditions and DC-EMA Maps Appendix B: Government Correspondence/Meeting Minutes Appendix C: Photographs Internal Revenue Service Building Appendix D: Photographs Department of Justice Building Appendix E: Photographs Department of Commerce Building Appendix F: Photographs Old Post Office Annex Appendix G: Flood Event Supporting Information SETTY & ASSOCIATES, LTD. TOC-ii

6 1. EXECUTIVE SUMMARY 1.1 Overview The approach and methodology of this study focused primarily on the scope of work and alternatives presented in GSA s Flood Damage Recovery Phase II directive. Principally, the charge was to determine what happened in June, 2006, and then to identify alternatives to mitigate risk of similar future flooding, and if the building envelope is penetrated again, how to avoid catastrophic building failure. The existing conditions and physical characteristics of each building in this study (Department of Justice (DOJ), Internal Revenue Service (IRS) Headquarters, Old Post Office (OPO) Annex, and the Department of Commerce (DOC) at Ariel Rios and its surroundings within the Federal Triangle were evaluated within the context of mitigating future flood damage. Mitigation alternatives focused the following elements: Enhancing protocols between the Federal Government and the District of Columbia Water and Sewer Authority (WASA) Creating physical barriers around the buildings to block floodwaters Relocating critical building systems to points above the flood level Providing a better means to physically extract flood waters infiltrating the buildings Utilizing a pumping station and storm drain upgrades to reduce flood depths on Constitution Avenue, NW Each of these measures may be considered in whole or in part, and each of them have varying degrees of physical impact to the use, occupancy, operations, and historic fabric of each building. The impact to the existing and possible future spatial configurations will require consultation and coordination with each building s facilities group. The integration of these measures should also be evaluated within the context of future building modernization plans (not presently within the scope of this work). In addition, there are significant cost implications associated with each measure considered. The restoration measures taken to date at the IRS and DOJ buildings have only brought the buildings back to pre-flood conditions. The Federal Triangle is located in Northwest Washington, DC, within the Pennsylvania Avenue National Historic District. The buildings included in this study are prominent and historically significant structures within the Historic District. As a result, any and all proposed measures to mitigate future flood damage which impact the site, surroundings, façades, and historic fabric will require coordination with GSA s Historic Preservation Officer, a Section 106 Review, and approvals by the Advisory Council on Historic Preservation, State Historic Preservation Office, National Capital Planning Commission, and the Commission of Fine Arts. Individual building measures will be reviewed within the context of the overall planning guidelines established by these agencies for the monumental corridor. In addition, these measures would also interface with the National Capital Urban Design and Security Plan. 1.2 Results and Findings The most intense 24-hour portion of the June 2006 storm event dropped 7.01 inches of rain. The historic rainfall data indicates at least three other 24-hour rainfall totals on record that were approximately 7 inches. By comparison to standard design storm events for engineering studies, a storm event in the DC area that is believed to have a recurrence interval of 50 years (a.k.a. the 50-Year Event) would result in approximately 7.04 inches of rainfall over a 24-hour period. By comparison, the DC WASA system for street drainage is reported to try and achieve a 15-year, SETTY & ASSOCIATES, LTD. PAGE 1

7 24-hour performance standard (approximately 5.5 inches of rainfall). It is important to note that the flooding began on Constitution Avenue at 10:30 p.m. after only approximately 2.25 inches of rain had fallen in a 3-hour period. If the rain had stopped at the time of the power failure, the 2.25 inches of rain would have been considered much less than the 15-year event that the WASA sewer system should be designed to handle. According to the NOAA Precipitation Frequency Data Chart in Figure 1-1, the June 2006 event came very close to a 3-hour rainfall for only a 5- year event. The preliminary results of the analysis seem to indicate that each building was capable of handling the storm water until such time that the infrastructure in the adjacent roadways failed to accommodate the flow of storm water and overflows started to occur. This failure resulted in an extreme and rapid rise in floodwaters on Constitution Avenue, resulting in the backup of storm water into the buildings and subsequent disruption of electrical service to support pumping causing additional rise in floodwaters and further failure of interior building systems. Estimates of water infiltration volumes suggest that the Internal Revenue Service Building flooded with approximately 6 million gallons and the Department of Justice Building flooded with approximately 3.5 million gallons. This is compared to an estimated 38 million gallons of storm water in Constitution Avenue at peak stage. According to information obtained through interviews, the main flooding of the Department of Justice Building occurred between 10:00 p.m. and 1:00 a.m. An IRS building security guard report stated that the power failed at 10:32 p.m. and power resumed at 10:42 p.m., when the emergency generator started. The lights began flickering at 10:45 p.m. and at approximately 10:55 p.m. the emergency generator was overwhelmed by the flooding and failed. Video surveillance tapes provided by the Department of Justice Building show that the water level on Constitution Avenue rose most substantially between 10:00 p.m. and 10:30 p.m. It is important to note that both the Department of Justice Building and the Internal Revenue Service Building flooded, but in very different manners. The Internal Revenue Service Building had water penetration at the perimeter moats along 10th Street, Constitution Avenue, and 12th Street. Excessive hydrostatic pressure built up and caused a number of window assemblies to fail. Alternately, the Department of Justice had a 15-inch storm water sewer main fail in the basement, causing severe flooding near an adjacent electrical room. Water did not penetrate the Department of Justice Building through the moats. Both buildings had secondary flooding through electrical service duct banks, abandoned duct banks, and miscellaneous pipe penetrations. When water started entering both buildings, the electrical rooms located on the lower levels, as well as emergency power equipment, were flooded and failed. After primary power and emergency power failure, the storm water pumps could no longer operate and the buildings quickly filled with water due to the street flooding and also from the building storm water system. The Department of Commerce Building had a lesser problem with floodwater. The primary entry point of water was the steam tunnel, adjacent to the building and connected by tunnel doors. The tunnel was flooded to a depth sufficient to break through the steam tunnel doors. This occurred on both the east and west side of the structure and allowed flooding in some areas to a depth of 3 feet above the basement floor. The flooding allowed the water to enter the sub-basement as well. SETTY & ASSOCIATES, LTD. PAGE 2

8 Flooding at the Old Post Office Annex (OPO) occurred through common walls between the IRS and the OPO which contain 25 windows behind drywall partitions. These windows did not have blast assemblies installed as part of the modernization project. The water level in the two buildings was at an identical elevation and it is believed that the two buildings may have contributed to each others flooding. It is known that the IRS moat (window well) windows on the upper part of 10th Street near Pennsylvania Avenue had window failure and water intrusion. The Annex is further north on 12th Street at a higher grade level and would not have had as much opportunity to flood except through the IRS wall immediately adjacent to the Annex Court. The Annex wall did not appear to be breached, although other areas may have leaked. If the floodwater had reached a level higher than 11.0 feet, even greater damage could have resulted at this common wall location. It should also be noted that the penetrations through this wall may pose security and fire integrity issues as well. Precipitation Frequency Estimates (inches) ARI* (years) min min min min min min hr hr hr hr hr day day day day day day day NOTE - Worst-Case Rainfalls in June 2006 was 3.73 (3hr), 5.91 (6hr), 7.01 (24hr), 9.41 (48hr) and (7 day) Source - WASHINGTON REAGAN AP, VIRGINIA ( ) N W 22 feet from "Precipitation-Frequency Atlas of the United States" NOAA Atlas 14, Volume 2, Version 3 G.M. Bonnin, D. Martin, B. Lin, T. Parzybok, M.Yekta, and D. Riley NOAA, National Weather Service, Silver Spring, Maryland, 2004, Extracted: Thu Sep Figure 1-1: NOAA Precipitation Frequency Data Server 1.3 Recommendations The recommendations for the IRS and Department of Justice buildings are numerous, starting with a single level and proceeding to a multi-level effort. Consideration will be given to the reliability of each proposed alternative, including consequences of a failure of the proposed method to adequately control floodwaters entering the buildings. Since the Department of Commerce Building and the Old Post Office Annex flooded in clearly defined ways, there are more defined alternatives available to prevent future water intrusion. The Internal Revenue Service and Department of Justice buildings by comparison have multiple alternatives which need consideration as viable to move forward. A feasibility study should be pursued to clearly assess the best available alternative. SETTY & ASSOCIATES, LTD. PAGE 3

9 MATRIX OF FLOOD MITIGATION ALTERNATIVES AREA DESCRIPTIONS LEVEL OF PROTECTION COMMENTS COST RANGE Protocols A. HIGH LEVEL DIRECT COMMUNICATION HIGH Direct communications between WASA, DCEMA, and GSA Minor Site and Exterior BETWEEN GOVERNMENT AGENCIES B. EMERGENCY ACTION PLAN FOR EACH BUILDING HIGH Minor A. UPGRADE WASA STORM WATER CAPACITY FOR A 50-YEAR WASA system designed for a 15-year event currently EVENT HIGH Large capital improvement costs TBD B. PUMPING STATION & CONVEYANCE SYSTEM MED Viable alternative requiring interagency cooperation $5 M - $10 M C. CATCH BASIN MAINTENANCE IMPROVEMENTS LOW Controlling litter may avoid system blockages $10 M D. SIDEWALK LEVEE SYSTEM HIGH Significant impact to surroundings $9 M - $15M IRS Building A. SEAL ABANDONED FEEDERS HIGH Recommended, easy to implement $20k - $50k B. WATER TIGHT FIRE PUMP ROOM HIGH Life safety equipment must remain operational $100k - $150k C. FLOOD GATES/REMOVABLE BARRIERS MED Minimizes water infiltration $200k - $500k D. GROUND WATER PUMPING STATIONS MED Extensive modifications to building infrastructure $1 M - $2 M E. RELOCATE EMERGENCY POWER EQUIPMENT HIGH Recommended $2 - $4 M F. IMPROVED STORM/BLAST WINDOWS MED Minimizes water infiltration $3 M - $5 M G. WINDOW WELL WATER-TIGHT COVERS MED Deployment difficulties $3 M - $5 M H. EARTHEN BERMS LOW Impractical $4M - $6M I. MOAT WALL EXTENSIONS MED Minimizes water infiltration $7 M - $10 M J. RELOCATE MAJOR MECHANICAL AND ELECTRICAL SYSTEMS HIGH Extensive modifications to building infrastructure $40 M - $50M DOJ Building A. STORM WATER PIPING MODIFICATIONS HIGH Recommended, easy to implement $25k B. SEAL UTILITY PENETRATIONS HIGH Recommended, easy to implement $20k - $50k C. ISOLATE ELECTRICAL ROOM HIGH Recommended, easy to implement $100k - $150k D. ISOLATE FIRE PUMP ROOM HIGH Life safety equipment must remain operational $100k - $150k E. FLOOD GATES MED Minimizes water infiltration $800k - $1.2M F. RELOCATE EMERGENCY POWER HIGH Recommended $1.5M - 2.5M G. RAISE RETAINING WALLS ON CONSTITUTION AV ENUE LOW Existing moats provided protection during event $2 M - $3 M H. RELOCATE MAJOR MECHANICAL AND ELECTRICAL HIGH Extensive modifications to building infrastructure $30M - $40M DOC Building A. STEAM TUNNEL ACCESS STUDY HIGH Recommended, easy to implement $100k - $200k B. NEW REINFORCED HEAD WALLS AND DOORS HIGH Recommended, easy to implement $250k - $500k OPO Annex B. WATERPROOF WALLS HIGH Recommended, easy to implement $200k - $400k A. INFILL WINDOWS AND WATERPROOF WALLS HIGH Recommended, easy to implement $300k - $500k Legend High = No interruption of building operations Med = Limited interruption of building operations Low = Major interruption of building operations SETTY & ASSOCIATES, LTD. PAGE 4

10 2. INTRODUCTION The Washington, DC Metropolitan Area received heavy rainfall during the period of June 25 to June 28, As a result, city streets were flooded, as well as two Metro stations and the 9th and 12th Street tunnel under the mall. Businesses were closed due to flooding and power outages. A 100-year-old American elm tree fell near the front door of the White House and the House of Representatives canceled votes scheduled for June 26 because some members could not fly into Washington, DC. A state of emergency was declared in the District of Columbia and officials have estimated the resulting storm damage in the tens of millions of dollars. The General Services Administration has contracted Setty & Associates, Ltd. to investigate the heavy rainfall that occurred in June 2006 for its impact on limited buildings in the Federal Triangle area. The focus of this study is limited to four prominent buildings, including the Department of Justice (DOJ), Internal Revenue Service (IRS) Headquarters, Old Post Office Annex (OPO), and the Department of Commerce (DOC) at Ariel Rios. The study area is bounded by Constitution Avenue, NW; Pennsylvania Avenue, NW; 13th Street, NW; and 9th Street, NW. The study includes a description of the June 2006 flood, analysis of flood severity in comparison to historical events, causes and extent of flooding within the study area, an investigation of emergency event protocols for various parties involved, and concepts for mitigating or reducing the likelihood of future flooding problems within the buildings included in the study. The study will not serve as a guideline to protect the entire Federal Triangle area from future flooding, but only as an investigation as to protecting the aforementioned buildings. Proposed modifications to the site, surroundings, façades, and interior historic fabric resulting from the recommendations contained in this report will require further research, design details, and close coordination with the GSA s Historic Preservation Officer, a Section 106 Reviews, and approvals by the State Historic Preservation Office, the National Capital Planning Commission, the Commission of Fine Arts, and the Advisory Council on Historic Preservation. The Scope of Work for this study is as follows: A. Review the operations of the District of Columbia s storm and sanitary sewer system, WASA, and its Blue Plains treatment plant to ascertain what, if any, relationship these have to the flooding conditions occurring in the foreseeable future. 1. Make any recommendations for appropriate communication protocols between GSA and the District in future events of comparable rainfall. 2. Review reports of rapid water reductions on the Constitution Avenue corridor at approximately 4:30 a.m., Monday, June 26, Review the current maximum capacity/throughput of WASA s Blue Plains treatment plant to handle combined stormwater and sanitary sewage and WASA s future plans. B. Provide study services including cost estimates for each building listed below: 1. IRS Building a. Investigate, document, and verify the modes and sequence of flooding. SETTY & ASSOCIATES, LTD. PAGE 5

11 b. Provide analysis and recommend actions the government can take to prevent similar flooding. Compile data including, but not limited to, photographs. Interview GSA building managers and agency personnel. Indicate priority of work. The A/E shall explore all alternatives including but not limited to: 1) Multi-stage ground water pumping systems with emergency power. 2) Berms / Barriers. 3) Window well watertight coverings. 4) Improved storm/blast windows. 5) Recommendations to move all the HVAC/electrical equipment to other areas utilizing the Flood Damage Report. c. All recommendations need to comply with relevant codes and governing authorities requirements; National Capital Planning Commission, Commission of Fine Arts, National Historic Preservation Guidelines, DC Department of Public Works Streetscape requirements, etc. d. Utilize information contained in the following reports: 1) Flood Damage Assessment Report for the IRS Building dated July 5, 2006, by Jacobs Facilities Inc. 2) Flood Damage Phasing Construction Assessments; draft dated August 2, Department of Justice Building a. Study the existing garage doors at basement level to act as floodgates in similar flood events. Provide recommendations to modify garage doors to behave as such. b. Study and make recommendations to make utility penetrations at the basement and foundation walls watertight, such as PEPCO electric feeders. c. Evaluate the feasibility of raising retaining walls on Constitution Avenue, raising equipment bases/footings and relocating HVAC and electric equipment from basement/sub-basement to the roof and other areas. 3. Department of Commerce Building a. Study and make recommendations to eliminate water infiltration at the doorways to the GSA steam tunnels in the basement. 4. Old Post Office Annex a. Study and provide recommendations to make the common wall between the IRS Building and the Annex watertight. SETTY & ASSOCIATES, LTD. PAGE 6

12 3. JUNE 2006 THE FLOOD EVENT 3.1 Peak Rainfall The month of June 2006 was the 5th wettest ever recorded in Washington, DC, at inches of rainfall and the wettest since August The worst case 24-hour rainfall depth was measured starting on June 25, 12:00 p.m. at 7.01 inches, which is officially second only to the 7.19 inches recorded when remnants of Hurricane Agnes passed through the region in June The worst case 2-day rainfall total accumulated to 9.41 inches by midnight on June 26 and the resulting weekly rainfall total was inches. The table below shows the worst case hourly rainfall totals including the 3-hour total (3.73 inches) and the 6-hour total (5.91 inches) for June Figure 3-1: Hourly Rainfall for the Worst Case 24-Hour Period, June 25 June 26, 2006 Chief meteorologist, Jim Lee, from the National Weather Service in Sterling, Virginia, stated that the cause of the heavy rainfall was a tropical connection that funneled an extremely wet air mass up the East Coast. The moist air was up against a stationary front that had hung over the Mid-Atlantic region for that past week. The following figure outlines some of the problems caused by the heavy rain in the District of Columbia Metropolitan Area. SETTY & ASSOCIATES, LTD. PAGE 7

13 Figure 3-2: Chaos created in the DC Metropolitan Area by the June 2006 Inundation 3.2 Peak Stage / High Water Marks Peak stage for the June 2006 event was not as historically significant as the extreme rainfall that is noted above in this study. The U.S. Army Corps of Engineers has indicated that the Potomac River peak stage was measured at 9.5 feet at the Little Falls Gauging Station in their letter to the U.S. Attorney General dated July 14, 2006, included in Appendix B. This peak stage is a little higher than the peak stage indicated on the United States Geological Service (USGS) website of 7.94 feet (76,800 cubic feet per second) on June 29, Either 9.5 feet or 7.94 feet is a low peak stage when compared to historical records for the Little Falls Stream Gauge (USGS ) as shown in Figure 3-3. The March 19, 1936, event was the worst at Little Falls, with a peak stage of (484,000 cubic feet per second). The June 2006 event, from a peak stage standpoint, would be among the smallest of the 76 storm events since 1931 that are listed in Figure 3-3. It also should be noted that the Potomac River was not at flood stage until June 29, 2006, which was three days after the heaviest rainfall occurred. In summary, it appears that the river peak stage had little to do with the flooding that occurred in the Federal Triangle in June SETTY & ASSOCIATES, LTD. PAGE 8

14 Both peak stages reported for June 2006 were also well below the Federal Emergency Management Agency (FEMA) regulatory flood stages in the Potomac and Anacostia Rivers near downtown Washington, DC. FEMA maintains detailed mapping (AE designation) for the 100-Year Event in these major rivers, and nearest the tidal basin the regulatory floodplain elevation for the Potomac River is approximately 13.2 feet. The regulatory floodplain elevation is approximately 11.0 feet nearest the District of Columbia WASA main pumping station on the Anacostia River. POTOMAC RIVER NEAR WASH, DC - USGS PEAK STREAMFLOW DATA Date Flow, cfs Stage, ft Date Flow, cfs Stage, ft April 3, , March 27, , May 14, , April 3, , April 22, , February 24, , March 15, , June 24, , (Hurricane Agnes) December 2, , October 8, , March 19, , December 28, , April 28, , September 27, , October 30, , January 3, , February 5, , October 11, , April 22, , March 16, , April 7, , February 26, , May 24, , October 12, , October 17, , April 15, , May 9, , June 15, , September 20, , April 26, , June 4, , February 16, , March 17, , February 14, , April 16, , November 7, , June 20, , April 19, , February 3, , May 20, , December 6, , May 18, , April 29, , May 31, , November 23, , October 25, , March 3, , April 24, , August 20, , March 6, , July 21, , March 30, , April 7, , January 17, , May 7, , January 21, , June 4, , December 3, , May 10, , March 22, , February 21, , March 20, , March 23, , February 21, , March 21, , March 23, , March 6, , April 24, , March 7, , September 21, , (Hurricane Isabel) February 15, , December 12, , March 9, , March 30, , March 18, , June 29, , Maximum Flow = Peak Stage = 484,000 cfs ft Figure 3-3: USGS Stream Gauge Data at Little Falls SETTY & ASSOCIATES, LTD. PAGE 9

15 This study included data collection in the field, but there were no apparent June 2006 high water marks (i.e., stains, debris, etc.) visible. Reports varied as to the depth of the flooding since it occurred in the middle of the night, however, the videotape seemed to indicate floodwaters near the top of the concrete planters along Constitution Avenue, which is approximately an elevation of 11.0 feet (3-foot depth of flooding on sidewalks). The high watermark at the intersection of Constitution Avenue and 15th Street NW was also considered. This watermark is believed to indicate a worst case flooding near the Federal Triangle of approximately 38 inches above the sidewalk elevation (11.2 feet) on February 12, The actual flood depth and condition on Constitution Avenue was obtained from the watermark as shown in Photo Historical Flooding Events There are many historic storm events resulting from either a peak stage in the Potomac River or flooding in city streets due to excessive local rainfall. Some of these are described below for further comparison to the June 2006 event. Photo 3-1: 1881 High Water Mark on Constitution Avenue The old pump house at the intersection of Constitution Avenue and 15th Street NW is marked 38 inches above the sidewalk elevation (approximately 8.0 feet) and is labeled February 12, History documents that during the flood of 1881, raw sewage, which had inundated the swamp at Potomac Flats, mixed with the floodwaters and reached to within three blocks of the White House in this area. The 1881 flood prompted Congress to fund the dredging of Potomac Flats, creating what is now known as Potomac Park. On June 2, 1889, a 2-day rainfall of 4.4 inches caused a peak stage in the Potomac River of 19.5 feet, which is a crest elevation 12.5 feet above flood stage. This is still the unofficial record and the photograph below shows where flooding along Pennsylvania Avenue between 9th and 10th Streets was between 1 and 4 feet in depth. Photo 3-2: Pennsylvania Avenue in the June 1889 Flood (Library of Congress) SETTY & ASSOCIATES, LTD. PAGE 10

16 On August 12, 1928, a 1-day rainfall record totaling 7.31 inches occurred from a hurricane passing just to the southeast. On October 17, 1942, floodwaters reached to the steps of the Jefferson Memorial after a 5-day rainfall total of 6.27 inches. Heavier rainfall of 10 to 15 inches fell to the west of the District of Columbia, causing the Potomac River to crest at 17.7 feet which is still the official peak stage record for Washington, DC. Photo 3-3: 1942 Floodwaters around the Jefferson Memorial (NOAA Library) Hurricane Camille passed nearest the District of Columbia area in August 20, 1969, however the worst flooding occurred just prior to the hurricane on July 22, This peak rainfall event dropped 3.29 inches of rainfall in one hour (4.38 inches total rainfall), causing localized flash flooding throughout the District of Columbia. The June 2006 event is reported in this study to have dropped 3.16 inches in approximately one hour, which is very similar over a short duration of time. Photo 3-4: Search & Rescue during the 1969 Flash Flood (Washington Post) SETTY & ASSOCIATES, LTD. PAGE 11

17 The remnants of Hurricane Agnes passed through three years later on June 21, 1972, when Agnes dropped a total of 7.19 inches in a 24-hour period. On November 27, 1993, flash flooding occurred when 6 inches of nearly continuous rainfall fell across the city in a 12-hour period. Floods from January 20 to 23, 1996, were a result of a combination of up to 2 inches of snowmelt and up to 3 inches of rain. The river crested at feet near Wisconsin Avenue. At Great Falls, 15 miles upstream, the Potomac River raised a reported 8.5 feet in 48 hours. Photos 3-5 & 3-6: Rapid Rise of Floodwaters in January 1996 at Great Falls (National Park Service) More recently, the eye of Hurricane Floyd passed just southeast of the District of Columbia late in the evening on September 16, Up to 6 inches of rain fell across the District of Columbia, with 4.57 inches measured at Reagan National Airport. Two years later, flash flooding on August 11, 2001, dropped an estimated 7 inches of rain in one day in Northwest DC, but only 2 inches in Southeast DC. The 2001 cloudburst caused a reported $6 million in damage to 50 governmental buildings and more than 3,000 homes in the Metropolitan Area as storm drain systems were overwhelmed. In some parts of the District of Columbia, between 5 and 7 inches of rain fell in less than three hours, following heavy rainfall from the preceding day. On September 23, 2003, heavy rain fell on ground previously saturated by Hurricane Isabel, which had struck a few days before on September 18, Numerous roads began flooding during rush hour, including Constitution Avenue, and rainfall totals were approximately 3 inches for the event. The June 2006 event has similarities to many of these historic events and will be considered in future years as another flash flooding event resulting from heavy rainfall in short durations. The resulting flooding and overwhelmed storm drainage systems can be expected to continue in the Federal Triangle area in the future. Photo 3-7: Street Flooding during a Flash Flood August 2001 (WJLA) SETTY & ASSOCIATES, LTD. PAGE 12

18 4. CAUSES AND EXTENT OF FLOODING 4.1 Constitution Avenue: Street Flooding Evaluation In evaluating the design event necessary to protect GSA buildings in the Federal Triangle, the maximum rainfall, peak stage in the Potomac River, street topography, and the storm and combined sewer systems in Washington, DC, must be considered. Using this information, the following conclusions were reached as the basis of the flood mitigation alternatives study. Maximum Rainfall The National Atmospheric and Oceanic Administration (NOAA) National Weather Service (NWS) Precipitation Frequency Data Server was utilized in comparing the June 2006 rainfall totals with reported design rainfall events. This data represents the latest statistical analysis of rainfall at the Reagan National Airport, last updated in September Highlighted in red are rainfall depths that most closely resemble the measured June 2006 rainfall over 3-hour, 6-hour, 24-hour, 48-hour, and 7-day lengths of time. Highlighted in yellow is the range of recurrence intervals associated with the June 2006 event, which was determined in this study to fall between a 50-Year and 200-Year Event depending on the duration of time evaluated. In comparison, the DC WASA system for street drainage is reported to achieve an estimated 15-Year, 24-Hour performance standard (approximately 5.5 inches of rainfall). For the purposes of this study, alternatives for the June 2006 actual event are described instead of applying design events reported in the table below. This is because the June 2006 event falls within the range of design events that are considered reasonable and appropriate to evaluating flood protection alternatives in the Federal Triangle area. Precipitation Frequency Estimates (inches) ARI* (years) min min min min min min hr hr hr hr hr day day day day day day day NOTE - Worst-Case Rainfalls in June 2006 was 3.73 (3hr), 5.91 (6hr), 7.01 (24hr), 9.41 (48hr) and (7 day) Source - WASHINGTON REAGAN AP, VIRGINIA ( ) N W 22 feet from "Precipitation-Frequency Atlas of the United States" NOAA Atlas 14, Volume 2, Version 3 G.M. Bonnin, D. Martin, B. Lin, T. Parzybok, M.Yekta, and D. Riley NOAA, National Weather Service, Silver Spring, Maryland, 2004, Extracted: Thu Sep Figure 4-1: NOAA Precipitation Frequency Data Server SETTY & ASSOCIATES, LTD. PAGE 13

19 Peak Stage For the purposes of this study, the estimated high water mark of 11.2 feet from February 12, 1881, is used since it is very similar to the 11.0 feet indicated in the videotapes for June Other historic events indicate that a flood stage of 11.0 feet has occurred along Pennsylvania Avenue and Constitution Avenue on other occasions. The use of 11.2 feet provides a baseline in this study for the June 2006 event instead of applying design peak stages in the Potomac River (such as the FEMA 100-Year Flood Stage of 13.2 feet). The use of a lower flood stage for this study is reasonable because: High water events in the Potomac River typically provide a few days of lead time and the Corps of Engineers will continue to use sandbags to protect against inflows through Potomac Park in this area; and The Corps of Engineers has plans described in the letter they provided to develop a more permanent flood protection system in Potomac Park to protect against high flood stages in the Potomac River of 13.2 feet. This approach to using the 11.2 foot flood stage is considered reasonable and appropriate to evaluating flood protection alternatives in the Federal Triangle area. Peak Volume / City Topography City topographic mapping of Washington, DC, at 1-foot contour intervals was also used for the study. The mapping shows a low section of Constitution Avenue in front of the IRS and DOJ buildings at elevation 8.0 feet street centerline. This creates a bowl in the city street system which will fill up with water during a flood event, unless the underlying storm drain and combined sewer systems have enough capacity to keep up with the rainfall. Other low lying areas indicated on the topographic mapping reviewed include the Tidal Basin (Potomac Park) and 3rd Street in front of the U.S Capital. It appears from the topographic mapping that storm water can break out from Constitution Avenue onto 3rd Street at an approximate elevation of 12.0 feet and onto 17th Street NW at an approximate elevation of 14.0 feet. City topographic mapping was also used to determine the total water accumulation volume on Constitution Avenue. For the worst case flooding which occurred in February 1881 and appears to have in some ways reoccurred in the June 2006 event, both accumulated approximately 38 million gallons of water in the streets (at elevation 11.0 feet) as shown in Photos 4-1 and 4-2. TABLE 4-1: WATER ACCUMULATION ON CONSTITUTION AVENUE Elev. Area Water Accumulation Water Accumulation System (ft) (sq.ft.) (cubic feet) (gallons) Notes bottom street gutter elevation 8 110,800 27, ,196 street centerline elevation 9 1,446, ,408 6,031,932 flooding <18" deep in streets 10 2,135,092 2,597,262 19,427,520 building flooding begins 11 2,871,866 5,100,741 38,153,543 approx. peak stage for June 2006 SETTY & ASSOCIATES, LTD. PAGE 14

20 4.2 Street Level Photos 4-1 & 4-2: Street Flooding at Federal Triangle, June 26, Internal Revenue Service Building The IRS Building is located between Pennsylvania Avenue and Constitution Avenue, and 10th and 12th Streets and is listed in the National Register of Historic Places as part of the Pennsylvania Avenue National Historic Site. The site slopes from a high point of El /- at Pennsylvania Avenue and 12th Street and of El /- at Pennsylvania Avenue and 10th Street to a low point of El.8.0 +/- at Constitution Avenue. The existing first floor is at El.11.63, the basement is at El.(-)1.37 and the sub-basement is El.(-) The building consists of four quadrants and Courtyards A through D, and the Old Post Office Annex. The service entrance, loading dock, and parking garage ramp are located in Courtyard A and are accessible from 12th Street. Courtyards B, C and D are interior. The childcare playground is located in Courtyard C. The annex and quadrant C adjoin the Old Post Office Pavilion. Moats are located around the perimeter of the building as well as the interior courts. The primary cause of flooding at the IRS Building resulted from water infiltration at the building perimeter moats along 10th Street, Constitution Avenue and 12th Street. The total amount of water accumulation attributable to rainfall on the building and site represented only 8 percent of the total water volume that flooded the structure, clearly indicating that flooding from the exterior was the major contribution to the problem. (Refer to Table 4-2 for total water accumulations in the basement and sub-basement of the IRS Building and Table 4-3 for a tabulation of all water that fell on the roof of the building from the point when flooding began). Storm water overflowed the moat gratings approximately 1-foot above grade level, overwhelmed the drainage system, and filled the moats. Excessive hydrostatic pressure was placed on the original double hung steel frame windows and the recently installed operable interior blast window assemblies. A number of the window assemblies failed under the excessive pressure, allowing water to flow into the basement and sub-basement levels. The existing steel frame windows were not air/water tight and the blast window systems were not designed to be waterproof assemblies. The windows were designed only to mitigate flying glass shards following an explosive event. The damage assessment of these windows indicates that the laminated cases absorbed the hydrostatic load placed on them, the glass fractured within the frame, and the load was transferred to the frame with the resultant deformation of the assembly. This level of damage is consistent with the performance criteria for GSA s Level C criteria, however, the deformation and damage of the assembly obviously allowed for the infiltration of SETTY & ASSOCIATES, LTD. PAGE 15

21 water. Figure 4-3 designates the locations of the window wells where water entered the building, with the darker blue arrows indicating heavier water infiltration. As documented in the July 2006 Flood Damage Assessment Report, prepared by Jacobs Facilities Inc., the majority of the window damage was observed along the 10th Street perimeter, some damage was observed along Constitution Avenue, and no damage was observed at the southwest façade at 12th Street. Figure 4-2 illustrates how the water infiltrated through the window wells of the IRS Building. Figure 4-2: Final Water Levels in the IRS Building SETTY & ASSOCIATES, LTD. PAGE 16

22 Figure 4-3: Points of Water Infiltration into the IRS Building SETTY & ASSOCIATES, LTD. PAGE 17

23 The conditions at the interior courtyard moats were quite different than the exterior moats. No window damage or significant water infiltration was observed at the interior locations. This supports the conclusion that the building storm water drainage system and specifically the moat drains were handling the rainfall until such time that the power and pumps failed. Two conditions in service Courtyard A present points of potential water infiltration into the building during an extreme flooding event. The first condition is the parking garage ramp to the basement and the second condition is the entrance at stairwell No The high point of the ramp is at El.9.13 and the low point at basement El.(-)1.37. The entrance at stairwell No is at mid-landing and El.9.8 +/-. Water infiltration at the exterior doors at this point would flow down the stairwell and flood the basement level and potentially the sub-basement. A secondary contribution to flooding originated from water infiltration at an electrical service duct bank along 12th Street. The duct bank was abandoned and the concrete plugs on the interior of the building appeared to have failed. Evidence at adjacent buildings suggests that the PEPCO street vaults were flooded and resulted in water infiltration through the duct banks. The total water accumulation within the IRS Building as a result of the flooding was an estimated 6.1 million gallons, indicated by Table 4-2. The sub-basement level was completely inundated under 13 feet of water and the basement was flooded to an average depth of 4 to 5 feet (see Figure 4-4). TABLE 4-2 Amount of Water accumulated in IRS building Area (sq ft) Water Depth (ft) Water Accumulation (cu. ft.) Water Accumulation (GAL) SUB BASEMENT 7, , ,657 BASEMENT 181, ,308 5,440,264 Total 6,149,921 SETTY & ASSOCIATES, LTD. PAGE 18

24 Figure 4-4: Flood Level in Basement and Sub-basement of IRS Building For comparison, Table 4-3 shows the total amount rainfall that fell on the projected roof and courtyard area of the building between the hours of approximately 10:30 p.m. and 6:00 a.m. on June 26. Calculations show that the roof and courtyard areas, which feed into the storm drainage system, accumulated only 492 thousand gallons of water. This represents only about 8 percent of the more than 6 million gallons which flooded the basement and sub-basement areas. TABLE 4-3 Actual rainfall on IRS building projected area (Roof and Courts) Area (sq ft) Water Depth (in) Water Accumulation (ft^3) Water Accumulation (GAL) Court A 11, ,910 29,246 Court B 11, ,910 29,246 Court C 11, ,910 29,246 Court D 11, ,910 29,246 Roof 147, , ,367 Total Projected Area 194,071 Total 492,352 SETTY & ASSOCIATES, LTD. PAGE 19

25 4.4 Department of Justice Building The Department of Justice Building is located between Pennsylvania Avenue, Constitution Avenue, 9th and 10th Streets. The Building is listed in the National Register of Historic Places as part of the Pennsylvania Avenue National Historic Site. The site slopes from a high point of El /- at Pennsylvania Avenue and 10th Street and of El /- at Pennsylvania and 9th Street to a low point of El.8.0 +/- at Constitution Avenue. The existing first floor is at El.12.0, the basement is at El.(-)1.0 and the sub-basement is El.(-)15.5. The building consists of four quadrants and courtyards A through E. The service entrance and parking garage ramps are located in Courtyard A and are accessible from both 9th and 10th Streets. The Attorney General s entrance ramp is located under Courtyard E off of 10th Street and the Solicitor General s entrance ramp is located under Courtyard D off of 9th Street. The moats and basement windows along each of the building s façades are protected by 42-inch high walls from the sidewalk level. Figure 4-5: Final Water Levels in the Department of Justice Building Based on interviews and surveys, it appears as though the DOJ building pumps were initially able to handle the storm run-off into the building. Eyewitness accounts put the water level of Constitution Avenue at approximately 36 inches high at its deepest. This height reached near the top of the planters shown in the photo below. However, the water never entered the front doors and it did not overtop the moat walls (see Photo 4-4 on next page). No water accumulated in the moats and the moat drainage system operated as designed. There was a large amount of debris in the moats and the drains appeared to be clogged, but they did not flood. SETTY & ASSOCIATES, LTD. PAGE 20

26 Photo 4-3: High Water Mark - Planters Photo 4-4: High Water Mark Moat Wall The buildup of water on Constitution Avenue was eventually compounded by the water cascading down 9th and 10th Streets. At approximately 10:30 p.m., the water pressure in the main storm discharge line built up, causing the service weight gasket to blow on the main U tube fitting on the line (see Photo 4-5 and Figure 4-6). This fitting is not designed to take larger pressures and it is likely that 5-10 psi of pressure would have dislodged this seal. The seal is designed to relieve the pressure in the pipe so that water does not back up the pipe and flood other floor drains. Photo 4-5: Storm Water Main which Failed Photo 4-6: Flooded Switchgear Room Once the pipe had been compromised, the room flooded quickly. Adjacent to this room through an open passageway is the electrical switchgear room. The water quickly entered both spaces and shorted out the electricity. The water level reached 51 inches in the electrical room (see Photo 4-6). The damage was not as severe due to the fact that the equipment was already on a 36-inch platform, which afforded some protection. When the power shorted out, the pumps stopped working initially until the emergency power started. However, the emergency power is supplied by generators which are all located on the basement level. These generators were soon overwhelmed by the floodwaters and ceased operation. Reports stated that the emergency power ran the four sets of building sump pumps for approximately 15 minutes before the generators were inundated and became inoperable. After emergency power was lost, the rain continued for almost three hours with no means of pumping the water out of the building. At this point, water was entering in the building from the Attorney General s and Solicitor General s ramps, overwhelming the trench drains. SETTY & ASSOCIATES, LTD. PAGE 21

27 Figure 4-6: Primary Means of Basement Flooding, Department of Justice Building A secondary cause of flooding resulted from water infiltration at an Attorney General s Ramp at 10th Street and the Solicitor General s Ramp at 9th Street (see photos 4-7 and 4-8). Additional water flowed into the parking level from the ramps at Courtyard A, overwhelming the trench drains at the base of the ramps (see photos 4-9 and 4-10 on next page). It was also noted that the existing gratings do not span the entire width of the ramps and heavy rainfall tends to flow to the side curbs, overshooting the gratings. Photo 4-7: Attorney General s Ramp - Flooded Photo 4-8: Ramp Doors - Exterior SETTY & ASSOCIATES, LTD. PAGE 22

28 Photo 4-9: Flooded Courtyard and Tunnel Photo 4-10: Garage Trench Drains Water was also entering the basement through the PEPCO feeders in the electrical room, which was also the case at the IRS Building (see photo 4-11). As the water level rose on Constitution Avenue, this duct bank started to channel the water into the electrical room. The rate of water entry is not known but eyewitness accounts said that water was flowing through the duct bank. Photo 4-11: PEPCO Feeders Photo 4-12: IRS Moats and PEPCO Feeders Water entered the sub-basement mainly through a trap door which is used for moving equipment in and out of the sub-basement. The trap door is located in the loading dock, where the water reached nearly 30 inches in depth at its peak (see photos 4-13 and 4-14). Photo 4-13: Flooded Subbasement Photo 4-14: Sub-basement Trap Door Access SETTY & ASSOCIATES, LTD. PAGE 23