Do you have any information about saturation, field capacity, wilting point or residual water of your soil? This could be a good starting point.

There are many methods that give you a SWCC, but first you need to know the precision that your model need. There are pedotranfer tables that can give you one approximation based on your soil texture or sophisticated methods that measure SWC in soil samples at different pressure heads... and both are adequate for different model precisions.

Dear Hassan,

In addition to what Jose has stated, the following publication entitled "A simplified method to estimate the soil-water characteristic curve"  by Kheng-Boon Chin et al. demonstrates a simple method for estimating the Soil Water Characteristic Curve.

Abstract:

This paper proposes a simplified method to estimate the soil-water characteristic curve (SWCC) for both coarse- and fine-grained soils using one-point SWCC measurement and basic index properties. Parameters of the Fredlund and Xing SWCC equation were correlated with the basic properties of 60 soils: 30 soils each of coarse- and fine-grained types. Sensitivity analysis revealed that the location of the one-point measurement at matric suctions of 10 and 500 kPa gave the most reliable SWCC using the proposed method for coarse- and fine-grained soils, respectively. The validity of the proposed method was evaluated using a total of 62 soils collated from published literature with 31 soils each of the coarse- and fine-grained types. The proposed method gives a good estimation of the SWCC and uses fewer parameters when compared with existing one-point SWCC estimation methods.

http://www.nrcresearchpress.com/doi/abs/10.1139/T10-033#.V04QSfl97IU

https://www.researchgate.net/publication/237152552_A_simplified_method_to_estimate_the_soil-water_characteristic_curve

Hoping this will be helpful,

Rafik

Article A simplified method to estimate the soil-water characteristic curve

thank you for your valuable links Abhishek Raj & Rafik Karaman