Assessment the effect of floodwater spreading practices on topsoil infiltration rate (Case study: Chandab- Varamin Basin)

Floods deposit huge amounts of suspended and dissolve materials of different sources on alluvial fans and therefore change soil characteristics such as permeability over the time. This research was carried out in Chandab- Varamin basin to assess the effect of floodwater spreading practices on topsoil infiltration rate using Double Rings. 10 cm of topsoil layer was collected from the profile and analyzed in the laboratory. Results showed that fine sediments (silt and clay) have been deposited in soil surface layer. Meanwhile، the permeability rate in the first row was measured control about 50 percent، in the third row of about 35 percent and about 42 percent of total area has decreased compared to the control area. Also، infiltration rate was decreased about 73 percent in the first band، 31 percent in the third band and about 52 percent in the whole area compared to the control area. Comparison of clay amount in control and treatment areas showed that their accumulation on soil surface changes negatively، soil physical characteristics including soil texture and makes soil more crusty which gradually decrease soil infiltration in floodwater spreading site.