Investigation of the Effects of Land use Change on Low flow Indices (Case study: Taleghan catchment)

Low flows are the most important parameters for the qualitative and quantitative hydrological analysis of the catchments and have a significant role in the planning and water resource management. Several factors are involved in low flow trend, including, land use and vegetation that directly and indirectly affected by the interference of humans. Low flow data, within a watershed is used for a wide range of activities including: drought planning, investigation of ecosystem status, planning water demand, water pollution issues, development projects in the field of power generation and environmental studies. Low flows from various aspects have been investigated. Some of these cases can be pointed to research Riggs (1990), Warner (2003) and McMahon and Nathan (1991). They were used a linear correlation and multivariate regression methods to estimate low flows. For prediction and investigation of the effect of land cover variation on flow parameters, several studies have been done, including research of Zhao, (2010) and Wei and Zhang (2010). The impact of land use and climate change on the hydrology of Alabama coastal basins by Ruoyu, et al was evaluated by hydrological modeling. Direct and indirect effects of human in land use changing and its role on water resources have studied by some researcher. Including: Kashaigili, (2008) and Delgado et al (2010) the aim of this study was to investigate the role of land use change on a number of low flow indices in Taleghan catchment.
In this research, by using topographical maps with the scale of 1:250000 and 1:50000 and Positioning the Galinak gauging stations in Taleghan river, the study area was Determined. Then using aerial photographs with the scale of1:20000 and TM and ETM satellite images of 1366 and 1381, land use map in the four-level of rangeland, dry land farming, irrigated and rock outcrop were prepared. Then land use change was calculated. Base flow index using daily data and based on, one parameter recursive digital filter algorithm were extracted by HydroOffice, 2012. Low flow indices with 3, 7, 15, 30 and 60 days duration using daily data were extracted. Then relationship between low flow indices and land use in the period of study were investigated. In this research, land use changes in the basin using the interpretation of aerial photographs and satellite imagery in three intervals of the years 1349, 1366 and 1381 were investigated. Base flow index using daily data and one parameter recursive digital filter algorithm were extracted. Low flow indices with 3, 7, 15, 30 and 60 days duration using daily data were extracted. Then relationship between low flow indices and land use in the period of study were investigated.
The results showed that all of the low flow indices in the first period of study have experienced a steep upward trend. This trend in the second period during the years 1349 to 1366 also shows an increasing trend but with little slope. In the period 1366- 1381 all indices, including base flow index and other low flow indices a minimal decline have experienced. Increasing rangeland coverage of 81 with respect to 49 was in accordance with the increasing of indices in the period studied.
Land use Changes due to direct and indirect human intervention has a direct impact on the trend of low flow indices.Conformity of vegetation cover trend in 49 to 81 years with trend of low flow indices, indicating a positive role of rangeland on increasing the low flow indices. So rangeland protection to ensure, base flow continuity in the research area, is essential.