Zonation of health dynamism for the Shazand Watershed based on low and high flow discharges

Developing an understandable and comprehensive conceptual model for watershed health assessment is one of the main priorities of many various managerial and policy making projects in the world including the mega project on the integrated watershed management of Iran. Towards this, the present study as the pioneering research in the country has been conducted to customize the reliability, resilience and vulnerability (RelResVul) conceptual model based on hydrological data to assess watershed health. To this end, firstly the long-term data of discharge of the Shazand Watershed that located in Markazi Province was prepared and the flow duration curve was accordingly derived. Secondly, the appropriate thresholds of low and high flow discharges as prerequisites for watershed health assessment were applied to the RelResVul conceptual model. Hence, the reliability (Rel), resilience (Res) and vulnerability (Vul) indicators were calculated for four node years of 1986, 1998, 2008 and 2014. Finally, the general health state of the Shazand Watershed and its different sub-watersheds was zoned on the basis of two low and high flow discharge criteria through the geometric integrating of the mentioned indicators. The results showed that for the four study years respectively, 59, 53, 68 and 66 % of the watershed in terms of low flow discharge as well as 19, 22, 54 and 38 % of the Shazand Watershed in terms of high flow discharge were situated beyond relatively healthy state. The watershed health index assessment indicated the moderate and relatively healthy states with improving trend for low flow discharge criterion and moderate healthy state with constant trend for high flow discharge criterion. In addition, the results were verified the spatial changeability of watershed health state in different sub-watersheds for the study years.