We continue the investigation of 2D P colonies introduced as a class of abstract computing devices composed of independent agents, acting and evolving in a shared 2D environment where the agents are located. Agents have limited information about the contents of the environment where they can move in four directions. In this paper we continue in the research of modelling of surface runoff by 2D P colonies. We add to the simulation environment information about flow direction and amount of water in pits (places without runoff, lakes,...). We compare the data from the simulation with the data generated by simulation model of water erosion SIMWE.