# Cracks in Arch Dams: An Overview of Documented Instances
## 1 Introduction  
Clean water and renewable energy sources are indispensable, particularly in those areas that have suffered large population increases (resulting in an increase in the demand for resources) or in areas that are undergoing desertification processes. Dams are essential for both of these purposes, and it is therefore necessary to develop policies and research studies focused on the efficient performance of dams. Dams are designed to harness and manage water resources and play a key role in providing essential services critical to human development. They are essential and sensitive infrastructures and perform different important functions by fulfilling a variety of significant economic, environmental, and social benefits, such as flood control, water supply, hydroelectric power, etc.  
The safe performance of dam systems is highly relevant, as their deterioration or malfunction can lead to economic costs and loss of human lives. In that way, the benefits of dams are sometimes counterbalanced by the risks they can entail in downstream populations and properties, making dam health studies an integral part of the effort to achieve efficient dam operation. This risk becomes critical for large dams and, according to the International Commission on Large Dams, ICOLD, more than 61,000 large dams have been built around the world [1]. Therefore, it is necessary to pay close attention to the design, performance and maintenance of a dam to ensure its reliability, safety and stability and to minimize the probability of major failure. The American Society of Civil Engineers report classifies dam risks as (i) high (potentially causing human losses), (ii) significant (economic losses), (iii) low and (iv) undetermined. Approximately 17% and 12% of dams fall into each of the first two categories [2], so it is essential to conduct structural health monitoring to protect dam structures.  
From the moment of construction and throughout their entire operational life, dams are subject to complex physical and chemical factors. This is especially true in the contextof climate change, which alters the maximum and minimum values for temperature oscillations, the main cause of cracking in arch dams. This translates into the fact that, in some dams, aging occurs more rapidly than expected, sometimes reaching at an early stage a critical degree of degradation [3]. This complexity leads to dam engineering problems being among the most challenging in civil engineering [4] not only due to their particular geometry, but also due to the interaction of different material phases (e.g., solid-fluid), the fact that the construction material is continuously changing over time (concrete, asphaltic membranes, permeability of earth dams, etc.) surrounded by a large amount of material that causes a higher degree of heterogeneity and lastly, due to the diverse nature of the loads applied.  
Research studies, such as the one presented below, categorize previously recorded events in arch dams, their characterization, evolution and causes. With this objective in mind, this state-of-the-art research is focused on arch dams that have suffered some type of cracking with the particularity of being limited to the dams for which public data about the cracks are available. This restriction greatly reduces the number of cases available, sometimes leading to very limited sources of information on the cracks presented. The following sections of this article are carried out as described below. In Section 2, a detailed compendium of the studied dams is presented, while Section 3 of this study provides a comparative analysis and discussion of the relationships between dam features and crack features. As previously stated, this analysis scale is severely limited by the small number of cases, rendering it therefore difficult to establish conclusions of a global scope.