Due to snow melt, water yield is significant even during spring and summer.ĥ.2.2.4 Forest Watershed: These are the watersheds where natural forest cover dominates other land uses. The areas downstream of the mountains are vulnerable to flooding.
Due to steep gradient and relatively less porous soil, infiltration is less and surface runoff is dominantly high for a given rainfall event. Once a watershed is urbanized, its land use is almost fixed and its hydrologic behavior changes due to changes in precipitation.ĥ.2.2.3 Mountainous Watershed: Because of higher altitudes, such watersheds receive considerable snowfall. Thus, an urban watershed is more vulnerable to flooding if the drainage system is inadequate. As a result, there is pronounced increase in runoff and pronounced decrease in soil erosion. For a given rainfall event, interception and depression storage can be significant but infiltration is considerably reduced. As drainage systems are artificially built, the natural pattern of water flow is substantially altered. These features reduce the infiltrating land area and increase imperviousness. These are dominated by buildings, roads, streets, pavements, and parking lots. This, in turn, leads to changed infiltration characteristics.ĥ.2.2.2 Urban Watershed: These are the watershed areas having maximum manipulation for the convenience of human being. The soil structure is altered by regular application of organic and/or inorganic manure. The small channels formed by erosion and runoff in the area are obliterated by tillage operations. There is lesser development of streams in agricultural watersheds. When the fields are barren, falling raindrops tend to compact the soil and infiltration is reduced. Depression storage is also increased by agricultural operations. This usually leads to increased infiltration, increased erosion, and/or decreased runoff. It experiences perhaps the most dynamically significant land-use change. Mixed - a combination of two or more of the previous classificationsĥ.2.2.1 Agricultural Watershed: Agricultural watershed is the watershed in which agricultural activities (crop cultivation) is dominant. The watershed classification based on the land use can be given as below.
The channel networks and channel phase are well-developed, and, thus, channel storage is dominant.ĥ.2.2 Land Use – Land use defines the exploitation (natural and human interactions) characteristics of watersheds which affect the various hydrological processes within the watershed. Overland flow and land phase are prominent.ĥ.2.1.3 Large Watersheds: These watersheds are less sensitive to high-intensity-rainfalls of short duration. Rather than size, shape of the watershed plays a dominant role. The watershed is highly sensitive to high-intensity and short-duration rainfalls.ĥ.2.1.2 Medium Watersheds: Being medium in size, the workability in these watersheds are easy due to accessible approach. Channel phase is relatively less conspicuous. Small Watershedsĥ.2.1.1 Small Watersheds: Small watersheds are those, where the overland flow and land phase are dominant.
Based on size, the watersheds are divided into three classes. As the watershed size increases, storage increases. The spatial variability of watershed characteristics increases with size, therefore, large watersheds are most heterogeneous. The descriptions of different watershed classifications are as below.ĥ.2.1 Size – The main implication of watershed size appears in terms of spatial heterogeneity of hydrological processes. Two watersheds of the same size may behave very differently if they do not have similar land and channel phases. However, the main classification of watershed is discussed broadly on the basis of size and land use. Watersheds can be classified using any measurable characteristics in the area like- size, shape, location, ground water exploitation, and land use.
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