Hydrological Analysis module provided by ArcGIS

The hydrological analysis module provided by ArcGIS is mainly used to establish the motion model of the surface water, assist in analyzing where the surface water flow is generated and where it is to flow, and reproduce the flow process of the water flow. At the same time, the application of hydrological analysis tools can also help to understand some basic concepts and key processes of drainage systems and surface water flow processes, and how to use ArcGIS hydrological analysis tools to obtain more hydrological information from DEM data.

1) flow ction: Flow Direction extraction. In ArcGIS, The D8 single flow direction method is used for Flow Direction Analysis.

2) Sink: Land computing. The land area is the place where the water flow direction is unreasonable. You can use the water flow direction to determine where the land is, and then fill the land area. It must be clear that not all land areas are caused by data errors, and many land areas are also the true reflection of the surface form. Therefore, before filling up land areas, it is necessary to calculate the land depth, determine which areas are land based on data errors and which areas are real land forms, and then set a reasonable fill threshold during the fill process.

3) Fill: Fill the land.

4) flow accumulation: confluence analysis. In the process of surface runoff simulation, the confluence accumulation is calculated based on the flow direction data. For each grid, the size of its confluence accumulation indicates the number of grid flows in the upstream of the grid passing through the grid. The larger the confluence accumulation value, this area is more likely to form surface runoff.

5) flow length: the flow length. The water flow length usually refers to the projection length of the maximum ground distance from a point on the ground along the water flow direction to its flow direction starting point (endpoint) on the horizontal plane.

Water Flow length is one of the important factors in soil and water conservation. When other conditions are the same, the strength of hydraulic erosion is determined by the slope length. The longer the slope, the larger the aggregation flow, the higher the erosion force, the longer the water flow directly affects the speed of the ground runoff, thus affecting the erosion force of the ground soil. Therefore, the extraction and analysis of water flow length plays an important role in soil and water conservation.

Currently, there are two main ways to extract the stream length: downstream and upstream. Downstream computing is a horizontal projection that calculates the maximum distance from each point on the ground along the flow direction to the drainage outlet of the point; streamcompute calculates the horizontal projection of the maximum ground distance from each point on the ground along the flow direction to its flow direction starting point.

6) Map Algebra: Uses Map Algebra for river network extraction.

Currently, the commonly used method for river network extraction is to use the surface runoff manflow model for calculation: first, the water flow direction of each grid is obtained by using the maximum slope drop method on the non-land DEM; then, the grid data in the direction of the flow is used to calculate the number of accumulated grids in the direction of the flow, that is, the convergence accumulation, the obtained confluence accumulation indicates the number of grid flows in the grid. If each grid carries a flow of water, the Convergence accumulation of the grid indicates the flow of the grid. Based on the above idea, when the amount of confluence reaches a certain value, it will generate a surface water flow. All the grids with a confluence larger than the critical value are the potential water flow paths, A network composed of these flow paths is a river network.

7) stream order: River Network classification.

8) basin: a watershed segmentation tool.

Watershed: a watershed segmentation tool.