Summary of the Glacial Lake Handbook

SUMMARY OF THE GLACIAL LAKE HANDBOOK THE GLACIAL LAKE HANDBOOK REDUCING RISK FROM DANGEROUS GLACIAL LAKES IN THE CORDILLERA BLANCA, PERU Palcacocha Lake in 1932 before the GLOF (top) and after in 1941. Right: The red arrow points to Lake Palcacocha in 2012; blue lines are streams leading from several glacial lakes into Huaraz, where an estimated 5,000 people were killed in the 1941 flood. Servicio Aerofotográfico Nacional del Perú (Peru’s National Aerial Photography Service) This summary distills the 68-page Glacier Lake Handbook for the benefit of mountain dwellers and policymakers worldwide. ReFer to the complete document for detailed explanations and case studies: http://highmountains.org/blog/glacial-lake-handbook-cesar-portocarrero-rodriguez Peru’s history with dangerous glacial lakes: Peru has experienced what most experts are now predicting for other glaciated mountains throughout the world: shrinking glaciers with emerging lakes that sometimes release deadly glacial 1 SUMMARY OF THE GLACIAL LAKE HANDBOOK lake outburst floods (GLOFs). Through a long history of managing their glacial lakes, Peruvians have developed expertise in glacier hazard management that is perhaps unmatched in the world. The safety dam on Palcacocha Lake as construction was The safety dam on Palcacocha Lake with ice debris in 2003 being completed in 1974. (César Portocarrero) after a flood. Photo: Glaciology Unit Office Archives The first risk-reduction efforts in Peru’s major mountain range, the Cordillera Blanca, began in 1942 after a GLOF destroyed much of the city of Huaraz, killing an estimated 5,000 people. Nine years later, in 1951, the national government officially established the Control Commission of Cordillera Blanca Lakes that is today known as the Glaciology and Hydrological Resources Unit. The glaciology office conducted engineering projects to reduce the risk of 34 dangerous glacial lakes. By draining and containing glacial lakes before they produce outburst floods, these engineers have likely prevented many catastrophes. It is believed that these efforts saved the cities of Huaraz in 1959, Huallanca in 1970, Carhuaz in 1991, Huaraz in 2003, and Carhuaz again in 2010. And that’s only the known close calls, considering that most of these lakes lie high in the mountains where events go unnoticed. Working with limited government resources—a situation similar to that of other developing countries—Peru’s Glaciology Unit is now a leader in tropical glacier research and glacial lake engineering to prevent outburst floods. So that the world may benefit from this Peruvian expertise, the USAID-funded High Mountains Adaptation Partnership (HiMAP) feels that this knowledge should be shared with mountain dwellers worldwide. The complete technical report, The Glacial Lake Handbook, captures the lessons learned by Ing. César A. Portocarrero Rodríguez during the course of a 40-year career devoted to the reduction of GLOF risks in the Cordillera Blanca. The experience and guidance provided by the Handbook is intended to support decision makers, engineers, local people, and scientists in other regions of the world who are currently experiencing the phenomenon of receding glaciers accompanied by the formation of potentially dangerous lakes. This summary is a brief overview of the report’s most important lessons. How moraines lead to dangerous lakes: Moraines are the accumulations of rock and earth eroded by glaciers and dropped at their edges. Where the sediment is tightly compacted and cohesive, the moraine can create a dammed basin capable of holding water. As a glacier melts and recedes, the space it once occupied is often replaced by glacial lakes trapped by this moraine. A large GLOF typically includes a rupture in the 2 SUMMARY OF THE GLACIAL LAKE HANDBOOK moraine that leads to a violent flood that transports morainal material mixed with water and ice downstream. The risk from glacial lakes depends on many factors: Preventing glacial lake outburst floods first requires identifying the risks. In Peru, this typically requires visiting each lake in the field by traveling long distances on foot or on horseback. During the last decade it has become possible to use satellite images for the glaciological inventories, but these have proven unreliable for tracking dangerous lakes because the satellite images are usually out of date and do not necessarily reveal all of the important details. Thus, on-site verification must be conducted on a frequent basis in order to detect critical changes as dangerous lakes develop. The following factors need to be considered when assessing the risks of glacial lakes: • Glacier characteristics: These include slope of the glacier, the magnitude of crevassing, the magnitude of fragmentation, and estimated thickness. • Slope of the bedrock: Steeper slopes often increase the likelihood of ice avalanching into the lake. • Geometry and structure of moraines forming the lake basin: GLOFs can be triggered by moraine material sliding into the lake. • Length and slope of the downstream valley: A GLOF’s kinetic energy and destructiveness depends on the physical characteristics of the path of the downstream flow. • Presence of hanging glaciers: Masses of ice on steep slopes without support from below can cause huge avalanches that may result in dangerous surges if they fall into a lake. • Glacier tongues undermined by glacial lakes (calving): Glaciers flowing directly into lakes can collapse inside the lake, creating a large surge wave. • Volume of the lake: The destructive potential of a flood depends largely on the how much water is in the lake. • Seismic and tectonic factors: Earthquakes can result in glacial avalanches, rockfall, and possibly moraine failure. Methodology for reducing the risk from dangerous glacial lakes: Safety measures adopted for glacial lakes in the Cordillera Blanca rely on three primary steps: (1) decreasing lake volume, (2) building drainage systems that maintain the volume at desirable levels, and (3) building reinforced dams that can contain or withstand tall waves resulting from falling rock or ice. These three steps have been followed in nearly all managed lakes in Peru. Diagram of the excavation process to lower water Cross section showing the characteristics of the spillway (left) levels of glacial lakes held by moraine dams or other and a lateral view of the canal showing the restored security loose debris. Diagrams by César Portocarrero dam that will contain surges resulting from falling ice (right). 3 SUMMARY OF THE GLACIAL LAKE HANDBOOK The standard methodology for managing lakes is as follows: Basic research: • Create an inventory of glacial lakes. • Carry out an initial assessment of lake characteristics including surrounding glaciers. Diagnosis: • If the initial assessment finds characteristics that indicate downstream risks, further study is warranted. • Analyze the hydrology of the watershed. Treatment: • Establish logistical access. • Implement safety measures based on information collected from the in-depth studies. • In most cases, the theoretical best solution is to completely empty the threatening lake. For practical reasons, one must look for an intermediate volume reduction that eliminates most of the threat at an affordable cost. Cuchillacocha Lake and its control dam, which was completed in 1974. The dam is circled in red in the left aerial photo and viewed from ground-level view on the right. Right photo by César Portocarrero Lazo Huntay Lake showing the massive hanging glacier in 1990 that still threatens the lake (left). Lazo Huntay’s newly completed safety works, also in 1990. Photos: César Portocarrero 4 SUMMARY OF THE GLACIAL LAKE HANDBOOK • The most common methods for reducing lake volume in Peru have been: o Cutting the downstream face of the moraine into a V shape. Lake levels should first be lowered by pumping or siphoning prior to cutting into the moraine. o After the opening has been cut, a reinforced concrete pipe is installed to maintain the reduced lake level. An earth dam with a stone façade is then built over the pipes. o Drainage tunnels can be drilled if the above isn’t practical or sufficient. o Filtration (seepage) can be used in very permeable terminal moraine dams. • All techniques require the highest standards in construction. Peru’s experience is that sometimes the safety infrastructure is not put to the test until many decades after its construction. Debris and flood lines on walls in Urubamba in 2010. Lower right: The path the Chicón River took through Urubamba in 2010. Photos: César Portocarrero Managing glacial lakes is inter-institutional: Understanding glacial lakes and risk mitigation requires research across a wide range of disciplines, including geography, climatology, anthropology, animal science, and botany, as well as the social and political sciences. Mitigation strategies should include the development sector because 5 SUMMARY OF THE GLACIAL LAKE HANDBOOK managing water as a resource is as important to many local populations as is disaster risk management for GLOFs. This inter-institutional work is most productive when done cooperatively. Social policy considerations in glacial lake management: Disaster risk management needs to fit into overall development planning to ensure that efforts are sustainable for the long run. This affects not only the technologies used for managing the lakes, but also whether and how these lakes are utilized to support a region’s water management planning. Water resources today are being seriously affected

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