ANALISIS KOEFISIEN DEBIT (CD) PADA BENDUNG MERCU BULAT DENGAN VARIASI JARI-JARI DAN KEDALAMAN DIATAS MERCU (ANALYSIS OF DISCHARGE COEFFICIENT (CD) ON ROUND CREST WEIR WITH RADIUS VARIATION AND WATER DEPTH ABOVE CREST)

Abstract

Crest is the part of weir which has a function to raise the water level, flow the flood discharge and control the water level at upstream weir. From the various type of crest is known that round crest has a large discharge coefficient. The discharge coefficient (Cd) is a coefficient to change theory discharge to real discharge. The objective of this research was to obtain the value of discharge coefficient from round crest with multiple radius variation and to find out correlation between discharge coefficient and radius variation. This research was conducted at Hydraulic Laboratory FTSP UII by using fixed weir model with round crest variation, with R1= 1 cm; R2 = 2 cm, R1 = 1,5cm; R2 = 3 cm, R1 = 2 cm; R2 = 4 cm, R1 = 2,5 cm; R2 = 5 cm, dan R1 = 3cm; R2 = 6 cm with height 15 cm and width 10 cm. it was tasted by putting the model weir on the flume and flowing it with varies overflow height (h1). Data was taken on each variation overflow height. The result of the analysis shows that the value of the laboratory discharge coefficient (Cd) not much different with the value of the discharge coefficient obtained using by the KP-02 graph. With the relation between x (comparison of radius with h1) and y (discharge coefficient) is closely related to proven determination value that occurs more than 88 %. Where the influence from the length of the crest radius will affect the value of the discharge coefficient. The longer the crest radius will made the value of discharge coefficient close to 1, which means that the field discharge equal to the calculated discharge