You’re analyzing the water flow on a landscape. What’s the best tool to use?

1 What is a DEM?

A digital elevation model, or DEM, is a representation of the surface elevation of a landscape in a grid format. Each cell in the grid has a value that indicates the height above a reference level, such as sea level or a local datum. A DEM can be derived from various sources, such as satellite imagery, aerial photography, lidar, or surveying. A DEM can be used to create contour maps, slope maps, aspect maps, and other types of spatial analysis.

2 Why use a DEM for water flow analysis?

A DEM can help you analyze the water flow on a landscape by simulating how water flows downhill from one cell to another, following the steepest path. By applying different algorithms and parameters, you can calculate the flow direction, flow accumulation, flow length, watershed boundaries, stream networks, and other hydrological features. A DEM can also help you identify the areas of high and low runoff, infiltration, erosion, and sedimentation. A DEM can provide you with valuable information for designing drainage systems, stormwater management, irrigation, erosion control, and water conservation.

3 How to use a DEM for water flow analysis?

To use a DEM for water flow analysis, you must have access to a GIS software such as ArcGIS, QGIS, or GRASS GIS, as well as a suitable DEM with a high resolution and accuracy. You can obtain a DEM from online databases, government agencies, or private companies, or create your own from field data if you have the equipment and skills. The basic steps for using a DEM for water flow analysis are to import it into the GIS software and check its quality and projection; fill any gaps or errors in the DEM that might affect the water flow; apply the flow direction algorithm to determine the direction of water flow for each cell in the DEM; apply the flow accumulation algorithm to determine the amount of water flowing through each cell in the DEM; apply the flow length algorithm to determine the distance of water flow from each cell to the outlet or boundary of the DEM; apply the watershed algorithm to delineate the watershed boundaries and sub-basins for the DEM; apply the stream network algorithm to identify the stream channels and segments for the DEM; and visualize and interpret the results of the water flow analysis using maps, charts, and statistics.

4 What are the benefits of using a DEM for water flow analysis?

Using a DEM for water flow analysis can offer you various advantages, such as saving time and money by decreasing the necessity for field surveys and measurements. It can also give you a comprehensive and thorough view of the water flow patterns and processes on your site, enabling you to identify the opportunities and constraints for your landscape design and planning. Furthermore, a DEM can help you evaluate the impacts and alternatives of your design interventions on the water flow and the environment, as well as communicate your design ideas and solutions to your clients and stakeholders.

5 What are the limitations of using a DEM for water flow analysis?

Using a DEM for water flow analysis can also have some limitations. For example, the quality and resolution of the DEM might not capture the micro-topography and variability of the landscape. Additionally, the choice and parameters of the algorithms might not reflect the actual water flow behavior and dynamics. Furthermore, the scale and extent of the analysis might not match design objectives and requirements, while uncertainty and variability of the water flow data and conditions may change over time and space.