Final answer:
The distance between relief culverts should be approximately 8 diameters side-to-side and 15 diameters deep, according to a rule of thumb.
Step-by-step explanation:
In the context of relief culverts, the distance between them should be determined based on their size. One rule of thumb suggests that the distance should be about 8 diameters side-to-side and 15 diameters deep. For example, if the culvert has a diameter of 2 meters, the distance between culverts should be approximately 16 meters side-to-side and 30 meters deep.