Rapid vs Waterfall

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Rapids and waterfalls are both hydrological features but differ in their formation and the flow of water.

Comparison chart

Rapid versus Waterfall comparison chart
	Rapid	Waterfall
About	A part of river where current is very fast and rough	A permanent flow of water over the edge of an erosion-resistant cliff.
Formation	Forms due to increase in water flow characterized by a river becoming shallower.	Forms due to sudden break in elevation or nickpoint of a rock due to water flowing over it.
Created by	Four factors, separately or in combination, can create rapids: gradient, constriction, obstruction, and flow rate.	Creation of a steep, vertical drop and a plunge pool into which the water of river falls.
Examples	Violent water below Niagara Falls, Des Moines Rapids, etc.	Angel Falls, Boyoma Falls, Victoria Falls, etc.
Types	Six	Ten

What is a rapid and what exactly is a waterfall?

A rapid is a part of river where current is very fast because of relatively steep gradient of river bed at that place causing an increase in water flow and turbulence. It is the hydrological feature between a smoothly flowing part of a stream (run) and a sudden downpour (cascade).A waterfall is a permanent flow of water over the edge of an erosion-resistant cliff. It is a geological formation resulting from the sudden break in elevation or knickpoint of rock.

Formation of rapids vs waterfalls

A waterfall flowing over an erosion-resistant rock forms due to a sudden break in elevation or knickpoint. Streams become wider and shallow just above the waterfalls, and generally there deep pool at the place where water falls due to kinetic energy of the water hitting the bottom. On the other hand, a rapid forms due to shallowing of the river characterized by some rocks exposed above the water surface. These rocks are generally more erosion-resistant as compare to its neighborhood rocks beneath the water flow.

Creation factors for waterfalls vs rapids

Four factors, separately or in combination, can create rapids: gradient, constriction, obstruction, and flow rate. Gradient, constriction, and obstruction are streambed topography factors and are relatively consistent. Flow rate is dependent upon both seasonal variation in precipitation and snowmelt and upon release rates of upstream dams.On the other hand, when a river flows over a bed of rock that resists erosion, weaker rocks downstream are worn away, creating a steep, vertical drop and a plunge pool into which the water falls. This eroded rock and vertical drop and plunge pool are the factors influencing a Waterfall. Over time, continuing erosion causes the waterfall to retreat upstream forming a deep valley.

Examples of rapids and waterfalls

Waterfalls are common in the mountains. This is due to the sudden and catastrophic change in stream course in hilly areas. It can also be because of water flowing over the same rock for many years and also sudden environmental changes like land slides, earthquakes, etc. Angel Falls in Venezuela is the highest waterfall in the World; Boyoma Falls has the largest volume of water (600,000 cubic feet per second); Victoria Falls is the widest in the World. Violent water below Niagara Falls is one of the examples of a rapid. The Des Moines Rapids is one of two major rapids on the Mississippi River

Types of rapids and waterfalls

While there are six types of rapids, there are 10 types of waterfalls.

Types of Rapids

The various types of Rapids are classified on the basis of navigational difficulty. The six types of rapids are:

Class I rapid – Has small waves in fast moving water and very few obstacles.
Class II rapid – Has wide channels and rapids that are easy to navigate, without many turns or obstacles. Small waves less than two feet high.
Class III rapid - Intermediate. Strong currents require training and ability to maneuver quickly and effectively. From this class on, rafters require a guide. Not suitable for young children.
Class IV rapid - Advanced. Powerful rapids for strong paddlers that can handle fierce turns and spins. Drops and waves are common.
Class V rapid - Expert. Violent, dangerous rapids, usually formed through obstructed channels, tight turns, and soaring falls.
Class VI rapid - Unrunnable. Likelihood of death in attempting class 6 runs.

Types of waterfalls

The types of waterfalls are:

Block: Water descends from a relatively wide stream or river.
Cascade: Water descends a series of rock steps.
Cataract: A large waterfall.
Fan: Water spreads horizontally as it descends while remaining in contact with bedrock.
Horsetail: Descending water maintains some contact with bedrock.
Plunge: Water descends vertically, losing contact with the bedrock surface.
Punchbowl: Water descends in a constricted form, then spreads out in a wider pool.
Segmented: Distinctly separate flows of water form as it descends.
Tiered: Water drops in a series of distinct steps or falls.
Multistep: A series of waterfalls one after another of roughly the same size each with its own sunken plunge pool.