Total sediment transport in the lower reaches of Þjórsá at Krókur : results from the year 2002

Abstract

This report introduces results from the year 2002 assembled in an extensive sediment sampling program that was initiated in the lower reaches of Þjórsá in 2001. The main objectives of the study were to evaluate the quality of suspended sediment samples taken at Urriðafoss by comparing them to suspended samples taken at the new cableway at Krókur and with the new hydraulic winch on the old cableway at Urriðafoss, and to collect additional suspended and bedload samples on the lower reaches of Þjórsá. The results show that grain size of suspended samples at Urriðafoss and Krókur varies greatly among sediment campaigns and among sampling sites at Krókur. Both the Urriðafoss and the Krókur samples appear to underestimate the sediment concentration of the total and coarse suspended material compared to the samples taken at the old cableway at Urriðafoss. Total bedload transport ranged from 1.3-134.3 kg/s, and was highest at 50 and 70 m stations. Coarsest bedload was transported at 70 m, but the finest material was usually transported at 40 and 140 m.