A method of flood runoff estimation in an ungauged catchment (Ok Mani) in the highlands of Papua New Guinea : a thesis submitted in partial fulfilment of the requirements for the degree of Master of Arts in Geography at Massey University

Abstract

Ok Mani stream is one of the major tributaries of the Ok Tedi River in the Western Province of PNG. The catchment is located south of one of the world's biggest open-cut gold and copper mines, the Ok Tedi Copper Mine. The catchment is in one of the areas in PNG that receives the highest rainfall annually and is located within a region of very unstable geology. One of the mine's overburden storage dumps is located in the Ok Mani catchment and it subsequently failed due to the increasing weight of the overburden. The failure resulted in major changes to the morphology, sediment loads and the biota of the stream and the rivers downstream. The fieldwork of this dissertation was part of a major investigation undertaken to locate an alternative site in the catchment to store the mine's overburden. The dissertation presents the results of a study undertaken in the headwaters of Ok Mani stream. There is a discrepancy in the current runoff-rainfall record from the catchment, where runoff appears to be significantly greater than the rainfall. The study attempts to quantify the storm runoff from different sub-catchments and seeks to confirm or not the possibility of extra-catchment sub-surface flows into the catchment. The results indicate that the measured runoff and rainfall are not reliable and that discrepancies between runoff and rainfall did not support the hypothesis of extracatchment flows. There is evidence that rainfall increases significantly with increasing catchment elevation. However, the study undertaken for this thesis was very short and thus the results obtained are very limited. Therefore, further research into the sources of the excess runoff to that of the rainfall gauged at MAN04 is required before the runoff-rainfall discrepancy is put into perspective.