Effects of improper land-use in increasing flood damages in Karaj river floodplain (north central Iran) and damage control strategies.

Floodplains are flat land areas which are part of a river system and usually experience floods during heavy rain falls. One of the most important floodplains in northern Iran, close to the Capital city of Tehran is "Karaj" floodplain which is produced by the Karaj River. This floodplain is of great importance not only geographically but also in terms of industrial activities, population growth and density and socio-economically. Due to its low water level during the dry seasons, and lack of governmental control, the river banks and peripheries have been heavily used for urban and industrial developments. Since the river is flowing in a flat floodplain, construction of levees and dams or any other structure along the river in order to prevent flood damage might be ineffective and requires great expenses and can not be justified. Therefore, other means of flood damage prevention (i.e., non-structural) must be planned. In the present paper, "SARJOOY" village, a newly urbanized area in Karaj River floodplain, was chosen as a case study. Floodplain mapping was conducted using HEC-RAS hydraulic model. The results were processed in GIS environment using ArcView GIs, and hazardous and sensitive zones were determined. Outputs of HEC-RAS used for calculating water surface levels in urbanized area and two types of residential structures (with and without basement) in 100-yr flood event boundaries were chosen for damage calculations. By using floodplain regulations in developed countries and choosing flood insurance as an indicator and calculating the expected costs and insurance rates for each criteria and expected annual damage (EAD) for each structural type, guidelines for managing this floodplain have been compared and the best method for management is proposed.