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Historical Flood Events

This page contains summaries, multi-media resources and background information on past flood events in Pima County.  It is by no means comprehensive, and it does not include many localized flood events on small washes.

Historical records of flooding in the Tucson area date back to the late 1800s.  As one would expect, the frequency of reports of flood damage and loss increased over time as the population of the metropolitan area grew.  By the late 1970s, the population in Pima County had grown to almost 500,000.  By 2000, that number had risen to nearly 850,000.  Additional Southeast Arizona Flood History is also available from NOAA.

When the District was formed in June 1978, the greater Tucson area had recently experienced two presidential-declared flood disasters, with a third about to take place. It was a busy time for a fledgling flood control agency.  During the 16-year period from July 1, 1977 to July 1,1993, the Tucson area experienced six presidential-declared flood disasters:  October 1977, March 1978, December 1978, October 1983, July 1990, and January 1993.

Photographs and Videos of Floods in Pima County

 

Photos

Various flood photos in Pima County


Videos


Video of flash flood in Silvercroft Wash, August 27, 2003


Video of flash flood in Posta Quemada Wash in Colossal Cave Mountain Park, July 29, 2017 (video credit: Nicole Fyffe)

October 1983 Flood

The October 1983 flood was the largest flood of record in the Tucson area. In an unusual occurrence, between 6 ½ to 7 ½ inches of rain fell across the Tucson basin over a 5-day period. Flood and erosion damage was greatest along the Santa Cruz River, with extensive damage incurred on Rillito Creek, Tanque Verde Creek, and Pantano Wash. Damage to public infrastructure was estimated at $64 million, and four people died in flood related incidents. Due to the magnitude and extent of flooding and related damage, this flood is the one to which subsequent floods have been compared.

A number of reports were written to document the flood, the damage it caused, and the repairs and hazard mitigation activities completed to reduce future flood loses.  These reports are available via the links below.

January 1993 Flood

During a 14-day period in 1993, January 5th through the 19th, significant rain fell over most of central and southeast Arizona, resulting in flooding along most major watercourses. This flooding was noteworthy for three reasons: 1) although these were the most damaging floods to occur in almost 10 years, no lives were lost and no residential and commercial structures were destroyed, with the exception of some horse barns associated with a business along Rillito Creek; 2) the high water levels in the streams lasted almost two weeks, rather than the typical few days; and 3) according to the U.S. Geological Survey, record-setting volumes of floodwater were discharged along Rillito Creek.

Estimates of damage to public transportation and drainage infrastructure for unincorporated Pima County, the City of Tucson, and the Town of Marana included $3.4 million in emergency repairs and $13.9 million for long-term improvements. This compares to an estimate of $105.7 million in repairs and improvements after the 1983 flood.

By the end of calendar year 1996, flood repairs and improvements initiated in response to the 1993 flood were largely completed. A detailed description of the January 1993 flooding can be found in the January 1993 Floods, Pima County, Arizona, Summary Report (Pima  County Flood Control District, July 1993).

September 3, 1996 Tucson Area Flood Event

In the early morning hours between 5 a.m. and 8 a.m., an unusually strong thunderstorm with high winds battered the greater Tucson area, resulting in three to five inches of rain in some locations. The highest rainfall depths were reported in the foothills of the Santa Catalina Mountains northeast of Craycroft Road and Sunrise Drive. Lesser amounts of rainfall, but still over one inch, were reported across the Tucson Valley.

Although this storm occurred during part of the morning rush hour, there were no fatalities reported. A woman and her daughter were rescued after spending more than one hour in their car, which was swept off the River Road crossing at Tanuri Wash (east of Craycroft Road), and carried downstream toward Tanque Verde Creek. A 5-year old boy and his mother were rescued from a car stalled in six feet of water in the flooded downtown Stone Avenue underpass.

In addition to street flooding and closures throughout the metropolitan area, residential flooding was reported near River Road and Craycroft Road, and near Dodge Boulevard and River Road where the Finger Rock Wash drains into Rillito Creek. Scattered power outages were reported throughout the metropolitan area, and a few water mains broke. Almost 250 storm-related emergencies were called in to city and rural fire departments. Large flows were reported on the lower Tanque Verde Creek and its tributaries, Rillito Creek and tributaries east of Country Club Road, and the Santa Cruz River and Brawley Wash.

August 18, 1998 Central Tucson Flood Event

A highly localized, but intense storm occurred in central Tucson around 8 p.m. A 39-year old man was swept away in the Arcadia Wash at-grade crossing of Fairmount Street near Rosemont Boulevard. When the floodwaters receded, his overturned vehicle was found in the Arcadia Wash. His body was recovered approximately eight miles downstream in Rillito Creek near Stone Avenue.

1999 - Two Events

Two notable flood events occurred in 1999.  Details of each event can be found below.

July 26, 1999 Earp Wash Flood Event

A very small, but highly intense monsoon thunderstorm positioned itself over the Earp Wash Watershed near Valencia and Alvernon roads shortly after 2:00 p.m. One rain gauge volunteer reported that 1.5 inches of rain fell in approximately one hour. Runoff inundated the residential properties along Alvord Road, Palo Verde Road, and Milton Road. The American Red Cross provided assistance to those residents whose properties were flooded. The storm also impacted a Tucson Electric Power substation, which caused power outages impacting 1,912 customers.  Please read the Earp Wash Flooding Report for more information.

July 14 and 15, 1999 Tucson Area Flood Event

In the summer of 1999, a wet tropical air mass combined with daytime heating resulted in light to moderate rainfall over much of the Tucson area between July 12th and July 15th. Several streets were flooded at various times. On the evening of July 14th, three people were rescued after their van was swept into floodwaters of the Alamo Wash near Broadway Boulevard and Wilmot Road. Two adults were pulled from the van, and in a dramatic rescue, a child was plucked from the water after being swept through the box culvert at Wilmot Road.

On July 14th, light rain began falling on the upper Sabino Canyon watershed early in the day, and continued throughout the night. The early morning hours of July 15th marked the beginning of flooding in Sabino Creek that would rival the October 1983 and January 1993 floods, the largest in recent history. On the 15th, between 2:30 a.m. and 4:30 a.m., 1.3 inches of rain was recorded near the top of the watershed. During the next two hours, a torrential downpour dropped another 4.6 inches on the upper watershed, for a four-hour storm total of 5.9 inches, which exceeds a 100-year, 24-hour storm.

This storm was atypical in that the rainfall intensity was unusually high, and the storm was centered over the Sabino Canyon watershed. Significantly less rain fell on adjacent watersheds. The storm was, however, typical in its “flashiness.” Flow depths increased rapidly, resulting in the need for several rescues.

Sixteen people were airlifted out of the Sabino Canyon Recreation Area at about 7:30 a.m. and several horses, pigs and chickens were moved out of the Hidden Valley Ranch area a few hours later. Two residents who stayed with the horses during the worst of the flooding, who sought refuge on the rooftop of a barn, were brought out with the horses. Approximately six residences located within the creek bed received flood damage, as did the animal corrals and horse barns in the Hidden Valley area.

Flows from Sabino Creek and other foothills washes drained into Tanque Verde Creek and Rillito Creek, resulting in significant flows on these watercourses, as well. A 12-year old boy had fallen into Rillito Creek and was rescued near La Cañada Drive.

The greatest amount of flood damage occurred along the Catalina Highway (a.k.a., the General Hitchcock Highway), which experienced catastrophic failure in three locations north of Molino Basin. Severe erosion and undermining of the roadway, as well as several rockslides, resulted in the closure of the highway for a couple of weeks. This left up to 800 residents of the Mount Lemmon community stranded. Although an alternate access route was available from the north (the Oracle Control Road), it is an unimproved dirt road that can only be traversed with a four-wheel drive vehicle, and it takes several hours. Permanent repairs will be completed as part of an FHWA project that began in March 2000. This FHWA project was planned prior to the occurrence of the July 15, 1999 storm.

2003 - Three Events

Three notable flood events occurred in 2003.  Details of each event can be found below.

July 29, 2003 Gibson Arroyo Flood Event, Ajo

Ajo, Arizona, is an unincorporated community located within Pima County, Arizona, and lies approximately 160 miles west of Tucson. On July 29, 2003, the community of Ajo experienced a severe thunderstorm producing significant Rainfall - approximately 1.3 inches of rain in just over one hour. Flooding occurred primarily along the Gibson Arroyo and tributaries located south of the arroyo.

The Flood Control District quickly responded by providing immediate assistance with clean up and maintenance of streets, bridges, and portions of the Gibson Arroyo. In addition, the District immediately requested and received approval to enter a portion of the Gibson Arroyo owned by Phelps Dodge in order to dredge along an extensive stretch of the channel to provide increased hydraulic capacity.

As part of the District’s response, a consultant was hired to provide an emergency evaluation and report on the flooding including new aerial-topographic mapping, a field review of the flooding, data collection, and preparation of preliminary hydrologic and hydraulic analyses. Accordingly, a Master Drainage Plan was developed to recommend specific approaches to address these floodprone areas including the Second Avenue Bridge and southern tributary flooding.

Second Avenue Bridge Replacement

Eyewitness accounts of the July 29, 2003 flood provide ample evidence that debris and sediment effectively blocked the conveyance area of the bridge and increased flooding conditions during the flood event. The bridge is a 3-cell structure with a relatively low profile with two pier walls between the cells, which restrict the amount of debris and sediment that can freely pass downstream. Hydraulic modeling of the existing bridge reveals that if the opening were not clogged by debris and sediment the 100-year flow depth at the bridge would be reduced by about 1.3 feet. A new bridge can be designed to accommodate debris and sediment, thereby reducing flooding.

Curley School Site Detention Basin

The southern portion of Ajo contains several tributaries to the Gibson Arroyo. This area maintains poor drainage infrastructure such as private culvert systems that run under residential structures. The most effective way to alleviate the flooding problem is to reduce the peak discharge by storing the flood volume in a flood control basin. The former football field at Curley School is a prime location for the detention basin as this is a sizeable piece of property capable of sustaining a detention basin. Therefore, the planning has been initiated in concert with the renovation planned for Curley School.

Summer 2003 Aspen Fire

 The Aspen Fire consumed 85,000 acres of land and 335 structures between June 17, 2003 and July 17, 2003. The incendiary point was located near Marshall Peak on the Aspen Trail. By nightfall of June 19th, the community of Summerhaven was engulfed in flames.

One of the principal dangers resulting from significant fires is increased flooding; erosion and debris flow due to the destruction of large quantities of vegetation. A mountain fire, such as the Aspen Fire, increases the magnitude of this danger, due to large topographic relief and flow concentration into more urbanized areas. Early estimates from the United States Forest Service indicated that watersheds in areas severely burned could produce up to five times the quantity of runoff from a given area.

In order to address these dangers and other related issues, District staff launched a comprehensive and multifaceted program to provide an enhanced early flood warning system, mitigate the newly developed hazards, and to better characterize the nature of the hazards.

As a first step, the Pima County ALERT Flood Warning System damaged by the fire was quickly repaired and supplemented with additional weather and stream gauge monitoring sites in order to provide enhanced early warning, if potential post-fire flood dangers became imminent threats to urbanized areas downstream. ALERT System repairs and enhancements costs were $47,000. Second, Pima County worked with the Natural Resource Conservation Service to quickly develop and implement a multi-phased program under the Emergency Watershed Protection Program to reduce the potential damages that could be caused by increased flood and debris flows through containment of ash from burned structures, revegetation and structural erosion control efforts. Third, the District launched a total of four hydrologic studies to evaluate, in more detail, the hydrologic conditions within the different watersheds in the post-fire era. Emergency Watershed Protection Revegetation and Erosion Control Program costs were $727,061. Several emergency contracts and agreements were required to implement the elements of this Flood Control District program. The total contract amount to successfully complete this three-tiered effort was approximately $944,000. Hydrologic Studies are estimated at $170,000 to study the front-range watersheds of Ventana, Sabino, and Molino, the Upper Cañada del Oro Watershed, and agreement with the United States Army Corps of Engineers to study Carter Canyon.

The only waste materials generated during the implementation of the post-fire Flood Control Program were from activities associated with the removal of debris from major drainage channels within the Summerhaven area. This activity was necessary to prevent the formation of large and potentially hazardous debris dams (mostly vegetative waste) within the watercourses. A breach in these unstable debris dams, due to hydrostatic and hydrodynamic forces, could have exacerbated downstream flash flooding. These removal activities are one of the most significant efforts in the Revegetation and Erosion Control Program requiring repeated efforts to remove debris from vegetation and felled trees that continued to appear within the drainage courses. Vegetative debris measuring less than 12 inches in diameter was chipped and taken to the landfill to be used as daily cover, whereas larger debris was cut up and removed from the channels.

The District worked closely with the United Stated Forest Service to secure access, as necessary, for the installation of additional monitoring stations, as well as the staging areas required for aerial revegetation.

The District worked closely with the Natural Resource Conservation Service and local conservation districts throughout the course of the revegetation and erosion control program including co-staffing the “yellow tent” located within Summerhaven for the first six weeks after resident reentry in order to answer questions pertaining to erosion hazards and revegetation methods, among others during the post-fire healing process.

Hydrologic work was coordinated with the USACOE for the Carter Canyon watershed. The program was implemented by the District, which successfully addressed the immediate needs of providing enhanced warning for downstream residents of the potential for increased flood flows due to the fire, provided erosion protection and flow attenuation through revegetation processes and other constructed measures, and provided protection for the remaining facilities and water quality. Additionally, the hydrologic studies provided information necessary to determine the design criteria needed to provide appropriate future protective measures.

It is expected that most of the structural treatments completed under this project will remain viable and functional for several years until the natural recovery processes returns the hydrologic conditions back to pre-fire conditions.

August 25, 2003 - Cañada del Oro Watershed – Catalina, Arizona

The Aspen Fire changed the hydrologic characteristics within the Cañada del Oro watershed. Moderate to high burn severity through much of the watershed denuded the drainage basin, greatly increasing the chances of flooding during the summer monsoon season.

On August 25, 2003, a significant rainfall event occurred resulting in flows of approximately 7,000 cfs—a 25-year flow. Sheriff’s deputies evacuated the area and most of the homes within low-lying areas both east and west of the channel. Immediately following the flood, the District began efforts to assist the residents by accepting applications to the Floodprone Land Acquisition Program from residents who wanted Pima County to appraise their properties for possible acquisition.

The acreage consisted of 75 parcels totaling almost 200 acres of land. As of July 2004, 151 acres of land or approximately one-third of the total acreage within the Cañada del Oro floodplain was acquired.

The cost to the District has been substantial—$7,880,641 for real property and $1,120,524 paid out for relocation benefits to displaced property owners. The District, however, garnered a federal grant of $3,000,000 to contribute to the enormous costs generated by this project.

The acquisition of continuous parcels of property containing rural characteristics created an interest, particularly with the Pima County Natural Resources, Parks and Recreation Department. The community of Catalina, Oro Valley, and the area residents welcomed an opportunity to create a rustic, equestrian-oriented recreational space for this northwest cluster of communities, which could evolve into a well-planned, multiuse facility for area residents as well as in surrounding developments.

2005 - Two Events

Two notable flood events occurred in 2005.  Details of each event can be found below.

August 14, 2005 Brawley Wash Area Flood Event

On the morning of August 14, 2005 a large storm system moved from east to west over the Sierrita Mountains, south of Tucson. Brawley Wash (located west of Tucson downstream of Three Points) and many small washes in the Diamond Bell area exceeded their capacity— resulting in flooding of residential areas and roads throughout Avra Valley. Many families were stranded for days due to high water and damaged roads. Rain gauges and Doppler radar indicated a large area of the Brawley Wash watershed received between two and four inches of rainfall during a six-hour period. The highest rainfall intensity measured by an ALERT gauge was 2.32 inches in one hour. Stream flow on the Brawley Wash at Highway 286 was the highest flow measured at this location since 1984. Maximum depth was approximately 10 feet with a discharge of 11,800 cubic feet per second.

During these storm events, information provided by the ALERT system aided the NWS and emergency teams with their decisions to warn the public of potential flooding and their response to emergency situations where people and infrastructure were in danger from the rising floodwaters.

August 2005 Southeast Tucson Area Flood Event

In late August 2005, a heavy rainstorm produced two to six inches of precipitation impacting the area near Old Nogales Highway south of the Tucson International Airport also known as the Old Nogales Highway Colonia. This area predominately contains older mobile homes on one-acre lots that do not have the benefit of infrastructure such as sewer lines, streets, sidewalks, street lights, etc. Many of these one-acre parcels were the result of lot splitting in early 2000 - most were not financed by traditional lenders who would have required flood insurance.

This storm, estimated to be a 25 to 50-year event, left many residents with extensive flood damage to their homes. FLAP purchased one parcel in this area. Additionally, in an effort to improve existing living conditions for other damaged properties, the District made a contribution of $200,000 to assist the Pima County Community Development and Neighborhood Conservation Department with rehabilitation efforts. The District also replaced five mobile homes using mobile homes acquired from other FLAP acquisitions, replaced damaged roofs, provided new doors, windows, electrical appliances, and new cooling and heating systems. Overall, forty families benefited from these outreach activities.

Summer 2006, including July 27-31, 2006 Catalina Foothills Area Flood Event

Two memoranda discuss the significant flooding events in the 2006 monsoon season.  The first is a Preliminary Damage Report Regarding the Floods of July 27 through 31, 2006 from County Administrator Chuck Huckelberry to the Board of Supervisors.  The second is a memo titled 2006 Monsoon Season and the July 27, 2006 to July 31, 2006 Flood Event from Flood Control Director Suzanne Shields to County Administrator Chuck Huckelberry detailing the flood events of that time period, with additional analysis and reporting.

Summer 2008, Sahuarita Heights - Delgado Watershed flooding

A memorandum was prepared in response to resident complaints in the Sahuarita Heights - Delgado watershed area during the 2008 monsoon season.

July 30, 2010 Tanque Verde Flood Event

Heavy rain in the Tanque Verde Creek watershed on July 30th caused a flash flood late that night in which Tanque Verde Creek flowed out of the main channel and onto the north overbank, where it flooded approximately two dozen homes in the Fortyniner's Country Club Estates neighborhood and caused other property damage. According to District’s ALERT system precipitation gauges, the total rainfall throughout the upper Tanque Verde watershed during this storm event ranged from 1.26 inches to 3.90 inches with rainfall intensity of up to 3.23 inches/hour were reported in portions of the watershed. Based on observations of the extent of flooding at Fortyniner's, the estimated discharge at the peak of the flood was 12,000 cfs there, which is similar to what would be expected during a 25-year flood. The high intensity of the storm over a relatively short duration caused the flood waters to rise and fall quickly, catching many by surprise. relatively short duration storm also resulted in a flood wave what attenuated as it flowed, resulting in a peak discharge that was considerably higher than 12,000 cfs upstream of Fortyniner’s, and considerably less than 12,000 cfs at its confluence with the Rillito.  Please see the 2010 Tanque Verde Flood Investigation Report for more information, maps and photographs of the flooded areas.

Even though many homes avoided damage from the flood, sometimes by just a few inches or less, it is important to note that neither the peak discharge nor flood volume of this flood were as high as the anticipated base flood, often called the regulatory flood or 100-year flood, and many homes that were not flooded during this event are expected to be flooded by the base flood.

September 2011 Storm Events

The City of Tucson and Pima County experienced two large rainfall events in September, 2011 but regional detention basins on Earp Wash, Rodeo Wash and the Kino Environmental Restoration Project (KERP), constructed and operated by the Pima County Regional Flood Control District, prevented these large rainfall events from becoming large flood events.  Please see the report titled Mitigation of the Sept 10th and Sept 15th 2011 Flood Peaks by Pima County Regional Detention Basins for more information.

2012 Monsoon Season

There were no major, wide-spread flood events during the 2012 monsoon season, but intense localized thunderstorms did result in at least 8 homes being flooded. None of the homes were located in a FEMA floodplain, and only one was located in a locally mapped floodplain. One storm event destroyed a portion of Silverbell Road when the Idle Hour Wash experienced a close to the 1% annual chance (100-year) flood. Please see the Memorandum entitled Preliminary Assessment of the 7-29-12 Flooding at the Idle Hour Wash for more information about this event.

2014 Monsoon Season - Two Events

The 2014 Monsoon season resulted in two notable flood events. 

Corona de Tucson, July 7, 2014

An intense, localized storm with rainfall intensities of 2 inches per hour or greater hit the Corona de Tucson area in Vail on July 7, 2014.  The effects of that event are summarized in a flood report memo titled Corona de Tucson area storm damage response for July 7, 2014 event.  Photos of the area after the event are attached to the report.

Why, Arizona, July 9, 2014

An intense, localized storm with rainfall intensities of 2 inches per hour or greater affected Why, Arizona on July 9, 2014.   Several structures were damaged during the event.  Details and photographs of the event are provided in a flood report memo titled Why, Arizona Storm Damage Report for the July 9, 2014 Storm Event.

Sopori Wash Flood - September 2, 2018

On September 2, 2018, an intense rainfall event with up to 7 inches of rain in a short time span within the Sopori Wash watershed resulted in significant flooding within the town of Amado. Several structures experienced three or more feet of water within them. Some of these structures were in Pima County and others were in Santa Cruz County. The District hired Stantec to perform a post-flood analysis to determine the return-period of the flood. Please read the Sopori Wash-Discharge & Recurrence Event Analysis report for more information.