Puerto Rico’s Ageing Dams

Today’s blog by Matthew P. Johnson relates his article in Environment and History ‘Thirsty Sugar Lands’: Environmental Impacts of Dams and Empire in Puerto Rico Since 1898‘, (online first Autumn 2019, due in print August 2021) to the recent United Nations University report on ageing dams.

In September 1928, Hurricane San Felipe, one of the most powerful storms in Caribbean history, swept across Puerto Rico. The hurricane took the lives of hundreds of people and tore apart homes and other buildings, leaving hundreds of thousands more homeless. Upon surveying the wreckage after the storm had passed, then Governor Horace Towner compared the island to ‘war-devastated areas of France or Belgium.’[1]

Among the infrastructure the storm imperilled was the island’s big dams, which held back reservoirs containing tens of thousands of cubic metres of water. In 1908, the Puerto Rican government—under US control after 1898—created an Irrigation Service charged with building dams to irrigate sugar cane, the island’s leading cash crop. In the 1910s, it built three big dams and a canal system in island’s semi-arid southeast, which was then the domain of wealthy absentee sugar companies from the mainland. The following decade, it built a fourth big dam, Guajataca, in the northwest. Engineers completed the dam in 1927, and the irrigation system began operating the following January, just in time to face the coming storm.

Figure 1. The calm before the storm. Photo from 1927 showing two Rockefeller Foundation malariologists boating on the recently created Guajataca reservoir looking for signs of Anopheles mosquito breeding in the inundated vegetation. Photo courtesy of the Rockefeller Archive Center, Rockefeller Foundation Records, photographs, series 100-1000, series 243: Puerto Rico, subseries I: Malaria, box 58, folder 1334.

Guajataca Dam escaped the powerful hurricane relatively unscathed. The governor’s report for that year noted that the storm had caused almost no damage, apart from some mudslides alongside irrigation canals, which were promptly remediated. Overall, the report concluded that the storm ’caused little damage to the system.’[1]

 Nearly a century later, another powerful hurricane nearly destroyed the dam. In the aftermath of Hurricane Maria in September 2017, torrents of water toppled over the floodgates and ripped a hole in the spillway. The rapidly deteriorating spillway raised fears that continued erosion would compromise the earthen dam itself, putting tens of thousands of people in immediate danger. The fear of collapse caused widespread panic and prompted evacuation orders. Over the following weeks, teams of engineers from different government agencies hurriedly worked to reinforce the dam, and they successfully forestalled disaster.[1]



Figure 2. Efforts to shore up the dam. Photo from October 2017 showing a helicopter placing barriers to strengthen Guajataca’s destroyed spillway. Photo by Pfc. Deomontez Duncan. Source: The Army Corps of Engineers

Guajataca, now 94 years old, is among a global cohort of ageing dams that have suffered near-collapse or collapse in recent years. Together, these incidents have highlighted the catastrophic potential of dam failure and encouraged researchers to investigate the degree of the threat. In January 2021, the United Nations University published a report on ageing dams with the stated goal of bringing attention to the subject and encouraging international efforts to deal with it. Subsequent articles helped shine an even bigger spotlight on the issue. The UNU report highlighted that tens of thousands of large dams across the world are reaching the end of their expected lifetimes and will thus require costly retrofits and repairs to remain safe. The report also explored the potential for decommissioning obsolete dams, which the authors argue is cheaper than repairing them.[1]

Puerto Rico and the rest of the Caribbean, which the report does not cover, face at least three exceptional circumstances that make the challenge of maintaining ageing dams especially arduous. 

First, Caribbean dams must contend with hurricanes and rapid siltation. Heavy rains and intense flooding batter the dam structures. Storms also cause severe erosion upstream, leading to massive amounts of sediment accumulating in reservoirs. Because of these storms, Puerto Rican dams silt up at a much faster rate than dams in most other regions of the world. Rapid sedimentation, which my article in Environment & History discusses at length, limits the amount of water that reservoirs can store, which makes them less able to control floodwaters that overtop spillways. Earthquakes are another natural hazard that Puerto Rico’s dams face. The island sits near an active fault line, and though big earthquakes are infrequent, they have the potential to be disastrous. 

Figure 3. Sedimentation after a flood. Photo taken in 1921 showing silting in the Guayabal Reservoir and efforts to clean the sluice gates. Source: Archivo General de Puerto Rico, Series: Irrigation (Aguas), Record Group: Public Works (Obras Públicas), Box 511, Folder 1.

Puerto Rican engineers, well aware of these threats, have repaired and retrofitted dams in response to major flooding events and the findings of annual assessments. In the 1950s, engineers retrofitted the Guayabal Dam – one of the Irrigation Service’s first three dams in the southeast – after a flood. Over the subsequent decades, engineers retrofitted the spillways and intakes of the southeast’s other two big dams, Patillas and Carite. Thus far, Puerto Rico’s ageing irrigation dams have performed well during hurricanes, but, as Guajataca attests, the hazard potential remains high and will rise higher as a result of climate change, which is projected to bring fiercer and more frequent storms. The government has also periodically dredged reservoirs, but such efforts are infrequent and costly. 


Figure 4. Retrofitting the dam. Photo from 1950 showing construction crews upgrading Guayabal Dam’s spillway. Source: Puerto Rico Water Resources Authority, “Annual Report 1949-50,” page 80, Archivo Histórico de la Autoridad de Energía Eléctrica. 

The second exceptional feature of Puerto Rico’s ageing dams is that decommissioning them is not an option because the island relies on them for municipal water supply. The UNU report suggests that removing dams is a cost-effective means of mitigating the threat of collapse in some scenarios. Dams can become obsolete when demand for water or electricity disappears, or when replacement sources are found. Indeed, Puerto Rico’s old dams are obsolete as irrigation dams: during the second half of the twentieth century, the island gradually abandoned sugarcane, and manufacturing became the leading economic activity. Yet, these dams immediately took on a new purpose, which they retain today: municipal water supply. People moved to cities that depend on water storage reservoirs (94 percent of Puerto Ricans now reside in urban areas). Puerto Rico is a small island with few alternatives for securing fresh water, and groundwater cannot replace surface storage.

Figure 5. Guayabal Reservoir. Author’s Photo, August 2016.

Third, Puerto Rican dams also face exceptional financial constraints. The island is currently in the throes of a severe recession and debt crisis that has cut the amount of money available for maintaining infrastructure. The island’s debt crisis has its long-term origins in a series of policies implemented by both the imperial and local government throughout the twentieth century. These policies created an economy catering to companies from the mainland that siphoned income off the island, and also encouraged the local government to use debt as a means of balancing its budgets.[1] The debt crisis began in earnest between 1996 and 2006, when the federal government phased out tax exemptions that had attracted manufacturing companies to the island. Businesses pulled out, triggering a recession. The 2008 global financial crisis and a series of natural disasters have compounded the catastrophe, along with increasing emigration to the US mainland, which has reduced the tax base and local purchasing. Puerto Rico’s debt is now more than US$70 billion and is mostly held by wealthy hedge and vulture funds.

Puerto Rico’s debt crisis has been exacerbated by the island’s political status as a commonwealth territory. Its status means that the government cannot apply for bankruptcy protection, as municipalities on the mainland can, and it cannot borrow in global markets. Its subordinate status also enabled the federal government to take over its finances. After the commonwealth government defaulted on its debt in 2016, the federal government created a Financial Oversight and Management Board to control the island’s spending. The Board consists of seven members appointed by the US Congress, only one of whom resides in Puerto Rico.[1]

Guajataca’s close call after Hurricane Maria had the smallest of silver linings: the crisis compelled the release of funding for repairing and retrofitting dams. In the aftermath of the near collapse, the Federal Emergency Management Agency (FEMA), granted US$150 million to the Puerto Rico Electric Power Authority (PREPA) to repair the dam, and the state-owned company has since requested roughly US$1 billion more to retrofit both Guajataca and Patillas, two of the island’s oldest and most important dams. PREPA is also preparing requests for FEMA funding to dredge its reservoirs, though the US$200 million it hopes to secure would only cover the removal of sediment that FEMA deems Hurricane Maria responsible for.[1]

Such funding would help, but it would do little to mitigate the long-term sedimentation burden, a problem that is costly to remediate.

Figure 6. One of Puerto Rico’s oldest dams. Photo circa 1910-1914 showing construction of the Guayabal Dam. Source: James Beardsley, “Memoranda of Porto Rico Irrigation Service,” December 1914, National Archives and Records Administration, record group 350, Records of the Bureau of Insular Affairs, series: General Classified Files 1898-1945, Box 10.

Puerto Rico is entering the age of ageing dams with grounds for both optimism and serious concern. On the one hand, the island has teams of capable and dedicated engineers who oversee dams that have performed well during the past century’s storms. On the other hand, their dams face the threats of hurricanes and rapid siltation, the former of which will likely become more intense as a result of climate change, and the latter of which will continue to accumulate in the absence of dredging. Moreover, the government is hamstrung by the debt crisis and related funding shortages, and the island’s territorial status impedes its ability to get resources from the federal government that US states can access.  

Matthew P. Johnson is an environmental historian of modern Latin America and the Caribbean. His dissertation is an environmental history of the Brazilian military dictatorship’s mega dams, which he recently defended at Georgetown University. For more on the environmental history of Puerto Rico’s dams, check out his articles “‘Thirsty Sugar Lands’” in Environment & History, and “Swampy Sugar Lands,” in the Journal of Latin American Studies. Both are about the South Coast Irrigation Project (built 1910–914). The former discusses socioeconomic inequalities and sedimentation, and the latter discusses the role of the irrigation system in engendering malaria.


[1] Quoted in Stuart B. Schwartz, Sea of Storms: A History of Hurricanes in the Greater Caribbean from Columbus to Katrina (Princeton: Princeton University Press, 2015), p. 233.

[1] Horace A. Towner, Twenty-ninth Annual Report of the Governor of Porto Rico (Washington DC: Government Printing Office, 1930), p. 62.

[1] Frances Robles, “Cracks in a Puerto Rican Dam Send Neighbors a Message: Leave Now,” New York Times, 23 Sept. 2017; Carrie Kahn, “Guajataca Dam’s Failure Highlights Puerto Rico’s Infrastructure Issues,” National Public Radio, 9 Oct. 2017.

[1] Duminda Perera, et al., Ageing Water Storage Infrastructure: An Emerging Global Risk (Hamilton: United Nations University Institute for Water, Environment, and Health, 2021); Fred Pearce, “Water Warning: The Looming Threat of the World’s Aging Dams,” Yale Environment 360, 3 Feb. 2021.

[1] César Ayala, “Behind Puerto Rico’s Debt: Corporations that Drain Profits from the Island,” published online by the Committee for the Abolition of Illegitimate Debt on 10 Dec. 2018; Amelia Cheatham, “Puerto Rico: A U.S. Territory in Crisis,” published online by the Council on Foreign Relations, 25 Nov. 2020. 

[1] https://oversightboard.pr.gov/

[1] Phone call with Engineer Jose Miguel Bermudez, Chief Engineer of the Puerto Rican Electric Power Authority’s Division of Dams and Reservoirs, 1 March 2021.





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