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Catchment zone in Nattai, Australia containing drinking water. Catchment hydrology is the study of hydrology in drainage basins. Catchments are areas of land where runoff collects to a specific zone. This movement is caused by water moving from areas of high energy to low energy due to the influence of gravity.
Watershed delineation is the process of identifying the boundary of a watershed, also referred to as a catchment, drainage basin, or river basin.It is an important step in many areas of environmental science, engineering, and management, for example to study flooding, aquatic habitat, or water pollution.
When the response factor A can be determined from the characteristics of the watershed (catchment area), the reservoir can be used as a deterministic model or analytical model, see hydrological modelling. Otherwise, the factor A can be determined from a data record of rainfall and runoff using the method explained below under non-linear reservoir.
Other terms for a drainage basin are catchment area, catchment basin, drainage area, river basin, water basin, [3] [4] and impluvium. [ 5 ] [ 6 ] [ 7 ] In North America, they are commonly called a watershed , though in other English-speaking places, " watershed " is used only in its original sense, that of the drainage divide line.
The runoff model with a non-linear reservoir is more universally applicable, but still it holds only for catchments whose surface area is limited by the condition that the rainfall can be considered more or less uniformly distributed over the area. The maximum size of the watershed then depends on the rainfall characteristics of the region.
Example 1 The linear-reservoir model (or Nash model) is widely used for rainfall-runoff analysis. The model uses a cascade of linear reservoirs along with a constant first-order storage coefficient, K , to predict the outflow from each reservoir (which is then used as the input to the next in the series).
Each subregion includes the area drained by a river system, a reach of a river and its tributaries in that reach, a closed basin or basins, or a group of streams forming a coastal drainage area. [6] Regions receive a two-digit code. The following levels are designated by the addition of another two digits. [7]
Intuitively, a drop of water falling on a topographic relief flows towards the "nearest" minimum. The "nearest" minimum is that minimum which lies at the end of the path of steepest descent. In terms of topography, this occurs if the point lies in the catchment basin of that minimum. The previous definition does not verify this condition.