In this video the driver has taken an easy, shallow river crossing too fast essentially converting his tyres into a pump which saturated inside of the bonnet instantly flooding the engine with water.
The primary lesson here is not that a snorkel was required but that you should always approach your crossing in a safe manner with safety and impact in mind. While it may be fun to smash through and create the largest waves, we need to consider the impact we may have on our vehicle and the environment. After all, If we all rip up the tracks today, we'll have no tracks tomorrow.
Personally, Before engaging my first river crossing without a snorkel the first thing that I did was check the location and height of my air intake, then watched some videos to get an idea of approximate how deep I could go at various speeds and the depth expected on my trip.
No amount of preparation can tell you exactly what to expect as river depths can change depending on rainfall (either local or off in the distance) so perhaps the best prepared you can be, is being prepared to say no if the conditions aren't right.