How to Perform Hydrology Analysis and Flood Risk Mapping in ArcGIS? A Complete Tutorial.

Introduction

This tutorial provides a comprehensive guide on performing hydrology analysis and flood risk mapping using ArcGIS. By following these steps, you will learn how to utilize digital elevation models (DEM), land cover data, and precipitation data to assess flood risks effectively. This knowledge is crucial for environmental planning and risk management.

Step 1: Load Required Data

To begin your hydrology analysis, you need to load the necessary datasets into ArcGIS.

1. Download the required data from the provided link: Flood_mapping.zip.
2. Extract the files from the ZIP archive.
3. Open ArcGIS and create a new project.
4. Add the following data layers:
   • Digital Elevation Model (DEM)
   • Slope data
   • Land cover data
   • Precipitation data

Step 2: Create Hillshade and Shaded Relief Map

Generating a hillshade or shaded relief map helps visualize the terrain, which is essential for understanding hydrological patterns.

1. In ArcGIS, navigate to the 3D Analyst Tools.
2. Select Surface Analysis and then choose Hillshade.
3. Input your DEM and adjust the settings for azimuth and altitude as needed.
4. Click OK to generate the hillshade map.
5. To create a shaded relief map, repeat the process using the Shaded Relief tool.

Step 3: Perform Hydrology Analysis

This step involves several critical processes to prepare your data for flood risk mapping.

1. Fill Sinks:

   • Navigate to the Hydrology Toolbox.
   • Select Fill and input your DEM.
   • This step ensures that all sinks in the elevation data are filled.

2. Flow Direction:

   • Choose Flow Direction from the Hydrology Toolbox.
   • Input the filled DEM and run the tool to create a flow direction raster.

3. Flow Accumulation:

   • Select Flow Accumulation and input the flow direction raster.
   • This will show areas where water accumulates.

4. Extract Streams:

   • Use the Stream Order tool to generate streams from the flow accumulation raster.
   • Set a threshold to define what constitutes a stream.

Step 4: Analyze Proximity to Streams

Understanding the proximity to streams is essential for flood risk assessment.

1. Use the Proximity tool in ArcGIS.
2. Input the stream layer and set the distance parameters.
3. Run the tool to create a proximity raster that indicates distances from streams.

Step 5: Reclassify Criteria

To evaluate flood risk, you need to reclassify all the criteria based on their importance.

1. Select the Reclassify tool in ArcGIS.
2. For each layer (slope, land cover, proximity to streams), define the scoring system based on your analysis criteria.
   • For example, classify steep slopes as high risk and flat areas as low risk.
3. Run the tool for each layer to create reclassified rasters.

Step 6: Generate Flood Risk Map

Combining all criteria will enable you to create a comprehensive flood risk map.

1. Use the Raster Calculator to combine the reclassified layers.
2. Assign weights to each layer based on their significance in flood risk.
   • For instance, give more weight to proximity to streams compared to slope.
3. Execute the calculation to generate the final flood risk map.

Conclusion

In this tutorial, you learned how to perform hydrology analysis and create a flood risk map using ArcGIS. Key steps included loading data, performing hydrology analysis, and combining various criteria to assess flood risk effectively. For further applications, consider exploring additional GIS tools and techniques for environmental analysis and site selection.