Many of you have heard of concepts such as high water and high water. But not everyone knows about what a low water is. This is one of the phases of the water regime of the river, which will be discussed in our article.
The regime of the river and its main phases
In the world there are several million rivers and streams. And each of them is unique in its own way! Each river has its own "character" and its own regime. Under the regime of the river is meant a complex of all seasonal changes in the state of the watercourse, which are caused by the physical and geographical conditions of its basin (primarily the climate of the territory).
Seasonal climate changes affect the state of almost all the rivers of the Earth. On some - stronger, on others - less noticeable.
In the summertime, when high temperatures are set in temperate latitudes, water from the earth's surface actively evaporates. Accordingly, all rivers in these latitudes gradually become shallow; algae begin to multiply actively in them, staining their channels in a bright green color. In early spring, on the contrary, the rivers become full-flowing. First of all, due to the melting of ice in the riverbed and snow within their catchment areas.
The regime of any river includes three main phases. It:
- High water (the highest water level in the river).
- Flood (a sharp and short-term rise in the water level in the river, provoked by heavy rainfall).
- Low water.
What is a low water? In geography, this is one of the phases of the watercourse regime. In more detail about the features of this phase we will describe further.
What is low water: definition and essence of the concept
So, we found out that each of the rivers has its own water regime. Now let's look at what is a low water, what features are characteristic for this phase of the river regime.
Low water - this is the lowest water level in the river, as well as a relatively long period of time at which this level is maintained. As a rule, this period is at least 10 days. At this time, the river feeds mainly on groundwater.
In the temperate as well as high latitudes of the Northern Hemisphere, the low water begins in late summer or autumn (less often in winter) and continues until ice formation begins. On mountain rivers, it can be temporarily interrupted by powerful floods caused by heavy rainfall.
To better understand what a low water river is, you should find out what factors it depends on. These factors include:
- geographic location of the basin;
- climatic features of the region in which the catchment is located;
- terrain
- geological structure of the territory;
- vegetation prevailing within the river basin;
- the degree of human influence.
In general, low water is a rather unstable, variable phase of the water regime, which is explained by the "fragility" of the river system itself. Even the smallest impact can significantly change the nature and duration of the low water river.
What is low water: the meaning and origin of the word
Why does the riverbed suddenly become less? The answer is simple: this occurs as a result of limitation (or complete cessation) of the supply of a watercourse from one or another source. In the arid regions of the planet, the riverbed during the low water period can even dry out. And sometimes it even manages to become covered with sparse vegetation.
What is low water from a philological point of view?
The origin of this scientific term is most likely associated with the word “boundary”. This is the boundary between something. In this particular case, we are talking about the border between the seasons of the year. Probably, in the old days, seasons were delimited precisely on the basis of the water level in local rivers.
Types of river low water
Low water is different. Depending on the weather and climatic conditions of the area, hydrologists distinguish:
- summer (or summer-autumn);
- winter low water.
The summer-autumn low water begins immediately after the spring flood (in July-August) and continues until the period of autumn floods. If the latter are not observed, then this phase can continue all winter, until the next spring flood (winter low water).
Depending on the time criterion, the river low water happens:
- short-term (lasts from 10 to 30 days);
- long (lasts more than 30 days).
But in most cases, the low water is torn in time, intermittent.
Low water criteria
It is immediately worth noting that the allocation of low water (like any other phase in the water regime of the river) is quite subjective. Especially when it comes to its time frame. That is, it is not possible to specifically and unequivocally determine when the low water begins on a particular river.
The main criterion for determining the low water is considered to be the change in runoff volume in the river channel. So, if in a certain period this indicator does not exceed 10-15% of the total annual runoff, then we can talk about low water during this specific period of time. An interesting fact: on large-scale topographic maps, the contours of river channels are depicted precisely by their state during the low-water period.
Most Russian rivers and rivulets are characterized by summer-autumn low water (from August to November). Summer rains on the territory of Russia, as a rule, are short-lived and are not able to significantly affect river floods. The only exceptions are the mountainous regions of the country, as well as the Far Eastern region, where low water may not be observed at all on the rivers.