THE USE OF RETENTION POND TO PROTECT THE LAND FROM FLOODING IN LAMASI RIVER LUWU REGENCY SOUTH SULAWESI INDONESIA

Luwu Regency, South Sulawesi Province is an area, encountering a lot of flood problems because in particular the rivers in downstream are relatively flat increase sedimentation in the lower reaches of the Lamasi River. In this study one of the rivers in Luwu district, which often experiences flooding every year and has a length of 76.43 km and an area of river basin 432.80 km2 . The flooding caused losses of nine villages in the area surround the Lamasi river. The objective of this study is to determine the optimal capacity of the retention pond and the dimensions of the retention pool used based on the analysis using the Gumel and Nakayasu methods. The type of research based on the data is done by using a quantitative approach by collecting secondary data from the Central Office of the Pompengan and Jeneberang River Region in South Sulawesi province. The result showed that the optimal capacity of the retention pond is 1,600,000 m3 at 9.3 m elevation while the pool volume in the pond at the 10-year return period was 901,131.78 m3 and the water elevation in the pond is at plus 8.43 m. The dimensions of the retention pond are 3,069 m long and vary from 100 m to 300 m and within an average of 3 m, the height of the embankment is 1.50 m with the width of the embankment 5 m with an optimal reservoir of 1,500,000 m3 . The age of the retention pool functions effectively because of the sedimentation of 4,481.01 m3 per year estimated for 133 years