How is soil water potential (matrix and positive pressure potential) related to water flow through the soil and pore size distribution?

Most ecohydrology studies quantify matrix and positive pressure potential when assessing the benefits of trees in reducing the risk of flooding. Comparisons are usually made between forested and non forested sites using pressure transducer tensiometers. I would like to know how soil potential is related to water flow in the soil. The significance of water potential in establishing soil moisture retention is clear, but that of pore pressure,water flow and pore size is still hard for me to understand