Necati Agiralioglu

Diverging overland flow

Abstract This study investigates divering overland flow utilizing kinematic wave theory, which does not appear to have been dealt with previously. Explicit analytical solutions are derived in dimensionless form for space-time invariant rainfall. Analytical solutions do not seem to be tractable for time-varying rainfall. Depending upon the duration of rainfall, equilibrium and partial equilibrium cases are distinguished explicitly. The effect of divergence parameter on the hydrograph shape is shown. The adequacy of kinematic approximation for characterization of diverging overland flow is tested against laboratory watershed results. The diverging overland flow model is found to yield results which compare well with observations and with those of a plane model.

The analysis of 2004 flood on Kozdere Stream in Istanbul

The climatic and physiographical factors of the Kozdere Creek Watershed are examined to find out the causes of the flood of August 11, 2004. Actual land use has been obtained from forest management stand plans and classified satellite images. The multispectral digital satellite data set belonging to years 1992, 1993, and 2005 was used to determine the status of land use. Physiographic factors, including the slope and the aspect, have been identified from digitized ortho-photo maps in the GIS environment. Since flow records of Kozdere are not available, flow values corresponding to different return periods were obtained using regression analysis of neighboring streams. No noticeable alteration of the land use occurred between 1992 and 2005. Since the physical factors are the same as they were during the 1985 rain, the flood after the 2004 rainfall cannot be due to the physiographical factors of the upper watershed. The existing channel in the neighborhood is not enough to convey even the 10-year return period flow. Thus, the 2004 flow did not fit into this cross-section and flooded houses on the alluvial fan. The cross-section of the Kozdere Creek passing through the PTT neighborhood should be increased, and the surface roughness should be decreased by covering the channel with concrete in order to prevent floods.

Overland flow on a diverging surface / Ecoulement superficiel sur une surface divergente

ABSTRACT Many basins in nature diverge or possess diverging elements. This study formulates a diverging flow model utilizing kinematic wave theory. The kinematic equations are solved using a first order explicit finite difference scheme. The model is tested using data on a number of laboratory basins reported in the literature. A comparison of this model with the plane model shows that they yield different concentration times and hydrographs that differ in shape, depending upon the degree of divergence.