The challenges of the Brazilian electric energy regulatory agency on mitigate effects from 2024 Rio Grande do Sul floods
The high volume of rainfall caused various impacts, such as: loss of access, collapse of slopes and hillsides, damage to road structures and erosion. Power and communication supplies were also interrupted. By design, the 14 de Julho dam was dimensioned to withstand a flood that represents El. 111.50m in the
upstream reservoir, and the downstream level at El. 110.52m. Thus, in the limit load situation, the expected upstream/downstream gradient is less than 1.0m. On 02/05/2024 at 13:23h, with the reservoir level at 111.61m, there was a partial breach of the structure of the 14 de Julho Hydroelectric Power Plant from the right shoulder, the controlled spillway gates were partially open and unable to continue the opening process. Due to the loss of measurement of the level downstream of the dam, it was estimated from a photo taken on 01/05/24, with the downstream level approximately at the trunnion beam, which represents El. 98.00m. In this condition, there is an upstream/downstream gradient of approximately 13.6m. This gradient is a consequence of the impossibility of opening the gates fully and represents a load above the limit for which the structure was designed. Figure 12 shows the damage caused to the dam structure after collapse.
Figure 12. 14 de Julho dam after partial collapse[CERAN, 2024] The EAPs have been operational since 30/04/2024. When the EAP was activated during the event,
there were no difficulties in liaising with the regional and municipal Civil Defenses and other parties involved.
On spillway region, the post-event inspections results identified some adhesion loss between the roller- compacted concrete (RCC) and conventional concrete (SCC) layers, which could indicate that no bonding mortar was used between the RCC layers. Between the construction joints of the face layers of SCC, it was also not possible to identify the treatments between layers. In view of the observations regarding concrete technology, it was recommended that an investigation
plan be carried out, using boreholes, water loss tests, borescopy, ultrasound and laboratory tests, in order to support the preparation of the executive project and any treatments. Nevertheless, post-event inspections showed that the remaining structures are stable for the plant’s operating flows. Although there is no structural risk, the plant has been maintained at a Safety Level of ‘Alert’ until the dam restoration is completed, in accordance with REN 1.064/2023.
5.2. Salto Forqueta small hydroelectric power plant The dam, located on the Forqueta River in the municipalities of Putinga and São José do Herval, partially broke due to structural damage on its right bank caused by landslides. In addition to the emptying of its reservoir, there was flooding in its Powerhouse.
Vol XXXIII Issue 3 | Dam Engineering | 169
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