Experimental study of flood detention basins capacity in unsteady flow conditions

Document Type : Research Paper


1 Associated Professor, Dep. of Water Engineering, Faculty of Water and Soil, Gorgan University of Agricultural Sciences and Natural Resources, Golestan.

2 Dep. of Water Engineering, Faculty of Water and Soil, Gorgan University of Agricultural Sciences and Natural Resources, Golestan.

3 Department of Water Engineering, Faculty of Engineering and Technology, Imam Khomeini International University, Qazvin, Iran.


Due to increasing negative environmental impacts of storage dams, detention basins have been considered as an alternative solution instead of construction of concrete dams for reduction of flood damage in recent decades. Literature reviews on detention basins show that there are limited numerical and experimental studies in this regard. In this research the effect of bed roughness height of main channel on the inflow discharge has been investigated by considering the effective factors on the efficiency of basins in laboratory of Gorgan University in 2018.  Also, the general ability of using steady flow equations for unsteady flow was investigated by calibrating some of the discharge coefficient equations. For simulation, a metal tank was connected to a channel through a broad side weir. Three bed roughness heights of the flume in the range of 0.06 to 15 mm as well as three lengths of side weirs in the range of 30 to 90 cm were utilized. The experiments were carried out under unsteady flow condition by three inflow hydrographs with peak discharges of 17, 25 and 33 l/s and a base time of 504s. The flow depth was measured instantaneously by transmitter and the average inflowing discharge into the detention pond was calculated. According to the results, use of lateral flow discharge coefficient relationships of the steady flow cannot be generalized for unsteady flow. So, based on dimensional analysis of the Π-Buckingham theory, some relationships have been proposed for calculation of the average inflow rate into the detention pond and also for filling time of the pond. The maximum errors for calculation of the average inflow rate as well as the filling time of the basin were less than 15 percent. Also, increasing the streambed roughness can increase the average inflow rate to the detention basin by 25 percent.


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