Investigation of Temporal Variations and Trend of Low Flow Analysis in Selected Alborz South Mountains Basins

Abstract

In recent years, over using of water, climate and land use changing in different river basins, have had different impacts on the river flow, particularly low-flow. With respect to the extraction of the groundwater resources and its effect on event time and the length of this time, it is essential to study the low-flow in different stations. The purpose of this study was to investigate and determine the trend of spatio-temporal low-flow in selected hydrometric stations in Alborz south mountains basins. For this purpose, daily discharge data were collected for different hydrometeric stations within the study area and 39 stations were selected. Daily discharge of these stations were reconstructed with correlation method and outliers were eliminated. Then, the time series of 5, 7, 10, 15, 30, 60 days of stations were calculated. Basins were then clustered into two classes including plain and no plain. The trend of low flows was calculated using Mann Kendall, Teil-sen, and spearman tests. For each cluster, a regression relationship was established between the low flow trend and basin upstream area. Results showed that about 10 stations had no significant trend and other stations found have significant negative trend at 1, 5, 10% levels. Plain basins experienced lower negative low flow trends as the basin area increased, which could be attributed to the over extraction of groundwater resources, but in no plain basins direct correlation was obtained as area increased.

Keywords

• groundwater resources
• low flow
• south alborz basins
• trend tests