The drainage basin is fundamental to the understanding of the hydrologic cycle because each drainage basin acts as an individual hydrological system, receiving quantifiable inputs of precipitations, which are transformed into flows and storages and into output of evaporation and runoff.
As a result, the drainage basin is the most commonly used unit for modeling hydrological processes, for water balance studies, for chemical budgets and for examining human impacts on hydrological systems (Ward and Robinson, 2000).
Drainage Basin Defined
A drainage basin is the topographic region from which a stream receives runoff, through flow, and groundwater flow (Pidwimy, 2006).
Another definition of the drainage basin is by Gallagher (2011), who defined it as an area of the earth’s surface occupied by a surface stream or other water body together with all of the tributary streams, surface, and subsurface water flows. Having defined a drainage basin, let us examine its basic features.
Features of Drainage Basin
A drainage basin consists of a branched network of stream channels and adjacent slopes that feed the channels. It is bounded by a drainage divide, which mark the boundary between slopes that contribute water to different streams or drainage systems.
According to Pidwimy (2006), drainage basins are divided from each other by topographic barriers called watershed. A watershed represents all of the stream tributaries that flow to some location along the stream channel.
The number, size and shape of the drainage basins found in an area vary with the scale of examination. It should be noted that drainage basins are arbitrarily defined based on the topographic information available on a map. The quality of this information decreases as map scale becomes smaller.
Large-scale features of a drainage basin include the size, shape, and relief of the basin. Small-scale features include measurements of channel length and slope, storage capacity and drainage density of the stream network within the basin. Each of these geomorphic properties can be used to compare basins.
Drainage basins are open systems. Inputs to these systems include precipitation, snow melt, and sediment. Drainage basins lose water and sediment through evaporation, deposition, and stream flow.
A number of factors influence input, output, and transport of sediment and water in a drainage basin. Such factor includes topography, soil type, bedrock, climate, and vegetation cover. These factors also influence the nature of the pattern of stream channels.
In a typical stream network within a drainage basin, each tributary receives runoff from a small area of land surface surrounding the channel. This runoff is carried downstream and merged with runoff from other small tributaries as they join the main stream. The drainage system thus provides a converging mechanism that funnels overland flow into streams and smaller streams into larger ones.
Drainage basins are important to understanding the characteristics of stream habitats. The boundaries of a drainage basin are used to explain biogeography distributions of fish species (Gallagher, 2011).
Basin features are a factor in predicting flood patterns, estimating sediment yield, and predicting water availability and quality. The downstream transfer of water, sediment, nutrients, and organic material all influence the characteristics of stream habitat.
It is therefore important to understand the geologic, hydrologic, morphologic, and vegetational setting of a stream in its basin. In addition, understanding drainage basin attributes aids habitat investigators when interpreting field data.
Drainage Basin Patterns
As earlier stated above, factors such as topography, soil types, bedrock type, climate, and vegetation cover influence input, output, and transport of sediment and water in a drainage basin.
These factors also influence the nature of the pattern of stream channels. Consequently, five common drainage patterns can easily be identified. They include trellised, rectangular, parallel, dendritic and deranged.
Trellised Drainage Pattern – It tends to develop where there is strong structural control upon streams because of geology. In such situations, channels align themselves parallel to structures in the bedrock with minor tributaries coming in at right angels.
Rectangular Drainage Pattern – This occurs in areas with tectonic faults or bedrock joints causing a stream to take on a grid-like or rectangular pattern.
Parallel Drainage Pattern – They are often found in areas with steep relief or where flow is over non-cohesive materials.
Dendritic Drainage Pattern – They are typical of adjusted systems on erodable sediments and uniformly dipping bedrock.
Deranged Drainage Pattern – It is found in areas recently disturbed by events like glacial activities or volcanic deposition. Over time, the stream will adjust the topography of such regions by transporting sediment to improve flow and channel pattern.
In summary, the discussions on the drainage basin have further supported the idea that drainage basin is the most commonly used unit for modeling hydrological processes.
Therefore, the understanding of the concept of the drainage basin will foster a better understanding of the hydrologic cycle and the processes involved in it.
A drainage basin is the topographic region from which a stream receives runoff, through flow, and groundwater flow.
Drainage basin acts as an individual hydrological system, receiving quantifiable inputs of precipitations, which are transformed into flows and storages and into output of evaporation and runoff.
A drainage basin is bounded by a drainage divide, which mark the boundary between slopes that contribute water to different streams or drainage systems.
A drainage basin is an open system, with an input of precipitation, snow melt and sediment, and output of evaporation, deposition and streamflow. There are five major drainage patterns – trellised, rectangular, parallel, dendritic and deranged.