Experimental Investigation of Water Entrainment of Salty Density Current Over the Bed with Cubic Roughness

Abstract

Each year rivers transport a lot of sediments, especially for flood times, to dams’ reservoirs and the main cause for this transportation is density current phenomenon. This phenomenon forms when a liquid with a density of ( ) flows in another liquid with density of ( . This density deference could be due to the temperature, or dissolve solids, or suspended solids deference or a combination of them (Graf and Altinakar, 1998). Vargavand (2013) made a density current using the solution of water and salt and investigated the effect of a bed with cylindrical and conical roughness on water entrainment coefficient. His results showed that the water entrainment coefficient not only affected by Richardson number but the height of bed roughness is also an important parameter. Daryaee (2014) investigated the water entrainment coefficients for four bed slopes, two sediment concentrations and four different bed roughness height in a sedimentary density current. The results of this research showed that by increasing roughness height velocity decreases and this increases Richardson number and a result water entrainment coefficient decreases. However, roughness blocks cause for more turbulent flow which extended up to interface of density current and ambient water and this phenomenon makes more water entrainment. The aim of this research is to investigate the effect of bed roughness, bed slope, and hydraulic parameters of density current such as flow rate and concentration on water entrainment of a salty density current.

Keywords

• bed roughness
• turbidity current
• water entrainment coefficient
• dams reservoirs