Abstract:
Ketro Dam is one of several dams in Sragen District, East Java. The dam is located on the Bengawan Solo river network and fulfills irrigation water demand for 400 hectares of irrigation area. It has been running since 1984 and is considered one of the oldest dams in Indonesia. Like two sides of a coin that cannot be separated, the massive amount of water from this dam can either preserve human life or destroy it in times of disaster. One of the most catastrophic disasters that exist because of this infrastructure is the risk of having a dam-break event. Hence, this research seeks to create and implement an EWS (Early Warning System) for dam-break events in Ketro Dam. Dam-break cases have caused significant losses in life and economic damage due to the absence of the Early Warning System (EWS). A proper EWS in Indonesia is even more challenging due to insufficient data. Hence, this study proposes a simple-yet-effective EWS using a macro approach based on the evacuation time or the so-called Evacuation Clearance Time (ECT) for a data-sparse region. By comparing the ECT value with the arrival time of the floods from the affected areas, the required additional evacuation time can be obtained and used as the basis to determine the EWS. Based on the analysis, the proposed EWS for Ketro Dam is given in 3 levels of warning indicated by the reservoir water level: +100.35 m, +100.44 m, and +100.48 m. A dam-break disaster is an event that is difficult to predict. It is, therefore, possible for a catastrophic dam collapse to occur long before the hypotheses are carried out in the subsequent analysis. Therefore, to ensure that the proposed EWS can be accounted for, additional analysis of the downstream area of the dam is required for return period flooding without dam collapse. The research will be carried out by running a 2D flood inundation routing model using the HEC-RAS application. In addition to this analysis, the final EWS is proposed in the form of three warnings according to reservoir water elevation (+99.47 m, +100.44 m, and +100.48 m). With the proposed EWS, the results show that 100% of people are expected to reach the evacuation point safely. The case study show that the proposed EWS could reduce the risk impact of the dam-break events.
