Investigation of Spillway Design Flood Hydrographs and Flood Operation Rule Curve for Ubol Ratana Storage Dam

Abstract

Ubol Ratana storage dam was constructed on Pong River in 1966. The dam crest was increasted due to
the massive floods in 1987. Due to the limitation of the meteorological and hydrological previously used for the dam design and also the dam was constructed over 50 years, the factors used in spillway design flood hydrographs should be changed such as the present land use compared with those before dam construction and weather. Therefore, the spillway design flood hydrographs as well as existing flood operation rule curves for the dam should be investigated by using such updated data and information. The results of reservoir routing for the maximum water level at Ubol Ratana storage dam study is +183.50 m.(MSL.) because It is controlled by the height of Noonsang Dike located at the upstream area. The results of flood routing at return period 2-200 years show that the existing controlling of spillway gates is enough to manage the flood hydrographs. For the flood hydrographs at return period 500-10,000 years with the initial water level at the spillway crest, +182.00 m.(MSL.), and start to release water when the water level exceeds +182.00 m.(MSL.),
the results revealed that the peak of water level in the reservoir are higher than the maximum storage level. Therefore, the flood hydrograph at return period 500 years must start to release water in flood season at the minimum reservoir water level +180.50 m.(MSL.) The opening of spillway gates at the level of +180.50 to +183.50 m.(MSL.) will be controlled to open with the ratio d/Dh equal to 4. For the return period 1,000 years. It must start to release water in flood season at the minimum reservoir water level equal to +180.00 m.(MSL.) and start to release water when the water level exceeds +181.50 m.(MSL.) The opening of spillway gates at the level of +180.00 to +183.50 m.(MSL.) will be controlled to open with the ratio d/Dh equal to 5. For the return period 10,000 years. It must start to release water in flood season at the minimum reservoir water level equal to +177.00 m.(MSL.) and start to release water when the water level exceeds +180.50 m.(MSL.) The opening of spillway gates at the level of +177.00 to +183.50 m.(MSL.) will be controlled to open with the ratio d/Dh equal to 2 and the Noonsang dike crest must be installed a barrier height of 1.20 meters