Karst Water • Resources (Proceedings of the Ankara - Antalya Symposium, July 1985). IAHSPubl. no. 161 A MULTIDIMENSIONAL APPROACH TO RAINFALL-STREAMFLOW RELATIONSHIP IN MANAVGAT RIVER BASIN, TURKEY A. Ankan and M. Ekmekçi Hydrogeological Engineering Dept. Engineering Faculty, Hacettepe University Beytepe, Ankara, Turkey Abstract Manavgat river basin has an area of 928.5 km 2 in the Taurid Belt, a highly karst- ified region in Southern Turkey. The total annual discharge of Manavgat river is equal to 3.4 times as much as the avarage annual rainfall onto the surface catchment are which indicates an inter-relationship between the study area and adjacent basins (Giinay, 1981). It is believed that the complexity in the hydrogeological structure of the basin and karst systems cannot be explained unless some hydrogeological parameters are well defined. These parameters can be defined by studying the Karst Hydrogeology of the region using mathematical statistics because the hydrogeological variables and functions are mostly of random character. Thus one should define also the stochastic components besides the deterministic components. In this study the difference between the subsequent daily peak discharge values and the sequantial daily rainfall events corresponding to the peak discharges are analysed. This analysis revealed valuable information about the stochastic characteristics of the streamflow in the basin. The response of the karstic aquifers is too difficult to define in mathematical terms or expressions that it forces us to hold it as a stochastic process. After calculating the effective rainfall using two deterministic (derived) functions a semi - stochastic model is developed to reproduce streamflow hydrographs for Manavgat river. The model is applicable to any other karstic basin only when the needed deterministic parameters are well - defined for that basin. Introduction The study area, Manavgat basin, takes place in the Taurus Mountain (Southern Turkey) region which has a very great water resources potential that might be available for development in the immediate future. But the complexity in the hydrogeological structure of the region causes serious delay in the studies required to evaluate adequately 57