INTERACTION BETWEEN SEDIMENT TRANSPORT AND FLOOD FLOW: THE CASE OF KOMPSATOS RIVER BASIN, GREECE

For the flood event of November 1996 (27-30 Nov., total rainfall depth 264.5 mm), the hydrograph and the corresponding sediment graph at the outlet of the mountainous part of Kompsatos River basin (Thrace, northeastern Greece) were computed. The mountainous part of Kompsatos River basin has an area of about 567 km(2), consisting mainly of forest and bush. For more precise calculations, the basin was divided into 18 natural sub-basins. Kompsatos River has a length of about 65 km, from which 9 km flow through the flat part of the basin, and discharges its water into Vistonis Lake. The computation of the hydrograph was enabled by means of the following models included in the well-known hydrologic software HEC-HMS: (a) Soil Conservation Service (SCS) Curve Number, (b) synthetic dimensionless unit hydrograph of SCS, (c) hydrograph routing model Muskingum-Cunge. The computation of the sediment graph was enabled by combination of the above composite hydrologic model with the soil erosion model of Schmidt (1992) and the stream sediment transport model of Yang and Stall (1976). The flood hydrograph and sediment graph computed for the outlet of the mountainous part of Kompsatos River basin were routed in the flat part of the basin by means of the well-known hydraulic software HEC-RAS, for quasi-unsteady flow. The computational process is based on the Manning equation for the computation of energy slope, on the energy conservation equation for the computation of the flood depth, and on the sediment continuity equation, in combination with Yang equation, for the computation of the geomorphological bed evolution. From the computational results of HEC-RAS application, the water surface profile, the stream bed profile and the bed variation in the cross-sections of the flat part of Kompsatos River during the flood event can be visualised.