عنوان مقاله [English]
One of the crucial information, as input in modeling of hydrological processes, is relevant to soil moisture and especially the retention characteristic information available at catchment scale. This paper presents a method to relative approximation of these quantities shown. Accordingly, at the beginning, Determination and extraction of soil texture class's USDA method by Using soil texture class proposed by the Commission of the European Communities (CEC) (these method «CEC» has the 6 texture classes with codes 0 to 5) Was conducted. In continuation of these texture classes (texture classes USDA method) to estimate and AS a result in mapping the amount of field capacity and wilting point (for the whole country) is used. In these respect, the results showed that in general, the average range of soil moisture variations in texture classes by CEC method, for permanent wilting point is exceeded field capacity So that the changes for permanent wilting point than the average 6.77 to 10.9 and for the field capacity of 6.03 to 9.3 percent Is has the variations. Also in this study, according to expert opinion and utilizing scientific resources attempted to investigate the interaction between the effects of land use and slope of watershed in order to assess the information and the resulting the depth map of the surface layer of soil moisture retention. In this direction to assess and evaluate the applicability of the approach taken comply with the physics of the catchment, attempted to utilizing it (Effective depth map of the surface layer the soil moisture retention)along with wetting properties Maps of field capacity and permanent wilting point that was achieved the National Soil Map (the first stage of the research), In order to estimate and prepare a map of available moisture in areas of study there, Nishapur, Attaiyeh, Qaleh Meydan and Sabzevar as the regions chosen for study were used. The results indicate that the resulting map is proportional to the physics of the studied areas in order to achieve total available water and the role of the interaction basin slope, land use And well as the impact the moisture field capacity and permanent wilting point that was extracted from the soil map On Total available water is well evident. Accordingly, due to the integrated and comprehensive characteristics of moisture maps(field capacity and permanent wilting) for the whole country, this amount could be used as a primary domain of soil moisture characterized along with the method described in the effective depth of surface soil moisture retention on Hydrological modeling, particularly Understanding the phenomenon of a small amount of influence and power of water retention in the soil, the estimated components of water balance, etc. in order to prevent land degradation and soil and water resources management, to be used.