Classification of the Juturnaíba Dam: Potential Risk and Damage

A Dam Safety Program aims to reduce the risks to human life, property, and the environment from dam related hazards. In Brazil, despite of the contem-porary law about dam safety, there is still no cadastral information nor the classification of risk and associated potential damage to all dams. Besides that, the recent disaster caused by the failure of the Fundão dam, located in Maria-na city, Minas Gerais State, is an issue that aggravates the urgency of preventive measures and plans for disaster action. The present study proposes to classify the Juturnaíba dam, which maintains the largest reservoir for water supply in the state of Rio de Janeiro, Southeast region of Brazil. It was sought to analyze the risks and potential damage associated with the dam, in accor-dance with two classifications: one from the Brazilian Dams Committee and the other from the National Water Resources Council. It was possible to con-clude that the Juturnaíba dam potentially presents high risk and associated high rates of damage, both regarding losses of human lives and regarding environmental and socioeconomic impacts. This is mainly due to the poor state of conservation that it currently presents. It is recommended that future studies should assess the slope stability of the earth dam, and that repair work should be implemented on the degraded concrete structures, with recupera-tion or installation of instruments that would enable monitoring of possible movement of the earth dam.

precautions, a permanent residual risk exists [3]. [4] consider that the consequences of a possible accident involving water retention dams depend basically on the degree of danger associated with the flood, the degree of exposure and the vulnerability to destruction to which local individuals and assets are subject downstream of the dam.
Currently, there is a strong demand from society to understand the situation of the dams located in their surroundings from the safety perspective and their real risk exposure level from these structures. People are increasingly aware that safety is not an absolute condition but rather that there are risks that must be measured to know whether they are tolerable or not [5].
In this context, the purpose of dam safety programs is to recognize the potential hazards offered by these structures and to reduce them to acceptable levels.
Safe dams can be built, and potential deficiencies in safety can usually be corrected before they cause socioeconomic losses, loss of life or ecological disasters [6].
Thus, it is important to act in a preventive manner, particularly in the monitoring and inspection of dams. It should be noted that human, environmental and property losses, such as those of the Fundão dam (Mariana city, Minas Gerais State), are issues that aggravate the urgency of preventive measures and plans for disaster action.
In the state of Rio de Janeiro, the situation is similar: the Juturnaíba dam, which is the largest water reservoir for human consumption in this state, has been exhibiting serious problems in recent years. It is thus imperative that an intervention is made and that there be greater regulation and maintenance control of this structure in the future [7] [8].
Considering this scenario, this paper seeks to analyze the construction process and current conditions of the site and to classify the Juturnaíba dam by risk category and associated potential damage.

Literature Review
The causes of dam ruptures can be divided into human and natural causes.
Among the human causes, there are acts of terrorism and war, errors of design and construction, and operating faults. Natural accidents, however, cause unplanned demand or reduced strength on a dam, causing rupture. Among natural Journal of Water Resource and Protection accidents, exceptional floods have been observed that result in water levels rising upstream of the dam and overtopping to occur. This event causes a flood more severe than the project design flood or, in the case of dams with controlled spillways, when very high speed of water level rise, spillways are not activated in a timely manner. In the latter case, the issue becomes critical due to the dynamics of decision-making regarding the opening of floodgates, such as occurred at the Euclides da Cunha dam located on the Pardo River in the municipality of São José do Rio Pardo, which ruptured in 1977 due to a delay in action [9].
According to [10] and [11], out of the 5,268 dams built before 1950, 117 of them (2.2%) ruptured. After 1950, excluding China, out of the total of 12,138 dams built, 59 (0.5%) ruptured. Most of these ruptures occurred in dams with a height of less than 30 m. According to the authors, most of the ruptures occurred in newly built dams, often in the first 10 years (70%) and, typically, in the first year of operation.
For concrete dams, foundation problems are the most frequent cause of rupture due to internal erosion (21%) or low shear strength (21%). For soil and rockfill dams, the most common cause of rupture is overtopping (31% as the main cause and 18% as a secondary cause), followed by internal erosion in the body of the dam (15% as the main cause and 13% as secondary) and foundation problems (12% as the main cause and 5% as secondary cause). For masonry dams, the most frequent cause is overtopping (43%), followed by internal erosion of foundations (29%) [11].
According to [10], when a failure is related to the auxiliary structures, the most frequent cause is insufficient spillway capacity. In this case, when failure occurs, it is typically abrupt, causing an instantaneous wave, which rapidly increases water levels as it propagates downstream. This is the most likely accident to cause fatalities due to the short time available for warning. As stated by [9], soil or rock dams generally do not withstand overflows because the erosion process causes progressive rupture and cracking, through which the water flows freely.
To minimize the risks involved in dam construction, safety standards used globally, including in Brazil, establish that the design flood should be exceptionally severe as determined using the Probable Maximum Flood (PMF) concept. It is recommended that for a satisfactory safety level, the recurrence interval (RI) associated with the PMF is equal to 10,000 years (i.e., decamillennial) [9].
The criteria for dam classifications vary from country to country. In Brazil, the Brazilian Dam Committee (CBDB) classified dams based on risk potential, size and floods recommended for the design of the spillway, as shown in Tables   1-3  container containing hazardous waste; and associated potential damage category rated medium or high [12].
Resolution CNRH 143, dated July 10, 2012, established the general criteria for classification of dams by risk category, associated potential damage and reservoir volume [13]. To classify dams used for water accumulation, the volume of its reservoir is considered: small (volume less than or equal to 5,000,000 m 3 ); medium (volume greater than 5,000,000 m 3 and less than or equal to 75,000,000 m 3 ); large (volume greater than 75,000,000 m 3 or equal to 200,000,000 m 3 ); and very large (volume greater than 200,000,000 m 3 ).
The supervisory agent must then complete the tables in Appendix II of Resolution CNRH 143/2012 and cross-check the information for classification. The RC corresponds to the sum of CT (Table 4), SC (Table 5) and SP (Table 6), which determine the dam risk indicator. In the tables, the numbers in parentheses correspond to the score of the development.
The final result allows the dam to be classified based on the RC, as shown in Table 7. Table 8 shows the APD score, and Table 9 lists the final classification of the dam according to the score achieved.

Region and Site Characterization
The São João river basin covers an area of 2160 km 2 and is fully included in the state of Rio de Janeiro, Southeastern Brazil, as shown in Figure 1. The municipalities included in the basin are Araruama, Cabo Frio, Cachoeiras de Macacu, Casimiro de Abreu, Rio Bonito, Rio das Ostras, São Pedro da Aldeia and Silva Jardim [14].        Table 9. Classification ranges for the associated potential damage category (Adapted from [13]). It is noteworthy that the São João River basin is an Atlantic Forest conservation unit, called the APA of the São João/Mico-Leão-Dourado River Basin. In addition, the Poço das Antas Rebio is downstream of the dam [18]. As stated by [17], the damwas designed in 1972 by the Ministry of Interior, and the National Department of Sanitation Works (DNOS) was responsible for the management and supervision of the site. Initially, the dam was designed to accumulate water for the domestic and industrial supply of the Lagos Region to control the floods in the São João River and to provide water to irrigate the areas downstream of the dam. The work began in January 1979 and was completed in 1984. According to [15], the dam is located at 22˚35'S and 42˚16'W.
The main physical and hydraulic characteristics of the dam and civil structures are listed in Table 10.
According to [17], the left abutment of the dam is supported by the Crioulas Hill, while the right abutment is supported by the Madureira Hill. Downstream of the spillway a structural concrete bridge of 180 m was built, serving as a connection between the São João River's banks.  (21); (17) Type Labyrinth with 4 elements (21) Total width 163.5 m (21) Total development 710 m (17) Crest elevation 8.40 m (21) Bottom elevation 3.00 m (21) Height 5.40 m (21) Maximum water level on crest (NAmax max) 11.40 m (21) Flow corresponding to maximum water level (Q) 5600 m 3 /s (21) SLUICES WITH STOP-LOG FLOODGATES (22); (23) Right side of spillway 4 units (23) Left side of spillway 4 units (23) Width of each unit 1.20 m (23) Height of each unit 1.20 m (23) Minimum operating water level 3.00 m (22) Maximum operating water level 8.60 m (22)

Construction Aspects
On August 15, 1975, a technical team from the now-closed DNOS made up of engineers and geologists explored the site of the future Juturnaíba dam project to investigate the conditions of local foundations and concluded that the soil was peaty with layers of clay from soft to very soft. Given the differentiated foundation conditions along the axis, typical sections were proposed per stretch [20], as shown in Figure 2. Section I is 1300 m long and extends from the left abutment to Crioulas Island. Because the local foundation is in sand, it was suggested that a sealing trench wall be dug. However, during excavation, pockets of soft clay were found.  [20]). Journal of Water Resource and Protection same typical section as Section II, a study of the behavior of organic soils/soft clay was performed through the construction and rupture of an experimental landfill, built from February to April of 1980, which supported the study developed by [25]; this was required due to precarious foundation conditions caused by the soft clay layer, which ranged between 7 and 10 m in thickness.
The excavation of Section IV's foundations, which were located between the two islands, also began in May 1981. All soft material composed of peat and soft clay was removed, reaching a foundation in sands. Construction of this section continued normally, achieving the crest at the 12.0 m elevation in November 1981 [20]. Construction of Section V, which is located between piles 35 and 40, began in June 1982. An important detail was the execution of the drainage at the foot of the dam. Due to the possibility of a flood in the summer, it was decided in December 1982 to raise the dam in Section V up to 9.0 m in elevation. In February 1983, it was then decided to raise Section V with maximum increments of 50 cm of landfill in 3 days. At that time, the foundation settlings of Section V had reached 60 to 70 cm. A similar decision was made for Sections III-2 and II, when settling was found to range from 70 to 90 cm. Due to the scarcity of financial resources, construction took 5 years [20].
With regard to the design and construction of the Juturnaíba spillway, no documents related to the calculation worksheets of the design flow sizing were found. The only available document found was the drawing titled "Zigzag Spillway Model-Plant-Sections-Details" [21]. In the drawing, detail "1" shows the cross-section of the spillway, in which only the design flow of 5600 m 3 /s is identified without an associated recurrence interval. Thus, to evaluate the damping of this flood and its lamination through the spillway, [26] estimated the PMF and found the figure of 5587 m 3 /s, showing that the DNOS design flow is compatible with the 10,000-year flood; thus, the Juturnaíba spillway was dimensioned according to dam safety criteria. Figure 3 shows a reproduction of detail "1" from the original DNOS plant.

Current Site Situation
To understand the current situation of the site, a visit to the reservoir and Juturnaíba dam was conducted on January 13, 2016 with technical assistance from the Rio de Janeiro State Agency for the Environment (SEA).
Access to the dam allows the option for two different paths on a dirt road: one that leads to the crest, and another that leads to the foot of the dam. We decided to visit the crest of the dam. Along this access road, state agency signs can be seen, prohibiting the entry of vehicles and unauthorized persons, as well as the presence of barriers that prevent the passage of larger vehicles, such as trucks and tractors.
During the inspection, agricultural activities were visible in the area surrounding the lake. When crossing the ridge, the undesired presence of animals was observed, especially cattle and termites. Inspection wells were also observed, Journal of Water Resource and Protection Some of the covers in these inspection wells were found to be damaged by rust, while others did not have covers. Given the dangerous conditions, it was not possible to inspect the interior of the wells, Figure 4.
Following a dirt road, we arrived at the site of the hydraulic structures of the dam after passing Crioulas Island. The dam has a labyrinth spillway with 4 cycles and 8 sluices, 4 on each side. It was observed that each side of the spillway also has a concrete channel. This complementary structure would allow the construction of channels adjacent to the São João River, which would lead outflow water for irrigation of local agriculture. However, the irrigation channels do not exist.
The hydraulic structures on the right side of the spillway are damaged, as shown in Figure 5. The structure of the restitution channel on the right side had collapsed; broken concrete blocks were visible. Vegetation was also found where the complementary channel should be. In addition, four sluices were found to be closed by their respective floodgates; however, water still flowed downstream, indicating poor sealing.
The walls of the restitution channel on the left side of the spillway were also found to be collapsed, as shown in Figure 6 and Figure 7.      In the restitution channels on both sides of the spillway, grooves for the descent of the stop-logs panels were visible. However, the panels were not located in the grooves nor in any location near the observed location. Thus, if there is a problem or need for maintenance of the floodgates, water will flow through the dam restitution channels without any type of control.

Results and Discussion
Regarding the CBDB criteria listed in Tables 1-3, the Juturnaíba dam can be classified as high risk potential in terms of life and economic losses (Table 1) because there are extensive areas of agriculture and livestock downstream of the dam. Additionally, the 2nd district of Casimiro de Abreu, called Barra de São João, is at the mouth of the São João river and has a population of approximately 9000 inhabitants according to information from [27]. In the classification of the dam size (Table 2), the Juturnaíba site can be considered small in relation to height (5 to 15 m) but large in relation to stored volume (above 50,000,000 m 3 ).
In the classification of spillway design (Table 3), the associated risk was Journal of Water Resource and Protection Figure 11. Islands of sediments downstream and close to the hydraulic structures of the dam [26].
considered high because the design flood should have a recurrence interval of 10,000 years (i.e., 1 PMF) regardless of the dam size being medium or large. Tables 4-9 show the general criteria for the classification of dams by risk category, associated potential damage and reservoir volume, as established by resolution CNRH 143.
Regarding the technical characteristics ( Regarding the state of conservation (Table 5), the site achieves the following scores: reliability of the overflow structures (10); reliability of adduction structures (6); percolation (3); deformations and settlements (1); deterioration of embankments/walls (5); and locks (0). In some places, access was not possible during the field visit; however, it was determined that no instrumentation is in operation based on information from the technicians responsible for inspection. Therefore, it is not possible to monitor displacements and pressures on the dam body. The sum of SC points was 25.
Regarding the dam safety plan (Table 6), the site achieves the following scores: existence of documentation (4); organizational structure and technical qualification of the dam safety team (8); procedures for safety inspection and monitoring (5); operational rule of dam discharge devices (0); and safety inspection reports with analysis and interpretation (3). The total SP score was 20.
The final score of the risk category corresponds to the sum of the TC, SC and SP scores, and the result was 60. It should be emphasized that if the RC is greater than or equal to 60 or if the SC score is greater than or equal to 8 in any analysis Journal of Water Resource and Protection parameter, the dam is automatically classified as a high-risk category, requiring immediate action by the developer ( Table 7). The Juturnaíba dam was thus classified as high risk.
Regarding the associated potential damage (Table 8), the site yielded the following score: total reservoir volume (3); potential loss of life (12); environmental impact (5); and socioeconomic impact (8). The total score for the APD resulted in 28, which allows rating the dam as having high associated potential damage.
These results allow us to infer that by both the classification of the CBDB and the classification of Resolution CNRH 143, the risk potential associated with the Juturnaíba dam is high.

Conclusions
Both the potential and risk category of the Juturnaíba dam are high. Thus, due to the reservoir volume, potential human losses and environmental and socioeconomic impacts, potential damages can also be classified as high.
Efforts must be concentrated on defining prevention, mitigation, preparation, Conducting interventions on degraded concrete structures and recovering or installing instruments to monitor the stability of the earth dam are also recommended.