Computation of hourly sediment discharges and annual sediment yields by means of two soil erosion models in a mountainous basin

The objective of this study is the estimate of sediment discharges and sediment yields deriving from soil and streambed erosion, at the basin scale. For this reason, continuous simulations of soil and streambed erosion processes are performed in the mountainous part of the Nestos River basin, downstream of the Platanovrysi dam (Macedonia-Thrace border, northeastern Greece). For attaining the above, two composite mathematical models, each consisting of three submodels, are applied: a rainfall-runoff submodel, a soil erosion submodel and a sediment transport submodel for streams. The two models only differ in the soil erosion submodel. The rainfall-runoff submodel that is used for the computation of the surface runoff and the streamflow in the sub-basins is the deterministic distributed hydrologic model HEC-HMS 4.2. The first soil erosion submodel, utilized for the estimate of soil erosion in a sub-basin, is based on the relationships of Poesen [1985. An improved splash transport model. Zeitschrift fur Geomorphologie, 29, 193-211], while the second is the widely known Modified Universal Soil Loss Equation (MUSLE). The estimate of sediment yield at the outlet of a sub-basin, and finally at the outlet of the whole basin, is achieved by means of the stream sediment transport model of Yang and Stall [1976. Applicability of unit stream power equation. Journal of the Hydraulics Division, ASCE, 102 (5), 559-568]. The application of the latter mathematical models results in continuous hydrographs and sediment graphs at the basin outlet. The computed sediment discharge values are compared with field measurements. The statistic efficiency criteria utilized for the comparison between computed and measured values at the basin outlet provide satisfactory results. Therefore, it is concluded that the continuous hydromorphologic modelling can be successfully applied to the Nestos River basin.