Soil water content, suction and characteristic curves in the coastal watersheds of the Pearl River Delta

The underlying bedrocks of Zhongshan and Zhuhai in the Pearl River Delta are mainly granite. Weathered granite soils in this region contain large proportions of gravel and grit, giving the soils a peculiar soil water characteristic curve (SWCC). This literature focused on the coastal watershed of Zhuhai City and analyzed soil texture in the watershed using “Mastersizer 2000”. The soils in the watershed are mainly sandy loam and loamy sand. On this basis, changes in the characteristics of the soil water content, suction, along with the responses to precipitation and evapotranspiration were analyzed. A scatter plot of the soil water content versus soil suction illustrates that SWCC (including absorption and desorption processes) at all depths of the experimental plot follows an L-shaped curve. For the desorption process, SWCC for soils with larger proportions of fine particles shows an inverse S-shaped curve for low water content and high suction sections. In order to obtain desired effects, we propose the use of “Gauss” and “Dose-response (Bi-dose response)” curves to fit SWCC.