Waterfalls are a single point within the Earth’s larger water system, functioning as an overflow mechanism for a river or stream. The existence of a waterfall depends entirely on the continuous supply of water from its source. Therefore, waterfalls can and do run out of water. This variability is governed by the hydrological cycle and the specific geology of the surrounding area.
The Source: How Waterfalls Are Fed
The flow of water over any waterfall is directly controlled by its catchment area, also known as a watershed. This is the region where all precipitation collects and drains into the stream or river that feeds the falls. A larger catchment area generally gathers more water, contributing to a greater and more consistent flow.
Water reaches the waterfall crest through two primary pathways: surface flow and groundwater discharge. Surface runoff is the rapid movement of water across the land following precipitation or snowmelt, quickly increasing the stream’s volume. This process causes dramatic, short-lived surges in a waterfall’s flow.
Groundwater discharge, or baseflow, is water that has infiltrated the soil and percolated down to underground aquifers. This water slowly seeps back into the stream channel over weeks, months, or even years, providing a steady supply that sustains the flow long after a rainfall event has passed. Upstream lakes and wetlands act like natural sponges, absorbing high flows and releasing the water gradually, which helps to stabilize the stream’s water level.
Classification by Flow Type
Waterfalls are categorized by the reliability of their water source, which determines how long they flow during a typical year. Perennial falls maintain flow year-round, characteristic of waterfalls fed by large river systems or streams with consistent groundwater baseflow. For these falls, the water table remains above the stream bed for the majority of the year, ensuring continuous discharge.
Ephemeral falls only flow during or shortly after a significant precipitation event or snowmelt. These falls rely almost entirely on surface runoff and have little groundwater contribution to sustain them. They are temporary features that appear and disappear with local weather patterns, often found in arid climates or regions with distinct wet and dry seasons.
A third category, intermittent falls, flows predictably during wet seasons when the water table is seasonally high. The classification highlights that some waterfalls are designed by nature to run out of water once the immediate surface supply is exhausted.
Factors Leading to Flow Cessation
Even typically perennial waterfalls can cease flowing due to external pressures, both natural and human-induced. The most common natural cause is prolonged drought. Prolonged drought involves a significant deficit in precipitation over an extended period, which depletes the water stored in the soil and lowers the regional water table. When the water table drops below the level of the stream bed, the sustaining baseflow stops, reducing the stream to a trickle or drying it up entirely.
Many large waterfalls experience their lowest flows in the late summer and fall due to extreme seasonal shifts. This is a natural consequence of high summer evaporation rates combined with the time delay required for deep groundwater reserves to replenish after the spring melt. A less common natural event is stream capture, where a river’s course is diverted by erosion into an adjacent, deeper channel, cutting off the flow to the original waterfall.
Human influence poses a significant threat to the flow of established waterfalls. Upstream water diversion for agriculture, municipal supply, and industrial use removes a substantial portion of the river’s volume before it reaches the falls. This artificial reduction can severely diminish or completely stop the cascade, particularly during dry periods when water demand is highest.
The construction of dams and reservoirs upstream fundamentally alters the natural flow regime of a river. These structures store water and regulate its release, which leads to a drastic reduction in the downstream flow needed to maintain the waterfall. In some cases, the river is entirely redirected through power generation facilities, leaving the original channel and the waterfall dry.