Measuring v.s modeling sediment discharge, case study: Kalimanci reservoir, Macedonia

The modeling of sediment discharge in ungagged basins has been always a challenge. The aim of this paper is to compare two modeling approaches with measured data. The data for the deposited sediment was provided by bathymetric measurements of the Kalimanci reservoir. It was calculated that mean annual sediment deposition is 214,325 m(3)/year. The first modeling approach was established using the Gavrilovic method. The catchment of the reservoir was subdivided into smaller sub-catchments and using GIS and remote sensing, the sediment discharge and sediment production were calculated. It was calculated that annually 202,551 m(3)/year sediment was deposited in the reservoir. The main part of the sediment was distributed by the river Bregalnica, 127,490 m(3)/year or 63%. The second approach was established by employing hydraulic modeling (HEC-RAS). The main scope of this approach was to establish the deposition of the sediment in the river Bregalnica and how much of this sediment reaches the reservoir. As sediment input in the HEC model was used the data for sediment discharge of all the river and torrent tributaries of the river Bregalnica, calculated also with the Erosion Potential Method by Gavrilovic. The sediment discharge using the second approach was calculated to be 152,231 m(3)/year. It was established that 75% of the input sediment in the river Bregalnica is deposited in the hydro-morphologic extension of the river, mainly in the valleys, where the slope of the river bed flattens. We conclude that calculated and measured values are similar and beside this all three approaches generate different insights into natural process.