An overview of the Hydrology tools
Release 9.2 Last modified January 3, 2008	Print all topics in : "Hydrology (Spatial Analyst)"

An understanding of 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)

Delineating watersheds

Identifying stream networks

Hydrologic analysis references

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 Hydrology tools, provides a brief description of each, and identifies if the tool works in ArcToolbox, Map Algebra, or ArcObjects.

Tool	Description	ArcToolbox	Map Algebra	ArcObjects
Basin	Creates a raster delineating all drainage basins within the Analysis window.	X	X	X
Fill	Fills sinks in a surface raster to remove small imperfections in the data.	X		X
Flow Accumulation	Creates a raster of accumulated flow to each cell by accumulating the weight for all cells that flow into each downslope cell.	X	X	X
Flow Direction	Creates a grid of flow direction from each cell to its steepest downslope neighbor.	X	X	X
Flow Length	Calculates upstream or downstream distance along a flow path for each cell.	X	X	X
Sink	Creates a grid identifying all sinks or areas of internal drainage.	X	X	X
Snap Pour Point	Snaps selected pour points to the cell of highest flow accumulation within a specified neighborhood.	X		X
SnapPour	Snaps selected pour points to the cell of highest flow accumulation within a specified neighborhood.		X
Stream Link	Assigns unique values to sections of a raster linear network between intersections.	X	X	X
Stream Order	Assigns a numeric order to segments of a grid representing branches of a linear network.	X	X	X
Stream To Feature	Converts a raster representing a raster linear network to a feature class.	X		X
StreamShape	Converts a grid representing a raster linear network to a shapefile.		X
Watershed	Determines the contributing area above a set of cells in a grid.	X	X	X

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