Even in wetter regions with frequent rainfall, it is estimated that more than 50% of the total stream network consists of temporary streams. In fact, they contribute the vast majority of freshwater to the entire river network in arid and semi-arid regions.įor example, 95% of all streams in the Arizona Dessert are seasonal, of which a substantial amount are ephemeral. These streams play an essential role in supplying fresh and maintaining existing resources in at least three different ways: 1) Fresh Water Supply To Perennial Water NetworksĮven though ephemeral streams only flow during or after a spell of rain, the combination and frequency of these streams have a huge impact. Such a conclusion can not be further from the truth. It is only natural to conclude that ephemeral streams play an insignificant role in contributing to the Water Cycle and have any other beneficial influences on the environment. The stream itself is the actual flow of water that is transitory, while the channel it flows in remains a permanent fixture of the landscape. It is important to note that the ephemeral stream and the channel (arroyo) it flows in are not the same things. These dried-up channels are sometimes more accurately described as arroyos, which are synonymous with the arid and semi-arid areas where ephemeral streams occur. They can also continue to flow for a short distance before evaporating completely without reaching any significant point or being absorbed into the soil to form groundwater.Įphemeral streams flow for a limited time and dry up quickly, only leaving a dry stream bed behind. The paths these streams follow can link up with larger networks of intermittent or perennial streams and rivers. The stream can create a new path or follow an existing channel (also called a dry wash) established by previous occurrences of ephemeral streams. As a result, when a large enough amount of rainfall does occur, it often forms a temporary stream on the surface. In arid or semi-arid regions, precipitation occurs very infrequently.

The significance of the groundwater table height will become clear in a later section. It also occurs in predominantly dry regions, where the groundwater table forms much deeper below the surface.Īs a result of these two factors, ephemeral streams occur above the groundwater table, compared to more permanent streams and rivers, which riverbeds lie below the water table. Since these streams occur for such a brief period, it does not have the time to carve out a deep and wide channel, as is the case with a perennial river. The word 'ephemeral' is derived from the 16th Century Greek word 'ephēmeros,' which aptly means 'lasting for a very short time.' And it is the brief occurrence of an ephemeral stream that is its most defining characteristic. To be able to describe how and why this type of stream form, one needs to gain a clear understanding first of what precisely an ephemeral stream is: (Like the Rhine in Europe, the Amazon in South America, and the Nile in Africa.) An ephemeral stream, though, is not only transitory but is not even a seasonal occurrence. Most major river systems and larger streams flow throughout the year, meaning they are perennial. This post examines what an ephemeral stream is, how it forms, and how it differs from other types of streams and rivers. Yet, it is still just as an important source of water as any extensive permanent river system. It does not flow often and only for a short duration during specific occurrences. One such temporary stream is called an ephemeral stream. No matter what their size or frequency, they all form part of the Water Cycle that distributes and cycles water around the planet. Some of them are seasonal, and some only flow during specific events. Not all rivers and streams continuously flow throughout the year.

Ephemeral definition