Final answer:
The first step when building surface drainage structures is to determine the location and design of the structure.
Step-by-step explanation:
When building many types of surface drainage structures, the first step is usually to determine the location and design of the structure. This involves conducting surveys and assessments to identify areas prone to water accumulation or flooding and determining the best placement and size of the drainage structure. For example, in the case of a culvert, the first step would be to survey the area and determine the appropriate size and location for the culvert to effectively drain water and prevent flooding.