Studying the Relationship between Environmental Factors, Runoff Characteristics and Infiltration Depth Using Rainfall Simulator in Northwestern Rangelands of Iran

Runoff leads to the leaching of soil nutrients, transports the topsoil particles and deposits the sediments in water reservoirs. Recognition of different environmental factors affecting the runoff properties and water infiltration depth has a great importance concerning soil for the integrated management of watershed and the distinguishment of complex hydrological processes. Thus, this research aims to determine the environmental factors related to the infiltration depth (ID) and runoff properties including runoff coefficient (RC), time to runoff (TR) and time to stop runoff (TSR) after stopping rainfall using a rainfall simulator. Three catchments involving Shahrchy, Zanjanrood and Glinak were selected based on the rain intensity in 30 minute duration with a 10 year return period in northwestern rangelands of Iran in 2013. The rainfall simulator was established in the rangeland units of each district to operate regarding 30 mm/h rainfall intensity for 30 minutes. Afterwards, data collection with respect to the environmental factors including vegetation (canopy cover and four species diversity indices), topography (slope, height and direction) and soil factors (from 0-30 cm horizons) was fulfilled. Data analysis (71 samples) was done using Pearson correlation and multivariate stepwise regression method. The validity of regression models (18% gathering data equivalent to 15 samples) was tested by R2 and other statistic indices. Results indicated that 77% variations of RC variable were accounted for canopy cover, sand content, organic carbon, clay content and nitrogen content of soil. Such factors as soil moisture, sand content level, lime content level, species number and Shannon diversity indices explained 73% variations of runoff after rainfall. Similarly, clay content, organic carbon and gypsum content of soil explained 82% variations of time to stop runoff )TSR( and such parameters as slope, latitude, organic carbon and silt content of soil explained 60% variations of infiltration depth )ID.