An overview of the Hydrology toolset

The Hydrology tools are used to model the flow of water across a surface.

Information about the shape of the earth's surface is useful for many fields, such as regional planning, agriculture, and forestry. These fields require an understanding of how water flows across an area and how changes in that area may affect that flow.

When modeling the flow of water, you may want to know where the water came from and where it is going. The following topics explain how to use the hydrologic analysis functions to help model the movement of water across a surface, the concepts and key terms regarding drainage systems and surface processes, how the tools can be used to extract hydrologic information from a digital elevation model (DEM), and sample hydrologic analysis applications.

• Understanding drainage systems
• Exploring digital elevation models (DEM)
• Deriving runoff characteristics
• Creating a depressionless DEM
• Creating watersheds
• Hydrological analysis sample applications

The Hydrology tools can be applied individually or used in sequence to create a stream network or delineate watersheds.

The following table lists the available tools and provides a brief description of each.

Tools in the Hydrology toolset

Tool	Description
Basin	Creates a raster delineating all drainage basins.
Derive Continuous Flow	Generates a raster of accumulated flow into each cell from an input surface raster with no prior sink or depression filling required.
Derive Stream As Line	Generates stream line features from an input surface raster with no prior sink or depression filling required.
Derive Stream As Raster	Generates a stream raster from an input surface raster with no prior sink or depression filling required.
Fill	Fills sinks in a surface raster to remove small imperfections in the data.
Flow Accumulation	Creates a raster of accumulated flow into each cell. A weight factor can optionally be applied.
Flow Direction	Creates a raster of flow direction from each cell to its downslope neighbor, or neighbors, using the D8, Multiple Flow Direction (MFD), or D-Infinity (DINF) method.
Flow Distance	Computes, for each cell, the horizontal or vertical component of downslope distance, following the flow paths, to cells on a stream into which they flow. In case of multiple flow paths, minimum, weighted mean, or maximum flow distance can be computed.
Flow Length	Calculates the upstream or downstream distance, or weighted distance, along the flow path for each cell.
Sink	Creates a raster identifying all sinks or areas of internal drainage.
Snap Pour Point	Snaps pour points to the cell of highest flow accumulation within a specified distance.
Storage Capacity	Creates a table and a chart of elevations and corresponding storage capacities for an input surface raster. The tool calculates the surface area and total volume of the underlying region at a series of elevation increments.
Stream Link	Assigns unique values to sections of a raster linear network between intersections.
Stream Order	Assigns a numeric order to segments of a raster representing branches of a linear network.
Stream to Feature	Converts a raster representing a linear network to features representing the linear network.
Watershed	Determines the contributing area above a set of cells in a raster.