Effect of Missing Rainfall Data on the Uncertainty of Design Floods

Abstract

Hydrological data is a collection of information or facts about the hydrological phenomenon. Mistakes in the hydrological analysis have a fatal effect on the accuracy or accuracy of hydraulic building planning, whether in the form of planning for irrigation buildings, flood control structures, drainage systems, weirs. And others hydraulics structure design. As we already know, rainfall data is the most important data in the hydrological analysis. The minimum amount of rainfall data required in the hydrological statistical analysis is 10 years. To obtain this 10-year data, often encountered incompleteness in recording the rainfall data. Meanwhile, hydrological analysis always required for any design of hydraulic structures. Based on the above statement, an analysis has been carried out on how much influence the completeness of data and availability of rainfall data in an area of accuracy in predicting the discharge plan in different times and make a Rating Curve. In determining the unit hydrograph, the Nakayasu method is used. The results of this study indicate that the completeness of the data is not very influential. This is evidenced by obtaining the discharge value at a certain return period which is not much different. From the unit hydrograph curve, it can be seen that in the first condition with a return period of 100 years, a discharge of 801.775 m3 / s is obtained, for the second condition consisting of 11 rainfall data, a discharge of 833.848 m3 / s is obtained, and for the third condition, ignoring the rainfall data. The missing of rainfall data obtained a discharge of 816,489 m3 / s. Where the difference inaccuracy in the first condition is 3.846% against the second condition, and the difference inaccuracy in the third condition is 2.082% for the second condition. In the rating curve section of Batang Kuranji, the normal water level discharge is 169.948 m3 / s with an elevation of 2.89 m. At the same time, the maximum discharge at the cross-section of Batang Kuranji is 748,260 m3 / s with an elevation of 6.99 m.