Investigating the Impact of drought on the base flow using Standardized base flow index,Case study: Kaka-Reza catchment

Abstract

Understanding the interaction of drought phenomenon and hydrological response of catchments can lead to obtaining some information for optimal water resource management. The aim of this study is to investigate the temporal relationship between drought and groundwater contribution to stream flow, in Kaka –Reza sub catchment. In this study, the common period (1382-2017) was considered for the corresponding hydrometric and rain gauge stations. The standardized precipitation index (SPI) was then calculated at time scales of 3, 6, 9, 18, 12 and 24 months. Base flow and related index were calculated by B-flow-Line and Halick digital filter method in monthly, annual and total time bases. Then the standardized base flow index (SBFI), the base flow duration curve (BFDC) and the base flow duration curve shape index (SBFDC) was calculated. Changes in (BFDC) and the corresponding shape index and the relationships between (SPI) and (SBFI) were investigated and analyzed using the correlation method. The results showed that the average BFI during the research period was equal to 0.52 and its minimum and maximum were equal to 0.46 and 0.57, respectively. Also, the trend of bas flow changes is a decreasing trend with a low slope. The trend of changes SBFDC decreases over study period with a low slope. The rate of slope change is also from one to three percent, and close to the straight line, which indicates the tendency for base flow to be stable in the long time. The greatest impact of the drought phenomenon on the river base flow is in the time step of nine and twelve months. The correlation between SPI and SBFI with a coefficient of determination 0.87 confirms the increase in the groundwater contribution to base flow, with a delay of nine to twelve months.