Final answer:
A drainage ditch's location and size are influenced by topography, soil characteristics, river discharge, and the hydrology of the drainage basin area.
Step-by-step explanation:
The location and size of a drainage ditch are determined by a number of factors. Primarily, these factors include topography (relief), soil characteristics, river discharge, and the drainage basin dynamics. Topography dictates how water moves across the landscape, with steeper slopes causing more runoff and less infiltration, affecting the design and placement of drainage ditches. Soil characteristics influence how easily water drains through the soil and accumulates, which can affect both the size of a drainage ditch and its necessary depth. Lastly, the volume and speed of water flow, determined by river discharge and the overall hydrology of the area, dictate the dimensions needed for a drainage ditch to effectively manage water flow and prevent issues like flooding.