Water is very powerful and destructive force during a flood. Ask anyone who has survived a flood and experienced the loss of their home or damage to their property, and they will agree. This video shows the powerful effects of water in just a short amount of time.
If Noah’s Flood was worldwide, then all over the earth we would expect to find billions of dead things buried in rock layers that had been laid down by water. And, that is what we find.
When we read in Genesis about water coming out of the “fountains of the deep” (Gen 7:11), this has generally been understood as underwater volcanoes erupting and spewing out countless gallons of water all over the Earth. Also in that same verse, we find where rain fell from the sky when the “windows of heaven opened up.” Water fell to the earth and possibly came from underground reservoirs for a total of 40 days and nights, and it stayed on the Earth for a total of 150 days before it started to recede. During those 150 days, there was a lot of tectonic activity on the earth (there are technical theories to help explain this type of activity). You can imagine that the water was quite muddy as it churned all of the Earth’s sediments together like a blender. Then, as the waters started to recede, the sediments separated into layers according to their density.
If there was a worldwide flood, we would expect to find these sedimentary rock layers all over the world and fossils buried within them. Today, you can see layers of sedimentary rocks everywhere such as rock outcroppings along the interstate, the Grand Canyon, and other places where rock strata are exposed. In between the layers there is no evidence of erosion, which shows that they were laid down on top of each other in succession, not with a long span of time in between. This link provides more information on various types of causes for sedimentary formations.
Fossils are found in these rock layers. The majority of fossils we have today were formed during Noah’s flood. The animals were not able to escape the torrential rain, and during the 150 days of the water churning on the earth, the animals were buried among the sediments. If a fossil formed over a gradual period, we would not find much left of the animal. If it was buried rapidly, we would find the animal and sometimes the skin intact. In fact, there is a fossil of a fish in the process of giving birth, a fish in the process of eating another fish, and a fish with another fish in its stomach. This would not be the case if the fossil was formed gradually.
Another evidence is flood legends. There are about 300 flood legends around the world, and generally speaking, they tell basically the same story about a flood, a boat, animals being saved, and so forth.
More evidence for a global flood can be found here.