Dam Risk Reduction Case Study. Background Nashville and Davidson County, Tennessee, the population hub of Middle

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1 Dam Risk Reduction Case Study [NASHVILLE, TENNESSEE MAY 2010 FLOODING] Background Nashville and Davidson County, Tennessee, the population hub of Middle Tennessee with a combined population of over 635,000, was hit by destructive floods in early May 2010 in the aftermath of a major precipitation event in the region. Record rains fell across the Cumberland River basin, which stretches across north-central Tennessee to its headwaters in southeastern Kentucky. The Cumberland is 688 miles long with a basin area of over 18,000 square miles, Nashville lying roughly in the middle of the watershed. A rainfall event of the magnitude the area experienced occurs only every 5,000 to 8,000 years, and the resulting flood runoff volumes nearly overwhelmed the system of eight major flood-control/hydroelectric dams and reservoirs on the Cumberland and its main tributaries, including the Harpeth, Red, Stones, Caney Fork, and Obey rivers. Careful, compensatory emergency dam releases lowered dangerous flood levels in these reservoirs but at the inevitable expense of Nashville- Davidson, districts of which were inundated soon after the rains and releases and remained so for weeks after. The severity of flooding at this epicenter and elsewhere prompted federal disaster declarations in dozens of counties in Tennessee and Kentucky, followed by a lengthy recovery process. Chronology Some 13.5" of rain fell in approximately a 48-hour period from Friday, April 30 to Sunday, May 2, 2010 in Nashville-Davidson and the surrounding region, forcing the U.S. Army Corps of Engineers Nashville District into emergency flood-control operations of the dams in the Cumberland basin to ensure their security and minimize flooding downstream. On the Cumberland River, these massive public works projects include (all Tennessee except where noted): Wolf Creek Dam (Lake Cumberland) at Jamestown, Kentucky; Cordell Hull Dam (Cordell Hull Reservoir) at Carthage; Old Hickory Dam (Old Hickory Lake) at Hendersonville; Cheatham Dam (Cheatham Lake) at Ashland City, downstream of Nashville; and Barkley Dam (Lake Barkley), near the river s mouth at Grand Rivers, Kentucky. Other works involved include Dale Hollow Dam (Dale Hollow Lake) on the Obey River at Celina; Center Hill Dam (Center Hill Lake) on Caney Fork at Lancaster; and J. Percy Priest Dam (J. Percy Priest Reservoir) on the Stones River at Nashville. The three dams nearest to Nashville reached record elevations in the days after the rainfall subsided: Old Hickory at 451.4, J. Percy Priest at , and Cheatham at With some degree of flooding at Nashville inevitable, the COE reverted to a damage control strategy of coordinating floodwater releases between the dams upstream. Dam hydropower units were shut off to manage outflows and allow time for flood runoffs and river levels to subside; then, limited hydropower production and releases would resume to draw reservoirs down to safe target elevations. Spillways or sluice gates would also be operated on dams with them; for example, Cheatham Dam below Nashville remained in free-flow with all gates removed from its spillway throughout the week after the rains. Version January 31, 2012 The Association of State Floodplain Managers

2 In lower-lying areas of Nashville and Davidson County abutting the Cumberland, the river overtopped its banks as early as Sunday, May 2. The river reached its crest at Nashville the following day at 51.9', some 12 feet above flood stage. The downtown commercial district and Bordeaux, Bellevue, and Antioch neighborhoods were among the hardest-hit. Besides damages to private residences and businesses, floodwaters overwhelmed city infrastructure including Nashville Metro's antiquated sewer/storm water system, and prompted the closing of at least one of the city's water treatment plants. City authorities ordered the closure of 48 roads around the city and ordered residents to stay home and off the streets. On Tuesday, May 4, Tennessee governor Phil Bredesen officially requested of FEMA disaster declarations for 52 Tennessee counties. President Obama initially declared disasters in Nashville- Davidson, Cheatham, Hickman, and Williamson counties. Major highways across Middle Tennessee, many inundated and damaged, were closed. Deaths from the flooding, statewide, reached 20, including nine in Nashville. President Obama declared disasters in 13 more counties by Thursday, May 6, bringing the total to 21, while FEMA reported 8,500 flood victims had already applied for federal assistance. The same day, the Cumberland dropped below flood stage, to 39.54', earlier than expected. Nearly all flooded residential, commercial and industrial properties (parcels) were surveyed by Monday, May 10, with damages officially assessed at over $1.5 billion; Nashville Metro schools valued its flood damages at $1.6 million. These numbers were thought to be extremely conservative by many of those affected. FEMA declared disasters in dozens of Kentucky counties on May 11. On Friday, May 14, FEMA approved over $80 million in relief aid for Tennessee flood victims. Almost 29,000 Tennessee households (each eligible for up to $29,900) had registered for aid to date, almost 14,000 of those in Nashville-Davidson County alone, while over 16,000 FEMA home and property inspections had been completed statewide. Aftermath The flooding in Nashville-Davidson, the Cumberland basin, and elsewhere in Tennessee and Kentucky resulting from the historic storm event created a prolonged disaster from which it took months to recover. FEMA disaster declarations in Tennessee remained in effect until Tuesday, May 18, 2010, and in Kentucky until June 1. In total, 49 of 95 Tennessee counties were declared federal disaster areas 46 of which were eligible for individual and public assistance and three for public assistance only. In Kentucky, 83 of 120 counties received the federal disaster designation including 55 eligible for individual and public assistance, 21 public assistance only, and seven individual assistance only estimates placed the number of Davidson County homes not covered by flood insurance at nearly 4,000, with about 9,100 homes in Davidson and surrounding counties carrying insurance less than approximately 1.5% of all homes in the region. Ultimately, nearly 68,000 Tennessee residents applied for federal assistance. FEMA provided almost $250 million in response and recovery programs in Tennessee for disaster survivors and communities in disaster counties, including $166 million to individuals for housing and disaster-related losses and $55 million through the FEMA Public Assistance Program to state and local governments. About 7,300 residents registered for FEMA assistance in Kentucky, which state received some $30 million in relief, including $16.8 million in housing assistance and $2.9 million for other expenses or losses not covered by insurance. Together, Tennessee and Kentucky homeowners, renters, and businesses became eligible for about $190 million in lowinterest disaster assistance loans from the U.S. Small Business Administration. Sources: Why does the Nashville area flood? by Hargrove, Brantley. May 9, The [Nashville]City Paper. Photo is from this article. Assorted The City Paper Flood 2010 articles from May 3-14, Fema.gov disaster pages for Tennessee (mod. 8/24/11) and Kentucky (mod. 10/12/10).

3 Dam Risk Reduction Case Study [MINOT, NORTH DAKOTA JUNE 2011 FLOODING] Background The city of Minot, North Dakota experienced major extended flooding beginning in late June 2011 due to massive emergency dam releases upstream on the Souris (Mouse) River. A product of a large snowmelt and heavy rains near the head of the 435 mile long Souris across the border in Saskatchewan, the releases and consequent flooding caused unprecedented damage in Minot. Lying just 15 miles southeast downstream of the Lake Darling flood control reservoir (built in 1935), this city of nearly 41,000 and small nearby communities in predominantly rural Ward County (population 61,675) bore the brunt of the floodwaters and became the focus of one of the final episodes of an unusually severe flood season in the Missouri and Mississippi watersheds in Chronology Sudden, torrential rainfall across the Canadian border coupled with large scale reservoir releases in the upper Souris (Mouse) watershed there created the critical situation downstream near Minot in the third week of June The Souris basin in the vicinity of Rafferty Dam in Saskatchewan received four to seven inches of rain Sunday, June 20 into Monday, June 21. With little or no advance notice to the U.S. Army Corps of Engineers, the Saskatchewan Watershed Authority sent excess flows of about 24,000 cfs downstream, that is, flood heights surpassing the previous record by approximately two feet. This large pulse of water proved to be about three times more than Lake Darling could hold back, and the Corps of Engineers forecast a record breaking crest that could last two weeks. On Monday, June 20 the Corps of Engineers ordered initial releases of 7,500 cfs to prevent overtopping of the Lake Darling Dam. A Souris River gage reading as of 4 pm on the 20th put the river level at ' (above sea level), with a projected crest of ' by June 26 or 27 higher than both the 1969 flood (1555.4') and 1881 flood (1558'). Under its mayor's orders the City of Minot abandoned efforts to raise levees to handle 12,000 cfs flows as they could not be raised in time and overtopping was deemed inevitable. The city reverted to a defensive mode of building secondary levees to protect critical infrastructure including the water plant and schools, while sandbagging and the raising of dikes up and downriver at Burlington, Sawyer, and Velva continued. Version January 24, 2012 The Association of State Floodplain Managers

4 On Tuesday, June 21, FEMA announced the need to increase releases from Lake Darling Dam from 9,000 cfs to 16,000 17,000 cfs by June 22, with the corresponding high flows to reach Minot by June 23. FEMA also ordered a mandatory evacuation for all Minot residents in original evacuation zones 1 through 9 by 10:00 pm on Wednesday, June 22 about 10,000 total, plus others in outerlying areas near the river. By the 22nd, dam releases were at 9,700 cfs, and evacuations were well underway. On Thursday, June 23, the Corps was releasing 22,000 cfs from Lake Darling Dam (previous record being 5,000 cfs) with plans to increase to 28,000 cfs by Friday night. A new crest of 1566' was predicted for the Souris, eight feet higher than the existing record. The river finally crested at early on Sunday, June 26, with flows culminating at 26,000 cfs. Inundation in Minot and Ward County continued for several weeks as waters slowly receded, officials began to survey damage, and uprooted residents eventually returned and gained access to their homes and businesses. Aftermath The record crest of the Souris River at Minot produced the worst flooding in the city s history. According to the North Dakota State Water Commission, the river flooded 4,115 homes in Ward County (and 4,800 total structures), temporarily or permanently displacing nearly 12,000 residents. In addition to unquantified damages to homes and businesses, the City of Minot sustained over $100 million in damages to public infrastructure. In terms of areal extent, floodwaters inundated approximately 11,456 acres in Ward County under depths ranging from two to 15 feet, and spanned some 30 miles across the Souris (Mouse) River valley on either side of Minot. Sources: [both from NCRenegade.com] "Lake Darling Dam Swamps Minot, ND" by DeGerolamo, David. June 22, "Minot Flooding Update June 23" by DeGerolamo, David. June 23, Minot Recovery Information: The City of Minot s Official Public Information Website.

5 Dam Risk Reduction Case Study [PACIFIC, WASHINGTON JANUARY 2009 FLOODING] Background The city of Pacific, Washington, a community of over 6,600 (2010) in the greater Tacoma metro area, experienced severe flooding in January 2009 as a result of emergency dam releases upstream. Straddling the borders of King County and Pierce County, this small suburban community adjoins Auburn, Algona, and Sumner and is situated on the White (Stuck) River in the lower Puyallup River floodplain. The White River originates in the Emmons and Fryingpan glaciers on the side of Mount Rainier and flows 68 miles roughly northwest to its confluence with the Puyallup near Sumner, draining a total of 494 square miles. The fast flowing, glacially sourced White, after decades of improvised floodcontrol engineering, was finally impounded with federal completion in 1948 of the Mud Mountain Dam southeast of Enumclaw, about 10 miles upriver of Pacific. The highest rock and earth filled dam in the world, Mud Mountain is operated by the U.S. Army Corps of Engineers to control flooding in the lower Puyallup basin. Chronology Heavy, atypical winter rainfalls in the Puget Sound region left the normally intermittent, marshy Mud Mountain Lake sitting at capacity under 200 feet of water in early January The responsibility of the Corps of Engineers to preserve the impoundment s integrity and manage inevitable flooding led to its decision to initiate controlled releases of huge volumes of water into the lower reaches of the White River. Dam release induced flooding along the White River had occurred as recently as November 2006, when record rainfalls caused flooding in backyards and created a temporary 25 acre lake in Pacific City Park. The Corps of Engineers' goal was only to release enough water from Mud Mountain Dam for the White River to reach the top of its banks downstream and cause at most this 'nuisance flooding', that is, releases of up to 12,000 cfs. The city of Pacific only learned of Corps plans by Wednesday, January 7, when city fire and emergency personnel informed residents of some homes near the river to expect possible overflow in their backyards and lots similar to that two years earlier. Dam releases began Thursday afternoon, January 8, peaked at 11,700 cfs by evening, and were cut back to 9,700 cfs by the Corps Friday morning only when the severity of flooding became apparent. Residents along the river, particularly in the White River Estates development, reported significant flooding by early Thursday evening, which continued into the coming days. In short order, city officials were involved. By Friday morning, January 9, some 1,200 people (over one fifth of Pacific's residents) were evacuated from their homes. Hardest hit was the 81 house White River Estates, though some neighboring homes and businesses were inundated and damaged 101 homes, nine fourplexes, and seven businesses in total. The City of Pacific estimated property damages of $12 million to $20 million. Assistance to those affected by the flooding was Version January 17, 2012 The Association of State Floodplain Managers

6 provided by the Federal Emergency Management Agency. Four Pacific homeowners later pursued legal claims against the federal government for flood damages incurred, alleging negligence of the Corps of Engineers in releasing the waters that flooded the city. Hazard Miscommunication Even as the flooding in Pacific was happening, city officials sought to determine its causes. In large part, the city blamed the Corps of Engineers for lack of sufficient notice and for shortsightedness in calculating the results of such large releases in a short time. Miscommunication of the flooding hazard between the city, King County, and the Corps of Engineers controlling floodwater releases without a doubt led to unnecessary inundations and damages. Peak releases from Mud Mountain Dam continued even as the portions of the city on the White River flooded. The Corps of Engineers did not find out about the severe flooding in Pacific until about 12 hours after residents first reported it, and only after another few hours elapsed did the Corps drastically cut flows from the dam. Ineffective communication owing to an apparent misunderstanding of the proper chain of command in disaster response between the City of Pacific, King County Office of Emergency Management, and the Corps of Engineers was a clear culprit for the damaging floods in Pacific. In addition, chronic inaccuracies with a stream gage upriver of Pacific made it difficult for Corps personnel to know what the river was doing in a quickly changing situation. This gage had likely been damaged by debris or had shifted position. It is possible the White's tributaries accounted for a greater contribution to the river's overall flows than they did during the 2006 flooding, while sediment deposition may have decreased its carrying capacity. Inadequate Mapping Many residents impacted by the flooding in Pacific did not have flood insurance. Many of these were unaware their homes were within a flood zone, largely due to inadequacy of the existing effective FEMA Flood Insurance Rate Maps (FIRMs) for predicting where flooding would occur. Effective FIRMs for the area dated to the 1980s and were based on a Flood Insurance Study carried out in 1979, while even tentative revised maps based on an ostensibly definitive, then ongoing King County financed study proved to be flawed and showed the affected development to be outside the 100 year flood zone. The inadequacy of the old effective maps and tentative new maps would appear to be due to the volatile, fast changing nature of the White River, coupled with the presence of development and roads not accounted for on the maps and that increased flood elevations. The hard hit White River Estates and the roads through it, for example, were built in 1990, and thus are not on the effective FIRM. Misunderstanding or ignorance of the flood hazard, owing largely to outdated and ineffective flood mapping, was thus another contributor to the severity of the flooding in Pacific. Sources: [all The Seattle Times] Corps of Engineers' nuisance flooding creates disaster in Pacific by Erik Lacitis, Susan Kelleher, and Warren Cornwall. January 10, Dam discharge that swamped Pacific spurs finger pointing by Susan Kelleher and Warren Cornwall. January 14, Flood maps missed mark; Pacific homeowners got soaked by Warren Cornwall. January 26, 2009.