Extraction of Structural Curves, Regression Relations and Structural Regression Relations in the Tidal Limit of the Karun River

Abstract

The Karun River is the most important tidal river in Iran. Two factors are governing of hydraulic conditions of tidal rivers (fluvial flows and tidal flows). Fluvial flow concerns hydrologic and physiographic conditions of watershed and characteristics of rainfall while tidal flows are produced by gravity of moon and sun, reflection wave from beach, effects of shallow water in estuaries and the shape of beach. Because tidal flows move to upstream and fluvial flows go toward downstream in the tidal limit of the tidal rivers, hydraulic conditions of this part are very complex. The measurement of discharge and velocity of current is impossible in this part. For determination of discharge-stage curve in tidal limit, an especial approach was applied in this research. Structural curves (an especial type of discharge-stage curve) were developed by using of discharge of fluvial flow in the upstream and tidal height in the downstream. For convenience of using of structural curves, these curves converted to regression relations. For determination of correlated water surface elevations to different return periods, structural regression relations were extracted by regression relations, joint probability method and combination coefficient. In this research, four methods made used of determination of combination coefficient. These methods are conventional method, desk study joint probability method, analytic joint probability method and developed analytic joint probability method by researcher. The results of developed analytic joint probability method by researcher have the best fitness by observed data in the Karun River. At the end structural regression relations showed correlated water surface elevation to each combined return period of fluvial flow and tidal flow.