Site selection to create riverine wetlands in watersheds (case study: Tajan river - Razavi Khorasan Province)

Riverine wetlands are waterbodies that are located at lowlands alongside rivers and are inundated during floods or recharged by aquifers. In order to identify and locate suitable sites for wetlands, the hydrological properties including watershed physiography, river discharge and its temporal (seasonal) variation as well as groundwater table fluctuation should be studied. Continued population growth and urgent need to conservation, rehabilitation and expansion of natural and valuable environments such as wetlands which support environmental services required by human should be strongly considered for sustainable development. The aim of this study is to assess utilization of biological capacity of rivers to restore the riverine wetlands in order to improve the biological and ecological conditions of the country’s wetlands.
In this research, the potential of Tajan River within the Sarakhs county, was identified considering presence of the streamside tree cover, specific ecotourism capacity, specific bird watching capacity, appropriate morphology of the river and inundation characteristics of floodplains. Creation of riverine wetlands alongside the Tajan River can play an important role in flood mitigation through storing of precipitation induced surface runoff. To this end, all factors affecting on delineation of proposed wetlands boundaries including geomorphological and geological, hydrologic, hydrodynamic, economic, social and developmental characteristics of the Tajan watershed were investigated. During field survey from the study area, on the basis of predominant condition from biodiversity, species, ecological, hydrologic and hydraulic point of view, four sites were determined as suitable for riverine wetlands within the watershed. Then, the cross-section of each of these sites have been surveyed and measured in detail in order to assess their morphological and hydraulic characteristics.
On the basis of flow Hydraulics and river morphology studies, two out of the four selected sites which are located within the Sarakhs’ Jahanbani Forest, due to low velocity of flow and high width of river in these river reaches were assessed as suitable for implementation of vegetation and wetlands restoration measures. Analysis of monthly discharge data of Polekhatoon- Kashafrud hygrometry station in recent years, indicates that the Tajan river flow is nil or negligible during warm months. Therefore, to supply water for the suggested wetlands, it should be relied upon floods and annual discharges from their upstream sub watersheds.
The annual discharge of the Tajan river at one of the suggested sites for the riverine wetlands within the Sarakhs’ Jahanbani Forest was estimated about125.9 MCM. This site due to its high potential for tourism and high diversity of birds can be exploited from various perspectives if tourism activities are developed in the region.