Hydrological Safety of Vaturu Dam by Evaluating Spillway Adequacy

Abstract

Probable Maximum Flood is considered as one of the most adopted inflow design floods inassessing the adequacy of dam structure in current practices. It is the largest flood that could conceivably occurat a particular location and frequently estimated from Probable Maximum Precipitation (PMP). This studyincorporates hydrological modelling using HEC-HMS to simulate the outflow providing the results used in thecatchment procedure of translation of PMP to PMFs for a 24 to 168-hour duration. The adequacy of VaturuWater Supply Dams (CA= 40 km2) which is located in Fiji will be assessed in the context of extrememeteorological events of the PMP/PMF magnitude. The flood rise during these events should not exceed orovertop the dam crest level. Vaturu dam is a domestic water supply embankment dam built in the 1980s to caterfor the water supply needs of the Nadi and Lautoka supply zones. A conventional reservoir routing procedureusing the Goodrich method is then carried out for all PMP/PMF durations, i.e., 24 to 168 hours. During thisperiod, flood rise levels were noted to be restricted to the Dam Crest level of +532 m ASL. The results and itsanalysis validated the safety of the Vaturu Dam and the ability of the dam to discharge the onslaught ofPMP/PMF safely.