Analyzing the 60-day low flow from upstream to downstream in the Karkeh Basin

Knowing how the low flow changes upstream and its trend provides valuable information on water resources management, water rights, and the improvement of crop patterns. It also helps to identify suitable areas for water control management along the river from water resources management perspective. In addition to economic issues, the preservation of river ecosystems is an important matter that has not received much attention so far. The 60-day low flow time of occurrence differs between upstream and downstream. The spatial trend of discharge also varies from upstream to downstream. In this study, some hydrometric stations of the Karkheh basin were investigated, and after data analysis, annual 60-day time series of low flow in each station were extracted. The average annual discharge was also calculated and the ratio of 60-day low flow to mean annual discharge was obtained and it was used as an evaluation index. Multivariable regression between the above indices and 60-day low flow were established with effective morphometric parameters. The results showed that the 60-day low flow had a significant correlation with the basin area (R2=0.8), and the distance of each station to the output of the Karkheh basin (R2=0.2) had the most correlation with the flow indices. On the other hand, in the upstream, the ratio of low flow to mean annual discharge was lower than the downstream flow, and the indices increased towards the outlet of the basin. Therefore, more attention should be paid to rainwater harvesting methods to manage water resources in the upstream basins.