In December, 2010, the flood of record occurred in the Panama Canal Watershed. The investigators have been working in Panama for approximately 10 years studying the hydrometeorology, hydrology, in-stream wood transport and fate and landslides, and assisting the Panama Canal Authority in setting up a real-time weather and flood forecast system. This extreme event, with a return period thought to be between 100 and 200 years, provides an excellent opportunity to create a database of hydrometeorological, hydrological, and geomorphic features associated with this flood, as well as carbon cycling by large woody debris in a tropical mountainous watershed during an extreme event. Our project consists of field collection campaign, atmospheric simulations, and database creation components. Field studies will document landslides, large woody debris accumulations, high water marks, and geomorphic changes within the 414 sq. km old-growth upper Rio Chagres watershed. The Weather Research and Forecasting (WRF) atmospheric model will simulate the storms that caused the floods. Rain gage data provided by the Panama Canal Authority will be used in conjunction with the WRF model output to generated ground-truthed space-time rainfall series.

Collaborations with the Smithsonian Tropical Research Institute (STRI) and Technological University of Panama will assist in assembling data from disparate sources not readily available. The U.S. Bureau of Reclamation is a collaborator, as they have an interest in understanding the performance of the Madden Dam, which they designed in the 1920's. During the flood of December, 2010, the Madden dam was pushed to the limits of its design, even though it was originally designed to pass a 10,000-year flood. We will explore whether land-use changes in the watershed are responsible for this change in flood frequency. The long-term historical dataset owing to the existence of the Panama Canal, in addition to the existing hydrological and hydrometorological network will make this one of the best documented extreme flood events in any tropical mountainous watershed to date. The short-term, intensive once-off field campaign will also complement project EAR-1045166 that started on May 1, 2011.

Project Report

December 7 and 8, 2010, saw record flooding in the Panama Canal watershed. The Chagres river provides the majority of the water for Panama Canal operations. In those two days portions of the Upper Chagres watershed received over 936 mm (3 ft) of rainfall. The two-day average rainfall over the 1050 sq. km (407 sq. mile) Upper Chagres watershed was 500 mm (1.6 ft). A statistical analysis of this rainfall amount indicates that one would expect an event of this magnitude less often than once per thousand years. This was an exceptionally extreme and rare event. The resulting flood resulted in closure of the Panama Canal for approximately 17 hours due to high water levels, large flows of water into the canal and floating woody debris. This was the first time in history that the Panama Canal was closed due to flood conditions. Before this event, Canal closures resulted solely from landslides or military activity. The Panama Canal is highly important to the United States economy. Approximately 5% of world trade passes through the Panama Canal, including a significant portion of U.S. foreign trade with Asia. According to the US Dept. of Transportation, approximately 95% of U.S. cargo imports arrive by ship. As U.S. foreign trade increases in the future, so will the importance of the Panama Canal. Furthermore, since the handover of the Canal to the Republic of Panama in 1999, the Panama Canal Authority has embarked on an ambitious construction program to increase the size of ships that can transit the canal. The enlarged Panama Canal will require more water and may be more susceptible to the effects of floods and droughts. The objective of our project was to collect, archive, and disseminate data from this extremely rare event to enable improved modeling for risk analysis, canal engineering and operations. Our data collection activities were performed in collaboration with the Panama Canal Authority (PCA) in Panama, and the non-profit Hydrologic Research Center (HRC), in San Diego, California, through collaborative project EAR-1123498. The HRC has a long-standing relationship with the PCA, and maintains their flood forecasting and modeling systems. This extreme flood produced a large number of landslides in the upper Chagres river watershed. These landslides introduced copious amounts of fine-textured sediments such as clay and silt to the Chagres river. This massive sediment load was transported down the Chagres river to Lake Alhajuela, turning it muddy brown. This lake is the source of drinking water for the approximately 1 million residents of Panama City. The water treatment facilities were clogged with sediment, which shut off water supply for much of Panama City for two weeks. These landslides also introduced thousands of trees into the Chagres river. These trees were stripped of their branches by the turbulent flow of the steep Chagres river, and arrived in Lake Alhajuela as bare logs. Our data collection activities included field work in Panama. We conducted video surveys by helicopter to document the number and locations of landslides, as well as the number of logs stored in the river channel and discharged to Lake Alhajuela. Landslides were categorized according to whether or not they reached the Chagres river. Data from water level sensors previously deployed in the upper Chagres watershed were obtained for comparison with other events since 2005. Satellite images were obtained and used to estimate the large-scale distribution of landslides. The PCA has provided rainfall, streamflow, and Lake Alhajuela water level data. Our collaborators at the HRC used the Weather Research Forecasting (WRF) model to simulate the meteorology of this event. They have provided WRF rainfall output, and performed statistical analysis of the rainfall. Watershed processes in the tropics are poorly understood compared to those in temperate climates. The Upper Rio Chagres has a long history of data collection due to Panama Canal operations, and offers a unique setting to study an old-growth watershed that is 98% undisturbed. For this reason our data collection activities to document this rare event are of broad interest to the tropical hydrology research community, water managers, risk analysts, and engineers. We are creating an on-line database of the flood, and are communicating our findings to PCA, the Technological University of Panama, and the Smithsonian Tropical Research Institute in Panama. We have produced three draft manuscripts that will be submitted for publication in top journals. The project has engaged three graduate students from the University of Wyoming in important intensive field work. One of these students is a co-author on one of the draft publications. Our final results are included in the final report for collaborative project EAR-1123498.

National Science Foundation (NSF)
Division of Earth Sciences (EAR)
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Thomas Torgersen
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University of Wyoming
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